I just rebuilt my 800 and am now at 147 on the PTO and 148 on the MAG side. I only have about 40 miles on this rebuild so it may rise a little as the pistons seat but I am very happy with how it runs. If your sled has 4000 or more miles on it, I would rebuild it. If it has less than that, check it with another gauge to be sure it is not a bad calibrated gauge. I bought a professional quality gauge at the local auto parts store and a buddy has one I think he said he picked up at K-mart. Those two gauges differ on the same sled using the same gauge hose by almost 8 PSI continually, his being 8 psi lower than mine.
This thread may be of interest to you also. It talked about other items but a few of the post do discuss 900 compression.
If you have not shimmed the APV’s on your 900 yet, you should do it now also. The 800’s and 900’s have a problem with the APV’s scrubbing the pistons as the engine wears. If you have not done this, check out the thread I started a few weeks back when this was pointed out to me.
i have shims for my APV valves, just putting them in this weekend. motor i just bought off the net and is claimed to have 1400 miles and its very clean, doesnt look like a high milage motor, but i've checked with 3 different gauges.
That sounds like low comp for a 1400 mile motor. I am sure you are not excited to rebuild a new to you engine but it sounds like you might be into that. I would check crank run-out also before you get into this. If you are going to rebuild the top, you might want to go into the crank and have that trued and welded at this time also. 900's are known for cranks going out of phase and having the crank done now and a fresh top end would give you a great piece of mind IMO.
not excited at all. but i guess thats what i get buying over the net and not seeing in person. never again will i make a major purchase over the net, but i dont have a problem with other things. oh well. rebuild time.
i wouldnt rebuild it long as there even. these sled easily hit 6-8000 miles ive never had my compression gauge show me more than 135 on new/old engines so i wouldnt worry. ive seen friends gauges show 160 and my gauge show 125 so i wouldnt rely on a gauge long as there within 5-8 lbs