550 fan Jetting and burn-down issues....

I run a fleet maintenance shop at a ski resort. We have about 40 Polaris sleds (all fans) and have been running Polaris fans since about 1996, so for over 10 years now. I have two major problems that I can't sort out.
1. Burn downs. Our engines have gotten progressively more and more unreliable to the point that we're at now, which is that motors are lasting as little as 5 minutes! With old 488 fans, we used to see 8-10k miles from a new OR rebuilt 488 fan, and we ran Wiseco forged pistons in the rebuilds. In the 550's that dropped to 5-7k miles, and when the Nicasil cylinder came out, engine life dropped to less than 4k miles, so we started trying different things.

We've run Wiseco's, SPI's, and Polaris. None seem to work or last any better than any others. On the Wiseco's we set our piston to wall clearance at .005" and with the SPI's we use .003".

We've tried various brands and types of oils and none seems to be any better or worse than another. Our fuel is from the same vendor that we've used for the last 11 years, and is the same brand and type. None of the burn downs are detonation related. They're all seizures or broken skirts.

2. Jetting. We've been running 220 mains in the 550 for YEARS...since they introduced that downgraded motor (from the old 488 fan) and that jetting has been just right "forever" for the most part, for our elevation (7-9k') and temps. *Some* machines preffered 210 mains. Anyway, all of the sudden, this year, 220's aren't enough and machines are running lean. My mechanics aren't that great at reading wash and plugs, so yesterday I took it upon myself to dive into a freshly built motor and see what jetting it would like best. I started with 240's to be safe. WOT, for over a minute, cut it off clean and pulled plugs. The color change on the ground electrode was basically at the weld, and there was essentially NO piston wash. I went up to 260's and ran the same test. Results? Same. (!) WTF is going on here?? Floats are set to spec, new fuel filter and fuel lines, etc. I'm baffled. Also, I noticed that UNLIKE the old Gen II chassis sleds w/the 550's, these Edge machines see a HUGE...HUGE change to A/F ratio when run with and without the vent tubes hooked to the air boxes. (?)

Any insight as to what I (we) are missing would be greatly appreciated.


Additional Question: I have been a member on this forum for YEARS, but haven't been active for several years as my personal snowmobiling/modding has taken a back seat to other life endeavors. When I went to log on today, it seems that my membership/registration is gone. (?) Did the board go down and loose all data or something? What happened to ALL the posts I made, years ago?

-Tom

10 views and I haven't even gotten an answer about my "old" Username and or posts?

Tom400CFI said:

10 views and I haven't even gotten an answer about my "old" Username and or posts?

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They changed the forum over to a new server a couple years ago and everyone had to switch over.....
As for your sleds your problem may be in the fuel you are getting. Alot of places are now getting some form or another of oxygenated fuel in the winter months to cut down on emmisions. Most 2 strokes will need to run atleast 2 sizes fatter on the mains because of the added oxygen in the fuel. Hope this helps you.

tom, we prep a bunch of 550's for bush use and for 2 years we had a big problem with them melting down,polaris had us open up piston clearences on them to fix(but all the 550;s should be at that clearence now days) polaris reasoned that the sleds were overheating and swelling pistons until they stuck..on your rental sleds are they the standard 550 or the rental 550 sled(have the extra venting on the hood)? all we sell now are rental sleds and have had no more problems...

Thanks for the replies!

We have about three of the "rental" units that have the extra cooling ducting, and I do believe that those have been significantly better.

What piston to wall clearances should we be shooting for? With cast piston?

I dont recall the exact #'s(i think we opened piston/bore clearence by .002-.003 )..but the new motors should be coming now days with the bigger clearences.as far as I know every sled we fixed went down the trail with no more problems..If I was you I would add the rental ducting to your non rental sleds,personally I think getting the sled to run cooler is the biggest thing you could do to lenghten their life....polaris at the time was also saying we could jet 1 size fatter on the pto side but said it probably wouldnt stop them from heat seizing...

10-4 on all that. Thanks again for the input. At this point, ALL of our machines are or have been, rebuilt. They may be coming w/greater clearances "now days" but we'are way beyond that point at our resort. You should see how many cylinders are on the work bench right now for re-bore.

We are "over it" with Polaris at this point, so all our new machines this for year are Yamaha VK Pro's. Our 'Poo Trails range in age from '08 back to '05, with two '99 Gen II's...which by the way run flawlessly. All the problems -by our observation- started w/the Edge chassis, and got way worse w/the aluminum cylinders. At this point, we are simply looking to get our Trails to last the rest of this season (or at least last longer than "minutes"!). Then, we will dump them and go all 4 stroke.

Any ideas on why the machine I worked on yesterday showed zero response to the jetting changes from 220's all the way to 260's?

You need to contact your Polaris dealer. This exact issue was addressed for model year 2009 for fan cooled machines.

If my memory is correct, Polaris found that at constant low speed operation, like rental or guided rides, the oil pump would develop an air bubble and not allow any oil to the engine.

For model year 2009 there is a new oil pump and a vent hose to remedy this problem.

I am not sure if there is a retro kit for older machines or not. I believe there is but not positive.

Any more input here? Since I posted, we've had about 8 more sleds go down. At this point, nearly 1/2 of our fleet is down! This is insane!!

We're building 4 "test" motors now; two w/SPI pistons on at 3.5 thou clearance, and one at 5 thousandths clearance. Then two more motors using Wiseco pistons, one clearanced at the middle of Wiseco's recomondation and one at the max recomended clearance. We will customize jetting for each engine at 1/4, 1/2, 3/4, and WOT, then see which one burns down first. Shouldn't take long with what we've got going on here.

Can you post up some pics of the damaged pistons. I suspect you don't have burndowns but rather oil related issues. I can likely be of some help to you but need to see what you're dealing with. I have seen my fair share of these engines.

No problem. Here are a few pistons to look at. The first thing I notice is very little to no wash...

I would do a test sled with a different fuel supplier and or look at the oil supply

Yeah, we definitley seriously question the fuel. I called our vendor (same one we've used for 11 years) and they claim that there has been no change to the gasoline. I remain skeptical of that, however, NONE of the burn-downs are detonation related.

Update; We built anotehr motor w/the SPI pistons using .004" clearance this time, and loaded it up with measuring devices...





What did we find? Well, nothing that a good piston/plug reader couldn't have found with some quality observations. Engine ran at about 11-12:1 A/F ratio at anything over 1/2 throttle, and EGT's in the 800* range. Drop down to 1/4 throttle, and all of the sudden we were at 14,15, and even 16:1 A/F ratios(!) with EGT's in the 1000*+ range. There is a problem. We need richer nozzles.

Compfusion...ya left me hangin' bud! I posted pics for you...what do YOU see?

Did you just try raising your needles?

Tom,
Sounds like you are starting to get a handle on this. Where are your needles set at? There are 5 grooves on the needles with the top being #1 and the bottom #5. I would assume the clip on the needle is probably in #3. Try moving the clip up down on the needle to 4 or even 5 and see what kind of readings you are getting now. The lower you put the clip on the needle, the richer the setting. This affects your mixture from about 1/4 to 3/4 throttle.

bigfoot said:

Did you just try raising your needles?

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A while ago.

theultrarider said:

Tom,
Sounds like you are starting to get a handle on this. Where are your needles set at? There are 5 grooves on the needles with the top being #1 and the bottom #5. I would assume the clip on the needle is probably in #3. Try moving the clip up down on the needle to 4 or even 5 and see what kind of readings you are getting now. The lower you put the clip on the needle, the richer the setting. This affects your mixture from about 1/4 to 3/4 throttle.

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Our needles WERE set at the second groove down from the top (#2), from the factory. Even though we're at 7000-9000' elevation, we're moving all the clips to the middle (#3) position.

That hasn't helped much though. I BELIEVE that most of our burn downs are occuring at ~1/4 throttle. Getting objective data from the operators is tough though.

I assume your rental fleet of 550's is being operated by novices that are running them at a pretty constant speed and throttle settting. Most likely at the 1/4 throttle setting. I would for sure try a needle in #4 and see how it performs. Might need to try a little larger pilot jet as well. Those pics you posted, they looked lean for sure.

This fleet isn't rentals; it's at a ski resort. WE have 40 machines that are operated by staff, like lift mechanics, snow makers, ski patrol, etc. While they aren't "novices", they certainly aren't seasoned riders either, for the most part, which is why getting objective data from the riders is pretty much hopeless.

We are going down the "Nozzle" road as a first step. We went from Q-0's to Q-2's today and it did show an improvement at 1/4 throttle on the WB02. As I understand it, the needle has a larger effect from 1/2 to 3/4 throttle.