Polaris 800 owners DON'T replace your stock Pistons

[Merlin]

Dave,

I remember having reservations on using Wiseco pistons in a CFI2 a few years back but it was actually your feedback & track record with MTNTK's fix kit that made me reconsider my position. Wiseco has clearly changed the composition of their pistons over the years resulting a tougher skirt that is less susceptible to collapse. That said, I wouldn't hesitate to run their kit in properly prepped bores.

Regarding the AXYS engine with .014" / .015" PTCW clearance, where was the extra clearance actually coming from? Wear on the skirt or collapse of the skirt?

I only have experience with one aftermarket piston for the 800 CFI and that would be the one that comes in the MTNTK Fix Kit which is the taller Weisco piston and uses the cylinder shim.

I have installed approximately 35 of these kits with zero comebacks, 4 corner seizes, issue's, runnability issues, etc. since they came out in 2010ish. Some of them have been installed (with my perfection attention to detail) with your gusseted cylinders, other's just R&R'd, and some with brand new mono's, even with the 08-09 thin cylinders. I could not work on these my way paid by flat rate time.

In fact, I like this kit so much I was telling Justin I was going to ask you to build me a Longrod and shim that will allow me to run the MTNTK Fix Kit this summer.

As for your results, I completely understand your sample size and mine are different and could be explain some of the reason why we are seeing different results (if we're comparing results from the same piston). I also have to question the ability of some of the installer's, condition of the rest of the motor, not having the right tools, drinking alcohol during assy. and a multitude of other factors that could cause premature failures.


As for the stock piston goes, I think the success you are seeing might be because of the extra things you do and the care you take when the motor goes back together.

I just got done rebuilding a '16 Axys with less than 600 miles. Loss and faded RPM's. Installed Fix Kit and RPM are right back to 8,500. Rings were wasted and pistons had 0.014" and 0.015" clearance.

I have another one to do that is fouling plugs like crazy. 500 miles. Everything's been done to it outside going in. Carl's has told him it's time to go into the motor.

 

[diamonddave]

Dave,

I remember having reservations on using Wiseco pistons in a CFI2 a few years back but it was actually your feedback & track record with MTNTK's fix kit that made me reconsider my position. Wiseco has clearly changed the composition of their pistons over the years resulting a tougher skirt that is less susceptible to collapse. That said, I wouldn't hesitate to run their kit in properly prepped bores.

Regarding the AXYS engine with .014" / .015" PTCW clearance, where was the extra clearance actually coming from? Wear on the skirt or collapse of the skirt?

Hey Merlin,


I was leery throwing in that first fix kit. But after cracking a skirt with stock pistons in my "2010 updated" 2009 Dragon in only a total of 322 miles on the sled, I figured I didn't have anything to lose. That sled is still going has over 4,500 miles. Replaced the pistons after 2,000 miles, could have reused them.

As for the Axys, it looked just like all the Pro's. Knife edging on the bottom of the skirts and the skirts had collapsed. So to answer your question, BOTH.

 

[indydan]

Dave, I have found it is not piston collapse, it is piston wear on the bottom .500 ( the measure area ) 90 degrees from the pin as you know.

What happens is if the cylinder finish is to aggressive the piston wears a few thou prematurely and then the piston starts tipping in the bore loosing ring face ( squareness to the bore )

Several things happen if a cylinder finish is to rough.

1- Mentioned - premature skirt wear.
2- Piston tips in the bore and rings lose 90 degree ring squareness to the bore.
3- piston has to much clearance from premature skirt wear and it now can slap & rattle pounding itself & the cylinder sleeve extensions to death.

This process gets more interesting as we studied the Core motors. ( and customer feedback )
Effects that follow.........Once you lose ring squareness.

The ring starts to lose its ability to seal...... ( At this point the motor is trying to tell you something. )
1st - peak RPM drop & power loss in relation to when it was new.
2nd - combustion chamber heat goes by the rings and causes the Bottom end to run extremely hot prematurely burning up reed pedals.
3rd - ( the most misunderstood ) - once you lose ring squareness & piston squareness to the bore the piston itself starts to over heat...... the coolant in the water jackets loses its ability to pull heat away thru the rings and piston surface..... When the piston tips a small gap ( clearance ) is created between the ring face and the bore...

Just like insulation in a wall......this process compounds itself as the skirt wears, then gains room to slap.

This is where the thread gets its title - ( don't replace your stock Pistons )

The motor cannot make peak power if the Pistons have started to wear then tip and slap.

If the motor is as strong 2000 miles of 4 years later as it was when it was new it doesn't need Pistons.

If you find yourself dropping clutch weight, or searching for aftermarket performance parts because one of your friends has a fresh motor and he cleans your clock.....( chances are your Pistons are junk )


( I Will say this) ..... A fresh bone stock motor will out perform any worn out motor with every mod performance part made. ( as a matter of fact, there are very few performance products that actually improve on a 800 Small block other then a Turbo ) and Turbos are IMO are for a very select group unless you have 2 sleds and or......are a
Extremely good rider.

I have customer after customer make claim that their fresh PRO Long Rod is tearing up new Axys sleds.

Mind you most of the motors that are doing this I have actually taken port timing away and lowered the cylinders and increased head volume ( yes increased ) to counter the cylinder drop. This combination at elevation has seemed to be what our mountain customers seem to really enjoy...... Arm stretching low end torque.

There are several of these motors on the snow since early 2016 and some customers don't even know they have them..... And I can say this, these 800 PRO motors at elevation are a force to be reckened with. might even be a few test Axys Motors like this on the snow. ��

And then couple the old PRO with a set of axys spindles ( or some even better aftermarket front end kits ) & a new 2.600 axys track and your arms will hurt at the end of the day. ��

Dan

 

[Nyheim]

Interesting stuff to read, but I feel i must tell you my humble opinion.

My 2013 Pro RMK 800 with only 1500 miles was only doing 7900 RPM at sea-level, measured only 115 PSI on both cylinders. Oil pump was turned up when sold new (Oil consumption is 1:50 / 2%).

Replaced OEM pistons with forged Wössner pistons. OEM pistons looked great, but had some ring-groove wear. Cylinder was in spec. Installed Wössner pistons and compression immediately increased to 130 PSI and RPM stabilized at 8400 RPM. Had to install a clutch kit to get RPM down to 8200-8300.

Been running hundreds of miles on them so far, and everything is working like a damn charm. Engine runs great with 130 PSI still. Less vibrations on idle, and very smooth engine operation. Sheared of about 100 grams pr. cylinder with Wössner pistons. Imagine what 200 grams less moving up and down at 8250 RPM does.

I will never be going back to stock pistons.

BUT, don't gt me wrong. I have nothing against stock pistons. It's just what I prefer. I happen to know a lot of people who ran stock pistons up to 10.000 miles, and engine still runs good. Maybe not the compression it should have, but still running great. I think the "OEM piston being bad" rumour is way over-rated.

As for not honing your cylinders, I totally disagree, and I'm not even gonna argument over why I disagree. Honing marks are essential for oil to stick to cylinder walls for proper lubrication of pistons rings and cylinder wall. There's a reason why EVERY engine manufacturer in the world hones their cylinders, and I don't trust one guy to convince me otherwise. Honing also helps piston rings seat propely making a tight seal.

 

[tuneman]

Honing marks are essential for oil to stick to cylinder walls for proper lubrication of pistons rings and cylinder wall. There's a reason why EVERY engine manufacturer in the world hones their cylinders, and I don't trust one guy to convince me otherwise. Honing also helps piston rings seat propely making a tight seal.

Sorry, your statements are false. Indy Dan is right on, when it comes to honing. We're talking Nikasil plated cylinders here; it's a whole different can of worms. Read the "Cylinder honing update" thread. And I'm not just taking Dan's word for it. My background and experience can back it up. Not trying to start an argument, though. Just trying to help a fellow sledder out.

 

[indydan]

Honing myths

Nyheim:

A few years back I would've said your statement makes sense.

Cylinder honing of a cast iron or is simply done to illuminate the threading process of boring. And it seals the deal with an ( X ) called cross hatch.

Silicon carbide cylinder plating is applied through electronic process.
It's rockhard after application and must be sized. Diamond and/or superabrasives are the only thing to date that can cut it.....

The end result is crosshatch not favorable in a silicon carbide plated cylinder , The plating itself is porous enough to hold oil there is no need for crosshatch . As a matter of fact the crosshatch peaks created are distractive to pistons and rings faces.

I truly appreciate your input but on the subject of silicon carbide plated cylinders you're simply lacking research & and hands on testing.

 

[Nyheim]

Sorry, your statements are false. Indy Dan is right on, when it comes to honing. We're talking Nikasil plated cylinders here; it's a whole different can of worms. Read the "Cylinder honing update" thread. And I'm not just taking Dan's word for it. My background and experience can back it up. Not trying to start an argument, though. Just trying to help a fellow sledder out.

no no, if you got some good points on why, I'd really like to hear them I too, can learn new things. I just don't understand why manufactures of 2-stroke engines with nikasil cylinders hone them before install then?

This must be something that the engineers have figured out, especially since we have done it for years and years. The logic behind honing also makes a lot of sense.

Grooves in the cylinder will house more oil, than a completely smooth wall. Oil gets in between these grooves and sticks more easily causing better lubrication of the cylinder wall. Rings also will seat better with honing.

However, I agree that nikasil is easy to damage around ports. Nicasil is hard and thin, which can cause flaking if you are unlucky with a ball hone or stone hone around one of the ports. But usually this does not happen.

Thing about nicasil is, if you're using a ball hone or stone hone, the nicasil is so hard, you're not actually honing it. You're only degazing it, and that does not damage the nicasil at all. This is what most people do.

To hone it, you need a diamond hone due to the strength of nikasil.

EDIT: Indydan, I did not see you reply to me, until after I had posted this reply. I would not have repeated a lot of what you said if I had seen it. And yes, I do agree with you, you probably have more experience and knowledge on this matter than me, but you said crosshatches does not matter for nikasil due to the metal being porous, but I have read many places that if you were to lubricate your cylinder wall "through" the porousity of nikasil, your engine would blow up. Not enough oil can be contained in the porues of the nikasil to lubricate enough. You STILL need crosshatchings for the oil to seat in.

And what about ring seating? Without honing, its a problem.

 

[Nyheim]

I must admit, I have been talking about honing from factory, not by private people in their garage. For piston replacement I've been talking about deglazing, not honing. Bad choice of words from me, I'm sorry.

Does it exist some kind of deglazing tool made especially for 2-stroke nikasil cylinders? Indydan?

 

[indydan]

I must admit, I have been talking about honing from factory, not by private people in their garage. For piston replacement I've been talking about deglazing, not honing. Bad choice of words from me, I'm sorry.

Does it exist some kind of deglazing tool made especially for 2-stroke nikasil cylinders? Indydan?

No-problem, I understand this goes against a lot of past thinking.

deglazing not required on a plated cylinder.

The first set of rings has done a great service to the next set of piston & rings.... The second set of pistons & rings will out last the first if you don't touch the bore.

HG7 is one better ( its smoother then a run cylinder ) - then just install and go.

 

[gtwitch]

Ditto Dan and Tuneman!!!
gtwitch in wyoming

 

[raleigh111]

compression

Dan
I have a 2013 pro and on the last trip i was only pulling 7800-7900 rpm. I have some clutching to look at yet before any wrenching on the engine but i was curious what you like to see for compression at sea level on a warmed up engine? I live about 20 miles from you which is around 900ft. Also are the tachs on these things fairly accurate? i remember back in the old days they could be off as much as 500 rpm and we were always re calibrating them.
Thanks Robert

 

[Ratchit]

Yes they are heavy, and one of the reasons they are so heavy is the massive
Gussets they use from the wrist pin boss to the skirt.

Titanium wrist pins, Hmmmm.......interesting

Yes Dan.

I have been using titanium Ti 17 with dlc(diamond like coating )
for many years in racing and just riding. Saves 40% weight vs stock wrist pins. Polaris wrist pins weigh approximately 100 grams and cat wrist pins are about 95 grams . I get them to 55-59 grams with the Ti 17 titanium.
The biggest problem with the Polaris 800 is piston weight and the taper is to large. It's around 584 grams per hole and should be around 500 grams .
Wossener makes a great direct replacement piston that is lighter , tapers less and tighter tolerance. Add my titanium wrist pins and you have a great engine package. Of course the proper honing like you explained as well

 

[Davajn]

I have been using titanium Ti 17 with dlc(diamond like coating )
for many years in racing and just riding. Saves 40% weight vs stock wrist pins. Polaris wrist pins weigh approximately 100 grams and cat wrist pins are about 95 grams . I get them to 55-59 grams with the Ti 17 titanium.
The biggest problem with the Polaris 800 is piston weight and the taper is to large. It's around 584 grams per hole and should be around 500 grams .
Wossener makes a great direct replacement piston that is lighter , tapers less and tighter tolerance. Add my titanium wrist pins and you have a great engine package. Of course the proper honing like you explained as well

Interesting. Have you seen any longevity problems with ti wristpins?

Whats the price for a set?

 

[Merlin]

Ditto to the questions below.

Also, what is done to the ti pins to provide acceptable wear characteristics?

Interesting. Have you seen any longevity problems with ti wristpins?

Whats the price for a set?

 

[Merlin]

Sorry, please disregard my question above. Somehow I missed your comment on the diamond coating.

I need slowdown and RTFS. LOL

I have been using titanium Ti 17 with dlc(diamond like coating )

 

[gtwitch]

Rachit, Where are you getting your Woosner pistons and what is the part number for both Polaris 800 and Arctic 800. More info on where and now much $ on the Ti pins?? Thanks!
gtwitch in wyoming

 

[Ratchit]

Rachit, Where are you getting your Woosner pistons and what is the part number for both Polaris 800 and Arctic 800. More info on where and now much $ on the Ti pins?? Thanks!
gtwitch in wyoming

I have a machine shop making the highest quality Ti 17 titanium with dlc. Been proven in race cars for years with valves, wrist pins, etc..
Stronger then the steel that's used stock and lighter. Plus the dlc coating is wear resistant. So it's all good. Been using titanium since 2002 in two stroke motors with great advantages.
Pm me for pricing please .

 

[Johnwi3]

2010 switchback 800

Great information on the 800 motor...all of which I was unaware of until recently. I own a 2010 Switchback 800, just rolled 5200 miles, no major issues thus far (knock on wood) Although I think I just lost my VR this weekend.

So my question is this...my motor is 9 years and 5200 miles old, 100psi compression in each cylinder, runs good but not as smooth as it once was which is to be expected. Indydan has some great info as I was going to freshen up my top end this summer, his post made me question. So do I run it until it blows or is there a time that prompts a rebuild?

Thanks in advance!

 

[caddylover]

with compression on the low end why wouldn't you rebuild it? I put the sk1396 wiseco kit in my sled last summer. Put 900 miles on it this season with a .0062 PTWC. It was damn cold here in the prairies this winter and never had an issue with these pistons. Was i worried about seizing and all the internet boogie man saying they are crap, damn right... but nary a burp on these and sled runs great.

I don't know why you would wait till it blows, just fix it and have piece of mind.

 

[gtwitch]

Back in the first part of this thread Dan hit on an issue that I also found in 2011/14 time frame and that was the ring locating pin and the way it is used or designed on the Polaris OEM pistons and the CAT 800 pistons and I also found that SPI direct replacements used the same locating pin method. I had several MTN TEK kits with Wiesco pistons fail in less than 1 to 2 hundred miles and had traced these failures to the way that the ring was held in place (or not). Since that time, all of my rebuilds have been with either OEM or SPI as I have stopped using CAT because not using FIX KIT spacer plates anymore and have not honed a cylinder since that time frame either as using Dan's process or not touch a nicely polished cylinder from the previous pistons with good measurements. I have not had a single rebuild go down for 5 years from a upper end piston/ring failure, have had a couple of crank failures in the PRO 800 engines IMO from the origonal oil pump settings from the factory being set too lean and I did not catch these and turn them up soon enough! Sorry for the long windage here, Thanks Dan for your input.
gtwitch in wyoming