Q: If on a radial engine (specifically a Warner) one finds one stud broken at the flange level, would you recommend replacing all the affected cylinder studs? I assume cylinder movement caused the break.
A: I believe in this particular situation I would only replace the broken stud. However, I would very closely inspect all of the other studs and inspect the parting surfaces of the cylinder base and where it attaches to the crankcase for any sign of fretting or indications of metal movement.
The only reason I am suggesting you replace the broken stud is simply because of the low compression of this engine. It would concern me more if the engine compression were higher, which could have caused a more serious condition on all of the components.