Tappet Cover Oil Seal

[Graham Barker]

After struggling unsuccessfully to make cork gaskets seal the tappet cover properly, I gouged out all of the cork and laid a large bead of a silicone sealant in the groove that had been intended for the cork.  The sealant is shown in the photo below.  I had difficulty making a nice straight bead, as you can see.  But that didn't matter because after two days of curing in our hot water cupboard, the silicone bead was firm enough to sand.  
I sanded the bead on a sheet of 120 grit sandpaper taped to a bench top. By pushing the cover backwards and forward with sealant face down, I was able to create a flat face on the sealant along the complete bead.
When the cover was installed it was completely oil-tight and after 300 miles of use it was still oil-tight.
I removed the cover recently to adjust the tappets.  The sealant separated from the cylinder block without any adherence to the block and held the sanded shape perfectly.  I have now reinstalled the cover without any more attention to the sealant and it again is sealing perfectly.  I guess I have created a seal that can withstand many removal and reinstallations without any fuss.

[Nick Salmon]

Well done on getting a successful seal Graham. 

I don't know if you are aware but the Seven Workshop sells a ready made silicone seal for the tappet cover - and they work.

[Chris KC]

Well done Graham. 
Next time, instead of sanding. why not try setting it up gently against a flat, non-stick surface while it cures?

[AustinWood]

I glue the cork strip into the tappet cover. Place it face down on a flat surface with weights on it until the glue has dried. It can then be fitted with a smear of grease on the mating surface. It should then be removable without damaging the cork seal so it can be reused.

[Reckless Rat]

After a recent engine rebuild (actually it was in June 2019 but whatever) I replaced all the important gaskets on the engine with silicone ones. Despite their effectiveness I was still annoyed with what appeared to be a leak from the valve chest cover. I finally solved it by sealing up the four breather holes and fitting a remote breather, as in Graham's photo, which vents below the n/s chassis rail. What appeared to be a leak at the valve chest was actually oil venting out the breather holes and accumulating at the rear of the block/crankcase interface, above the oil pump core plug. Result. a leak-free engine.

Well, almost.

[Steve Jones]

The problem with the tin tappet chest covers is that they distort easily if overtightened. Many have been distorted at some time in their past even if you've been careful to treat them properly now. I've given up with them all together and now make my own covers from a length of 3" wide, 1/8" thick aluminium plate. Fitted with a rubberised cork sheet gasket behind them, you can tighten them down with no risk of distortion and no leaks.

   

Steve

[Ruairidh Dunford]

I tightened a cover down once and it pulled a piece out of the block, engine ran beautifully, with a constant stream of water pouring out of the side!

[Fencepost]

I have the earlier tappet cover with the flat cork gasket. Mine was also leaking even with a new gasket. Finally realised I was using the cover as the template for gasket and the cover wasn't straight along the top edge. There is so little meat to seal on that a few mm taper meant it wouldn't seal. Made the gasket a perfect rectangle and it worked.