Quick loss of compression on a Polaris

[DaveB]

I fixed some old fan cooled Polaris 440 snowmobiles for a rancher friend of mine that had been sitting out in his field for many years. One of them that was running fine started be real hard to start. I found that the compression was down to 60 PSI. When I first fixed it it was 110. It didn't get ridden that much so I am curious as to why it would drop so fast. I haven't pulled the heads off yet to look. Any thoughts ?

 

[BCGPER]

Broken reed valve, or piston rings would be my guess (I'm assuming two stroke?).

 

[DaveB]

Broken reed valve, or piston rings would be my guess (I'm assuming two stroke?).

Yes its a Fuji 2 stroke. Both cylinders went down the same amount. I don't think it has reed valves.

 

[Rot Box]

Moisture can cause the cylinder walls to rust and when the engine starts the rust quickly wipes out the piston rings. I've seen this on snowmobiles and motorcycles in the past--most of which sat outside/uncovered for several months without use. Was it stored indoors or under a cover? Something as simple as washing it off with a garden hose can get water where it doesn't belong..


Just a guess though hard to say without pulling it down :-\

 

[DaveB]

Moisture can cause the cylinder walls to rust and when the engine starts the rust quickly wipes out the piston rings. I've seen this on snowmobiles and motorcycles in the past--most of which sat outside/uncovered for several months without use. Was it stored indoors or under a cover? Something as simple as washing it off with a garden hose can get water where it doesn't belong..


Just a guess though hard to say without pulling it down :-\

They were stored outside without covers so rust is a good possibility.