Hi, I have a 95 Polaris xplorer 400 that I made the mistake of horribly cross threading the spark plug in the head and after pulling the head was wondering if I should just rebuild the motor while I have it apart? It has some where between 2000-3000 miles on the motor and has been running good minus fowling a few plugs due to bad/old gas and having the exhaust gasket blow off not long ago (replaced). The cylinder shows no wear marks and feels completely smooth. I have not pulled the cylinder to check the piston but it looks to be just as good as the cylinder walls (original). I'm wanting to see if I should replace the head and ride or pull and rebuild the Top end while I'm in working on it?

 

This is your call. Depends on how it was running before. Compression is the key,should be at least around 120 psi or more,but it's a catch 22 as you need the head and gasket installed to get a good reading.But if in doubt and a lot of time/hrs on the machine a fresh top end can save some future headaches down the road if the piston skirt were to shatter.Many people have waited until that happens and ended up doing more damage.

 

In that case I'll probably go ahead and just put a new piston in and hone it. It's not riding season so I might as well just replace it so I don't have to worry as much in the future. Would a Wiseco piston work good or is their a better piston to buy? I've used anywhere from $30-$140 pistons this last year in the snowmobiles I repaired but never replaced an atv piston and want to get the best since this is my main (and currently) only atv. Thanks old Polaris tech!

 

Wiseco is about as good as it gets. Usually first or second over 83.25-83.50 will clean up most stock bores,but measure the cylinder to be sure.May be able to find complete kits cheaper than this.http://www.ebay.com/itm/Wiseco-Top-End-Piston-Kit-Xplorer-400-L-95-02-83-25mm-/390966038353?pt=Motors_ATV_Parts_Accessories&hash=item5b07644f51&vxp=mtr

 

I'm guessing by 83.25 - 83.50 you mean boring the cylinder? Do I need to bore the cylinder even though I see and feel no imperfections? I was thinking a standard size piston with a light honing to reapply crosshatches would be what I needed?

 

Don't guess on this! Just because the cylinder looks ok doesn't mean it's not egg shaped and worn. Many people make the mistake of sticking in a standard piston.Especially one that's 20 years old now,plus may have already been bored before.. .25 is first oversize .010, .50 is second over size .020. If you don't have the snap gauges and micrometer, just take the cylinder to any dealer or machine shop and have them measure it.

 

I'll just send it out to a company I've gone through before and have them bore it out. The closest machine shop is about a 3 1/2 hour drive and my local Polaris Dealership is horrid (Took my other atv in to have front chain and sprockets replaced before I started doing all of my own work and they charged me $800 but never replaced the chain, replaced the one broken sprocket and charged me for all parts.)

 

Once back together don't forget to bleed the 10mm bolt on the cylinder head to get rid of trapped air. A lot of people have done that,some have ruined new top ends when they super heated while breaking them in. Just open the bolt until nothing but coolant comes out,no air bubbles,then close the bolt.

 

Thanks for all of the help! After getting it back together it is running stronger and better than ever before! Even though I'm still in the break-in period I can tell it's gained a huge amount of power and runs much more smoothly. Thanks! The "horrible" dealership I talked of with it's new owners seems to be a much better place that I was lucky to be hired on in recent weeks and am loving working at.

 

The song "Isn't It Ironic" by Alanis Morissette comes to mind.