I know its been a while since my last update when the bike broke. I’ve been slacking . If you’ve been following this series, you know I was really enjoying the TM MX 300 and suddenly had a bottom end failure. It took only 7 days to get all of the parts with nothing other than ground shipping (and some of them had to come from Italy). That is pretty damn quick.
There wasn’t really any sign of what caused the rod bearing failure. Which sucks because it would be nice to be able to say exactly what caused the problem. The theory is a a little piece of dirt, reed (one of the reeds was missing a small chunk) , or metal got in the bearing just right, causing it to fail.
All of the parts I needed added up to $524.50, here’s the breakdown:
Piston Kit: $317.58
Gasket Kit: $26.99
Rod Kit: $109.95
Main Bearings (02-07 CR 250): $29.99
Main Bearing Seals: $39.99
*Prices listed are MSRP, I’m sure you can find the parts cheaper
As you can see pricing wasn’t horrible, the piston was Vertex and you could probably find it cheaper somewhere if you did some looking around and ordered it through Vertex instead of TM.
Once the cases were split we noticed that the rod is directly from Pro-X and even has a part number on it. The rod was from an 02-07 CR 250. It was a lot cheaper to buy the rod from Pro-X than from TM even though it was the same part. We also used CR 250 main bearings when putting the bike back together because they were slightly cheaper but the same quality component.
When putting the bike together it was found that the water pump impeller was damaged and spinning on the shaft. We believe this caused the bike to get hot multiple times, causing the bottom end failure. Sucks when a $5 part causes so much damage.
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