A little more background is that the engine was rebuilt about 5 years ago and has only been turned until recently. I would rotate about every 6 months 1 turn but a couple weeks ago put oil into it iand started turning with the starter. I always kept spark plugs in it until recently when I took them out in order to turn easier with the starter. Later today I'm going to check the rods and rear main. I'm thinking it is the rear main and possibly something with the seal after it soaked up oil and expanded.. I'll post what I find.
