I have a 95 Magnum 425 that has a ton of hours on it. I am now having oil spray out of the Crank Case ventilation into the air box. Pretty much need to do rings and piston and have heard that a 500 cylinder bolts right on. Just want to confirm that this is in fact true as a found a cylinder/piston kit on Ebay that I am looking to get. Does anyone know if a 500 Cylinder will bolt right onto my 425 case? If so is it specific year 500 Cylinders?
Thanks

 

Nope,can't do it. If it was just the bore difference a 500 cylinder and piston wold work,but the rod stroke is 70 mm on the 425 and 75mm on the 500.

 

Thanks for the input. I was wondering where the increase came from. Any ideas on how much the original head could be bored? I also was unable to find Wiseco pistons for the 425. Any ideas who else may make a higher compression piston for it?

 

Hard to find any after market pistons on the 425. On oem parts the cylinder can be bored up to .020/.50mm over.Before you order best to measure the cylinder bore as to the piston size needed to clean the bore up. No sense in boring it all the way out if it isn't needed. Not that much to gain. Here's one place to get oem parts as some other places online don't carry them. 1995 Polaris 425L Magnum 4x4 W958144 Parts, 1995 Polaris 425L Magnum 4x4 W958144 OEM Parts - BikeBandit.com
Plus here's a pdf service manual that you can look over the engine section and see how to measure the cylinder.Index of /ORV Manuals/Polaris/1985-1995 - All Models

 

Thanks again for the advice. I have yet to check the compression to be 100% sure but it sounds to me that I am getting blow by which is building up the pressure in the case then blowing oil up the breather tube. Like I said it has a lot of hours on it but has been very reliable (after I replaced the cam a year ago) and use it mainly for trail riding on our hunting grounds and some light mudding. To be honest, I really do love this quad after doing my work to it but will be getting another utility for my Son soon also. Bike bandit.com is actually who a friend of mine who has a Harley shop deals with. Have you seen the issue I have been having with blowing oil out the breather (only when riding it hard)?

 

 

Too much oil/ wrong weight can cause this plus check that the tank vent is fully open plus check the crank case vent also. Plus as you said worn piston/rings can cause this also by engine oil blow by. Since it has the cam decompression lever the average compression reading on a good engine should be between 55-90 psi. Anything less could be time for a new top end.

 

Checked oil on last oil change to make sure that wasn't the issue. The tank vent and crank case vent I am not sure were they are. I have a shop manual for it but didn't see anything in there about those two vents. Where are they located? I am also running the Polaris oil recommended for the bike.

 

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It appears #3 plate,vent,oil tank is what I need to check? Also I assume I should check #15 screen,oil filter to make sure it is not clogged? I really appreciate your knowledge. Seems like most of the Polaris techs around here never worked on the 425 and are more interested in selling a me a new one that fixing this one.