SXViper top-end/rebuild kit recommendations

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Bronc_twister

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Joined
Dec 23, 2014
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Montana
My '03 SXViper Mtn. is in need of a top end we suspect as the PTO cylinder is below spec on compression. It does have Bender painted triple pipes and supposedly an Optikool gasket. The miles on it are supposedly at 2838 (when I bought the sled the PO claimed it had 2100 miles but the odometer showed 3600. He claimed that it was actually 2100 and that the original gauge burnt up and they replaced it with a used unit with higher miles). The odometer currently shows 4338 miles. Either way I think a top end would be a good idea. I think a run out test on the crank and crank seals would be a good idea too. What kits have you guys had good luck with? I was thinking about going with SPI.
 

I'm using SPI pistons and the oem yamaha rings, was told that the pistons are of good quality ,but the spi rings are a little weak, spi and oem components are interchangable.
 
It is normal for the PTO to run less than the mag and center. The head has a bigger dome for the PTO cylinder. If I remember correctly it should run about 10-15 psi less than the center and mag.
 
I can't remember what the center and mag cylinder are at (I wanna say 125 psi). My PTO cylinder is at like 98 psi. It runs good... but with that number on the PTO, I'm guessing it could run considerably stronger. It concerned my tech who used to work at a Yamaha dealer for years and knows his shit.
 
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That's definitely more than the normal difference. I personally like to use oem parts. Having said that when I bought my viper the previous owner just rebuilt it using a mcb top end kit. I found the oil cable bracket broken so I decided to rebuild it again. I was going to get new oem pistons and rings but decided to just get new rings and use the mcb pistons. Knock on wood but over 1000 miles on it so far and no problems. If you haven't been in the carbs yet double check the jetting. Sometimes people do weird things. When I bought my srx I found the pto cylinder had the smallest main jet you could get for some reason. Also if you are willing to change the crank seals that wouldn't be a bad thing. You could spray some carb cleaner or starting fluid behind the clutch with it running and listen for a change in the engine to see if your crank seal is leaking. Generally the mag and center cylinders have problems before the pto so it is possible the crank seal could be leaking air.
 
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