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Old 08-19-2011, 01:00 PM
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mapbike mapbike is offline
Motorized Bicycle Elite Member
Join Date: Mar 2010
Location: Central Texas
Posts: 5,379
Default Re: what did you do to your motor bike today?

Pulled head, Jug, carb and piston from my Kulana bike today, and what I found was surprising.

I knew I had a knock on the top end of this engine and that is why I had it down until repair, I figured it was the wristpin bearing causing the problem but this wasn't the case entirely, after getting the piston off of the con rod I pulled the wrist pin out or actually drove the wrist pin the rest of the way out being it was very tight in the piston and noticed that the bearing looked in perfect condition but the wrist pin itself was hammered out and flattend on one side where the bear rides on it, I also noticed that the wrist pin in this engine was a much larger dia. than in any of my other engines and the needle bearing was narrower also, the standard piston, wrist pin, needle bearing or clips would not interchange in this engine, I bought this engine used so I'm not sure of the manufacturer but I do know it is an older one because it sat in a fellas garage for 1.5 years before I got it and it was used when he got it, anyway........

I had a new standard size domed piston, rings, pin, clips, and some of the heavy duty needle bearings I had ordered from motion industries so I just pulled it down, cleaned everything up real good, made a new jug-block gasket, put some high tack permatex sealant on each surface and after a quick light criss X cross hone job of the jug with a brake cyclinder/small engine hone, I got it all back together, fired it up and went for a 10+ mile ride averaging 30-32mph almost the entire way, never missed a beat and ran very good considering the new rings and piston haven't had a chance to seat well yet, this bike has a 34T Alum. Kings sales Sprocket and I hit 41mph for just a short burst going down a slight decline, and it hit 38mph on the flat pretty easy, the exhaust is just a throw on bunch of stuff I had laying around until I get another SBP expansion pipe ordered for it, but it pulls good, runs smooth and NO MORE KNOCKING.....!

Anyone else ever run into the different size wrist pins and bearing before?

This was a first for me, the external size of the needle bearing is the same it just has real tiny rollers and is much thinner and narrower in width than the standard bearings.

below is a pic that may not be real clear but will hopefully show what I'm talking about with the size difference of the pins and bearings.

Sorry about the book here guys.!

Peace, map
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I dont always ride WOT, but when I do..I do my best to keep the rubber side down..Ride safely my friends!
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