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 - MGB GT oil leak

Hi, back again..
problem this time is a combination of issues.. mainly oil leak - since the mot and service, I had a small oil leak, which with use I can except, but now it has become more of real issue. Short trip over the weekend - made me aware of smoke drifting from back exhaust. After arriving and quickly calming my better half, I returned to find a pool of about 12" round of oil under the engine. Checked the rocker cover, for which I had replaced the gasket and rubber seals, but this is still spitting oil, possibly looking at changing completely. A quick question - do the rubber seals that are attached to the nuts on the top of the RC, go inside the rocker cover or outside..? Back to problem..oil level was fine on the dip stick..started back home, driven about 2/3 miles when smoke appeared.. slowed down, pulled up at lights, smoke appeared from passengers side not from back of car..managed to get back, to find the oil dripping on exhaust!, not good plus from what I can see at different points under the engine oil dripped onto tray..I am guess at what to tackle first..?
Any advice would be much welcome..
Thanks
Jim
J Giddins

The rubber seals are grommets and so should be half inside and half outside the rocker cover. If the rocker cover is leaking enough that the drips turn to smoke on the hot exhaust, then there's something badly wrong with the gasket. Are you sure you got the new gasket seated properly before you replaced the cover? If you take it off can you see where it's been leaking and does it look damaged in that area? A few years ago there were some very poor quality gaskets about - not as thick as the originals and the ones that are currently available. If you look at the way the gasket lies in the recess on the bottom of the rocker cover, then is the gasket material thicker than the depth of the recess?
Miles Banister

i had a similar problem, and it was several reasons too. Firstly my rocker gasket wasn't sealing propperly and i used some evo-stik to glue it on the rocker cover. also wiped down the sealing surface on the head. Second was the breather seal, somehow it had worked its way loose and dripped oil onto the exhaust manifold. I simply tightened it up. Lastly i had and still have a breather problem where the engine seems to suck oil out of the breather and into the intake causing smoke in the exhaust at high revs. Hope this helps.
A P New

Actually - they aren't quite grommets, more like half grommets. The bulk of the rubber goes on the outside, but they should fit snugly in the holes too.
Miles Banister

The compression washers fit on top of the rocker cover, under cupped washers. There is just a narrower shank which protrudes down inside the hole in the cover. These effectively press the cover down onto the cork (or rubber) gasket that sits on top of the head and provide a constant pressure on that gasket. If you have the 'nuts' with the shank that goes through the cupped and compression washers, with the stud on the top for the heater return pipe, then those can be tightened down onto the nuts on the head studs, which eventually limits how much pressure can be applied to the cork gasket. However it does seem that in order to get this far the nuts do have to be overtightened, distorting the cover, bulging out the sides and depressing the top somewhat, after which sealing to the head is a bit iffy.

However a 12" pool forming after (one assumes) the engine was switched off does seem rather a lot to come from the rocker cover gasket. I suppose a badly distorted cover could also split (although mine hasn't ...) which would make for a more significant leak. Oil level still being fine after having *driven* with an oil leak at that apparent rate is also surprising. Before doing anything I'd be running the engine to see just where it was coming from. If it *is* the rocker cover then being at the top of the engine it should be obvious.
PaulH Solihull

PS. If you find the nuts are 'bottoming' before you consider there is enough pressure on the gasket you can add 'shims' between the cupped and compression washers to pack it out a bit. At the risk of distorting it even more of course.
PaulH Solihull

Hi Just an update..Thanks Paul, Miles, re-fitted the rocker cover, as one of the bolts connecting the cover was not fully screwed down. This has then allowed oil to escape from that part of the rocker cover - ie nearest the window.
A tighter fit and degreasing the engine, show's that no oil has leaked from either end!. The rocker cap (plastic) seems to have let some oil leak though..new one needs to be ordered. Noticed straight away oil pressure went up to 60, where as before it would build up to 50/55 and then settle at 60!
The leaking from below is still evident, which I will be checking out with a local mechanic who is letting me use his car to investigate.
Will let you know how this develops.
Thanks
Jim

J Giddins

Can't see how anything you have done would affect oil pressure. Unexpected changes like that could be a concern and must be kept an eye on.

As for the leak it could be the sump gasket, oil fittings, front cover oil seal to pulley, rear crank seal, front gearbox seal or gasket. Only the first one could conceivably get onto the exhaust, the last two will be dripping from the hole at the bottom of the bell-housing which should have a split pin in it (just to keep it clear).

No reason to think there is only one oil leak, you could well have had a leak from the rocker cover, which could have been the source of the oil on the exhaust. That's now fixed, leaving the other one. Looking at what is immediately above the middle of the puddle is the starting point.
PaulH Solihull

Nobody seems to be mentioning those two big rectangular holes in the LH side of the block...
The ones with the gaskets that regularly fall out, since the bolts get loose and it is a PITA to tighten them.
Right behind the exhaust, with lots of oil on the other side.

FRM
FR Millmore

Doh ...
PaulH Solihull

This thread was discussed between 27/09/2010 and 29/09/2010

MG MGB Technical index

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