Wrist pin play

[ahlers77]

Ive had a rattle in the top end a few days after rebuilding it which i kinda chalked up to being a normal sound that these 2 stroke air cooled motors make but today i tore it down so i can replace both crank seals & decided id take a look at the piston & cylinder while i was at it...they look fine so i put the jug back on & was turning the flywheel by hand to check & make sure the rings wasn't catching & when I got to TDC I wiggled the flywheel back & forth & i can hear a lot of play at the wrist pin which is the sound I'm hearing while its running I guess. The piston,wrist pin & circlips are all new & the wrist pin needle bearings are all good & in tact with no flat spots that i can tell so does anybody have any ideas why there is a lot of play?

 

[scotj77]

I just went out and checked mine and there is no play at all. sure it isn't in the bottom end rod bearing.

 

[Braaaptor]

Sounds like the Big End bearing on the rod is on the way out. Since you have had a recent new top end done, as long as the wrist pin and corresponding bearing fit together snugly, there won't be enough play present there to cause a knock. Most knocking from a Blaster seems to come from piston slap and/or a dying lower rod bearing. Assuming the machinist did a proper job on the new top-end, piston slap is highly unlikely.

A worn-out rod bearing (on the crankshaft, in the bottom end) will, however, cause a persistent knock while the engine is running. This is likely the problem. Take the top end off and remove the piston from the rod. Then, try to wriggle the rod up and down on the crankshaft. Any up-and-down play indicates a worn bearing. The rod should only move slightly side-to-side .002-.004" on the crankshaft. Anything more, and you need a new crank. If your engine failed due to lack of proper lubrication (the piston would have likely showed signs of metal transfer and scoring on both intake and exhaust sides), you can bet that the Big End bearing on the rod didn't get enough oil to it, either, and was damaged when the engine blew up before you put a new top end on it.

 

[ahlers77]

Its not the crank bearings, the rod only moves side to side & there is no up & down play at all...its for sure coming from the wrist pin area. I have the head off & can easily turn the flywheel to get the piston to TDC & can feel & hear it when i turn the flywheel back & forth. Im guessing I should have used a new wrist pin bearing but the old one i put back on didnt show any signs of wear that i could see.

 

[Whitty21]

are the wrist pin and piston matching, like both stock, or both wiseco, there could be minor manufacturing differences, or there is just slight where on the pin making it fit loosely? just tossing stuff out there

 

[royalt67]

The wrist pin bearing can be worn without having flat spots. Just buy a new one. Shoulda got it the first time. Lesson learned.

 

[sicivicdude]

I actually have a new wiseco one out in the garage.

I bought it with a top end BUT someone f*cked me with the 3mm stroker I have, it uses a 20mm small end, not a 21 like it's supposed to.

I'll get rid of it cheap if you need one.

 

[ahlers77]

The wrist pin came with the piston as a top end kit & yep lesson learned...shoulda just spent the few extra bucks & got the wrist pin bearing also. How much do you want for the 1 you have sicivicdude?

 

[sicivicdude]

The othr brands sell for about $15 shipped. I'll let the wiseco one go for $10.

It's the wiseco bearing without the wiseco bag it came in although if I looked hard enough I might be able to find that too... PM me about it.