I run in every engine, regardless of type, using 25% all castor because there's more parts in an engine to run in than just the piston/liner. Mainly the conrod. If you read the Jett instructions they say it takes around 30 minutes to run in the rod while the piston/liner is done in the first few minutes. Castor is a far better oil for a plain bearing to run on so that's what I give them at the beginning of their life.