Compression on the 800 Pro RMK
- Thread starter sdmc
- Start date
Mine is the shop now. 2300 miles and 105/105
They are working on it monday
They are working on it monday
compression
SDMC
I would take a look at the pistons on the 110 psi sled. Can be viewed by removing the power valves. Clutch side requires taking the cap off power valve and unbolting the top steering post mount and pulling it forward. Have new power valve gaskets on hand.
SDMC
I would take a look at the pistons on the 110 psi sled. Can be viewed by removing the power valves. Clutch side requires taking the cap off power valve and unbolting the top steering post mount and pulling it forward. Have new power valve gaskets on hand.
O
ottawaair
Active member
I would be disassembling the 110 psi motor.
Mine started new at 123
Over the course of one season it went to 118, then 112, down to 107 when I took it apart.
Excessive ring wear and the piston crown starting to lift, especially on the pto side.
New stock pistons/ rings brought it back to just under 120.
I wasn't happy with that so I replaced them with wossners which got me 127 psi.
I'm now running Kelsey's head and cranking compression is 147 at last check.
All reading taken on the same gauge, 5 pulls with throttle wide open.
Mine started new at 123
Over the course of one season it went to 118, then 112, down to 107 when I took it apart.
Excessive ring wear and the piston crown starting to lift, especially on the pto side.
New stock pistons/ rings brought it back to just under 120.
I wasn't happy with that so I replaced them with wossners which got me 127 psi.
I'm now running Kelsey's head and cranking compression is 147 at last check.
All reading taken on the same gauge, 5 pulls with throttle wide open.
My 2011 with 1700 miles was around 100 on both. Tore motor down and seen the rings were flaking. The pistons had little scoring and cylinders looked good. I put in the mtnk fix kit and a par 13-1 head. Comp is now 125 but that was a cold motor just after assembly so the rings never had a chance to seat yet so hopefully the compression gets a bit higher. Heres pics of the origina pistons and rings
S
Sledneck_1987
Member
my 2011 was at 108psi on both cylinders. tore down and installed terra alps piston fix kit with shim. 13.5:1 head and also some minor porting on exhaust. not at 165pis and pulls way harder 
I was going to post pics of my pistons and rings but they were taken through the exhaust port. Not easy to get a decent shot. Mine looked just like the pics posted above.
M
Mech Engr
Well-known member
Pro Compression
Mine was 125 for both on my 2012 Pro. That was taken new with zero miles a few weeks ago. I will take it again when it has been properly broken in. I just put the first 61 miles on it yesterday in NorCal. My thought is that once the rings seat during break in, the compression should come up a bit...we'll see.
It's important to note that the altitude at which you take the compression plays a big part in the number you get (this is why Polaris doesn't give you a spec). My tests are all done at 2000 feet where I live. They would be higher if I was at sea level and lower if I was at say 6000 feet.
I don't think it's nearly as important what you get (within reason of course) as long as both cylinders are the same.
John
Mine was 125 for both on my 2012 Pro. That was taken new with zero miles a few weeks ago. I will take it again when it has been properly broken in. I just put the first 61 miles on it yesterday in NorCal. My thought is that once the rings seat during break in, the compression should come up a bit...we'll see.
It's important to note that the altitude at which you take the compression plays a big part in the number you get (this is why Polaris doesn't give you a spec). My tests are all done at 2000 feet where I live. They would be higher if I was at sea level and lower if I was at say 6000 feet.
I don't think it's nearly as important what you get (within reason of course) as long as both cylinders are the same.
John
W
waxer
Well-known member
I checked my 14 when I brought it home from dealer and it was 120 ea side. Checked it today with only 30 miles and it was about 115 ea side. I have lots of oil in the fuel as well as turned the pump up, plugs were fairly wet so not sure if this makes a difference. I have been breaking it in slower than I normally do but next time out it will be braap braap! I'll take a test again at around 100 miles or so. Just FYI my 600 rmk always has run between 125 & 130.
Well I had the dealer check mine when I took it in to get a busted motor mount fixed and then clutch work done. They said it was around 100 psi and that was just fine. I wish i did more research instead of just believing the dealer as I am new to Polaris. Well 200 miles later and I need new pistons, cylinders, and a crank! Of course my warranty is up now! Here's what my pistons look like now. Bad thing is I didn't ride that sled the last 200 miles. I have been riding my 14' so it was all friends that ride that sled those last miles. Nobody said anything until it seized.
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W
waxer
Well-known member
Well I had the dealer check mine when I took it in to get a busted motor mount fixed and then clutch work done. They said it was around 100 psi and that was just fine. I wish i did more research instead of just believing the dealer as I am new to Polaris. Well 200 miles later and I need new pistons, cylinders, and a crank! Of course my warranty is up now! Here's what my pistons look like now. Bad thing is I didn't ride that sled the last 200 miles. I have been riding my 14' so it was all friends that ride that sled those last miles. Nobody said anything until it seized.
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What year and how many miles on the it?
Yep 2000 miles should be just getting started on these sleds. I got the 4 year warranty on my 14 though. Never will go without it again with Polaris. Warranty is up then the sled will be up for sale.
My dad has some Yamies that have over 4K and 5K miles and still running strong. It might be the way i ride my sled though too. I am a little harder on my own stuff than I am with his sleds. But seriously 2000 miles and I need a new freaking motor is ridiculous.
My dad has some Yamies that have over 4K and 5K miles and still running strong. It might be the way i ride my sled though too. I am a little harder on my own stuff than I am with his sleds. But seriously 2000 miles and I need a new freaking motor is ridiculous.
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