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MG Midget and Sprite Technical - To vent or not to vent

Chaps

73 RWA has the 1/2 inch vent from the oil separator on timing chain casing freely venting to atmosphere.
The hose is fine by the by.

There have been a few drips of oil from the bellhousing area lately - nothing too serious - but as I guess as the rear seal is an oil scroll, free and easy breathing/partial vacuum is required in the crankcase.

Add to that it stinks!

Thus - would I be advised to retro-fit the breather vac valve on the manifold and connect up the breather hose to it - as per original design? Cannot fit breather into carbs as these are larger non-standard items. Would such a retro-fit improve the oil drip situation and could it muck up the mixture in any way...

Rocker cap is also vented with a pin prick hole, but it is one of these cheapo chromed things rather than the genuine item - Again, would I be better served by fitting the real thing?

Many thanks


Mark




Mark O

Yepp....it will leak, if not connected

If you hook the hose to the intake, it creates ALOT of vac....so you may need a catch can

Id think you would also want some kind of inline PCV valve

PRop
Prop and the Blackhole Midget

If you can't connect the breather hose to the reduced vacuum point on the carbs (via a Y piece), you'll have to connect to the inlet manifold, and you'll definitely need the Mushroom vacuum valve device. Otherwise you will definitely suck up oil, as well as drastically weaken the mixture.

Are you certain there is nowhere in the carbs to connect the breather? What carbs are they?

As for improving the current situation. Yes, no more fumes, and yes it will aid in rducing the dripping oil, but might not cure it completely. Depends how much sump pressure there is, and the state of the oil scroll and cap.

As long as there is a hole in the rocker cover filler cap, and it's not blocked, you don't need to change it.
Lawrence Slater

Lawrence - Many thanks. It confirms what I thought. The item on MGOC website looks to be the jobbie

http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_1275_129.html

Item 26 plus fittings


Present carbs are two oversized HS4s courtesy of PO - Lord knows their origin, and there is no attachment to connect up the breather on either of them.

Incidentally is there an easy way of cleaning out the oil separator can - rather than removing the timing chain cover?
Mark O

I disagree with Lawrence about the chrome cap with pin hole, I was told years ago that the plastic vented filter caps are better, only £3.95 from MGOC Spares ( alot more expensive elsewhere) - item 7 here - http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_1275_167.html

or I've a few new unsed spare so for the price of postage and a few coins in your regular pub's charity box you could try one out cheap either way


Nigel Atkins

I've got the Plastic filler cap on mine, but in what way are they better than the chrome ones? All the wire mesh does is keep crap out, -- as the air is sucked in. as long as the cap can breath -- whichever type it is, I don't reckon there's a lot of difference as long as it has a hole in it.

Timing cover breather mesh.
"Incidentally is there an easy way of cleaning out the oil separator can - rather than removing the timing chain cover?"

If it's dried up and clogged, the only way is a solvent, like petrol, and that won't help the sump oil at all. So if it is clogged, it's gotta come off. Before doing that though, make sure it really needs cleaning. Are you sure your's does.

Some people have hooked the old mesh out, and refilled it with the likes of a stainless steel Brillo pad I think. ---- minus the soap of course. :)

Carb breather connection.
I seem to recall someone saying they had connected the breather pipe to the back of the air filter intake. Anyone remember that?
Lawrence Slater

Lawrence,
it's a sad day for you as I can remember and you can't :)

we had this conversation before, chrome ones can have small vent hole and close baffle(?) below that doen't vent as well

or clogs up easier

tbh I can't remember the details :)
Nigel Atkins

Ah. I've only used the cheapo plastic ones, and they last yonks. Yup, if the chrome type hole clogs, then either clean regularly, or but the cheapo.
Lawrence Slater

Lawrence,
spend money unecessarily, you surprise me!

if the chrome one has a very small hole wouldn't you try drilling it larger before that wasteful use of the readies :)

Nigel Atkins

My only comment is that when I fitted a new genuine BL filter cap the problem I had with oil being sucked up the breather pipe went away. The original seemed fine. I have NO explanation why it did this. My recommendation is stick with original spec.
Bob Beaumont

perhaps the filter was blocked(?) (see my photo earlier)
Nigel Atkins

I reckon drilling a bigger hole might upset the balance.

However, on the other hand, the air through the original plastic variety, is very free flowing (you can easily breath through them -- I've tried ). So maybe drilling a larger hole in the chrome one would work ok, and may in fact be desirable.

And thinking about Bobs comment. I was wondering how just changing the breather cap could solve the sucking problem.

Maybe, if the cap was sufficiently blocked, and the timing cover breather system was working properly, the blocked cap would cause a build up of +ve sump pressure, hence pushing the oil from behind, whilst the vacuum from the inlet sucks at it.

So in theory Bob, if you put the old cap back on -- if you still had it -- your problem should return. Assuming that was all you did, and everything else was equal too. lol.
Lawrence Slater

I used the plastic vented ones for years, fitted to an alloy rocker cover. Worked fine.
Last year I succumbed to the lure of a matching chromed one, also vented. It works just fine too. I didn't have to do any drilling or other modification. Looks rather neater with the alloy cover than the plastic one did, but that's all.
Guy W

perhaps it's just a case of a system that's not at its best more readily shows up the weaker areas

or it just need servicing :) - (a good clean)
Nigel Atkins

Nigel,
You are right, there was some discussion about possible problems with the chrome type caps. But as I don't always believe everything I read on the BBS I decided to risk it when I bought mine. For me it demonstrated that the tale was just a myth, or certainly didn't apply to all of the chrome ones available.
Guy W

"Over sized HS4s".....

Hmmm, bigger is not better ....have you considard dropping to just the one oversized HS4 carb, or going to HS2 carbs... I bet you would get alot more performance...not to mention better gas milage
Prop and the Blackhole Midget

Guy,
I quite agree you can't trust all you read, not sure it was a myth more likely as you say doesn't apply to all caps or perhaps it only applied to certain caps at a certain time but best to be aweare of it to do as you done and make a judgement once you've checked and cross referenced a reasonable amount of information

like rubber fuel hose some may not believe the troble I had with that for the last 6 years but if you'd be there the times it caused problems you would - perhaps the problem has passed now but old batches may still be around
Nigel Atkins

In my book its as much down to inconsistency of the suppliers' manufacture as anything else. Items made down to a price with poor quality control from companies who don't always understand the significance of random changes to specifications or the quality of materials used. Sometimes the result is ok, other times there are problems. And you don't know if you will end up lucky or not !
Guy W

I blame the 10 year old little china girl that makes out parts for 26 cents a day... She really needs to take her work more seriously...she is just slacking off. And we are paying the price for her laziness...i mean come on... 16 hours a day working, its not like she still has 8 hours a day left for meseing around or going to school

Prop
Prop and the Blackhole Midget

>>And you don't know if you will end up lucky or not !<< unfortunately I do

Prop,
shall we open the can of worms about me blaming tight fisted owners for this - (?)

o perhaps not, I must accept the faults of my fellows as they mine

or vent off on forums :)

and why wont they employ two five year olds for the same wages to double the productivity

if you carry on Prop I'll post a link to the Jam 6 year old assasin :)
Nigel Atkins

Hahaha

Its a sad day when slave children just dont care about the bottom line like there over see' er masters do.

I know i joke, but gez i hate to see this kind of human devaluation to that of a dog in the street, and sadly when i say 10 year old children for penjies a day... Im not that far off...just sickening what our planet has become esp conserning children...i cant belive we wont pay a huge socity price in 25 years from now when they inherit the political powers of the planet
Prop and the Blackhole Midget

If im not mistaken.... Arent the chrome caps act like a one way valve they allow air in but not out the cap... Where s the old plastic breath both in and out
Prop and the Blackhole Midget

Lawrence

I have still got the old cap. may be worth seeing if thats the problem. It was quite a few years old but the cap breathed normally from what I could see and the gauze wasn't clogged with gunge etc. The Rad recently sprung a leak and is being rebuilt just presently so may be a couple of weeks until I test.
Bob Beaumont

That'll be perfect timing then Bob. It'll be freezing bloody cold again -- just like most of this summer. lol.
Lawrence Slater

Going back to one of the original points if I may, my recently aquired '68 Mk111 has been fitted with a K & N type breather off a separator pot on the timing chain cover. You can see where the original breather valve connection has been blanked off on the inlet manifold and as I kept the whole breather valve assembly off the old Mk11, would there be any advantage in fitting it?


M J Chapman

MJ,
I would say yes, but I suppose it also depends on whether or not you have a problem with excess sump pressure causing an oil drip from the rear scroll.

If not, then the only advantage in reinstating the original system --- and some may say it's an important one ---, would be to positively remove fumes from the sump under vacuum, rather than just allow them to vent to air under whatever sump pressure there is. -- Helps the oil stay effective for longer.

Personally I favour the vacuum connected system as originally designed.

You say "recently aquired".

So have you driven it enough to know if there's a rear scroll oil drip problem? Do you know why the original system was disconnected in the first place?

Lawrence Slater

LS, yes there's certainly an oil leak under there somewhere. I think I'll put the old system back on and see if that makes a difference. The PO only had it a couple of years and was not a technical chappie so I'm a bit short on the history. However, I know it has an unleaded head,LCB manifold and cherry bomb silencer so I guess the breather was done around the same time.
M J Chapman

if it was the valve type check the diaphragm is in good condition and fully functioning

don't expect to fully loose any oil drips :)

if the oil cap comes apart as in my previous photo it's easy to check that and clean if required
Nigel Atkins

MJ

Your predicament sounds very similar to mine. PO on my recently acquired 73 RWA seemed not to be a mechanical genius, and my breather simply vents to atmosphere. Your engine set up is similar, my carbs are way oversize, and there is no facility to hook up the breather to them.

I too have a bit of a drip, and of course a stinking engine bay. No idea why the breather is not as per spec, but I rather suspect it is simply because the carbs do not allow it.

Not sure of my manifold either, but there are a couple of plugged tapped holes for the breather valve I have since ordered.

My thinking being it cannot do much harm to re-instate as per original design. Also ordered original filler cap
Mark O

It's a trade off; maintaining negative crankcase pressure to reduce oil leaks from the rear crankshaft scroll, versus adding oil fumes to the intake fuel mixture which lowers the octane rating of the charge. You pays your money and takes your choice!

P O may well have consciously decided to accept oil drips in preference to a lowered octane rating, especially if the compression ratio has been increased. Or in some cases owners simply don't understand or accept the designed principle of the negative crankcase breather system and think that venting to atmosphere is as good. Which it isn't.
Guy W

Guy

On a point of academic interest only...if adding the fumes at the manifold, you could be weakening the air/fuel mix. This could be compensated for by enriching the mix slightly at the carbs - after first obtaining correct mixture without the fumes being introduced via the breather valve.

I guess you could not get correct mixture using the carbs with the breather valve in situ, as air is being introduced after the jets.

Then again, the amounts of air being introduced compared with the amount being sucked in at the carb intake may be so minimal as to have neglible effect - especially at running revs....
Mark O

Mark, l see where you're coming from, but in the standard 1275 set up that would be the norm. So the carb adjustment and needle would be designed for that arrangement from the start. The issue is with the oil vapour which lowers the octane rating, rather than about the mixture strength which can be adjusted for. For a standard compression engine that is tolerable, but not when it's much increased.
Guy W

Hi Guy,

In the long thread about oil sucking, I seem to remember the subject of octane rating degardation coming up. Wasn't the conclusion that if you don't race the car, and aren't chasing every last drop of hp, it really doesn't matter much?
Lawrence Slater

Mark,
as your car is a '73 using the valve is a going back to an earlier type of system (because of your carbs) rather than original for your car, not that it matters
Nigel Atkins

I thought I remembered reading that the octane required is related to compression ratio rather than power, bearing out what Guy's put
Nigel Atkins

It'll be more likely to knock if the octane is lower and the compression is higher.

FYI : On my RWA I have two breathers, one from the mechanical fuel pump hole and the timing chain one, that vent to a catch tank.
Philip Dodd

Chaps


I will suck it and see - literally!

Mark O

Lawrence, at what degree of power tuning the issue of oil reducing the octane becomes significant will depend on how much oil is added, and in part on the fuel available. Some sources are lower rated to start with so the margin is less in some countries. And high compression isn't limited to out and out track cars. At one time l was using a 12:1 head on my car, which l think is about the limit. I am now back down to a 10.5:1 ratio, but still quite a lot higher than standard. Compression is the easiest way to gain extra horses !

All just a matter of degree.
Guy W

Update time - The breather valve and hose to oil separator is now fitted, as is the proper oil cap.

One must be aware that the non standard carbs just have the choke enriching the mixture. I have yet to bodge something that opens the throttle a little simultaneously as per normal operation.

With that in mind, previously it took an age for the motor to settle down to idle off the choke without throttle. Now it takes but a couple of minutes before it can run with choke fully off and no throttle.

It could be that I had an air leak at the manifold beforehand, but so far, success, and the engine seems to run a little smoother. Yet to try it out on the road.....
Mark O

all this sounds good - of course it could just be a coincidence as you've put, I don't think so, but easy to check by going back to previous set up

with respect Mark this is a usual pattern for an owner new to a classic car, a little bit of tinkering (or hopefully servicing) and the car appears to run well but as more servicing, maintenance, repairs and regular driving are done things improve more and the car runs even better

unless you can drive a car in good mechanical condition of the whole car you haven't a bench mark to compare to

the incremental improvements add up so that after a year of regular driving, servicing, maintenance and repairs the car is hard to compare to when purchaced

of course the engine and carbs are just two items to have the car running well the brakes, tyres, suspension, steering, transmission and drive need to be in good order too

I'm sure your Spridget will continue to improve because of your ownership
Nigel Atkins

Nigel---Nag nag nag ---one thing at a time! I jest of course, but brakes are OK apart from needing a bleed, tyres are good, suspension - yes new polybushes required, steering OK as it goes where I point it - but I do like those Moto Lita steering wheels, tranny OK, but clutch still a bit stubborn, and my drive has spots of oil - hopefully now cured.

Engine work is now hopefully complete - for the moment!
Mark O

me nag !?! narh I just don't see that

if the brakes just need bleeding then get on with it :)

my braking was improved just recently by changing from worn (but not that worn to some people's standard) to new tyres despite the new tyres not being as grippy as the worn tyres

steering wheels (and boss) are expensive save the money for a future unpleasant surprise - yes I'm pessimistic - from repeated experience :(

clutch, could that just need bleeding or a flush and change of fluid, master or slave - worth trying a bit to save engine & g/box out (unless you enjoy that sort of thing)

we've had 4 good driving days out of 4 since the start of the SORN season so plenty of regular driving opportunities
Nigel Atkins

SORN? what's that, I'm a converted all year round driver...
Pete Ottewell

SORN has a Season?
Lawrence Slater

well done Pete, I'm sure you'll not regret it and get to enjoy those crisp top down days as well as the dry and sunny ones

L,
for most it's from 1st October to 31st March, also coincides with when most car shows are on and full or halfday club runs
I was going to count how reasonable and good driving oppitunities days there were in a SORN season but soon realised it'd be easier to count the days that weren't
Nigel Atkins

Well given the summer we've had, if you're that way inclined, you might think most of the year is a SORN season then. :
Lawrence Slater

I wonder how many actually bother to SORN a Spridget for the winter months. Seems hardly worthwhile in the UK really, whether or not the car is used as a winter driver. Certainly on pre 1973 cars there is no financial advantage on the tax, and probably little or none on the insurance side either. So what's the point? For post '73 cars you would save a bit of tax, that's all.

Quite apart from this, my guess is that there are many more owners who continue to use their cars all year round, at least on occasional days if not daily, than those who decide never to use them at all in the winter.
Taking the car off road during the winter for refurbishment or some significant mechanical work is a another matter. The logic there is quite different.
Guy W

some classics and sports cars are hardly used during the good weather in summer months so the owners know they wont drive the car in SORN season plus they save 6 months RFL

some owners think classic cars are so unreliable and let in so much water with very ineffective heater that they can't be used

and as I put some only want to show the car off at shows or runs during the summer

some have a fleet of cars so rationalise their use

obviously it's a personal choice

I'd guess a greater proportion of Bs get SORN'd than Spridgets but Spridgets do get SORN'd for 'winter'
Nigel Atkins

What is ... SORN ???
Prop and the Blackhole Midget

Statutory Off Road Notice - you notify so that you're not chased up for not paying your 'road tax'

the car needs 'road tax' to be used on the road even if it's no charge (for pre-73 built cars)
Nigel Atkins

Back to Mark O's original query: There are PAGES and PAGES devoted to issues about using carb vacuum to impose a negative pressure on the sump. There are potential problems using the pressure control valve (PCV - mushroom) because there are a lot of reported instances where the manifold suction can draw up oil into the carbs and chuck it out the back as an impentrable cloud.
I went down just this route for the same reasons as you. When I first did the conversion the oil level was just above minimum on the dipstick and all was fine. When I topped up, that was when I had problems. I thought I had experienced a major mechanical failure because of the exhaust and when I checked the pcv was full of oil.
There are theories about the oil not getting away from the timing cover sufficiently fast and so flooding the intake to the pcv pipe. Whatever the reason, when I removed the pcv and left the open vent on the timing cover all was well (and no oil ever ran out into the collecting pot on the open end). It could also be that like many pattern made S&M parts, the pcv is rubbish and doesnt work as it should.
And the leak didn't stop either!
Graeme W

your post made me scroll back and I realised I'd, as usaul, not put me point well
>>as your car is a '73 using the valve is a going back to an earlier type of system (because of your carbs) rather than original for your car, not that it matters<< (I should have added) about originality
Nigel Atkins

I think the point which is sometimes missed is that when the PCV is removed - perhaps due to the oiling issue as described above, and the breather left open to atmosphere - the oil leak will still remain. I've found you need at least three 1/2" open breathers to effectively reduce crankcase pressure to the point where the scroll can keep the oil in. So in addition to the one on the timing case chimney, I have another on the rocker box and a third where the mechanical fuel pump lived. I have 2 warmed over 1330's like this and neither drop any oil.
F Pollock

The control valve was phased out in the late 60s and replaced by a Y fitting in the suction tube with connections to the bodies of the SUs by way of a spigot tube drilled into the main body, whereas the PCV was connected directly into the manifold. I must admit that I haven't sat down and tried to conclude why in one case the suction pressure can be applied directly to the sump whereas in the other it needs a complex valve arrangement. Presumably the posion of the butterfly valve relative to the suction take off position is important in reducing the extent of the vacuum.
I am sure that in either case the vacuum transferred to the sump would be beneficial to the rear oil leak, but in my case it was a disaster!

Fergus: I can see your point about risks of removing the pcv. Surely multiple breathers are just going to try to keep sump pressure at atmospheric although some suggest that dropping the free end of the breather into the moving air under the car creates a bit of suction by way of air flow passed the end (1959 ground effect!). The pcv (or the carb take off arrangement) gives the opportunity for very high suction to offset the positive pressurization in the sump. Or if it goes wrong, emptying the contents of the sump into the manifold.

Mark O: It doesn't sound as though you have had the opportunity to give the breather a thorough try yet and I hope it works for you. If you have problems this is a good read if you have half a day to spare: http://www.british-cars.net/mg-midget-sprite-technical-bbs/engine-breather-2012021613512829381.htm
Graeme W

Graeme - yes I think the PCV is designed to cope with a more or less standard engine inside of tolerance - once applied to a heavily modified and/or a worn engine you will often get oil ingestion - which is why people leave them off. In these cases the PCV cannot deal with the amount of blowby and is simply overwhelmed, allowing positive pressure to feed directly into the inlet. So my suggestion of leaving enough breathers open to atmosphere attempts to put the crankcase at atmospheric - and if the scroll clearances are close enough, it will actually work well enough for the oil to be retained.
As additional reading take a look at this explaination of how the PCV works. http://mgaguru.com/mgtech/engine/cv103.htm
F Pollock

Fergus - that's an interesting item. Bit early in the day to digest properly but I'll come back to it again.

My valve was brand new and fitted to a standard 1275 engine. As I commented, with "near mimimum" oil I had no problem but when I topped up I managed to get real liquid oil (not condensed vapour) into the valve and the manifold. At one point oil sprayed out of the pressure balancing hole in the top of the valve and the engine wouldn't stop running even with ignition off. That was such a close call that I wouldn't even try it again!

I do have serious concerns about the quality of the new valves. The article you list indicates that their operation is a careful balance of pressures and I wonder if that translates correctly to the pattern made ones?

THe contraversial issue is how oil can get there in the first place which can only really be explained by a build up of oil in the timing cover which then floods the outlet to the tube connected to the pcv. Some say this can't happen but what ever the why's and wherefore's if oil IS sucked up, it is not a pleasant experience. It's a recreation of a 1950s London smog!
Graeme W

As I have a heavily modified 1275 (EFI and supercharger) I ran into lots of trouble keeping the oil. I ended up with drastic measure, modifying the sump. This did the trick, I have only limited leaks now.... Was quiet a puzzle


a.o. arnold

Hi Graeme,

Where were you in March this year, when the very subject of oil being sucked into the manifold was discussed?

393 posts to the thread titled "engine breather"

Bob Beumont started it, by saying.
"After starting from cold after about mile or so my Frog blows a big cloud of blue smoke from the exhaust it clears and is not repeated"

I recognised it as a problem I had, and then set about trying to convince the doubters that it was actually happening, EXACTLY, as you are now describing.

My conclusion, is that, yes the timing cover must fill with oil, and the only remaining question is precisely why that happens. I have and still do suspect a dodgy cam end plate cover, but that is not the only suspect.

btw, it also happens with the Y piece arrangement. That is my experience, and many others who posts I collected.

Where are you in Kent?
Lawrence Slater

Were you using the correct gauze oil filler cap at the time? If you had a shiny chrome one (with or without a pin hole) the PCV would suck harder on the timing cover and this could be enough to draw oil up and into the manifold - and once inside the PCV the pooled oil would likely stuff the fine balance described, and then on the over run produce a crazy James Bond smokescreen.
F Pollock

Lawrence: in March I was a happy bunny, not knowing what a pcv even was! By about May I was on my way up a fast learning curve having just fitted the kit and then removed it. I did read the 300+ posts at that time (I remember the sun came up over the horizon by about post 250, having started the night before!) together with a number of other posts on other forums. PCV and oil carry over must rank with "front wheel bearings" as S&M most debated subjects! And neither really have a satisfactory conclusion.

Fergus: shiny chrome! But surely (?) the only way oil can come up the breather is if the bottom end at the timing cover is flooded in oil. If you put a tube in a bottle half full of water and suck, you can only get water up the tube if the bottom end is submerged. Once it is underwater, even a relatively slight suction will pull up the water. I can't see the pcv controlling the pressure sufficiently delicately to only draw the oil half way up the tube. If there is oil there it will come over (won't it?)

I think it is significant in my case that the difference between bottom level on dipstick and top level was sufficient to cause the problem.
Graeme W

Hi Graeme, well I hope you enjoyed both long threads. ;)

It's great, though unfortunate for you, that we have a "live" account of this happening. I know it happens on the Y piece connection, and you, and others, know it happens with the PCV too.

So to me, the issue isn't the manner of suction, it's as you conclude, the level of oil in the timing cover. Why does the oil level get, and remain high enough, to allow the vacuum to get hold of the oil, and pull it up into the inlet system?

What Fergus says, might be the case with some though, esp as Bob changed his rocker cover cap for a new bog standard plastic one, and so far, his problem has been resolved. And as I put earlier, if there is sufficient sump pressure, and that can't escape via the potential blocked rocker cover cap, it would aid the vacuum. The sump pressure would push from behind the oil, whilst the vacuum would pull from the front.

However, if there was insuficient sump pressure, and the rocker cap were blocked, as no air could be drawn into the sump, eventually there would be an increase in negative air pressure in the sump, and wouldn't that pull against the vacuum from the inlet, thereby resisting the suction of oil?

What condition is your engine Graeme? Standard tune? High milage? Is the oil dip stick the correct one, and thus reading the correct oil level?

It's on my list of things to do, to rig my spare engine with a clear fronted timing cover, and manually crank it over to watch the oil delivery from the front cam bearing.

Lawrence Slater

I dont mean to walk into this confined elevator sized room, pop a silent rotten egg smelling fart and walk back out just before the door closes for that slow travel to the lobby,...BUT, here goes.

What about just changing the rings and a fresh cly hone and a valve clean up...

Basically ... Just cure the primary issue of the blow by

Prop...Im exiting the elevator now, group hug, discuss, enjoy.
Prop and the Blackhole Midget

Hi Graeme,Lawrence et al, I must admit being the one that suggested Graeme purchased a PCV to cure his oil drip problem. it does seem to me that negative crankcase prssure works. My engine does not drop oil, honestly! I even leave cardboard underneath to check. I did assemble the rear main very carefully using a thin film of hylomar on the rear cap/block face and took care to ensure the gaskets and seals on the sump all fitted snugly together. I did however, have the blue cloud problem. BUT the combination of a new old stock vented filler cap and a new pipe to the Y piece on the carbs has cracked the problem. I have run all summer with not a wisp of blue smoke and the engine burbles along happily. I have retained the old cap which looks and seems fine but clearly changing it had the desired effect. It is meant to be changed every 12,000 miles and it had certainly done that. IMHO something to be said for keep things standard!
Bob Beaumont

before Lawrence puts it I will :) - see my photo of a new standard vented/filtered cap, you can pop the base off to clean out the filter, if you want to, and it will last a lot longer
Nigel Atkins

Hi Bob,
I don't dispute that changing your cap and the tube to the Y piece, fixed the problem. But it's not clear why.

When it first happened to me, I changed my cap too, and it didn't fix the problem. I also installed a clear plastic tube, so I could watch as the oil was sucked into the carbs. I was never able to fix the problem, and lived with it until I replaced the engine with my spare rebuilt engine, which also did it, until I changed to an HIF44 single SU. Less suction perhaps?

Also, there are plenty of cars out there that are running with the PCV, and don't have the oil suck problem. So I reckon suggesting the PCV is quite reasonable to cure an oil scroll leak. I don't reckon there's anything in particular wrong with the PCV. The problem of oil sucking must lie elsewhere.

Prop, you've missed the fact the many who have experienced the oil suck problem, have already rebuilt their engines.

If someone with the oil sucking problem (Graeme perhaps?), was willing to put their PCV back on, just to experiment with changing the rocker cover cap for a new standard plastic one, maybe that might or might not shed some light on it.
Lawrence Slater

Lawrence, I am not commenting on your oil sucking problem as I rather feel that aspect has been flogged to death already. Not that I don't think it good to try and rationalise these problems once and for all. But I would just say that common symptoms do not necessarily mean common causes. Enough!

What I was going to add though is that I understand (i.e.from reading around the subject,) that there was a developmental progression during the life of the A series. The early engines (A30 pre Sprite)just breathed to atmosphere via the rocker cover. Then that was plumbed into the air filter, but mainly to get rid of smelly fumes (A35/A40).
As the engines developed both in capacity and more particularly in engine speeds they breathed from the tappet chest cover as it gave more direct connection to the crankcase. Further development of the engine output began to overcome the effectiveness of the rear scroll so the passive to atmosphere breathing needed to be developed as a negative crankcase system. This required a more sophisticated control so the PCV (as used on the MGA engine)was added. The problem with this was that, as has been described, the PCV is a quite finely tuned device that will only work effectively within certain range of conditions.

One problem is of course in using manifold depression which is greatest on overrun, just when blow-by is likely to be at its least, creating too much suction when it is least needed. So the switch to a suction point upstream of the carb butterfly which more nearly mimics the occurrence of blow by. I suspect also that economics came into this as well. Y piece connection is a lot cheaper than a PCV valve!

Anyway, the point is that there are different systems suited best to different engines. Swapping breather systems around isn't necessarily going to come up with the most effective solution for a particular engine. And then add aftermarket engine and performance changes and you get a whole different range of issues and possibilities!
Guy W

Start up and tick-over was enough to pull the oil over in my case.

Compression is fine. After the incident I bought a compression tester because I suspected major issues in that area.

The dipstick is correct because I drained all the oil out and refilled the correct amount to see where it showed on the dipstick.

I do have high oil pressure and wonder whether that could be feeding the oil somewhere faster than it can get away? I have a new spring to try just in case the wrong one has been fitted to the oil pressure relief valve.

Once I have my back axle sorted I might feel tempted to investigate again and refit the pancake again. But I have to say that when it reached the point where the engine wouldn't stop I got "concerned". Hey, I can't keep buying new underpants!

Graeme W

Graeme,
If the PCV valve was faulty and porting the breather tube directly to the manifold, without any diaphragm control, then the manifold suction which is very high could draw oil up from the breather pipe.

Running on was presumably as a diesel, "oil burner", feeding itself from the sump oil. :-)
Guy W

There you go Guy, enough is not enough it seems. ;)

Good explanation of the developement of the breather system that. All makes perfect sense. But the subject of oil sucking keeps coming up, and irrespective of my introducing it -- which I didn't in this thread. Also, I do feel in this case that there must be an underlying cause/condition, which if it did not exist, couldn't result in oil being sucked into the inlet. So I don't think it's possible to flog this to death, until it's resolved. Just a personal opinion of course.:)

As Graeme has just said, and I also discovered, the correct oil level, even on tickover from cold, can result in oil being taken into the inlet system.

If the oil is sitting below the level of the internal entrance to the oil seperator on the timing cover, no matter how much suction there was, wouldn't result in a continuous column of oil being sucked up. The suction from the PCV or the Y piece would simply draw air and fumes from the sump, via the air being fed in from the rocker cover cap and any other air leaks. But as soon as the oil level reaches a critical level, up it goes. That's the issue as regards oil sucking, at least to me.

The issue of the oil scroll leaking is a seperate, but related issue.
Lawrence Slater

Lawrence,

Your comment regarding reduction in smoke after fitting a HIF44 is very interesting - it is a comment I've made on earlier threads - Vac only feeding down one carb suction hole not two.

I'm about to fit a HIF6 and was questioning if their would still be sufficient neg pressue vent to avoid the leak - although mine has a rear oils seal conversion.

R.

richard boobier

I'm getting the nightmares back now!
Must lay down. The blue smoke........
Quick... my tablets!
Graeme W

Lawerance...

If your sucking oil thur the oil seperator and into your carbs...

It sounds like a classic case of a missing or wornout gauze inside the oil seperator ((( thus the term oil seperator ))), the purpose of the gauze is as the oil fumes are sucked into the oil seperator on the timing cover, the gauze catches the oil mist vapor and the oil is cooled and then reliquified back to oil that drains back into the engine timing chain cover

So id say replace the gauze inside the oil seperator, and id think your oil sucking issue is solved....

If thats not the case ....its time for a new dip stick because you are putting way to much oil in the engine for the oil level to get that high to be sucked into the oil seperator

Prop
Prop and the Blackhole Midget

I can't speak for Lawrence but in my case it wasn't condensed mist, it was liquid oil. There was just so much of it - even enough to keep the engine running on. And that was after about a minute on tick-over.
I also know the dipstick is ok and that I'm not overfilling because I drained the sum and refilled with the correct quantity. I had hoped that an previous owner had put the wrong dpstick in but it wasn't the case.
The breather now leads through a short flexible tube into a catch pot. That has remained clear of oil.
Graeme W

If the the gauze is missing or wornout... Then you definatly will get liquid oil into the carbs....

The oil vapor mist only takes a short time for it to be cooled and reliquifid ....

When you pulled the gauze... What condition was it in ??? Was it shinny flexiable, and very filtery, or was it hardened, rusty black packed, and looked like a river rock and filtered about the same.

The answer to that questionis very important...dont just guess or assume.. actual eyes on gauze is a non exception


I surmise if an engine sits for long the gauze can clog up and rust thus the packed up mess they turn into...something that resemmbles a hardened minrial rock rather then a scouring pots and pan scouring Pad scrubber that oil mist can easily pass into and be captured... If its a minral rock stone then the oil mist vapor simply passes around the gauze and is cooled back to liquid in the vent hose on its way to the carbs ....thus liquid oil in your carbs

Yepp...its a pain to check, but what did sherlock homes say about improbable facts ...

Prop
Prop and the Blackhole Midget

Your catch can remained FREE of oil....Hmmm, now that sounds strange

If you had that much oil going to the carbs BEFORE the catch can, and now you have no oil in the catch can after the CC has been installed....

Im not seeing how thats possiable....i wonder if the catch can is acting like a oil seperator and the oil is draining back into the valve cover before it can reach the added catch can

Prop and the Blackhole Midget

Is your catch can vented to the carbs or it the catch can vented to the atmosphire by way of a filter or a filter with a one way valve installed just before the filter ???

The added catch can is vented in some way ...correct???

Thats a real brain teaser for the day

Prop
Prop and the Blackhole Midget

****in my case it wasn't condensed mist, it was liquid oil. There was just so much of it - even enough to keep the engine running on. And that was after about a minute on tick-over.****

To me that condition just screams burnt hole in top of piston, broken piston landing, some type of major failure that is allowing combustion pressure into crank case...maybe even some kind .of cracked head.... Pure guess at that

Because if its running on and that much oil comming out of the carbs in under 60 seconds from the time its started thats clearly mot a wornout gauze issue

But i cant under stand how an added catch can thats not collecting oil solved that issue

Prop
Prop and the Blackhole Midget

Prop: I think the oil was over coming over because the pcv connection was sucking it out.
The catch tank is just a plastic bottle down by the shock absorber with the end of the rubber tube from the timing cover dropped into it. No separator and it's open to atmosphere. The thought being that if pressure in the sump was forcing the oil over, it would end up in the pot. No oil does come over.
Haven't looked at the wire mesh because I didn't think it could be got at without removing the timing cover, which was an area i did'nt want to disturb.

My thought process was that the leaks off the engine aren't actually that bad, so how much did I want to dig into this complex can of worms. Just leave it and tackle the next priority.
Graeme W

Hi Prop,
I seem to remember you mentioning that you got bored reading the whole of the long thread titled "engine breather". As such, you are asking question that were already answered in there.

So to clear it up again, and now with the back up of a 2nd person describing EXACTLY the same thing that I described.

1). The oil is a continuous column of liquid oil. it is NOT, repeat, not, the result of condensate, and is not a catch tank issue.

2). The engines in question are in good condition, often having just been rebuilt. They don't have holes in the top of the pistons.

3). There is suficient oil being sucked up, to drip out of the tail end of the exhaust pipe. The exhaust note even changes when it happens, because, in my case at least, the silencer had so much oil in it. It made the same sound as it would make if you stuffed a rag or a potatoe in the tail pipe.

4). It has nothing to do with the existence or absense or the condition of the gauze in the timing cover breather. In fact the more contaminated and blocked the timing cover breather gauze becomes, the more likely it is that the oil won't be able to be pulled through in the same quantity.

5). I'm quite sure that as Guy has described and experienced himself, and has been confirmed by Bob b's recent experience, there IS an issue with contaminated breather tubes and or dodgy rover breather caps. However, that is a SEPERATE issue, that is being confused by some, with the issue of a continuous column of oil being sucked up.

Just as Graeme has described, I eventually got fed up trying to work out what it was, and lived with it. If you are interested in knowing any more, --- I bet you aren't though --- read the original thread. :)

Hi Richard, I'm assuming that there is a reduction in vacuum as a result of the single connection to the HIF44. If so, it doesn't seem to have cause my oil scroll to leak unduly. But that could simply be because I don't have much sump pressure. I have cords rings, and I reckon they are well bedded in.

Lawrence Slater

I wonder how Mark O is getting on? Perhaps lost the will to carry on I expect.




Graeme W

Hey lawerance,

Oh... Quite contrair, i actually enjoy the topic of vacume and crankcase pressure ...its WHEEL BEARINGS that make me sucidel...hahaha

Im at work right now... Give me a few hours and ill read up on the thread, are there other threads you have posted to about the same conditions....if you can, give me a basic run down of the issue...whats been tested, whats not, how it came about ect ect

Ill give it a good read and offer up any thoughts i have

Later buddy....Mmm nothing like cieling paint for supper tonight...hahaha

Prop
Prop and the Blackhole Midget

Prop - ur going to need a head start as it takes a lot of reading
http://www.british-cars.net/mg-midget-sprite-technical-bbs/engine-breather-2012021613512829381.htm

Ah, front wheel bearings......the nightmare continues!
Graeme W

Chaps

Well......I give the car a bit of a blast this weekend and so far


Cannot see any drips anywhere underneath - this is good news..

No more stinking engine bay - also good news...

However, I occasionally encounter a slight overrun when ignition turned off. I put this down to now using BP6Es instead of the previous BP8s on an engine with a higher lift cam - BP8s incidentally ditched as they were either duff or unsuitable- and I am not sure whether the exhaust is a little smokier - although that may be fine mixture tuning/normal.

In short, more testing/data required, and to keep a wary eye on oil consumption - in case it is sucking up the stuff. So far, no serious adverse effects
Mark O

Mark,
Sounds like you've cracked it. I wouldn't worry about oil sucking. If you had it, you'd know all about it. From what you describe, your running normally.

Overrun is possibly hotter plugs, but could be also be timing. If it wasn't doing it (overrun) prior to the fitting of the PCV, then it could also be fuel/air mixture.

I haven't had a rolling road tune up, but people on here swear by it. P Burgess often gets a mention, so if you can get to him and fancy the cost, he'll probably sort out all your tuning/carb/plug issues. If you're not near him, then I think there are others that people on here can suggest.

Otherwise,and since you're engine isn't standard, you'll just have to experiment and tweak with various settings.
Lawrence Slater

As mentioned in another thread I think you'll have a better time with BP7ES's. You can get them on eBay for £6.20 delivered.
F Pollock

Mark O: if you are pulling oil over, from my experience and that of others, you WILL know about it! You can't see behind. Pedestrians are falling over coughing. People are pointing!
And when mine ran on it was for 20 secs or so. And liquid oil sprayed out of the top of the pcv in fine droplets with enough oomph to cover both front wings (Bonnet WAS open!).
Not good!
Graeme W

as you've made changes you might need to check your timing again and reset your mixture

some have said they experienced run-on after a fill up of petrol and there could be a change in fuel for the colder weather at filling stations(?)

Peter Burgess does excellent value and effective rolling road tune ups, best by far of the three different tuners I've tried my present Midget on for value and effectiveness - he also sells and tunes 123

l'll advise you on the NGK plugs you need

RR tune ups are best done on a fully serviced car as obviously you can build better on good foundations
Nigel Atkins

Hey lawerance,

I when i hooked up a vac gauge in to the hose from the timing cover to the intake manifold, i got 9.5 psi...neg pressure, when i hooked up the hose to the carbs via the Y piece iI got 2 psi neg without the air filter

Sorry for using PSI... I know its supposed to be bars and hg, but my vac gauge is measured in psi


With 9 psi of vac at my intake manifold im not able to find a catch tank as they all get crushed, with in moments from the inside out,


My guess is everyones vac pressure will be differant even on new rebuilt engines, if your sucking colums of oil, i doulbt its due to the oil cap hole but more to do with dynamic compression ratio and the effect its having on the suction of the intake manifold

One theroy ive had for some time is the orginal truppet air cleane design... I think people that have replaced them with the popular K&N air filters may have a stronger chance of rear scroll leakage

If you look at the orginal truppet air cleaners its very restrictive and focas the air very tightly ....thus the air flows much faster into the carbs... Aka "constriction" ...like a shop vac, but with a much smaller hose creating more vacume....where as the K&N is much more open less restrictive and lots less constriction so the suction is alot less

Like i said, ita a thought.

Hey lawerance,

Did you ever replace the hose on the timing cover...if you did,it needs to be with a transmission type of hose...NOT HEATER HOSE, heater hose is okay for low suction but the hose will collapse or be sucked in on its self if you have if hooked up to the intake manifold... And the oil will definatly eat the inside of the hose out in a short time

So the hose needs to be inside oil resistant and constriction proof...if the hose is collapsing its going to add more constriction and thus more vacume

I really think the ansewer your needing is a baffled crush resistant oil sperator/catch tank that you can control the vacume on....

How do you control the vacume on a catch tank...im not sure, i thinking some kind of metered air inlet valve, but thats creating a vacume leak ....and that cant be good

Id seriously recommend sealing off the oil dip stick tube because that thing leaks engine vac at almost 1 psi when i measured it ... And measure your crank case vacume in the breather hose by way of the intake manifold and compare it to the vac on the carbs

Im betting you got some serious vac in the crank case much more ten the avg person and probably due to modifications to high performance add ons....

That said... Maybe a bigger hole in the oil cap would help to reduce the engine vacume in the crank case and allow you to hold more oil in the engine.

Anyway, there are just a few of my thoughts on engine vacume


Prop

Prop and the Blackhole Midget

Hey lawerance,

I forgot to mention... On a baffled oil catch tank/seperator with some kind of adjustable vacume valve....perhaps run the exit point of the vacume valve into the exhauste pipe...the force of the passing exhaust wont allow oxygen into the intake manifold...just a small minute amount of burnt exhaust gas. And that shouldnt have the effects of having a vacume leak of oxygen
Prop and the Blackhole Midget

HAAA !!!

Well... Ask google and you shall receive

An adjustable vacume valve... And cheap to $55

That solves my crushed oil catch tanks from the intake manifold

http://www.jegs.com/i/JEGS-Performance-Products/555/23630/10002/-1?parentProductId=756311#moreDetails

Prop
Prop and the Blackhole Midget

Oh this is even simpler then i imagined... It screws into the valve cover to control the engin vacume ...so you can hook up the timing cover hose to the intake manifold then control the engine vacume pressure thur this valve so as not to suck oil into the intake or crush oil catch tanks...very cool

Basically it ttakes the place of the hole in the oil cap

Prop


Billet Aluminum Adjustable from 0-25'' of crankcase vacuum. Bolts into valve cover with -12 AN jam nut. Designed to be used in conjunction with racing vacuum pump to maintain desired crankcase pressure
Prop and the Blackhole Midget

Hey prop

I think you may have found the answer to my conundrum. I had the oil mist problem but changed the oil cap AND THE HOSE. the hose was old and tatty and very much past its best. The new one was a proper oil resistant one with nice strong walls. Presto! the problem has gone.

Bob
Bob Beaumont

Hummmm....maybe thats a bad idea, i wonder if that would slow down the speed of the airflow in the intake manifold....maybe hook it directly into a catch tank and and run the hose from the valve in the catch tank to the intake manifold

Prop
Prop and the Blackhole Midget

Hey bob...

Great catch... When i built my engine i replaced the hose with a heater hose and when i hooked it up to the intake manifold i saw the new hose collapse under the vacume and talked to people smarter then me and they said to use the transmission hose instead...so makes scence the smaller the inside of the diameter gets the more suction thats created ..
Prop and the Blackhole Midget

Hey, you've been busy Prop.

I don't have a catch tank, only the standard rig on the timing cover, connected to the carbs. At first this was via the y piece to twin SUs, but now direct to the single HIF44.

I can't remember if I had the original air filters when I first had the oil suck problem, but definitely had it with K&Ns.

Never had a hose collapse. At first I had strong rubber hose, in good condition. I replaced it with thick wall clear plastic, so I could watch the column of oil, as it was drawn up from the timing cover. I still use this clear hose, connected to my single HIF44.

When we discussed all this before, Guy I think, or me, or someone anyway, proposed a release valve to check the vacuum if/when the oil began to suck. I think that's a possibility, but would rather ID the root cause, and then fix that.
Lawrence Slater

All your measurments got me thinking again Prop.

It's a pity I didn't try and get a measure of the sump +ve pressure, when this was first happening to my engine.

Putting to one side, the condensation/slug of gunge version, and concentrating only on the true column of sucked oil version, -----

The oil has to reach and cover the internal hole in the timing cover breather. So either it's because of too much oil being delivered to the timing cover, or because it can't drain away fast enough. Assuming correct delivery amounts, then why can't it drain away fast enough? When it's warmer, the problem disappears -- it did on mine. Thinner oil or better piston ring sealing?

If there's and excess of +ve pressure in the sump, over and above what's considered normal, then that pressure would try to escape through the very holes that the oil is trying to drain through, -- as well as perhaps up through the rocker cover and the larger "vent hole" in the face of the block.

I've been remembering when it first happened. I disconnected the breather tube, and left it to air. Apart from not liking the fumes, I also didn't like the rear scroll drip. So clearly I had +ve sump pressure, but figured that was normal without the vacuum to deal with it. What I can't know, is if I had more sump pressure than is so called normal.

Has anyone ever attempted to measure this, and establish a range? Maybe this would be impossible, since so many engines are modified. However, when it first happened to me, it was on a standard 1275, whose only modification, was a rebore to +20 thou. Otherwise, it was a standard engine.
Lawrence Slater

What you would need would be a pressure gauge that had a sticky needle - so that it would work a bit like a max / min thermometer. Connect it up, drive around for a bit, check the readings, reset, alter your breather system, retest - - - - you could learn a lot.
Guy W

Yup, I imagine it can't be very high presuure either. I might look for one, which as you say has a recording facility. Must be a digital version available these days I would think.

Block off the dip stick, the rocker cover cap, and the timing cover tube, and see what I get. No doubt oil and thus pressure escape from the rear scroll. But if several people did it, -- well at least it would be interesting. --- Depending on your level of interest lol.
Lawrence Slater

Mark,
just reading new posts and noticed a mistake in my last post - I of course meant Peter would advise you on the NGK plugs you need not I (he'll not I'll) but you probably guessed that
Nigel Atkins

Id try putting a hose on the dip stick with a hose clamp and a boost gauge into the hose...you could run it into the cockpit to watch as you drive around

Boost being both vac and pressure gauge
Prop and the Blackhole Midget

Congratz....another centry thread

Prop
Prop and the Blackhole Midget

Btw lawerance

I think the slow drain back is because oc the internal hole in the front of the block...its sits proud by 3 or so inches....if your pulling 8-10 psi of vac... Id say it will be hard to drain that oil back qiuckly into the engine
Prop and the Blackhole Midget

Not tried putting my finger over the end of the rubber tube I have on the timing chain cover breather. That would give an indication of whether there was pressure there.
Graeme W

Graeme, there must be some pressure there, just from the action of the piston travelling down the bore.

The question is, how much?
Lawrence Slater

I don't think movement of the pistons is responsible for any pressurisation of the sump as when one piston moves down, another is moving up so the total volume of the sump/crankcase remains the same. My theory would lean towards a small amount of "blow-by" of the rings, particularly caused by the very high pressure generated immediately after detonation.
M J Chapman

"when one piston moves down, another is moving up so the total volume of the sump/crankcase remains the same.

But does it? I seem to remember this discussion before, and someone said that the air drawn in by the ascending pistons is greater than can be expelled by the descending ones.
Lawrence Slater

X 2 lawerance

Moving parts in rapid motion does create pressure...think of a blender...chopping and pulping tomatos...pop that top off at full blend and watch what happens to your cieling
Prop and the Blackhole Midget

"someone said that the air drawn in by the ascending pistons is greater than can be expelled by the descending ones."
Drawn in from where? Surely the dynamic volume has to remain the same - who is this someone? Come out wherever you are!!
M J Chapman

I can't see how the pistons themselves cause pressure to increase in the sump. But, as menstioned, the detonation must leak passed the rings. That's how oil gets contaminated with combustion products.
Graeme W

I didn't say it was definitely the case, I asked if it was. I'm trying to find the discussion, it will be in the archives somewhere, and I think it was this year actually.

As to where the air might be drawn in, that's fairly obvious isn't it? The air is drawn in via the rocker cover cap, the dip stick opening, and maybe even the even the rear scroll. These aren't sealed.

If/when i find the discussion, I'll let you know. ;-)
Lawrence Slater

But, if as we all agree, the sump is pressurised, the innards of the rocker cover will be pressurised too won't they, since they are connected to the sump? Which means air flows "out" not "in".
Graeme W

Found some of what I remember, (comments by two esteemed members ) although not exactly as I remember it -- i.e volumes of air-- , it does discuss sump pressure, and why it might not be as simple as it appears at first look. Guy makes reference to another thread, but I can't remember which it was.

Guy, Cumbria, United Kingdom
Posted 27 February 2012 at 13:42:32 UK time
I would agree, Whilst it is easy enough to consider a static situation, A connects to B connects to C therefore.... it is all too easy to forget that in practice one is dealing with extreme dynamics in a running engine when all sorts of strange effects must be going on. In another thread I was mentioning piston speed and rapidly changing velocities and whilst in a simplistic view the pressure created by two pistons descending would be compensated for by the other two rising, in reality there must be some very strange turbulences and high speed pulsing with pressure waves and reflections all over the place!

David Billington, Bath, UK
Posted 27 February 2012 at 14:07:40

"Guy,
Due to the crank and conrod arrangement and the conrod being at an angle the rising pistons aren't fully compensated by the falling and this leads to pressure pulsing in the crankcase.
Lawrence Slater

This thread was discussed between 01/10/2012 and 14/10/2012

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