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MG Midget and Sprite Technical - smoking 1275

I bet this has been covered a hundred times over. My 1968 1275 engine has had the airpump devices properly removed and is in very good condition with no less than 175lbs of compression in every cylinder and fresh head rebuild with all new guides and valve seals. It smokes heavily sometimes after descent engine breaking and I think it is excess vacuum through the original crankcase venting system. Disconnect the vent hose at the diaphragm device and no smoking and no oil discharge either. So what is a good modification to this system that seems to exasperate the oil being syphoned or sucked from the engine. Also as a footnote, the crankcase breather connection is on the chaincase and not on the valve cover.

Brett
BEW Brett Wright

AAAAAAAAHHHHHHHHHHH!!!!!!!!!!!!!

You've opened up a whole bag of worms there. Hope it's not the Oil Sucking problem.

Where does the crankcase breather connect to? Is it too a Y piece then into the carbs after the butterfly? Or is it into a tapping off the inlet manifold?

Rob
Rob aka MG Moneypit

"Hope it's not the Oil Sucking problem."

Going by that description, it can't be anything else.

There are 2 solutions.

1). Strip and rebuild the engine to EXACTLY the spec that it left the factory.

2). Modify the crankcase ventilation system using the part in the picture. It's available from MiniMania.

It connects to the blanked off mehcanical fuel pump area. If you don't have a bolt on blank, you'll have to drill the block.

http://www.minimania.com/part/C-2A265/Crankcase-Air-Breather-Kit-Mechanical-Fuel-Pump-Mounting--Sprite-Mg-midget

Take the hose from the "chaincase" into a T piece. Then one of the T connections goes down to the newly installed adapter. The remaining connection on the T, goes to either the PCV valve, or the Y piece to the carbs, depending on your setup.

For more information see these threads in the technical Archives.

"Engine Breather OIL SUCKING. Yet another engine."
"Engine Breather and HUUGGGGEEEEE blue clouds !!"

If you fancy it, you can spend the next 2 years trying to fix it without adding that adapter or making your own. But having been down that route, if you'll take my advice, -- DON'T. You won't fix it. It's some kind of design flaw that only affects some engines and not all in EXACTLY the same way, --- just mostly.





Lawrence Slater

Here's one of my solutions. Others have done it differently. I got this idea from someone else. Forgotten who, but if you read those threads, you'll find out.






Lawrence Slater

These are just regular copper plumbing fitting, with some stainless steel wool inside. I've since solder all the joints bar one, so that I can pull the large section apart to clean/replace the s/wool if I ever need to.

Does it work?

Yes completely. NO MORE OIL SUCKING.


Lawrence Slater

Tom CRAUSE Illinois, USA . That's who's idea I copied for the copper fittings.

But he used the MiniMania adpater to fit to the engine block. I used copper tube through my own adpater plate.

And that's just about all you need to know.

So if that is the end of this thread, it will be the shorted oil sucking thread in the history of the world. LOL.




Lawrence Slater

Not quite the end though.

Here's another of my solutions. I have 3 engines that suck. I've got 2 different solutions. This is the second. It was connected to the timing chain cover (TCC) on an test bed engine. David or Dave(forgotten which) supplied it to me. It was I think an attempt to cure this very problem.

I cut it off and adapted it to fit on the engine block instead of the TCC.

You may not think it, but it works perfectly.

It splits the suction and no liquid oil reaches the carbs anymore. Only oil fumes, and blow by.

THE END!


Lawrence Slater

Lawrence

I don't think it was an attempt to cure this problem, it was an early 1275 engine and there was no other breather AFAIK.
Dave O'Neill 2

Rob, The ventilation tap is in the chain case cover

Lawrence, I think I understand your photos. The tee is obvious and then you are returning to the block where the mechanical fuel pump would have been, I assume? I need to check if my engine has a blank cover there.
BEW Brett Wright

Rob,
It goes to a tapping in the intake manifold
BEW Brett Wright

Hi Dave,

I didn't realise the early 1275's didn't have a breather on the TCC. Anyway, that canister is working very nicely on my Sprite engine.

Hi Brett.
Not quite. The fumes are drawn FROM the timing chain cover(TCC), AND from the engine block via the drilling in the fuel pump blank.

Air is drawn IN via the (VENTED)oil filler cap on the rocker cover. It passes down through the engine, and because of the suction from the inlet, it is pulled up from the TCC. But because of the ADDITIONAL tapping to the side of the block via the fuel pump blank, the suction is split. The tapping to the block is NOT a return, it's still suction. This has the desired effect of still maintaining -ve crankcase pressure, whilst reducing the pull on the TCC, and the large amount of oil in the TCC.

As you may have discovered already, when the engine is hot and the oil warm, the smoking stops. This is because when the oil is warm and thus thinner, it drains from the TCC before it fills it.

If yours still belches smoke when the engine is hot, then you have a different problem.
Lawrence Slater

This thread was discussed on 09/09/2015

MG Midget and Sprite Technical index

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