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MG MGB Technical - Breather fiasco!!!!

hi, i know there have been many breather related threads on here but im stumped on this one. My 68 GT which has the later 18v engine has a major problem with the breather. Whenever i use high revs my engine bay gets completely covered in oil, and i mean loads!!
First i checked my compressions for blowby, 159, 160, 161, 160psi. So that wasnt it. Its using HS4 carbs with the breather holes in them. They were blocked off with the tappet chest cover breather venting to atmosphere with a little filter. I then put an oil catch tank on the breather then a "y" peice with hose taking it back to the two carbs. I then started the engine and checked the oil cap was sucking which it was. I then went for a drive and made sure i was doing some high revs, then about after an hour i saw smoke coming from the back of the car. When i got home i lifted the bonnet and found the catch tank was completely full and hence oil was getting into the intake on the carbs. I checked the tappet cover wasnt blocked and it isnt and the gauze inside it solid and in good condition. Has anyone got any more ideas as im out of them!!! Everything else on the car is great, just this breather problem.
A P New

AP,

I can't quite visualize the details of the catch tank to carb set up. Is that a closed system?

Do you have the non-vented oil cap with the small restrictor vent elbow (crankcase breather intake port) in the valve cover?

Charley
C R Huff

it is a closed system now, it wasnt before but it didnt make much difference either way. Its a vented oil cap, without the restrictor vent elbow. Its currently set up with the breather on the crankcase going to the catch tank, then from the catch tank to the carbs.
A P New

AP. This is one of those interesting problems that really need someone who knows what is happening to examine the current system and assist you. All we can do is throw out ideas.

First, a compression check establishes that you have sufficient compression for the engine to run properly. Generally speaking, about 100 psi is sufficient to allow the cylinder to fire properly. But, a compression test is not a test of blow by or for blow by. That would be a cylinder leak down test. They test related things, but a good compression test does not, by itself, rule out blow by. However, I do not think that blow by is your problem.

You are using a home made catchment basin system with you are attaching to the carbs (source of vacuum) and the front tappet chest cover (vacuum applied), an area which has liquid oil running by it down the push rod holes. This seems to be an unrestricted vacuum source, applying full vacuum all the time. The system seems to be much like a Mighty Vac used with the brake bleeding adapter and having the reservoir jar to catch the brake fluid which has been sucked out of the lines. Thus, does your unrestricted system suck oil out of the engine and into the catchment container.

The 18V rocker arm cover has a 90 degree elbow attachment which goes to the filtered air (and vapors) in the charcoal canister. The attachment is mostly closed off with only a small opening to allow air and fumes to enter the engine system and be drawn through into the carbs or PCV valve.

It seems to me that you would be better off trying to use the 18V rocker arm cover, with its built in restricter, and a small filter to prevent dust and dirt particles from being drawn in, than using the original model rocker arm cover which allows unrestricted air flow through the system.

I might clean out my catchment tank, then run the engine at something like 2,000 rpm for some period of time (say 20 minutes) to establish how much oil was being sucked out of the engine and into the catchment tank. Then, I would place some form of restricter into the system and repeat my test to see what, if anything, had changed. It would be a valid test of my theory that there is too much air flow through the engine allowing liquid oil to be sucked out of the engine and into the catchment tank.

Les
Les Bengtson

Sorry to butt in but I am always interested in breather problems.
I am just wondering with this one is your oil level too high,(are you over filling it)

The reason I suspect this is that it would appear to me that oil is in the breather system and is being blown into the catch tank. Instead of only oil mist being blown!

Could very easily be something else, however!
Robert (Bob) Midget Turbo

Hi All,

AP

I remember reading of a similar problem elsewhere, and the cure was to replace the tappet cover, even though the old one looked OK it wasn't for some reason.

Les,

The ports for PCV on the carbs are not at full vacuum, as is the manifold. It is a low depression area, between the piston and the throttle disk. The following link explains it fully.

http://www.mgb-stuff.org.uk/enginetext.htm#breathingd

Herb
H J Adler

i thought about oil level before, as i have an aftermarket dipstick and no normail one to compare the markings with. Today i did an oil change and replaced what the haynes manual says with 4.25litres. after refilling i checked dipstick and it was about 1cm above the full mark, so seems i was running on low oil although ive always had good oil pressure, if 55psi is good, its within the 50 to 80 as in the manual. i may have to try and find a new breather plate and keep my fingers crossed.
A P New

Hi AP

Be careful with your oil heights. The 4.25 is probably with an empty engine, ie includes the oil filter. If you replaced the oil filter as well did you run the engine before checking your level, as the filter canister could take the "excess" oil?

On my 67 model, the MAX is 240 mm down from the top of the oil tube and the MIN is 250 mm.

Herb
H J Adler

Ditto Herb, although check the vapour/flame trap gauze is present and filling the space in the front cover at the base of the tube. Could also be excessive oil being pumped out of the rockers due to wear and running down that side of the engine. It's something pretty major if it fills a catch tank in an hour (although I don't know the size of the tank of course). It may be the crankcase is only pressurising at very high loadings, difficult to measure ordinarily, but with your catch-tank you could compare the amount of oil from a stint of gentle driving to a stint of high revs.

Capacity is only given for the 3-bearing engine so probably isn't change to the 5-bearing, at 4.26 litres, oil cooler as extra as that isn't drained. That's given as the *sump* capacity, so not clear whether it includes filter or not. Herb makes a valid point about checking the oil after running the engine and getting oil pressure, but 1cm across the surface area of the sump seems a helluva lot more volume that seems to come out of my suspended filter. If it was 1cm above after that then I'd be tempted to make new marks, although it is *over*-filling that is more likely to cause oil burning.

Incidentally the standard MGB breather system was never closed-circuit but through-flow as even the later positive systems let fresh air in to the crankcase from either the oil filler cap or the charcoal canister. Modern cars are closed-circuit as the crankcase inlet is usually taken from the space between the air-filter and the throttle body, this means that even excessive blow-by can never pump fumes out to atmosphere but are drawn through the engine and burnt, unlike on the MGB.
P Hunt

I'm glad this has come up, as I am still confused myself.
Years ago, I had a '62 chevy with a 283 V-8, [yes there is a point] that had a a 'fuely Cam' in it and would wind up to 7000 rpm.
When you did that, oil would pour out tof the breather that was at the front of the engine with a breather cap on it.
It would come out, get all over the drive belts, throw them off and you'd have no generator and P/S.

So now with my '72 'B' engine in my '77 MGB, I had a breather filter on the valve cover and at the side cover pipe.
Under autox conditions, would spray oil out and get the engine all oily.
Very annoying plus a oil loss.

WHY?

Trying to solve this problem, I installed a 'Crank Case Evacuation' system.
This has a welded bung in the header with a check valve to prevent exhaust pressure going back to the engine.
Mine has the side cover blocked off, and a breather cap on the top of the valve cover and inside a baffle, going to the hose to the header.

It has about 1 1/2" of vacuum at idle which should prevent other oil leaks and lower crankcase pressures to hopefully near 0 pressure.

All that being said, [I hope you understand] it still leaks some after shutoff.


And I am still confused as to why this happens.............
DCM McCullough

well i had a chat today with peter burgess (im sure you all know who that is). And he is very sure that its excess blowby. Obviously to sort it is to remove the head and pistons, then re-hone the bores and fit new rings. But.... thats a lot of work on an engine which runs so well and has bags of power so id rather just stop the flow. Would it work if i blocked off the crankcase breather and made a takeoff from the aluminium rocker cover with a small baffle going back to the carbs??
A P New

If you have that kind of blow by, then there is something wrong, like broken rings or worn ring grooves. An engine can have excellent compression and terrible oil control. Bad oil control at this level is a sign of something which is bad, and could get catastrophically worse. I had a customer with a Spitfire, which developed a terrible noise. It had somewhat low compression on all cylinders, and one was lower but barely passable. The noise was the pistons beating bits of piston ring into the head, in all 4 holes. Turned out that the top rings on all four, and the top two rings on the bad hole, had been broken for a very long time. The worst one had finally eaten up through the piston top, and the pieces had migrated through the inlet manifold to all 4 holes. There was evidence of rust rings where the piston rings had stuck to the bores during a several year layup, after which he had driven the car for several years before it failed. Car ran great in the meantime.

FRM
FR Millmore

If you apply the suction to the rocker cover you would have to fit a non-vented oil filler cap and put a small filter on the front tappet chest cover or you will only be scavenging the rocker cover and not the crankcase. If you don't there is little point going to the trouble of applying suction to the rocker cover. And it might not make that much difference anyway.

How did you have your catch-tank set up? If the suction is applied to the top and the tappet chest pipe goes in at the bottom then at times when there *isn't* excessive blow-by oil in the catch tank should hopefully run back into the sump. You might need to remove the gauze in the tappet chest cover as well.
P Hunt

Paul, I believe that the rocker box and crankcase are connected via the push rod holes/tappet chest. This area is always full of oil mist as it's where the crankcase breather attachs.
Stan Best

AP-
You put in 4 1/4 Liters of oil?!? Do you have the larger capacity oil sump used on the five-main-bearing 18GB, 18GD, 18GF, 18GG, 18GH, 18GJ, and 18GK engines on your 18V engine? This has a 50% larger oil capacity (9 pints, 9.6 pints with oil cooler system vs. 6 pints, 6.6 pints with oil cooler system). You can tell because the earlier oil sump has a bulge at its rear in order to allow for drainage from a slot in the earlier rear crankshaft main bearing cap. Its sealing lip will still match the flange of the later engine. Both oil sumps have the same bolt hole pattern and use the same gasket (BMC Part # GEG 504), as well as the same 18 bolts and washers.
Stephen Strange

"I believe that the rocker box and crankcase are connected via the push rod holes/tappet chest"

They would have to be, otherwise the rocker area would fill up and overflow! I was talking about lack of through-flow of ventilation in the crankcase if both suction and source were in the rocker cover.

That area may well have oil mist, but it's not 'because' the breather is there, more the other way round. The breather has to have a gauze to act as a separator and flame trap because there is oil running down past it. And normally this is effective in controlling excessive oil consumption via the breather.

The Leyland Parts Catalogue only shows one sump for all 5-bearing engines, which is different to the 3-bearing, even though neither the Workshop Manual nor Haynes gives a different capacity for the 5-bearing, which usually means they are the same.
P Hunt

Paul-
I, too, am aware that the official parts catalogue shows only one part number (12H 3541)for the oil sump of all of the five main bearing engines. However, if you consult your coppy of Clausager's Original MGB, on page 141 under the first entry for the 18V engines (August 1971), the last item mentioned is a "sump with less capacity". I've been unable to find a factory part number for this later item. Anybody out there know what the missing part number is?
Stephen Strange

Bentley reprint of "Driver's Handbook" 71-74 says:
Sump: 5 1/4 pts, 3 litres, 6 US pts
Sump with oil cooler: 6 pts, 3.4 l, 7 1/4 US pts
Sump Early cars: 7 1/2 pts, 4.26 l, 9 US pts
Sump with oil cooler (Early cars) 8 1/4 pts, 4.5l, 9.6 US pts.

FRM
FR Millmore

Fletcher-
Thanks for the confirmation. You wouldn't happen to know the part number for the later sump, would you?
Stephen Strange

No, but it must have changed c72, which was when they went to the stupid microfiche and/or the parts books with all the G$%&@ D#%@ symbols instead of words. Takes a hieroglyphics expert in Faustamazoullion to figure the bloody things out, which is likely why you can't find a number. If anybody knows it will probably be TRF.

FRM
FR Millmore

That's a big difference! However I'd have said my 73 takes more than 3 litres at an oil change. Moss Europe lists two sumps for the 18v, but the part number for the later one matches that in the parts catalogue (12H3541), and it gives a change point of 1974 from engine 18V797. Mine is an 18V582 so my perception of taking more than 3 litres does tie up with that. The earlier Moss part number is 12H1976.

http://www.mgbmga.com/tech/mgb17.htm goes into some detail but indicates all 18V engines had the same capacity i.e. changed in 1972.

http://www.studdsey.fsnet.co.uk/mgbtunings.htm gives the same 1972 change point, but says 12H3541 i.e. the later one in Moss has the larger capacity!

Most other suppliers only seem to list one.
P Hunt

Gentlemen. Might I suggest that the difference in the quantity of oil needed for an oil change might have very little to do with the sump? Having both an 18GF and several 18V engines to hand, the oil pans seem to be almost the same height. I suspect the only real difference in oil pans was that they got a new set of stamping dies which made an oil pan that looked slightly different but which contained the same volume of oil.

If this theory is correct, the difference in oil capacities is not due to the internal dimensions of the sump, but rather to the internal dimensions of the oil filtering device. As I remember it, the old cartridge type oil filter system took about one quart of oil to fill up. The later 18V inverted oil filter used a small canister style oil filter which holds about a cup of oil.

My 18GF engine had an 18V oil filter adapter on it when purchased. When changing the oil and filter, I never use a full four US quarts of oil.

A further indication that it might be the filtering mechanism which is at the root of the differing capacities is the fact that the same oil pump was used with all of the five main bearing engines. If the physical size of the sump was significantly reduced (by 1.5 US quarts), I would have expected BL to have to use a shorter pick up arm on their oil pump. Since they did not change either the arm, nor the strainer mechanism, it lends credence to the concept that the pans are interchangeable with only slight manufacturing differences to differentiate them.

Les
Les Bengtson

Les-
You may be onto something there. I never stopped to consider the issue of the pickup arm of the oil pump. However, Clausager does state that the later oil sump is of less capacity. The earlier sump is pretty deep, so perhaps the length of the pickup arm may not be significant in this case. I no longer have the original sump of my 18V engine, so I can't make any measurments to help resolve the issue myself. Since you have both types 0f engines (18GF and 18V), could you make a couple of careful measurements? The smaller capacity sump can be identified by the lack of the tell-tale bulge at its rear for drainage from the rear main bearing.
Stephen Strange

Less capacity does not necessarily mean less depth.
And the correct filter is certainly more than a cup, more like a quart. If you have one that only holds a cup, it is wrong. Such are listed in a LOT of online references; they list the same filter for Spridget and MGB. This can be a disaster, as I have previously posted.

FRM
FR Millmore

Roger Parker's opinion is that it is quite likely the sump volume wasn't changed to any greate extent, merely the *recommended* amount of oil that went in it, there were a number of different dipsticks and tubes over the years. One reason for this could be that with the oil cooler the oil was being kept too cool when hotter was considered better. Cheaper than fitting a thermostat to the cooler!

A quart for a spin-on filter? At about 3.5" diameter it would have to be six inches deep to accomodate a US quart, and be empty of any filtration material to boot. A cup-full is about all I get out of my 4" filters when emptying them.
P Hunt

Worth noting thst when the mushroom PCV was discontinued the breather on the tappet chest changed as well. I did try one of the later ones on my car but it was worse than the original unit. I took some pics of the 2 styles but would struggle to find them now.
Stan Best

Neither should cause oil consumption, but some engines do seem to suffer from it and it can be a pig to resolve, the only clear resolution I've come across was the fitting of a replacement cover even though both seemed to be correct and contained the separator/flame trap gauze.
P Hunt

i have an update for my breather problem, i found another breather plate in my garage and decided to give that one a try, its completely different to the other as shown in the picture. the one on the right is the one that was fitted to the car. today i took the car out and drove it hard, high revs etc and the catch tank doesnt have anything in it so fingers crossed i may have cracked it.
A P New

soon ill figure out how to use this picture thing propperly lol.

A P New

Tried to email you, AP, but it is getting bounced with a 'mailbox disabled' message.
P Hunt

i just updated my details, thats my old email. now its itsawindupuk@hotmail.com
A P New

I've never seen an oil seperator with a cutout like that. I doubt that it is original. It could explain all of your problems. RAY
rjm RAY

I did find a pic of the original fit on my car, and the one which is back on the car. This is the one that goes with the mushroom PCV valve. The one with the hole one end is therefore the later one. i think there were only 2 styles ever

Stan Best

And here is the later style, AFAIK it's the only one you can buy now. It didnt work on my car.

Stan Best

And here is the later style, AFIK it's the only one you can buy now. It didnt work on my car.

Stan Best

Hi Ray
Most of the breathers have the cutouts rather than the holes.

Well done if you have sorted the problem AP

Peter
peter burgess

Peter, that would seem to allow a lot of oil and fumes to rise up to the carbs. I'm suprised that there were not a lot more problems with the later design. I have a '67 with a Moss supercharger system and it uses no oil at all.RAY
rjm RAY

Ray. If you go way back in this thread, I mention that it might be necessary to go with the 18V rocker arm cover with its built in restricter in the elbow. That system was designed to work with the later, more open, form of tappet chest cover. The engines were designed to work as part of an integrated system. Swapping parts, without regard to this fact, will cause problems.

Les
Les Bengtson

Hi Ray

When the engines are in good condition and breathers are not blocked we do not see oil spraying around the engine bay at revs no matter what the tappet chest cover.
The breather should just be to remove fumes via the carb where there isn't much suck. We only see trouble with the PCV early system if it has an air leak anywhere from dipstick to flying saucer thingy atop the inlet manifold.
I think AP maybe disguising his problems with the small holed cover fitted now.He may well find a build up of that oily film around the oil filler cap that lets you know things aren't what they were internally. Under power there should be a gentle waft from the breather not a 'steam locomotive' output.

Peter
peter burgess

When i fitted the different breather i checked the oil cap and there was nothing to be seen, it was also sucking at idle and when i revved it up there was a slight breeze, or "waft". Ive booked a trackday at brands hatch so ill soon find out. incidently, if anyone else wants to come along its only 25 pounds. Its a track taster, one 20 minute session. Well worth a go for beginners, heres the link.
http://cmsvbooking.motorsportvision.co.uk/trackdays/trackday-order.asp?ProductID=5739
A P New

Good luck and enjoy the day, have you had it on a rolling road before? You mention the engine is still making good power?

Peter


peter burgess

i havent had it rolling roadedyet but i really want to. The spec is a later 18v engine, twin HS4 carbs with K&N filters and AAA needles. Overbore of 30 thou, 714 camshaft, ported and polished cylinder head, and a full stainless exhaust. the car is here on youtube http://www.youtube.com/watch?v=AWBPnDGCnhI . feel free to take the mick out of it doing the nurburgring slowly, but it was my first time lol.
A P New

An interesting comment from Peter, the dipstick boot on my car is in bad shape, it's the original and falling apart. I had never considered it might upset the breather circuit. Can you actually buy them? Also do they really restrict airflow into the dipstick tube?
Stan Best

They really can be a source of leakage when under pressure. The part is still in production, but I have been using an ignition wire boot from an spare 8 mm wire and it seems to do the job quite nicely. Peter, when I first purchased my '67 it had the mushroom PCV system. It never caused any problems, but the engine had very few miles on it and little blowby. RAY
rjm RAY

Hi Ray

I found out to my horror what a leaking dipstick can do on a pcv system on a land rover engine...brand new initial setup, had dipstick out to adjust ignition...cruised on rollers and then had unit filled with smoke....eventually put dipstick back in and smoke cleared after five minutes cruise on the rollers.

Hi Stan boots not a problem the pcv sticks had a better seal. If you are running a dipstick that touches the bottom of the sump don't let it vibrate freely as it can work it's way through the sump...use an oil seal from a valve stem or such to hold the stick slightly off the sump.

Peter
peter burgess

Surely if the dipstick is resting on the bottom of the sump it is the wrong dipstick, or the sump has been bashed in? In the former case that's likely to give the wrong oil levels, I would have thought.
P Hunt

Hi Paul

Some of the early B and the MGA dipsticks rest on the sump if the large rubber outer sleeve gets tired, it is common practice to lift the dipstick physically to stop it vibrating on the sump. It isn't the same as the later B dipstick.

Peter
peter burgess

Peter, my '67 has the dipstick that rests on the sump. I've had it since '72 and it hasn't worn through. Yet. RAY
rjm RAY

You are, no doubt, a gentle driver, or the roads you drive on are maybe smooth :) We have only seen the effect a couple of times.

Peter
peter burgess

The dipstick should not be so loose that it moves about, and if it does it makes a noise that will drive you batso chasing.
Various forms of seals, bends in the stick etc normally prevent this. On a straight stick that's loose (Magnettes sometimes), separate the two legs and put a bit of bend in the shorter one, so that it's fat/bowlegged in the middle when released = no more vibration. Must admit the prospect of dragging your dipstick on the ground is horrifying or amusing.

F{RM
FR Millmore

Gentle driver? Smooth roads? Not in Northern California where Winter rains wash away half of the roads. I don't drive my B very often anymore, but when I do it is with a pedal to the medal attitude thats brings the supercharger to life and a smile to my face. RAY
rjm RAY

This thread was discussed between 29/11/2009 and 17/12/2009

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