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04 RM 125 Bottom end

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So we get home from the race track. I wash the bike, fire it up and it is making a terrible rattling noise. Pull the clutch cover off, all fine. Take the head off, looks ok. Pull to pipe off, rattle, rattle, rattle. Small pieces of copper. Great.

Pull the cylinder off, piston looks fine, lots of side to side play in the crank. Look around and find large pieces of copper. Looks like a thrust washer or something came apart off of the crank. Ever seen this before? I have not.

Looks like a new crank and bearings are in order. This racing is expensive.

She had a good 3rd gear highside landing off a table top in the 2nd moto, so never did hear it run after the race. Pushed it back to the truck. She is fine, 3-4 barrel rolls, bruised hip and broken front fender. Those renthal twin wall bars are strong. They rotated down in the clamps, but did not bend. We are getting our money worth out of the ASV levers.

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yeah, from what you have said, you probably need a complete rebuild, new crank and rod (you can get hotrods crank assemblies for under $200 on ebay) and then a new piston/rings, prolite wiseco piston kit... You could easily get your bike running for under $300... the advantages of two strokes, but I still like my 4 banger...

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I just priced it out, hot rod crank kit, bearings and seals, piston kit, bearings, gaskets about $365.

But, have you ever seen a thrust washer disinagrate?

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Motosport.com has complete top (weisco) and bottom (hot rods) end kits for this bike for $369. It has everything you will need for a new engine, unless the cylinder itself is damaged. Did the throttle stick open in the crash? What ratio were you running? It has often seemed to me that bottom end problems are more likely with lean mixtures. IMO, 32:1 is best for power and engine life.

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nope, no throttle sticking, woman racer. Been running 40:1, but may need to go back to 32:1. Running Hondaline oil.

Going to switch to castrol though.

Cylinder looks just fine.

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