Hey All, looking at a high millage 2023 SKS 650 and am curious what compression numbers should be at 4500'. Not finding anything out there on the interweb! Thanks!
Polaris 650 Compression Numbers
- Thread starter kiwiforchrist
- Start date
you probably won't see much over 115-118 psi. compression will alert you to damage if one side is low but isn't a good indication of wear or condition. leak down is the best but a tester isn't as common. if you roll each piston up to tdc, use a pencil with eraser on the end or a small rubber tipped tool down the spark plug hole you will be rock the piston back and forth. its a good indication of piston collapse. if they rock and knock a lot its running on borrowed time. unfortunately its hard to tell the crank condition. rod bearings like to surprise you.
Thank you, I'm thinking that 110 at our 4500' would be realistic. Will see
Now if you had access to a bore scope and shoved it into the exhaust port and look at the exhaust side of the piston, that is the first place damage starts and is indicated by a smeared skirt and an extreme case is your rings are also smeared over but when that happens compression is nil. The intake side smearing indicates cold seizure which happens if the sled is started up and while still cold gets WOT. A compression test unusually tells a lot at both room temperature and warmed up.
For the records on the internet, at our elevation of 4500' with 6700 miles on this 2023 Polaris SKS 650, the compression on each cylinder was 119psi. That was WOT with 6 pulls. Engine was cold. I thought that was pretty good!
