Head gasket questions

[Lipdog]

I dug in today to fix this problem of leakage at one of the head bolts: https://forum.antiquemotorcycle.org/...k-at-head-bolt

I pulled the heads and inspected everything and have a few questions.

The vast majority of this problem is the bolt under the engine mount on the front cylinder, though there seems to be some light seepage around the perimeters of both of the head gaskets. It seems the guy who rebuilt this engine didn't use any sealant and just put the copper gaskets on clean. The cylinder decks have a relatively rough machined surface (looks original) and my thinking is that, without any spray-on sealant and using copper gaskets, they just didn't seal well. I checked the head surfaces and decks with a machinist's straight edge in several directions and all surfaces seem very flat and straight. The honing marks on the cylinder walls look good and fresh, though there was some oil or gas residue sitting on the pistons, which you can see. The other thing I should mention is that I performed a leak-down test on both cylinders before taking it apart, and the leakage on each cylinder was only about 10% at 50 PSI (at the rings, heard through the crankcase), which seems very good to me for a 1948 engine. If my assumptions are correct, I plan on cleaning it up, using spray-on copper sealant and new, annealed Cometic copper gaskets, and putting it back together.

My questions are:

1 - Is my assumption that the lack of any sealant coupled with copper gaskets and relatively rough machined cylinder decks would cause this sort of leakage?

2 - Is the small amount of oil/residue pooled on top of the pistons any cause for concern, or is this normal?

3 - Gaskacinch or Permatex copper spray?

4 - Any hints/tips putting it back together?

Thanks again!

[Oilcan]

Did you re-torque all the headbolts after a few cycles? I don’t believe copper gaskets need any sealants ( I’ve never used them, so not sure) as long as the surfaces are straight.

[scootertramp46]

It is a little late for a reply---but both surfaces(head and cylinder) should be smooth. You can't expect a good seal on uneven surfaces. I tape a sheet of 60 grit sandpaper to a flat surface and work the cylinder and the head across it until I see a smooth surface. When using and reusing copper gaskets, I use a flat file to ensure no burrs on mating surface. When re-using the copper---you need to anneal them. Annealing softens the copper to allow it to seal better. Some people use a copper spray/paint on the gasket---I have never used any. It looks like your engine mount may not have been sitting flush to the head. Sometimes they get bent at an angle that prevents laying flat to the head.