2015 800 pro compression

[Jay]

Just picked up a 2015 800 pro for cheap, tunnel is bad in the rh stirrup. I was wondering what the compression should be on this one. 4200 miles, 300 hours at 1800' I have 104 pto and 101 on the mag. Any ideas?

 

[GoHiSK1]

Time for a rebuild I would say . You will get a ton of options I assure .
Piston and rings at a minimum . If it was mine I would disable the entire engine and check for worn parts .

 

[Jay]

From what I can find I'm thinking compression should be 120 lbs +/- is this correct?

 

[slim800]

At that altitude you should have no less than 115.
But they are not the same from side to side so it needs an upper end done!!

 

[slim800]

Also are you holding the throttle wide open when you check it?

 

[BeartoothBaron]

I'd be concerned at those numbers. I parted out a clapped-out 800 VES that had higher numbers at 4000', and I've seen as high as 130 PSI at my elevation. I've heard 120+ as a good number, but gauges, the guy pulling the rope, the elevation, and so on all factor in. That's part of the reason a leakdown check is a better indicator than compression. It wasn't on a sled, but I've got a motor that had ok compression numbers, and within 10%. It was burning oil like crazy, so I did a leakdown check - two pistons at 30% leakage, and one at 55%! Anyway, I'd pull the exhaust valves and Y-pipe and take a look at the pistons and cylinders. Also, check crank runout if you can.

 

[PSI 800]

should 120ish for sure

 

[Jay]

I'd be concerned at those numbers. I parted out a clapped-out 800 VES that had higher numbers at 4000', and I've seen as high as 130 PSI at my elevation. I've heard 120+ as a good number, but gauges, the guy pulling the rope, the elevation, and so on all factor in. That's part of the reason a leakdown check is a better indicator than compression. It wasn't on a sled, but I've got a motor that had ok compression numbers, and within 10%. It was burning oil like crazy, so I did a leakdown check - two pistons at 30% leakage, and one at 55%! Anyway, I'd pull the exhaust valves and Y-pipe and take a look at the pistons and cylinders. Also, check crank runout if you can.

Haven't checked runout or done a leak down test yet. I know it's low, just wanted opinions on how bad this is. It's at a shop getting the huge cracks in the tunnel/stirrups welded right now. This is a real low budget effort.

 

[BeartoothBaron]

Yeah, I hear you. I'd check runout and leak-down on any new-to-me sled, but then I've got the tools for that. I'm also big on preventive maintenance on my Pro because used motors are hard to find and pricey (usually not much less than a used sled). You do have the Fuji crank at least, so that helps.

 

[Blancheeron]

Just picked up a 2015 800 pro for cheap, tunnel is bad in the rh stirrup. I was wondering what the compression should be on this one. 4200 miles, 300 hours at 1800' I have 104 pto and 101 on the mag. Any ideas?

Piston and rings at a minimum . If it was mine I would disable the entire engine and check for worn parts .

 

[Blancheeron]

Piston and rings at a minimum . If it was mine I would disable the entire engine and check for worn parts .

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