3 word's Clean-clean-clean. Make sure it's clean . Brake clean ,make sure no oil.you can tack the gasket if want. how many seting do you go throught try4-5 if there is a problem. Do you have a straight bar ,make sure head is not warped. don't take the shop's word. I was doing a 124/91 /300e freshin it up I would check to see if it needed borded.look at ring grove to{do not let them use WD-40 solfen's metal].and if It done, platic gage the crank/rod's. this happen to me I Checked the
pistion's they where fine after being bored they where with in tolerance. rebuild ,engine smoked bad I thought I broke a ring ,I remove engine, tore apart looked greet, back together, still smoke . Back out take apart, looked everywhere, looked greet, then I noticed I piston had been rubing. check hole with straight rod. When they bored it, it was not at 90 degree's , I donot know how they did that. I have bored block's before I do not know how he did it. after that I check out mach. work regood. Did you have the head checked for straightness did you have is shaved. before you send it out do some measurement's if they remove to much valve's will hit head. Wishing you all the luck.

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30 yr's still in love