Engine rebuild question

["Art Mavrode" <amavrode@domain.elided>]

Here it is.  I have just finished putting back my SD 220 after rebuilding and when I turned it over I got this real loud knock.  This knock is not noticeable...doesn't happen when I'm in idle only when in gear.

 

My old rings were in good shape so I didn't replace them.  Had a valve job done and the only other thing that I replaced other than the gaskets was the throwout bearing.  My main bearing and journals were in great shape so I believe that the engine was rebuild at least once before.  The pistons and cylinders also checked out.

 

Please help if you can.

 

Thanks in advance!

 

Art Mavrode

'53 R-110