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Discussion Starter · #1 ·
I have a newly aquired 900 T cat with zero knowledge of its past history. A compression test shows the center cylinder @ 100psi. with the outside two making around 120psi. After pulling all 3 pipes off and probing around with a flashlight the cylinder walls and pistons all look great with the exception of some darkish black shading under the bottom ring of the low center cylinder. Its not a caked carbon buildup but just some blackish color on the front of the piston body, there is no scoring that I can see on any of the three cylinders or pistons from what is visable through the exhaust ports. The sled purrs like a kitten at idle and has no obvious defaults while running.

My question is, is it time for new pistons/rings/nicasyll(sp)? Total top and bottom refressh? Or will just new rings suffice? pardon my ignorance but Im new to this whole two stroke thing?
 

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nah you should be fine to run it. if it drops lower tho you might want to think about a rebuild
 

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Others will know a lot more on motors than me, but from what I understand you really do not want more than 10 percent difference in the cylinders. 100 psi is getting on the low side, If I had the money, I would not ride too much more before rebuilding it. But you say it all looks good from what you can tell, it may go a while yet before it grenades. I would definitely keep an eye on the psi.
 

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Discussion Starter · #5 ·
Our season here is very short and parts generally have to come from online. I'll rebuild the whole thing now if need be, but if the pistons and jugs look OK then wouldndt the rings be the cuprit?

We run on average about 500 miles a year so If I can get another season out of fresh rings and gaskets then great, if not then I'l do whatever it needs.
 

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Put some penetrating oil in that cylinder (with the piston at the top of the stroke) for at least 24 hours, run it hard a while and then retest compression. It may only be that ring is stuck.
 

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i would check the compression every time after getting back from riding, if it were to drop below 100 i would throw some new rings in there the make sre the oil delivery going to that cylinder is good enough.
 

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Run it like it is and risk seizing the middle jug/piston?...I would change out the middle piston and rings before the piston scores the cylinder and you have to exchange/re-nikasil it and buy a new piston kit. If the piston is good, changing the rings out should suffice. I don't know how much of your season is left, but you should be good to ride it like it is if your seasons almost over..instead of wasteing the rest of your season dinking around with your top-end only having to wait until next year winter to ride it. Just my 2 Cents[thumb]
 

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Discussion Starter · #9 ·
The day I bought is is the last day we had even a faint amount of snow on the ground, I may have put 2 miles on it before putting it away. I re checked the compression with my new Snap On guage and and someone to hold the throttle and I had 125, 105, 115. I'm going to do a top end job this summer.

This is an older engine in a newer chassis so I have no real idea of the milage. How much harder/expensive is it to to the bottom end while its appart? What all does the bottom end consist of? Crank seals and bearings? Also how do you know how much nikasill is left in the jugs? Does Arctic Cat have cylinder specs that can be checked with a bore guage? I really like this sled, if I can touch up the bottom end for a reasonable cost while its appart then I will.
 

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28sstony said:
Our season here is very short and parts generally have to come from online. I'll rebuild the whole thing now if need be, but if the pistons and jugs look OK then wouldndt the rings be the cuprit?

We run on average about 500 miles a year so If I can get another season out of [highlight=yellow]fresh rings and gaskets[/highlight=yellow] then great, if not then I'l do whatever it needs.
Me personally I'd replace all three pistons,wrist pin bearings and rings, but only IF the jugs look good.
 
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