piston slap

Jason Luther /

does piston slap sound like a regular 'tick' that coincides with rpms? i think my morini is experiencing it, since i have ruled out every other cause and narrowed the noise down to the cylinder area. what are some signs i can look for, like on the piston or cylinder walls? (i havent seen any...) i dont have a manual, and unless a morini MO-1 has the same top end and the reed valve M-1, i dont know the specs for piston clearance. at really high rpms it sounds like its going to shatter apart.

Re: piston slap

Ben Van Zoest /

More likely some play/wear on the wrist pin bush, important how many miles?

Re: piston slap

they say that all pistons slap a little.. just due to piston-cylinder clearance.. The various forces push the piston to one side and then to the other side, and a slight rocking and some slap is always there. A coating of oil is supposed to prevent actual metal-to-metal contact

Check the piston skirt .. there sould be some evidence around the bottom that it's taking a beating. If so, smooth over any rough spots with fine paper and run the engine again.. and check it again.

factory piston clearance is gonna be somewhere near about 0.002 or 0.003 inch. (bore Dia minus piston Dia at the piston's widest point.. near the bottom of the skirt.)

Re: piston slap

Jason Luther /

its a definate rhythmic click, it has about 5000 miles on it. the manual only says to check for excessive play in the wrist pin componants, it has a needle bearing, but everything seems tight. this has been driving me nuts for about 2 years now. just thought id throw it back out there again

Re: piston slap

Ben Van Zoest /

Add another washer to the spark plug. I found a tiny contact dent in my Puch's piston, clearance was apperently non-existent or caused by the very little piston overtravel. Notwithstanding eliminating the wrist pin the big end still has the bush bearing yes?

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