1995 Polaris Sportsman 400 Compression

[bren7176]

What would be the compression on a 1995 Polaris sportsman 400 4x4  ?? Have one in great shape plastic is almost like new and the engine only has 90 psi which I figure is Capulet ...

 

brendan 

[MarkinAR]

Was that a 2 stroke? Can't remember. I would assume fresh rings and good seating would be more like 150 psi, I would think 100 PSI would be about the low end.  I had a 4 stroke Bayou 220 that ran like a champ with 80 psi but that's a 4 stroke....

If compression is at 90 I'd think that's about low enough to keep it from sucking fuel in and running right...if running at all.

[Frank Angerano]

Should be 130 to 140.  

[bren7176]

ya its a 2 stroke ,  Well took it apart and the jug looks bit beat up and the piston is not so good looky .. all scratched and and ruff .. looks like it was run with bad mix..  well it did sit at a hunting camp for over 20 years in a garage  not being used . sad thing ,  has less then 500 miles on it . time for a top end rebuild .

 

 

 

Edited February 4, 2020 by bren7176

[06kfx440]

Check the cylinder walls and bearings. Your In There so why not. Scuffed could mean trouble if not looked into


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[Frank Angerano]

I would buy a cheap cylinder honer and hook it up to a drill and run it up and down the cylinder for a quick second. 

Add a new piston and rings and you should be good to go.  

 

[Ryan Foster]

That was a painful 500 miles on that thing.

[MarkinAR]

That scaring on the skirt doesn't look that bad as the rings look pretty smooth.  If the cylinder wall isn't toast a quick refresh with a hone and some new good rings and i bet it runs like a champ.  I'd probably even buff out the piston skirt and reuse since OEM is always better than repop.  The scratches may just be years of sitting and then the carbon deposits flaking off when trying to fire it.  I've seen worse run.

[Frank Angerano]

I am always a fan of @MarkinAR but there is now way in hell i would have all that apart and not put a new piston and rings in.  Although Mark is  right about trying to find an oem piston however Wiseco makes a great quality piston that should last a long time.  

[MarkinAR]

Point taken @Frank Angerano.  The reason I was thinking recycle the piston is that the skirt never touches anything, it's just there to let oil pass to the rings.  Hell, if the skirt touched anything it would be tragic!  But with pistons, even Wiseco, not really being that big of an investment...it's probably better safe than sorry.

[JacobSlabach]

looks to me like the skirt was touching something in there😆  haha i dont know 2 stroke tho

[bren7176]

ya dont think the oil pump was worky as the cable was froze when i got it ..

 

 

Well time for rebuild ...

[Jennifer Schuler]

I would never waste the time or gaskets re-using that piston. If Pro-X makes one they are usually pretty reasonable. 

Look at this... WSM makes standard and 0.5mm and 1.0mm over.