My recently rebuilt Type IV is leaking oil between the cylinders and the case. This engine is now a 2.4 L (was 1.7) with no gaskets or shims between the cylinders and the case -- common practice. So what is the best sealant and best method of application?

I use Loctite 518 there. Applied with an acid brush. If it squeezes out the sides, you used WAY too much.

that^
that said i know fat uses 1211

hylamar blue

old tried and true permatex aviation. Jake uses it in his video, but that was admittedly a long time ago .

I used the lower cylinder sealing rings on the few type IV's I've built. Could be the sealing surface of the case has dropped a little, I could see where sealant would be beneficial.

Every engine I build I now see the deck out .002-.005.

These are 40+ year old cases

Yamabond 4 is my engine-builder pal's choice and notes that in his race experience, it holds up in cylinder to case applications that see 10K rpms regularly. This goo is a silicone based liquid gasket that fills gaps on a flange surface and prevents leaks. When cured, this product forms a rubber-like body that resists heat and seals joints subjected to high temperature. It is gear and engine oil resistant, Yamabond 4 Motorsports sets in 60 minutes so you have time to work with it if chasing rings etc.

Thanks for all the advice. Yamabond it will be

Yamabond 4 is the same thing as Threebond 1215, might be 1211, both of which are RTV.