2001 Srx 700 1/3 Good Pistons, What went wrong?

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Yamahaman1123

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Oct 4, 2015
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Saskatoon
Hi there i recently bought a 2001 Yamaha SRX 700 with 6800 miles on it. The engine had 140 psi compression on the 2 outside cylinders but the middle had 90psi. Took the head off and found the middle piston was missing a chunk out of the top and it had wrecked the head and scratched the walls a little. The exhaust side piston was on its last life, it had a indented spot in the top of the piston. But the cylinder walls and head are fine. The PTO side is all good, which is oddly enough the one that they Jet richer from the factory. The 2 wrecked pistons had 143.8 Main jets, while the good piston had 146.3 Main jet. Pilot jets at 42.5 if i recall correctly. I'm about 1700 feet above sea level. What jets should i be running? Ive also noticed my coolant tank had no coolant in it when i bought the sled, i don't see any coolant in the crankcase though so i'm not sure where it went. I don't have a whole lot of room to make profit on this sled that's why i wanna keep the rebuild fairly cheap but reliable. What's my best solution for the middle piston? I don't know if i can bore it out cause there are some deep chunks gone out of the ports and walls. I may have to buy a used cylinder wall and cylinder head and then replace the pistons and rings with new ones to fit the cylinders. Any help is much appreciated.
 

Ok I will change my jetting to that, Will that work for my altitude? Also I was thinking of buying used Pistons, head and cylinder and just put new rings in. Would that work?
 
Last edited:
You can get the o-rings individually as well as gaskets. I re-use both the base gasket and o-rings unless there's an obvious issue. On the base gasket (or any of the metal gaskets) Clean it good and use a thin coat of copper spray. Good used parts will work fine
 
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