low compression 1992 polaris

[Kh2gr]

Alright, got my engine put together and now got it running but with low compression in one cylinder... all new gaskets, but re-used the pistons and rings... inspected before installing and pistons seemed in good shape, I have about 115 psi in the two end cylinders, but the middle cylinder is getting between 80 and 90 could a piston ring be causing this much loss in compression, or would anyone more likely suspect something more serious? if its most likely the rings I will replace them in all three cylinders, hopefully to boost up the compression again.

also, my compressor gauge is pretty old... and I have heard that they arent acurate after many uses, anyone know of a good place to buy an affordable one thatll last me a year or two? or used one with little or no use?

[javiert99]

Re: low compression 1992 polaris

What was the original reason for the fresh gaskest? Engine seizure?

[douglee25]

Re: low compression 1992 polaris

Compression gauges can be found at any auto store for around $20 bucks or so. I too have seen a compression gauge go bad. Actually just two weeks ago after I rebuilt my ENTIRE motor, I used my girlfriend's dad's compression gauge. I was getting 75 psi in each cylinder. WTF I thought? I had my gauge in the car, so I popped that in and I found 120 psi in each cylinder. Thank goodness!

To answer your other question, yes, one ring could cause that much cylinder pressure loss. Your best bet is to do a leak down test first to determine if the gaskets are leaking anywhere. If not, your rings are suspect. If your bore is in spec, your piston to cylinder wall clearance in spec, deglazing the cylinder and throwing in a new set of rings will likely cure your low compression. Deglazing can be with a hone or even say 400 to 600 grit sandpaper. This is necessary if you want your new rings to seat. Depending on your budget, you may want to consider doing all three cylinders for peace of mind. If the cylinders and pistons have too much wear on them to get by with just a deglaze, boring it out to the next size is your only option. Ask me how I know?;)

Doug

[Kh2gr]

Re: low compression 1992 polaris

What was the original reason for the fresh gaskest? Engine seizure?

I bought the engine in pieces, and the reason the original owner had it in pieces was because he was putting in a new crankshaft: said that he was riding it and it just quit... didnt really know a whole lot about skis from the sounds of it. I would sespect that it was due to the fuel starvation problem that is common on this ski, but I do not know, I would have expected the pistons to be much more scared, pitted or colored if that was the case... they really looked to be in descent shape, just normal wear... though I have my doubts about the piston rings. I didnt thoroughly inspect them as I should have, this is why I ask if the loss in compression is likely to be piston ring only... maybe its the whole piston, but I really felt good about them through the inspection.