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Discussion Starter #1 (Edited)
2001 sportsman 500HO

Was out on the lake making a rink with the plow. Quad was running great. Parked it and it idled for about 20 min while we flooded with an ice auger. turned it off it was running great. 20 min later went to start it and it would turn over but no firing. Towed it back to the garage.

We have spark
We have fuel put directly in the cylinder

No firing.

figured maybe timing so checked cam lobes, valve clearances and timing. All is perfect and in pristine shape.

I don't have a compression tester but seems to be fine.

Any suggestions cause I have run out.
 

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If your cam lobes measurement is on spec according to the shop manual and timing is correct and valves are sealing with good compression then it would almost be a fuel thing.

One other posted about the same thing but it was his exhaust cam lobe that had worn. How does the automatic compression release ball look on the cam?
 

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Discussion Starter #3
I will pull it and check again but there was no wear visable at all on the cam. It was and has been running perfectly. There was no stumble, pop or anything.
 

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Did you try a new plug in it..just asking....Idleing long can glaze the ceramic isulation..will fire outside the machine but not under compression..plugs are funny...check muffler output when you crank it over to see if its a strong exhaust...
 

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Spend as much time on Google as possible before you go deeper.

We found a compressor tester for $25 that has been handy. It is the kind where you screw the hose into the spark plug hole then there is a quick connect for the gauge head (like on an air compressor hose) so we got the piston at the bottom of the stroke with both valves closed (325 engine) and pressurized the cylinder.

If it will pump up to the max limit of your air compressor then you know all is well in that department. If air comes out the exhaust or intake double check to see if you have the normal (.006?) play in the tappet arm to insure the cam is not holding one open a bit. We had to rock the cam a bit because we had air coming out of each valve at first but they were fine.

In our case the air was coming out of the hole where you check the engine oil level. In our case it was stuck rings due to the carb float letting the gas tank drain into the crank case and apparently moving the piston carbon build up into the ring groves. We changed the oil before starting it then it ran for about 10-15 minutes then the carbon 'coked' (got hard) and the engine quit running due to the compression dropping down to about 30 PSI.

It took me an hour to get the rings out of the grooves then get all of the carbon out of the grooves. I used Sea Foam but should have let the piston set in Seafoam over night but we had a goal to remove and replace the rod bearings (the 325 has automotive type rod bearings which means some can pull the connecting rod without splitting the crank case) and piston rings all the same day. We got lucky because the mail man brought our top end gasket set on Christmas eve. :)

Not saying you have lost compression but the air compressor test can give more info about the valves, head gasket and ring condition.
 

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Discussion Starter #6
UPDATE: Thanks to Galehawkins and the use of a compression tester we determined that the head gasket was shot and the valves leaked like crazy. Upon teardown we found that there was next to NO fluid in the motor at all. No leaks could be found.

It seems that the head gasket had let go and as it was cold enough the motor just boiled off the rad fluid through the overflow. The fan it seems was seized. There was no warning light as there was no fluid going past it to set it off. When we stopped it, there was not enough compression to restart it. There was no damage to the cylinder or to the rings, which is a miracle.

It is back up and running just the way it was before. It is not my quad so I take no blame for the rad fluid. ;) It seems like someone drained the rad and never refilled. The bottle always had some in it so we thought it was good. Pressure tested the system after we put it all back together and all is good now.



New valves, seals and gaskets, fresh rad fluid and we are back up and running.
 

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Glad you got it running with minimum parts cost. Polar makes some tough engine parts.

The project 2002 Magnum 325 (spun rod and messed up crank) top end was show some light marks on the piston skirt. We replaced the rings when we replace the rod bearings just in case the damaged crank held up but it ran fine with all of the old top end except the rings. We did get about 10 hours of idle time before it started knocking when giving it gas.

When we tear it down to put the used bottom end we bought off eBay (case, crank and piston rod all together) we are going back with the old top end at is OEM except for the rings because it ran so well before the bad crank took out the new bearing.

The plus side is we get to see how well the hexagonal boron nitride gave the inside the engine friction points a ceramic bearing surface. This is our first use of Liqui Moly Ceratec and now we get to see if it worked to ceramic coat the moving parts. I will be looking to see if the fine score marks on the piston skirt filled in or not.
 
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