What pistons

ullose272 · Mar 15, 2018

Going to do maintenance this summer, at 1500 miles i was thinking it was time for piston. what pistons is everyone using? I was looking at rktek or just going with stockers since it seems they have been fairly reliable. Im not opposed to a "fix kit" either. Extra power would be nice as well.

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edgey · Mar 15, 2018

U need to read indydan's post about pistons. Also have u done a compression check? U should check compression every 500 miles and keep track of the numbers no need to change pistons unless your seeing a drop in compression.

rydningen · Mar 16, 2018

https://www.snowest.com/forum/showthread.php?t=433563

x2 on that, read through this one.

I have run alot of forged pistons the last few years, Im back to putting stock polaris pistons in my engines.

SRXSRULE · Mar 16, 2018

OEM pistons, no fix kit, and I wouldnt spend the money at 1500 miles unless the piston skirts look bad.

I also check compression every 300-500 miles and I write the results on the clutch cover in sharpie. Use the same gauge and testing method every time.

ullose272 · Mar 16, 2018

edgey said:
U need to read indydan's post about pistons. Also have u done a compression check? U should check compression every 500 miles and keep track of the numbers no need to change pistons unless your seeing a drop in compression.

You have a link?

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Sheetmetalfab · Mar 16, 2018

rydningen said:
https://www.snowest.com/forum/showthread.php?t=433563

x2 on that, read through this one.

I have run alot of forged pistons the last few years, Im back to putting stock polaris pistons in my engines.

ullose272 said:
You have a link?

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Link right there.

TRS · Mar 16, 2018

Cheap insurance to replace them every 13-1500 miles. Use Polaris oem ‘15 Pistons. I would put ‘15 pistons in my AXYS also.

BD-Xtreme · Mar 16, 2018

Pistons

Though the pistons are better on the Axys motors, they still wear out the rings prematurely because of the short wristpin to crown height. Why do you think the new 850 (840) pistons are taller and they use it in there marketing even for the new motor. The short pistons are an issue.

The taller pistons last longer and do might slightly more power. Don't listen to the guys saying they add 6-7 hp, that's BS. But they do make a few more hp for sure. This is because the intake track to the motor is not blocked by the cylinder skirt as much with the spacer under the cylinder. This increases the opening size of the intake window of the crankcase by the reed valves. The larger opening allows increased airflow CFM which produces a little extra bonus horsepower.

Our kit also has machined dowels that aligns the crankcase and cylinder perfectly utilizing a step. The stock cylinder and crankcases alignment holes are machined to a slightly different diameter. Just a little tweak we did to make this kit a bit better than the rest. On sale for only $419.95 and comes with both base gaskets, not just one like some kits do.

http://www.bd-xtreme.com/index.php?id_category=98&controller=category&n=79

TRS · Mar 16, 2018

BD-Xtreme said:
Though the pistons are better on the Axys motors,

I respectfully disagree.

mountainhorse · Mar 16, 2018

Heres my 2 cents.

There are many factors that would lead me to replace a piston... and just looking at it through a bore scope or through a port window or compression tests are not all of them.

How is a piston holding up??? micro cracks, wrist pin bearings, collapsed skirts, locating pin on the ring, ring land cracking, etc etc.

Although there are certain reasons to say "run it till it fails"... I often take exception to that... one of the reasons being that when it fails, it can often ruin more than just itself.. and take some other expensive parts with it.

I've personally seen some high mile engines in the AXYS hold up well... and some low mile ones that did not... Leads me to believe that it is not one thing or the other, but rather a combination of things.

Plain and simple, IMO, mountain sled engines are loaded much more severely and suffer from these demands more than our flatland brethren... even the lake racers.

This is always a hot topic... and one that people take sides in over what product to use.
Some people "hawking their wares", others supporting their friends or vendors or sponsors, others just plain talking from the heart as to what has honestly worked for them... a blend if you will.

For me it is no longer a matter of cast vs. forged... It honestly used to be "CAST" for me up till about 6 yrs ago... but with the use of more appropriate materials in forged pistons (Like 4032 silicon alloy).... I'd say I'd put it up more to QUALITY of construction/Production than to the material itself.

With all that said, I've had good luck with the 'replacement' RK-Tec forged pistons and factory pistons and with in motors that I've put together...for others and for myself. (lately more for others though, Murph :face-icon-small-win)

BUT... I've heard more than a few accounts of pistons going and taking out cylinders early on... mostly ring issues (Pins)

I'm friends with the different 'gurus' on both sides of this argument.... and both sides have their heartfelt and experienced positions...which I respect and have used to learn more about these engines.

At 1500 miles, I'd think about pistons in any 800 CFI mountain engine...That is my OPINION... I lean towards preventive maintenance though... which might just cost me more $ than I may have otherwise paid... or maybe, just maybe.... it has saved me money.. :juggle::face-icon-small-win

.

AdrenalineAddict · Mar 16, 2018

I would positively look at replacing with stock piston at 1,500 miles, great preventative disaster maintenance. If your 800 is run hard you be lucky to see 2,000 miles. In my opinion compression checks are rather meaningless. I had a motor that lost about a quarter size chunk of piston dome and sent it out the exhaust port. When I took it to the dealer on account of it running weak, they said it appears your pistons and cylinders are fine on account of the compression being within 2 lbs. of each other. When I told them to pull the valves and give it a real inspection they said OMG, "How did that make it to the trailer". I've seen a lot of Polaris rings flake badly by 1,000 miles. The next thing you know you're down on running compression and having RPM issues although your motor may still run another 1,000 miles. My '17 Axys recently failed at 2,300 miles on account of ring failure.

TRS · Mar 16, 2018

AdrenalineAddict said:
I would positively look at replacing with stock piston at 1,500 miles, great preventative disaster maintenance. If your 800 is run hard you be lucky to see 2,000 miles. In my opinion compression checks are rather meaningless. I had a motor that lost about a quarter size chunk of piston dome and sent it out the exhaust port. When I took it to the dealer on account of it running weak, they said it appears your pistons and cylinders are fine on account of the compression being within 2 lbs. of each other. When I told them to pull the valves and give it a real inspection they said OMG, "How did that make it to the trailer". I've seen a lot of Polaris rings flake badly by 1,000 miles. The next thing you know you're down on running compression and having RPM issues although your motor may still run another 1,000 miles. My '17 Axys recently failed at 2,300 miles on account of ring failure.

Ring failure or locating pin migration?

mountainhorse · Mar 16, 2018

Tony, Got any photos of what you are talking about with pin migration??

.

TRS · Mar 16, 2018

Yes sir. Here are two pistons.

mountainhorse · Mar 16, 2018

What kind of mileage on those with pin issues Tony?

Those are factory Polaris Pistons??

.

TRS · Mar 16, 2018

mountainhorse said:
What kind of mileage on those with pin issues Tony??

.

The three we have. 845miles, 1332miles, and today another at 1328miles.

Edit: factory pistons in ‘18 stock motors, no mods, pipes or cans.

diamonddave · Mar 16, 2018

I've been running the MTNTK Fix Kits since the Dragon days. Not one single issue, I believe 35 kits now with another one currently in the garage ready to go in. To replace a highly respected engine shops Pistons that cracked after 100 miles which took out both skirts.

For such a simple idea, the gains in performance and reliability have been astonishing. All motors needed more clutch weight. The added case volume is a huge bonus on a 440/600 lower end.

Premature Ring wear has been an issue since the Pro came out in 2011 and has continued in the Axys. The last Axys motor I was in (for Lost RPM) had incredible ring wear at only 600 miles. Fix Kit brought her right back and more cause she needed 68's with a SLP Pipe at 4,000-6,000 feet.

Eric is correct about the new generation of forged pistons. I was leery in 2010 about the Weisco's for their reputation in previous years. But their reliability over and over has made me a believer.

I have zero affiliation with MTNTK. Do not sell their products and have only talked to Shawn a few times. He's too busy to talk to me about how well these kits work. He knows so. Just trying to help people out on this forum and make solid decisions about what works in this application. This motor has a lot of challenges inside and outside that need to be in working order for any piston to survive.

I will say that the stock pistons seem to hold up much better when boosted,

Ratchit · Mar 17, 2018

The new 800 axys pistons are better yes. The taper is a little much but there good pistons.
The wossners with .250” more compression height have less taper then stock and the shim gives you extra volume (added hp)
Kelsey’s new pistons for the axys are good too with less taper vs stock pistons.

Killer Time Racing · Mar 19, 2018

SRXSRULE said:
OEM pistons, no fix kit, and I wouldnt spend the money at 1500 miles unless the piston skirts look bad.

I also check compression every 300-500 miles and I write the results on the clutch cover in sharpie. Use the same gauge and testing method every time.

Clutch Cover ??? I thought my dealer was way to cheap .. That's it they keep the cover ! Must be why I never change belts ?

What pistons

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