So, l decided to properly pin down the source(s) of the fumes, which seemed to be both fuel and hot oil related. Looking down onto the engine bay, everything looked fine, dry and clean, so car up in ramps for a good look from underneath.
Aside from the standard small drip from the rear seal which doesn’t cause fumes, l could see that there were signs of a small fuel weep from the float bowl bolt on the rear carb, which handily is nicely positioned above the exhaust! So that’s the fuel smell.
Next I could see from below that both tappet cover plates were weeping slightly and one more than the other and as the oil runs down the block it builds up on the crankcase to sump flange close to the heat of the exhaust manifold. That should be the hot oil fumes then.
To get to the tappet plates requires removal of the carbs and inlet manifold and releasing the exhaust manifold. All straightforward. On removal of the side plates, it was obvious where the oil was leaking as the lower gasket face was wet with it.
Stopping oil leaks from the tappet covers is a challenge and judging by the amount of stuff on forums about it, an issue that troubles many B series engined classics.
As there’s a temptation to over tighten the single retaining bolts, there’s a strong chance that the covers can be distorted, so the first thing to do is to check the mating faces with a straight edge. If ok and both faces of plate and block are clean, then new gaskets need to be stuck to the plate face with a suitable gasket paste, allowed to set, before carefully replacing.
Care has to be taken not to over tighten, but the recommended 5 or 6 lbs torque seems too light.
Also, there are three different types of gasket available in the Moss parts list alone – standard thin cork original, a thicker 6mm cork and a fabulously expensive silicone version (£18.90).
personally, I think the original, carefully fitted is the one, as long as it’s the right size in the first place and not shrunk through age and storage. If that’s the case, when offered up to the cover face the gasket seems too small, then give it a soak in water and it should resume its correct size and shape.
With the carbs off and on the bench, it was clear to see that there was a leak from the rubber seals at the base of the fuel bowl. I tried tightening the bolt, but it was fully tightened, so I replaced the rubber seals with new and the problem was solved.
I’m waiting on the new gaskets before I can put it back together and see whether the fumes issue has been resolved.
mgarestoration 