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MG Midget and Sprite Technical - Breathers... sorry...

Oh dear... 200+ post thread warning!

Asking for a friend... Their car has a bog standard, stock as you like 1275. It consumes about as much oil as it does fuel, burning, not leaking.

From the symptoms and a cursory inspection I think it is being sucked up through the breather rather than the valve stems and it looks the "can" on the timing cover is empty. Should there not be some sort of "Brillo pad" in there?

Am I barking up the right tree and any tips on the corrective surgery, without taking half the engine apart...? (Who had the bright idea to make the timing cover and catch can thing all one piece... seriously?!)

Cheers,
Malc.
Malcolm

Anam will be along in a minute :)
Jeremy MkIII

Malc,
yeap there ought to be some sort of wire mesh there, are you sure there isn't?

You'd soon know if a lot of oil is going passed there as the hose there that goes to the Y-piece and the short hoses off the y-piece will bet wet (dripping?).

You could perhaps have the warmed engine idling and take the oil filler cap off and listen for any difference.

Is it a bling chrome oil filler cap with small hole or original type plastic with vents and filter?

Any non-standard parts fitted or non-standard plumbing arrangements?

Photos are good for details often, got any of friend's engine bay (is this a/the friend with a badger's ar*e car)?

Here's some photos from Blue Peter (nope can't find the breather hoses photo).
Nigel Atkins

I would start with a compression test.

And as "stock", does the breather hose go via a Y piece to the carbs, or via a PCV to the manifold? (depends on year model of 1275)
GuyW

Thanks Guy and Nigel.

Yes, same car. Less badger than it used to be but still some issues!

Totally standard, nothing bling, black plastic filler cap, PCV type system.

Did a compression test a while back, I can't remember the exact numbers, but they seemed reasonable and consistent across all four pots.

I had a look-see and took apart the PCV a few weeks back, it seemed very oily in there, although I have no reference as to what is normal.

Cheers,
Malc.
Malcolm

ETA: typed as Malc posted.

Good point about PCV valve I keep forgetting about the earlier ones, non-vented oil filter cap originally too.






Nigel Atkins

Do you know if the PCV has all the correct parts as I've got a feeling you can get variations - but I might be on Fantasy Island with that.
Nigel Atkins

Have this for a set.



Nigel Atkins

Yep, that last picture is the one Nigel. Just like that.
Malcolm

Exactly how much oil consumption? If it's a breather oil sucking problem, it will be obvious by the large cloud of thick blue smoke from the exhaust, just as the engine warms up. If you don't have that large cloud of thick blue smoke, then it's just your regular common or garden oil consumption variety.

There's always a bit of oil in the valve from condensed mist. If you think it is sucking up a lot of oil, connect the valve to the timing chain cover breather, with a clear thick wall(to stop it collapsing) hose. If you see a continuous column of liquid oil, then the valve isn't working properly. Convert to a y piece if you have the breather spouts on the carb's.

Have you got the correct oil filler cap as posted by Nigel?
anamnesis

Malc - is this the thread you are thinking of
http://www.mg-cars.info/mg-midget-sprite-technical-bbs/engine-breather-oil-sucking-yet-another-engine-2014091416212710294.htm

(I promise not to reanimate that thread at this stage via searching the MG Midget BBS Technical 2014 archive to locate it and replying with a post).

Best wishes
Mike
M Wood

Malc,
originally the oil filler cap was 13H2296 but if ordered now you get the vented and filtered cap I posted a photo of earlier (GFE6003).

Perhaps you could try blocking the vent openings to the vented, filtered cap to see what difference this makes.
Nigel Atkins

Suction at the Y type carb connection is much less than at the manifold, which is why that later type doesn't need a control valve. Suction at the manifold is quite strong, so a spring controlled diaphragm valve is needed to limit the suck. If the valve is not operating properly, sticking, damaged diaphragm or +? then it will likely draw oil up the breather too easily and give a high oil consumption. Even more likely if the wrong, sealed filler cap is used as without a route for air ingress it then draws through the only alternative, which is the oil!

The oil cloud that Anam mentions is a step change worse than that with probably a different cause or combination of factors. Check out the common basic faults first!
GuyW

Guy

I would very much echo checking the basics first. Many folk seem to go off on a red herring fishing expedition forgetting about the vast quanities of kippers already in the fridge.

Is is truly burning oil? Are the plugs black?

If so

Do compression test for sure.
Check all the valve stem oil seals - in fact if it is burning oil I'd just replace all of them.
Head gasket - check for bubbles in the coolant

After checking all of that at least, yes admittedly could be crankcase breathing. Remove or loosen the oil filler cap (to equalize pressure somewhat) and see if it still misbehaves. If it doesn't you may have a pointer. Clean it all up and skoosh through all pipework anyways....
Oggers

You can do partial or full blocking of vents with bluetac (or whitetac), marvellous stuff, also stops screwdrivers rolling into the engine bay to land in oil.

I was also wondering if the PCVs vary is the one fitted the correct one and/or fitted with all the correct parts to that model of PCV (unless all are exactly the same), just something at the back of my mind (or imagination?).
Nigel Atkins

Petrol works just fine Nigel. A ready source of supply. The added benefit is that when you become frustrated with the whole thing, just fling a lit match at it.
Oggers

I am really pleased this issue has been raised. You will see in the attached photos that my Sprite MK4 has an aluminium tank screwed to the inner right wing. It is superbly made with wonderful TIG welded seams and a glass tube on the car side to check liquid levels. There are two pipes attached to it, one to the rocker cover and the other to the canister on the timing chain chest. There is absolutely no oil in the tank. As far as I can tell this set up serves no purpose what so ever. It simply connects the breather on the chain cover to the one on the rocker box, via the tank. I do have an oil leak from the bell housing despite a Peter May lip seal conversion and have fitted a small catcher tank as a temporary botch job. I have thought of connections both breather hoses, via PCV to the inlet manifold but would welcome a description on how the breather system should work.

Jan T






J Targosz

Oggers I'm not thinking of cleaning but experimenting, Malc likes to play.

Personally I'd be looking for more badger fur as a quantity of it has previously been found.

The engine oil I use is so good it'd improve the fuel mixture and even though depleted return to the engine and carry on with its role of greater protection, I doubt soiled fur would do so.
Nigel Atkins

"About a litre a week" is what I have been told. I think they are driving it most days, but not particularly long journeys, maybe 150 miles a week.

It's not leaking, so I'm pretty sure it is burning, confirmed by them saying "a mate was following me yesterday... and said every now and then black* smoke came out of the exhaust"

(*I cannot confirm this colour diagnosis! I wasn't there)

PCV seemed OK when dismantled. So the filler cap and putting in some clear hose give me the next couple of freebie things to try next time I see them.

I see this thread starting to follow an exponential growth curve already... ha ha!

Malc.
Malcolm

Jan,
for a standard engine it's all in the relevant Driver's Handbook, obviously yours isn't factory standard (not many are).

Be interesting the comments Mocal tank and all, *Malc has really started something now, he's a very naughty boy, and he knows it! 🤣

ETA:
* I typed this before I saw Malc's post - so now confirmed! 😁

I'm calling Malc's friend Badger as he's promoting the classic car as an old banger stereotype, Malc he needs the seat of his shorts dusting with the toe cap of your plimsolls. 😉

Nigel Atkins

Jan, yours sounds like a good system, with just the extraction pipe from the catch tank wrongly connected. It needs to go to a Y branch connection and then to the carbs, if they have the attachment ports. If not, then it needs to go to the manifold, via a PCV valve.

Then the rocker cover shouldn't have a vent pipe, but the oil filler cap should have a gauze covered breather slot under the edge. It may work with the rocker cover open just to air, but I suspect it will allow too much free flow of air for the system to build up the negative crankcase pressure needed to minimise oil leakage past the rear crank.
GuyW

Black smoke from exhaust suggest rich mixture. It would be blue for oil!
GuyW

I think Badger's car normally has some black smoke so perhaps now it has a blue tinge, a colour chart is needed, perhaps Malc could take a sample by running his finger on the corner of the rear number plate or underside of bumper.

And perhaps Jan's car has featured in a past 'Oil Sucking' thread, or two, with previous owner(s).

Oh the joy, of certainties in life during strange times, we recently tottered on the edge with fwb but didn't fall in.

The 'Royal We' are amused. 😊
Nigel Atkins

Guy

but but he says "about a litre a week" which I've no idea what that really means as it's in foreign metric units.... Not to say that there is an oil leak somewhere and the smoke is - as you say - a rich mix as well, or possibly even burning both oil and petrol. Wonder if he's swapped engines for a two-stroke unit?
Oggers

Although I mentioned the smoke difference, I suspect it's more a matter of inaccurate reporting. Many people, observing a belch of smoke from a car, would assume and report it as black, unless they had been primed by experience or directed to look carefully for the colour.

Occasionally belching smoke implies to me with engine changing speed as when induction suction is greatest on the over-run. This could either suck more oil through the breather if the PCV is faulty, or more oil drawn down the valve guides as Oggers has suggested.
GuyW

Yep Guy, hence why I said I cannot confirm the colour. Knowing the source, I would take the "black" with a pinch of salt.

Malc.
Malcolm

Just checked the price of a MGB PCV from Brown and Gammons and they are quite expensive. Can anyone recommend one from a more modern car which can be found in a scrap yard.

Jan T
J Targosz

Edit time out - but it could also be running rich, as they did say they had been "messing with the carbs"... uh oh... :-)

Malc.
Malcolm

Jan, did you check the carbs for the two little intake ports beside the butterflies? They may be there, but plugged. It's a better suction point than via a PCV, and cheaper!
GuyW

Worn valve guides also messes up the air/ fuel ratio, plus ingesting oil lowers the effective octane rating. Both will upset the carb adjustments Having set up the breather wrongly and with worn guides the PO may have tried to correct things by richening the mixture?

Malc, yes, I recognised your doubt expressed about the reported smoke. 🙂
GuyW

Sorry, this is getting complicated with two different, though overlapping, problems on the two cars. Plus a badger apparently ? though whether that blows out blue or black smoke I am not sure. Maybe just a smokescreen. Oil drips will be from its anal gland.
GuyW

A litre of oil in 150 miles? That's a lot. For that amount being burned, I would expect wet plugs and exhaust tail pipe, plus plenty of blue smoke.

Jan T.
"-- would welcome a description on how the breather system should work.-"

Crankcase ventilation. The purpose is to remove harmmful (to the engine that is) burnt gasses and water vapour from the sump, to keep the oil in better condition longer, as well as reduce sump pressure. As opposed to just suction by a draught tube connected to the side of the block, 'Positive' ventilation is by a negative pressure being aplied to the crankcase. Either from the intake manifold or carbs, or by a scavenge pipe in the exhaust. The air flow, caused by 'suction', should be: in at the rocker cover, down through the block, out via a tapping and separator on the side of the block, or via a separator in the timing chain cover, and then into the induction or exhaust. There MUST be an air entry hole of limited size in the oil filler cap, which also contains a filter to prevent dirt entering the engine. Spridgets have a 'crude-ish' early version of what moderns still have. You don't need a catch can if it is working well.

No comment on the badger's orifice and it's emmisions.🙃
anamnesis

Adding to that, there is a fairly critical balance in the sizing of the air inlet under the oil filler cap, and the suction rate applied at the breather pipe. Too much air coming in, both through the designed cap and other routes such as maybe a loosely fitted dipstick and if a vented rocker cover from an earlier system has been used (!), Will prevent it establishing a negative crankcase pressure. This will worsen any oil leakage along the rear crank route. Obviously too small or an oil filler cap inlet, or if a fully sealed cap is used, and it won't get a through flow of air at all and will be more likely to drag oil up the breather tubes.

Jan, I would be interested in the oil catch tray device that you have designed for those occasional drips.
GuyW

And . . . The later version with suction at the carb ports, just upstream of of the butterflies is the better system as suction is greatest at WOT, which is also when any piston blow-by will be at its greatest. Plus it doesnt need the PCV.

By comparison, suction at the manifold is greatest on the over-run, when the throttle butterflies close, cutting off the air supply to the engine. As the revs drop, so does any piston blow-by so there is a bit of a functional mis- match there.
GuyW

Nothing really to add to this discussion save that my PCV with coffee can catch tank allows me to keep an eye on just how much oil is getting sucked. The engine's still being run in but the amount of oil sucked seems to be reducing as everything beds in.

The catch tank also allows me to recycle the oil rather than letting it blacken the plugs before disappearing up the exhaust pipe.

Any way, here are some badgers: http://youtu.be/fCzUft1PxhE

No sign of any badger emissions though.
C Mee

Fabulous video.

I feel ashamed to have used such a lovely creature's name for a carb-fiddler.

In future I will only think of him as B.A.. ☺
Nigel Atkins

Hi Guy,

The catcher tank is bodge up rather than a design and is only temporary until I can sort a more permanent solution. I made it from an old Ronseal wood stain tin can, cut off one side, soldered on a right angled bracket and fixed it to two of the bell housing bolts. I have put a sponge in the tank to stop any slosh and can use the former screw cap as a drain. Very Heath Robinson but it works. I will lift the car and take a photo for you tomorrow, I could even send one of the garage floor to show how dry it is!

Perhaps you can give me some advice on tappings in the carbs. I have checked out mine and there are blanking plugs but they are only about 3/16" diameter. They are just below the throttle spindles and are in a small profusion/boss on the carb flange and are on the engine side of the butterflies. I can easily open them up, tap threads and make adapters but the present hoses would be too bulky. There are thick spacers between the flanges and the manifold. Could I tap into these.

Cheers

Jan T
J Targosz

Nigel You called me ?

Regular visitors to the garden.

R.


richard b

Jan, I don't know about drilling the carbs to make those connections. These photos are what the stubs are like on my 1275, 1971 Sprite. Do they help?(these haven't been on the car for about 15 years as I use an HIF44 on it).

And my catch tank is made from a screw on topped illy coffee can. Incoming pipe extends inside to near the bottom of the can. Above the end of the pipe is a horizontal perforated baffle plate with a SS pan scrubber sitting on that. Then the extraction pipe which goes to the carb extends to just inside the lid so it draws the fumes through the wire mesh. It does collect a little oil, but not very much. Maybe 200ml per 1000 miles.






GuyW

Well done Richard, and there in black and white that they're not all black and white.
Nigel Atkins

Two more.

(not my car)






Nigel Atkins

Jan T.
"-There are thick spacers between the flanges and the manifold. Could I tap into these."

No. That would give you manifold depression. If you do that you will have to use the earlier pcv valve device. And there is already a tapping in the inlet msnifold for that, so no need to drill.

"Just checked the price of a MGB PCV from Brown and Gammons and they are quite expensive. Can anyone recommend one from a more modern car which can be found in a scrap yard."

You could buy one for a Ford from Burton power. Not expensive and would do the same job. Or this even cheaper.

https://www.ebay.co.uk/itm/124538238922?hash=item1cff0eb7ca:g:z0QAAOSwLEdgCVi0


But the later y piece into the carbs is 'cleaner'.


Take a picture of the brass plugs you mention. Those sounds like they could be the undrilled blanks for the 'ported' depression you need, which is lower than manifold depression. SU's are constant depression devices. The later pcv system makes use of this.
anamnesis

Hi Anamnesis,

Thanks for the advice. I have had a closer look at the carbs and the tapping I saw I now reallise is one for a vac advance distributer. There are no outlet stubs as you show in your photo. My current system is useless. A hose from the cannister on the chain chest and one from the rocker cover simply going to a very expensive catcher tank. There is no vaccum at all to pull out fumes or depresurise the crank case. I propose to buy one of the chepo, eBay valves you mention and connect this to the cannister and central tapping on the inlet manifold. If this helps with the rear seal leak I will buy an original PCV and fit this.


Thanks to all who advised me.

Jan T
J Targosz

JanT.
I have an old Ford with a pre crossflow engine. Originally all it had was a draught tube connected to the side of the block, well above the oil in the sump. It stank and dripped on the drive.

So I copied the system from the later crossflow engine, which is an oil separator into the side of the block, that into a pcv valve, hose to a catch can, then out of the can into the weber inlet manifold (so full depression at closed throttle). I have never had to empty the can, there is barely any oil ever in it after at least 5000 miles. I used the burton valve. I added the can as belt and braces, but in fact, it's redundant.

Have a read at this link. It will tell you all you need to know. Doesn't matter what engine make, pcv is pcv, is pcv.

https://www.burtonpower.com/tuning-guides/tuning-guide-pages/engine-breather-system.html

Does your engine by any chance have a bolt on blanking plate, where there would have been a mechanical fuel pump? Some did. If so, you can make very good use of it for additional venting into the pcv system.
anamnesis

Most common PCV fault is in the diaphragm, can be just a pinhole or the way it is clamped in. Either can prevent it shutting off at high vac. New diaphragms are available and are cheap.

A simple way to rule the breather in or out as a suspect is just disconnect for a while (blanking off the PCV and leaving the breather hose vent to atmosphere) and seeing if that changes the comsumption.

Paul Walbran

This thread was discussed between 09/06/2021 and 10/06/2021

MG Midget and Sprite Technical index

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