A couple of years ago i ran my Yanmar without the cooling water open. The engine smoked and quit it wouldn't start and I sailed back in (franticly). I phoned Yanmar and they said if it runs it's probably ok. Presently it's not starting I think due to the fact that I've been changing out my fuel filters etc and have air in my lines and it has sat all winter. BUT it occured to me that I may have scarred my cylinder and I cant get full compression. How do I check compression?