Piston has rotary play in cylinder

SkyenX

Member
Joined
Sep 3, 2019
Messages
37
Hi guys,
I was cleaning the carbon off my piston and while scraping, noticed that the piston can rotate ±5 degrees in the cylinder. Shouldn't it be completely constrained, except for up and down?
Is my wrist pin wearing out? Thanks for any help
 


GreasyChris

Well-Known Member
Joined
Jan 3, 2019
Messages
1,275
It sounds like it could be the wrist pin and or bearing. Maybe even the crank bearing. Could be related to your play in the bottom you described in your other post
 

Karl Snarl

Active Member
Joined
Sep 20, 2019
Messages
138
oh man, no no no. if it is twisting, you need a new gudgeon pin and bearing. its ok if it has a slightly side to side perpendicular to the rod, but twisting is a sign tht wrist pin ( gudgeon) bearing is bad or not the right one. i use a wrist pin bearing made for stihl chain saws. it's slightly wider and thicker than the stock bearing. i get it from a small engine and power tool shop a few miles from my house. they cost me like 5 bucks each. well worth the money when you compare to a new jug, pin, piston and rings.
 

SkyenX

Member
Joined
Sep 3, 2019
Messages
37
Sorry to bring up an old thread but I finally have my engine apart. The play isn't as bad as I thought before, but the main wear seems to be the crank bearing. Significant side to side play, but only about 0.1mm end play.
 

SkyenX

Member
Joined
Sep 3, 2019
Messages
37
Hahaha, you're joking 😂 I have about 1500 miles on it now, never saw what it was like when new
I take it i'll be okay to keep riding this crank?
 

FurryOnTheInside

Well-Known Member
Joined
Sep 23, 2013
Messages
3,942
Not joking. The generic 66cc engines are really that bad, right from new. I laughed for ten minutes when I unboxed and opened up mine. 😅
Idk what else you can do with it, unless you're actually set up for pressing cranks apart and back together. 😳
 

SkyenX

Member
Joined
Sep 3, 2019
Messages
37
Well hey, if it's been that loose from factory, it's definitely served me well.
Nope haha definitely do not have a press, I've only just bought a Dremel LOL.
I'll keep this crank then and put it back when I've finished port matching. Thanks for the help!
 
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