Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Matt,
I have seen this a few times on these M90s, the top of the liner sits in a recess in the block which is a tiny bit too deep to keep good pressure on the gasket. A very thin smear of gasket sealer where the gasket mates to the liner will fix it, or you could anneal the head gasket and try that (personally i had no success with this).
Hope this helps
Ade