MG-Cars.info

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

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 - Oil in combustion chamber after engine overall.

I have just completed my MGB 1800 5 main bearing engine (no engine number) overall as follows:

Engine totally stripped and cleaned.
New camshaft and followers.
New mains and big end bearings (bearing faces clean with no grooves).
New piston rings +0.060” (Bores showed little wear and no grooves)
Bores lapped to allow new rings to settle in.
Oil pump checked with little wear so re-assembled.
New timing chain and tensioner.
Head chambers, ports and valves de-coked (hardened valve seats already fitted).
Fitted new valve stem oil seals.
Complete gaskets throughout, new oil and filter (oil level just below minimum)

On start-up there was clouds of white smoke from exhaust even after about 3 minutes revving and driving it up and down the road to check gears.
Taking plugs out, they were coated in oil. Pushing paper tissue through spark-plug hole and then removing it showed it soaked in oil.

Removed head and cleaned chambers and ports of oil.
Cleaned piston tops and bores of oil (about a tablespoonful in each chamber!)
Refitted head with torque of 60 lbs/foot, an additional 10lbs to ensure sealed head gasket.
Did not fit Rocker cover so I could view rocker oil and drain.
Did not connect cover tappet chest to manifold and blocked hole in manifold.
Did not connect brake servo pipe and blocked hole to manifold.

On 2nd start-up there was the same clouds of white smoke after 30 seconds of revving and plugs oiled up! Hardly any oil had reached the tappets so no-way oil is getting down valve guides and no oil

It seems that I must remove engine and check pistons!!! They are marked +0.060” and had new matching +0.060” rings fitted after cleaning grooves etc. They are the three groove type fitted as per instructions correctly. Bores were lapped using sprung three type oil stones in electric drill so no material was removed, only glaze removed to allow new rings to bed-in.

Has anyone got any thoughts as to my problem and recommend a resolution?
Pete Dyble

Hi,
Sorry to hear of your troubles.

White smoke is from coolant. This, with the oil in the cylinders leads me to suspect faulty head gasket or cracked head.
When you did the head did you have it crack tested?

Herb
H J Adler

Hi Herb, I did not have head crack tested as perfectly OK before strip down. The smoke is from oil being burnt during firing. Perhaps light blue smoke may be a better description? I did think it may be the head gasket but 2nd time of start-up was only about 30 seconds so little time for oil to reach rockers, let alone get into each of the four cylinders and soak spark plugs.
Thanks Pete
Pete Dyble

Hi Pete, it is always upsetting and stomach churning when these things happen, I feel for you. It may well be a problem with the rings. If the oil control rings are three piece, the expander can overlap and fail to function, this can be a common problem with Grant's rings. The single oil control ring type has a mark showing up, once we found this to be so faint we only realised it was there when we worked out there was a slighlty different bevel angle so we could see the 'up'. The compression rings can cause a problem if fitted upside down but they are usually marked for fitment.
You can verify the rings being the correct size by fitting them in the bores and checking end gaps, they shouldn't be over 25 thou.
I hope this helps.
Peter
Peter Burgess Tuning

Hi Pete, I bought all my spares from MGOC so they should be of good quality. I did check the gap and they were only a few thou so should be ok. I made sure that they were fitted with 'top' clearly showing and believe I fitted the three piece oil ring correctly, although a bit of a fiddle! What is strange is the oil in all four cylinders after a short amount of time. I may have made a mistake with one of the pistons - but not all four? Odd isn't it!
I did spin the engine over without the head on and no oil came up the bores, although not the same result as would be running on its own. Do you think that the head gasket is faulty.
Thanks for feed back.
Pete
Pete Dyble

I think it would be impossible for the head gasket to do that, oil comes back down the pushrod holes and for it to go into the cylinders that easily it would be blown back through the pushrod tubes and oil everywhere.
The best bet is the rings, I have also seen where rings are not round and have high and low spots which allow passage of oil. Did you produce a crosshatch finish with your hone? Just going roundy roundy will burn oil like no tomorrow.
Of interest you say, a few thou ring gap, can you give a bit of a number to this? Too little clearance and the rings can butt up and break when they get hot for the first time.

Peter
Peter Burgess Tuning

" I bought all my spares from MGOC so they should be of good quality"??? A bit of a stretch to assume that! I always go for top quality, well known brands with many years of experience and a good reputation. The extra cost is well worth it when you consider the time, effort and extra cost of another re-build!
Allan Reeling

Peter, I originally ordered the wrong rings which had about 6mm gap when inserted into bore. When I checked the correct ones (+0.060) there was less than a 0.010" feeler. I must admit that I did not do a cross-hatch, just removed the glaze.
Allan, as someone who only fits rings once in a blue moon, how do I know what is the best make? I assume that the club supply the best. In your opinion what is the best make and where do I buy them from?
Appreciate all comments.
Pete
Pete Dyble

"A bit of a stretch to assume that!"

Have to agree on that, I've had duff stuff from MGOC as well as others. The MGOC (despite the 'Club' in the title) is a commercial operation and as such make commercial decisions like any other supplier. High quality will probably equate to high cost and consequently low sales, as so many buy on price.
Paul Hunt

Pete,
Hepolite is the name that springs to mind as far as quality and reputation goes.
Allan Reeling

Pete, the fact that you didn't hone the cylinders, to produce cross hatching, will indeed lead to immediate burning of large quantities of oil. Without cross hatching, the rings will never seat properly and the engine will continue to go through oil at an increased rate. The pistons will need to be removed carefully and the cylinders properly honed to produce a cross hatched finish. This finish holds the oil in suspension, on the walls of the cylinders, preventing it from being drawn into the combustion chamber and burned.While the pistons are out, the bores should be checked for being out of round and the diameters should also be checked to make certain that the pistons match the size of the bores. RAY
rjm RAY

For piston rings, and other engine components -

F W Thornton

Orleton Lane, Wellington, Telford, Shropshire, TF1 2BG, England
Ph: +44 (0)1952 252892 Fax: +44 (0)1952 246082 E-mail: enquiries@fwthornton.co.uk
J N Gibson

This thread was discussed between 22/02/2016 and 24/02/2016

MG MGB Technical index

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