MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - glazed bores

hi everyone, just had the valve seals done on my car as was useing excess oil and blowing out smoke,also had carbs adjusted as was told running very rich.only had car 2 mths so dont know how long it has been running like this. was told that it could have glazed bores which makes the rings not seat properly.car is running a lot better and not much sign of smoke over the first 10 miles i have done.does anyone know how to cure the glazed bore problem or is it a stripdown.
thanks in advance
bob, uk,
1970 bgt.
r taylor

Is it still using an excessive amount of oil?

I understand that to de-glaze the bores it is a strip down job but my MGC was using a vast amount of oil when I bought it. The car, however, had only done 4200 miles in 14 years since a rebuild and I was advised that the rings may have been sticking.

The solution to my problem was to fill the cylinders with 40cc of Redex and 40cc of WD40 and leave it in for 5 days. I then left the spark plugs out and turned the engine over to expel any fluid left in and then replaced the plugs and fired it up. Some smoke to start with until the Redex/WD40 had burnt off.

Since then, minimal oil loss.

Have heard of people using kerosene instead of Redex/WD40.

Worth a try before you start a strip down.

Robert

R Lynex

Bob. The actual term is "burnished". Burnishing is accomplished by working a smooth hard metal over a softer metal and produces a very slick, smooth finish.

When an engine just starts out, either brand new or after a rebuild, the bores have been roughened slightly using a hone. Normally, in automotive cylinder bores, the hone is used to produce a cross-hatched finish. This creates a series of very small "mountains and valleys" which hold a little oil. The rings are never a perfect fit into the cylinder bores, nor are they perfectly machined so that they are absolutely smooth. Thus, during the "break in period" the rings burnish the bores of the cylinder and, in turn, are perfectly worn in around the edge, making for an excellent piston ring/cylinder bore seal.

When you install new piston rings, the burnished pattern of the cylinder wall must be broken up (deglazed) so that the rings will wear in properly. But, when all is properly worn together, the bores show a well burnished appearance.

In Robert's case, the root of the problem seems to have been piston rings which had, due to lack of use, become stuck in the grooves in the pistons and they could not expand properly as the cylinder bores warmed up. Thus, soaking the bores in the penetrating oils allowed the rings to un-stick themselves and again provide the seal they need to provide if the engine is to run properly and not use oil.

Les
Les Bengtson

Several years ago, my engine in the GT was rebuilt and I experienced truly excessive blowby. My rebuilder ascribed it to using chromed rings in lieu of cast iron and "glazed" bores. He replaced the rings and honed the bores. He did this in situ via removing the oil pan and detaching the crank from the bottom, also honing from the bottom as well.

Seems to have worked, as I haven't had a problem in 16 years.
John Z

John. Not at all surprising. A chrome plated ring is significantly harder, on the surface, than a non-plated steel ring. Thus, the honing must be considerably coarser if the rings are to properly mate with the bore. A good machine shop will ask what kind of rings you are going to be using, if they do not have them at hand when doing the cylinder boring, and will hone the cylinders appropriate to the rings being used. This does not seem to have been done in your example.

Les
Les Bengtson

But it was attended to without additional charge!

IIRC (this was years ago, afterall) he used a mixed bag of rings - cast iron in the rear 2 and chromed steel up front. Given that he didn't have a lift and did the R&R of the pistons and the honing under the car on jackstands, it would be fair to say he learned a key lesson!
John Z

This thread was discussed on 09/10/2007

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now