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85 Yamaha 70 hp blown up

Mhill

New member
Hi all new to the site and to Yamaha ownership! I purchased a 85 70hp 2 stroke outboard for a fishing boat project and now the bad part I got it real cheep because it needs a piston. I have built many engines over the years both professionally and on the side having said that I have not had a Yamaha power head apart as the dealer I worked at was not a Yamaha dealer. I'm looking to find out if any one had a tell tail reason why the bottom cylinder would fail ?? It is lightly scuffed light enough a good cleanup and a new piston might be enough. Im guessing it was a oil pump issue? is there any check valves in the oil system or any other things I should be looking for on these motors ? common problems why that cylinder would fail and nothing wrong with the rest of the engine ??


thanks for the help and direction
 
You need to get a factory service manual.
You need to provide a model number
Probably not an oil pump failure.think about it ,how many cylinders how many oil pumps??
Most common,malfunctioning carburator,how many carbs how many cylinders?
 
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