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MG MGA - Smoking MGA

I'm sure that there's probably a thread somewhere, but until I find it...
I have a rebuilt 1961 MGA 1600 with a "smoking problem".

The crankshaft broke 2 years ago and over the course of a year or so a friend and I rebuilt it. The head was done by a local engine rebuilder - not an mg specialist , I admit.

The engine has 40 thou over pistons and rings.

The engine does NOT smoke when cold but smokes like a demon when it reaches about 190 F. It seems to have lots of power.

Before I tear the whole works apart, are there any tests that I can run to narrow down the problem ( ie compression, visual inspection, etc.) ?
I did a cold, dry compression test and got about 135 to 140 on all cylinders. When I warmed it up the pressure dropped a little ( one was 120 ) and a "wet" test ( oil in the cylinder) brought the pressure up - so is it rings? I'd like to be a little more methodical, so you suggestions would be welcome.

Also, I seem to remember another friend being abit unsure about which way one of the rings went on...is there a "tapered" set ?

As you can tell, I'm pretty green at this but I love this car ( had it since 1978 ) and although it keeps the mossies away in the summer, it is a bit embarrassing !!

Duncan
DA MacFarlane

I had a smoke problem on mine ayear or so ago- it turned out that oil was leaking out of the rocker cover into the exhaust manifold gasket after I had done the tappets - a new rocket cover gasket with some sealant and tightening up the manifold nuts cured it - worth checking - Cheers Cam
C Cunningham

Duncan, we must assume here that the smoke is emitting from the tailpipe in which case it's bad news. Your compressions are a bit low and this coupled with the smoke indicates to me that you have a problem in the bores/pistons/rings area. I think that you should schedule a strip down at your convenience and then get your machine shop to measure the bores and pistons to see whether or not they are fit for further service or indeed need rebored.

Just one further thought, did the engine smoke before you changed the crank and did you remove the pistons from the block. Did you then removve the rings from the pistons and then refit them. If you did this you would have disturbed bedded in pistons and rings and I'm not surprised that you now have a smoking problem. Whether or not this will run in again I very much doubt it.
Iain MacKintosh

Duncan, if the smoke is, in fact, coming out the tail pipe, is the smoke white, black or blue? White means water, black means fuel, and blue means oil.
/ gil
gil

Hi,

I only had the cylinders "honed " and stuck in new 40 thou oversize pistons and rings. Everything else seems tight. The smoking must be a ring/cylinder problem, as the compression comes up when I squirt a little oil into the cylinder via the spark plug holes.

I'm thinking about a rebore and 60 thou over...any thoughts ?

Duncan
DA MacFarlane

Duncan, anytime you have an engine this far apart you should have the cylinders checked for taper. If you have more than a .003" taper your new rings won't seat properly.
John H

This thread was discussed between 18/01/2006 and 24/01/2006

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