Wrist pin bearing on 2/stroke

i know this is an old post. but may help someone in the future. i swapped my small end roller bearing for a stihl chainsaw cage roller the same size and the motor never felt better. cost $15 and rated to 70,000 rpm.
 
jug3.jpgpiston3.jpgwrist_pin_and_bearing.jpgI just had my wrist pin bearing fail. Mileage - 2,896. This is the second engine that had a wrist pin bearing fail and the shards damaged the piston as well as the cylinder. At least it's an easy fix. Hopefully I'll get many more miles out of the engine.
 
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At least it's an easy fix.
HAHA, easy!? In the motored bike world? Nonsense! Well, it turns out I don't have any spare pistons for the long crank arm hole position(21mm from the top edge to the center of the wrist pin hole.). All my spare pistons have the shorter crank arm hole position(26mm from the top edge to the center of the wrist pin hole.) Blah! I was fortunate enough to have the other three replacement parts, cylinder, wrist pin, and wrist pin bearing. I've been riding for 5 years now and this is the first time I've known that there are two different pistons for the same friggin' size engine. Can anyone tell me what, if any difference there is in the performance between the two different designs? Anyhoo, I was able to order the correct piston on ebay for $10 shipped.
 
I think one has a longer rod, changing the compression height (distance between top of piston and pin location) you could change the cylinder height with thicker gaskets, if the ports match up. Of course, the ports never match up anyway. Some builders swear by a long rod, while others swear at them!
 
Well, seeing how this motor (longer crank arm) has lasted longer than the two spare parts engines (smaller crank arms) I'll stick to this design for now. I was going to mess with the gasket height but why work around something if I can get the right part – these things are hard enough to get right as it is let alone trying to jimmy-rig the set-up. Thank you for the input.
 
How do I install a wrist pin bearing on a 66/80cc motor?

 
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I have a question is the small end needle bearing supposed to float sideways on the pin? I can look at the installed piston and the needle bearings are exposed and are completely to one side of the pin and the rod is in the middle of the pin. Is this normal?
 
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