I have read a bunch of other threads and websites on the subject so I understand about hot vs. cold and mag to pto...................

BUT how much compression is too low? If your cylinders are both within a 1 lb of each other still is there a threshold that would be too low compression?

i think that really depends on YOUR compression tester for starters.My tester has always given low numbers compared to other guages.What i do is get a baseline from my sled and constantly check those numbers during normal usage to see if they are falling or staying the same.I also check my buds' sleds to see what kind of numbers i get on my guage .I then can use all those as a good base to tell who has higher or lower compression.Don't know if it is the right way,but it helped me discover that my sled was in fact low and in need of some top end work.Both my cylinders were close in compression by the way,but my bore was getting out of spec,as were my pistons and rings.Re-nicasil and we shall see.........

That is a very good question JU, personally i look at my motors a little different. I,am not so concern on how low the compression is but how even it is between cylinders with any guage......cheapo guage or Snap-on, don't matter. Its the difference between the cylinders.
Whats is important is the wear on the rings. Worn rings will leak compression into the base and eventually damaging the engine.
Worn rings on a compression test will not show well on 2stroke motors and are difficult to diagnose without taking the motor apart too many variables to be accurate.

Reason for not being realiable, can be from poorly seated rings, improper breakin. excessive oil on the pistons or intake tract, even a heavy fuel load in the base can change the compression readings.
Bottom line NEVER rely on a compression test for a 2stroke.
This is why i will monitor cylinder condition between cylinders with a compression guage for the soul perpose of monitoring changes during the season, just like monitoring piston wash and plug colors.
But i ALWAY pull the cylinders every couple of seasons to measure the ring gap. That is the only true way to know the ring conditions. Usually i endup replacing the pistons and rings.
Do this and how low your compression is will not be a concern, but how even it is will be.

FYI, compression readings can be low or considered low by some even with NEWLY installed rings. Also compression reading can be considered high or by some normal,with WORN rings.
Thats a good reason to pull the top end every couple of seasons to inspect the rings.

Thanks for the responses guys.......Lund I like your thoughts! My situation is that I have on 05 800 that has 2800 miles on it. I know I am probably getting into the neighborhood of some engine rebuilding but honestly just don't have the money to do it right now.......so I am hoping to make it through this season.

It has always run rock solid and is continuing to do so. Checked the compression and both cylinders were showing 120psi. So mag to pto is right on the money but I know I see guys posting numbers in the 150-160's. So I just wondered how low is too low.

I am hoping that it will keep on runnin' as I don't plan to tear into it just yet. I realize this is always a gamble and hope not to have to make any posts talking about my motor destruction.............but thats just how I am going to have to roll the dice right now.

Well at 120psi, i have seen many new motors ranging from 110-135. All with even cylinder compression though.
At 2800mile you are pushing your limits, the rings are most likely worn. A good way to check is to pull the Y pipe and look at the piston skirts, check for CARBON BELOW the rings........if its excessive you got blowby into the case.

You know you could just rering for now.
FYI, compression readings can be low or considered low by some even with NEWLY installed rings. Also compression reading can be considered high or by some normal,with WORN rings.
Thats a good reason to pull the top end every couple of seasons to inspect the rings.

like lund said.............maybe a re-ring will get you by if you are really worried about it. you can buy top end gasket kits for cheap and OEM rings are reasonable from BRP.

Good luck in whatever you decide.

id say ur pushing the limits too dude
think of it this way......$300 now for a new top end (assuming you and ur buddies can do it) or $1000 + chopper ride out

if it was me, if ur in there replacing rings & gaskets (which I know is a cheaper alternative) you might as well do the pistons

but i guess it depends what you want for a top end kit - OEM, SPI, Wiesco, RKT, SHR etc......big bore!

Oem rings are almost the same price as new spi pistons and rings.That would be the route to go if i was going to replace anything.Replace it all,because pistons will be wore as well.Get the cylinder bore checked as well.There is no point in replacing anything if they are out.It sucks ,I know.I spend so much on trying to make everything "tight" every season,but I refuse to lose any power ,but if you don't want to do anything,and it runs good.............then leave it alone.You might get lucky and have a perfect season.My old Gade has 3800 untouched miles (except ring update) and it is still strong.........probably because i never had MY hands in it

I think I am just going to ride it for now. Check compression again every 200 miles. I only expect to get another 5 or 600 miles on it this season.

like others have said, it is all relative. my sled with a fresh rebuilt by big john showed 125 psi each cylinder on my guage. i agree with you, ride it this year and monitor it regularly.

Also keep in mind that compression test readings will vary according to altitude; the same engine will read different at 8200' than 5200'. So, if your elevation is 8200' and you are getting 110 psi, you would likely get 130 psi at 5200'. Like everyone else mentioned, more importantly is to have both pistons balanced and use this measurement as a diagnostic tool as the season progresses.

Some interesting results. Both my Mod 880 and 860 with 14-7 head showed 130 psi at 5000 ft. with Boyesen reeds, Stiffer reeds will not allow much air at cranking speed,There is 10 psi more with softer stock reeds and with reed cage removed 155 lbs. Its difficult to pull a cord fast enough or consistant to use as a tool.It will measure left to right cylinders. The rave cut also has a factor on compression and with valves removed compression is decreases.

I would also pull the y pipe and check for blow buy and check the coating on the piston (forgot what its called) if the coating is wore off you might want to think about pistons. When I took mine apart piston coating was almost gone and scratches were starting to form on the pistons but they had 4000 miles on them also. The coating was wore more on the exhaust side than the intake side.

Cort