Tappet chest leak.

[Graham Honnor]

Thank you one and all for your excellent suggestions.
I shall try a silicone gasket as has been suggested and will report my 
results accordingly.
Hopefully this will be the end of at least this one leak.
Many thanks again.
Graham

[Rick F]

I use them on all three of my Sevens - two fitted with "RP" type engines and one with a 1929 coil engine. On the latter I use a later style cover with new fixing holes drilled and the old one filled in - I have never been able to get those flat cork gasket to seal properly.

I tack the silicone gasket in place with the tiniest dob of superglue at each corner, which just stops the gasket falling out while fitting.

I have found them to be oil-tight and would definitely recommend them. I also use silicone gaskets between the block and crank-case, but have yet to try one on the sump.

[Hedd_Jones]

I use a 1/4 diameter round extruded PTFE section. Pushed only into the groove. Seals perfectly every time.

[Graham Honnor]

As promised, I am reporting back with the results of my tappet chest cover seal.
I ordered a silicone one from Jamie along with new exhaust manifold gaskets which duly arrived the first day back after his well deserved Christmas break and I have just finished fitting them after a few evenings of cleaning and repainting engine parts while they were off.
I did as was suggested and glued the silicone gasket in each corner using a small blob of superglue and lightly clamped it to a flat board a couple of nights ago.
A smear of grease on the flat surface of the seal and it all pinched up a treat without resorting to any unnecessary over tightening of the centre bolts.
I took it for a few miles test drive which would normally have resulted in a small trickle of oil escaping from one, or both, of the bottom corners of the cover but not a drop to be seen. Result!
Well, so far so good but I will let you know if this latest attempt at a leak free cover goes wrong.
Many thanks yet again for all your time and help.
Graham.