Any difference in Pistons for Polaris top end?

spm731 · Mar 23, 2015

Hey Guys, I'm sure this discussion has taken place before, but I'm doing a maintenance top end this summer on my 11 PRO. I don't really want to discuss the merits of the 'fix' kits, I'm going to put one in regardless of whether they bring anything regarding durability. My question for you guys is what is the best piston or is there one? There are so many options available for these kits in terms of pistons, SPI, Wossner, Wiseco, Namura, etc. Any input would be appreciated, thanks!

Merlin · Mar 23, 2015

spm731 said:
Hey Guys, I'm sure this discussion has taken place before, but I'm doing a maintenance top end this summer on my 11 PRO. I don't really want to discuss the merits of the 'fix' kits, I'm going to put one in regardless of whether they bring anything regarding durability. My question for you guys is what is the best piston or is there one? There are so many options available for these kits in terms of pistons, SPI, Wossner, Wiseco, Namura, etc. Any input would be appreciated, thanks!

To answer the question in bold: The one that's installed with the correct clearance.

By all accounts, most pistons that are available for these engines are OK as long as the engine builder blue prints accordingly.

FWIW, I installed Wossner(RKT) pistons in my '11 but when the time comes to replace them again I will likely go with OEM or reputable cast aftermarket.

Forged pistons or their variants are susceptible to collapse resulting in excessive PTCW clearance. Something the '11 / '12 model year 800 CFI - 2 engines(cylinder skirts) do not tolerate well.

spm731 · Mar 24, 2015

Thanks for your input. I ran forged wiseco's in my old Edge 800, and always found as long as you warmed the sled up properly each ride there were no issues. Good to know the new ones don't handle the forged very well.

tuneman · Mar 24, 2015

Merlin said:
To answer the question in bold: The one that's installed with the correct clearance.

By all accounts, most pistons that are available for these engines are OK as long as the engine builder blue prints accordingly.

FWIW, I installed Wossner(RKT) pistons in my '11 but when the time comes to replace them again I will likely go with OEM or reputable cast aftermarket.

Forged pistons or their variants are susceptible to collapse resulting in excessive PTCW clearance. Something the '11 / '12 model year 800 CFI - 2 engines(cylinder skirts) do not tolerate well.

I'll probably dig into my '12 Pro in the off season to see if it should get new pistons. Hopefully not, but Merlin brings up a good point. To clarify what he said, forged pistons are known to grow more than cast pistons, when heated up. So, technically, they need additional PTCW(Piston To Cylinder Wall) clearance. If you give them more clearance, they'll have more opportunity to slap as they heat up, which may cause piston skirt or cylinder skirt collapse. The '11-'12 cylinder skirts are significantly weaker than '13 and up and are known to crack from excessive piston load. Seems a cast piston would be the better option. Maybe the new 2016 grooved pistons will fit??

Carls Cycle · Mar 24, 2015

PISTONS

The best pistons to run are the Pistons from the 2014-2015 model year. That is the only thing we put in any of the pro's when we rebuild sleds here at Carl's and have seen great reliability from them. They have the proper specs that will work on your 2011 and will not have the same issues. If you need pistons and any gaskets, we have everything here in stock and could get them sent out to you immediately.

Avoid the supposed "fix kits" as they are not all they are cracked up to be. You are better off going OEM, in our opinion.

Merlin · Mar 24, 2015

Carls Cycle said:
The best pistons to run are the Pistons from the 2014-2015 model year. That is the only thing we put in any of the pro's when we rebuild sleds here at Carl's and have seen great reliability from them. They have the proper specs that will work on your 2011 and will not have the same issues. If you need pistons and any gaskets, we have everything here in stock and could get them sent out to you immediately.

Avoid the supposed "fix kits" as they are not all they are cracked up to be. You are better off going OEM, in our opinion.

This feedback is intended as constructive criticism: The statement in bold is presumptuous as neither you nor any parts supplier can attest to the actual bore size on every engine. There will be plenty of cylinders that fall well outside the max. bore diameter spec. that need to be sent out for repair / re-sizing to achieve proper PTCW clearance.

If your shop is doing the piston install for the customer I can only assume that your techs. are looking after the blueprinting & subsequent cylinder repair(when needed), however if you are selling these pistons to customers for DIY projects you best be including the caveat that "these pistons work the best providing they are installed with proper PTCW clearance."

spm731 · Mar 25, 2015

Interesting, I don't know about the fix kits or not, just seems no one is interested in one of these motors in SK without a 'fix' kit. Was mostly thinking of resale down the road. Did get 3100 miles without issue on this original motor, with 6 mountain trips. Just rebuilding for preventative reasons. You comment about the 14-15 stock pistons has got me thinking. Thanks again for all your comments

pobuda01 · May 29, 2015

What is the pricing on a top end "kit" for a 12 pro 800? Id imagine it is significantly more expensive than an aftermarket kit.

Spaarky · May 29, 2015

Any advantage in going to the Axys pistons instead of the stock 15 pistons....

TRS · May 30, 2015

It would be nice if Polaris would offer pistons in A, AB, and B sizes to their dealers and the consumer instead of just the AB size. The cylinders are stamped accordingly and proper pistons installed from the factory but replacement pistons
are only available in one size from PI. It is difficult to obtain proper clearance using PI replacement pistons or anyone else's.
Merlin you hit the clearance issue perfectly.

gtwitch · May 30, 2015

SPM, Only my opinion here, but I think Carls is right to stay with cast pistons unless as you state that you understand the importants of warm-up and I feel this improtant in all cases weather forged or cast pistons.. I just did my 11 pro 800 with Sno-Pro cast pistons with the fix plate (Sno-Pro does not make stock length pistons for our Pro 800's) I like the Sno Pro pistons, as they are cast and lighter than the stock Polaris pistons. From my experience, make sure that you clearance the exhaust gilloutines as you are building this engine, this is very imoprtant!!!! If you have any questions here PM me at gtwitch@uwyo.edu. Indy Dan will do the exhaust gilloutines for you also. My 11 Pro 800 has the SLP Stage 3 with Power Commander and clutching, pipe/can. I lost a rod brng in March due to lube issues (I suspect Polaris issue from factory--TOO LEAN) Anyway, its up and running and I put the first 40 mile breakin ride on it day before yeaterday in 14" of new and still snowing (very wet though!).
gtwitch in wyoming.. Wrong piston name here , They are SNO-X not Sno Pro.

mountainhorse · Jun 1, 2015

From a previous thread about pistons... and NOT to endorse forged over cast or vice versa.

All cast and all forged pistons are not alike.

Also... a big factor is piston structural design even within the type of alloy used.

mountainhorse said:
The Wosner forged pistons for the PRO RMK's and aftermarket suppliers are made with 4032 forgings. 4032 alloy has a high silicon content.
These pistons are similar in thermal expansion properties to a hypereutectic Cast piston.

Wosner 4032-alloy pistons are different from the 2618-alloy used in MOST Forged pistons.... the 2618-alloy is what most of the "legend of forged" pistons is based on.

4032 has a high silicon content 11-12% silicon... which makes it much more user friendly... and generally more expensive than Hypereutectic Cast pistons.. and tougher than a cast piston as well because of the forged construction.

The stock pistons are Cast Hypereutectic pistons...with about 12-16% silicon content.

In high boost applications... a 2618 forged pistons works well... but are shorter lived pistons usually reserved for race engines or those that are not expected to stand up to high mileage/hours.... or in extreme high output engines or engines that might detonate, they are less prone to fracturing than Cast or 4032-alloy pistons. 2618 pistons have less than .2% silicon content and suffer from cold seize and other issues commonly attributed to THIS alloy when used in pistons... NOT true of the 4032 alloy.

Skirt collapse is much more prevalent in 2618 alloy pistons with long term use... and the clearances in initial setup must be larger than a cast or 4023 piston. That need for clearance also leads to piston slap when cold (which or sleds are most of the time relative to most engines)...That slap also accelerates wear....

The 4032 Alloy in the Wosner pistons does not need to have larger clearances... and runs clearances typically used with Cast piston applications.

.

mountainhorse · Jun 1, 2015

TRS said:
It would be nice if Polaris would offer pistons in A, AB, and B sizes to their dealers and the consumer instead of just the AB size. The cylinders are stamped accordingly and proper pistons installed from the factory but replacement pistons
are only available in one size from PI. It is difficult to obtain proper clearance using PI replacement pistons or anyone else's.
Merlin you hit the clearance issue perfectly.

Tony... If your cylinder is NOT marked "AB" would you recommend that the cylinder get sent in with pistons for plate/hone to spec?

Is this even possible if the cylinder is a hair to large as the Nikasil is super thin?

What are the options?

.

gerrman · Jun 1, 2015

MH Any idea about the alloy/silicon content in the forged Wiseco pistons? These seem to be a popular piston choice in various Spacer/Fix kits.

mountainhorse said:
From a previous thread about pistons... and NOT to endorse forged over cast or vice versa.

All cast and all forged pistons are not alike.

Also... a big factor is piston structural design even within the type of alloy used.

mountainhorse · Jun 2, 2015

I don't... but would be easy to find out with a call....Anyone??

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Any difference in Pistons for Polaris top end?

spm731

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Merlin

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spm731

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tuneman

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Carls Cycle

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Merlin

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spm731

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TRS

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