Tighten up that cylinder skirt clearance !

[2XM3]

Now that we have taken apart a few 08 and 09 Dragons I have noticed another glaring error by the good folks at polaris. The cylinder to case fit is also all over the board. We have measured from .003 to .016 gap between the cylinder skirt and case. This along with the insane piston clearance is just one more example of garbage quality control on these motors.

It is imperative that this clearance be reduced to zero to .001, as it it the only way the cylinder skirt will have any of the support needed with the crazy loose piston slapping aganist it. Every motor with jugs I have ever built, be it sled,vw,porsche,lycoming has a slight press to very snug fit it this area. If you look at all the busted pistons and broken skirts its amazing some run at all.

Figure if the piston has .009 and the cylinder skirt has .014 total, the skirt will actually move .oo7 each time the piston goes through its cycle. The cases we have seen all show signs of the skirt hitting the case bore (.007 or more away) So just like a aluminium can, how many times can you bend it .007 before it work hardens to the point or cracking and breaking off? So in some motors I suspect the cylinder broke before the piston, others the piston before the cylinder. Both are crazy clearances.

Now why do you think that Polaris uses so loose a clearance? Well because the cylinder is CRAP and the distortion it shows when brought up to temp is amazing, it will in fact go anywhere from .004 to.016 egg shaped..
(this was measured with case and head all torqued down and up to 150 deg) So on some motors if you run correct piston clearance of .004 to .005 the piston is sure to scuff or stick even if the fuel mix is spot on. others with better clearance and honeing may run OK. . Now if you hone it torqued and hot to round you have a distorted cylinder when cold. arghhhhhhh !!!!!

One sure fire fix for all these problem is the separate jugs of the carls 860 kit, but very high priced (4k) so not a good option. I think the "fix" is a great idea,and seems to take the load off the cylinder walls.
As far as the case clearance goes there are 2 ways to fix this, the first and best is to plasma spray material to the skirt to reduce clearance to zero. Well you have to have someone with the machine so thats out for most folks. second method is to when installing cylinder use a piece of the correct thickness shimstock between the cylinder skirt and the case to reduce clearance to zero this is risky on the intake side tho as the shim is not "trapped" and could fall out. Also use a SLIGHT amount of "the right stuff" silicone product on the sides of the shim to in effect "glue" it inplace. (applied in the thinest possible layer with your finger) this stuff is resistant to gas and oil and high temp. Now what about the intake side? well you can offset grind the dowell pins to shift the cylinder to the intake side to allow the skirts to touch there, and add your shim (or metal) in the correct thickness all to the exhaust side.

IMHO tighting the cylinder, using the fix kit, coating the pistons as milehigh stated and using a high quality piston as well as filling all case and cylinder voids with high temp epoxy or block fill these motors should have a good service life... Yes I do in fact have to much time on my hands and hunks of garbage like this being produced is why I am happy I sold my race engine shop and retired.....hahhahahahah....

 

[thefullmonte]

So, what you are saying is that there might be something wrong with these motors. Lol. Seriously though, thanks for posting that. Very good information and another great find. Sounds to me as though motor building should be left to the Japanese. Still a bad situation over there. In all my years of riding I just never saw Yamaha motors have issues. They used to make some very impressive two strokes. And that 165 HP Suzuki beast that Cat is using has to be the most flawless motor on the snow right now. You just never hear of failures.

It really makes you think twice about Polaris. To actually produce something with so many issues is unacceptable. Way too much corner cutting going on. You would think that Polaris learned nothing in all their years of building snowmobiles. This wouldn't have been acceptable even in the 70's.

And why is it that someone who is retired can find all these problems, but paid "engineers" can't seem to do it right. Not to mention all the companies with different fixes. Or, is it that Polaris just went to the lowest bidder and just flat out got the most out of tolerance parts on the planet. I suppose it just has to look good on paper and as long as the CEO and board of directors are all living comfortably everything must be OK.

 

[2XM3]

lmao....cause i'm a machinist/engine builder who gets his hands dirty and I learn from mistakes I see, although I do have a EE degree (hated it)

,but please don't hold that aganist me..

 

[augerin]

Looks like I am going to get a set of '08 cases and have them machined for the '10 jugs. That should solve that problem. Good post.

 

[ragincajun]

bill....wtf!? DONT BE GIVIN OUT OUR SECRETS! tell them send us your cyls. and case and we will fix them for $____ lol

 

[2XM3]

hahahahaha

 

[03RMK800]

I wish I had the piston skirt-case clearance cited above. I put a .035 feeler gauge between the piston skirt and cylinder at top of stroke. I guess I had great luck--the engine always seized before the skirt could break.
If Polaris pistons were true and full size, I would have had .07 clearance on the tight cylinder at the top of piston. However, with the undersize piston and the oversize bore, both were way out of spec.

 

[gerrman]

What the HE?? is next? It seems to be one after another. Fuel issue, add a PCV; piston clearance, fix it with the "FIX", extra coat of NicaCil for stock pistons, extra coating on pistons themselves; cylinder skirt to case clearance problem, use a 2010 cylinder; low on compression, replace with aftermarket head; Blow the motor again, replace with a Cat 2012 issue(not available due to earthquake) A bit facetious but....What's next and what does one do to hopefully make the engine as trouble free as possible for say 2000 miles without breaking the bank!!!!!!

 

[thefullmonte]

What the HE?? is next? It seems to be one after another. Fuel issue, add a PCV; piston clearance, fix it with the "FIX", extra coat of NicaCil for stock pistons, extra coating on pistons themselves; cylinder skirt to case clearance problem, use a 2010 cylinder; low on compression, replace with aftermarket head; Blow the motor again, replace with a Cat 2012 issue(not available due to earthquake) A bit facetious but....What's next and what does one do to hopefully make the engine as trouble free as possible for say 2000 miles without breaking the bank!!!!!!

Everything you just said. Lol. Polaris cheaped out big time on these motors. Poor quality parts from the ground up. The only way to fix it is aftermarket. Actually I think the best fix is the Cat. That motor is powerful and bulletproof. Suzuki doesn't take short cuts. That must be an American CEO decision. That's why they make millions???? Just wish I had the extra cash to get one. I have to stay married to mine for a bit longer.

 

[diamonddave]

Excellent find Bill. You seem the like geek that I am finding something like this. Polaris is not the only company suffering from Machining issues. What I am wondering though is if you have had a chance to use the FIX KIT and how tight their spacer is to the cylinder?

 

[INDEEP]

Polaris is doing its part to boost the US economy. I believe MTK, Indydan, the Gizmo guys, and Swain Tech Coatings all appreciate these sloppy motors. Who's going to be next to jump on this gravy train? Sounds like a company that can beef up your cylinder skirts.

 

[Kraven]

Excellent find Bill. You seem the like geek that I am finding something like this. Polaris is not the only company suffering from Machining issues. What I am wondering though is if you have had a chance to use the FIX KIT and how tight their spacer is to the cylinder?

What Dave, No pre-mix suggestions anymore?

 

[starfire99]

I have a strong notion that polaris's problems start with their fuel system.......they incorrectly believed that by placing the injectors closer to the point of cumbustion, they would create a more accurate combustion sequence, when in fact, it resulted in poor atomization and poor fuel burn...which would create a lean condition. With the four injector system, they battled a lag when the second set started metering....they programmed the system for the correct amount of fuel....it just wasn't burning. A lean system needs more piston clearance to survive...and combined with the high thrust design of this motor, we now have lots to talk about. Where does cat inject their fuel...outside the engine in the throttle body? How about F1 engines with their showerhead injectors outside the engine?? When fuel doesn't burn in the combustion chamber, how does it affect the lubrication factor?? I would like to know how the |Carls 600/800 conversions are working with carburetion. Anybody got one??

 

[2XM3]

ttt

 

[2XM3]

ttt

 

[Butta]

I have a strong notion that polaris's problems start with their fuel system.......they incorrectly believed that by placing the injectors closer to the point of cumbustion, they would create a more accurate combustion sequence, when in fact, it resulted in poor atomization and poor fuel burn...which would create a lean condition.

I disagree on this theory.....unburned fuel in the cylinder during combustion actually absorbs some heat and takes it out the exhaust, which is contrary to a lean condition. A lean condition is where ALL the fuel burns, and there is still more air available for burning and the temps go way up. Air can't hold a lot of energy, so the temperature really spikes when there's an abundance of leftover air after combustion. When there IS unburned fuel remaining, it will absorb energy to the point of igniting, drastically lowering internal temperatures.

The problems Polaris has with this motor is a long list. Most of it starting with poor quality control and a $hitty design. IMO....

 

[Vfrtrader]

2xm3,

What pistons do you recommend?

 

[2XM3]

for these motors first choice is carls 860 kit, uses separate jugs, works great, second would be the fix kit using weiscos, and id use the 2010 cylinder along with it. imho

 

[2XM3]

ttt

 

[2XM3]

ttt