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

Tom400CFI said:

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

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Sorry, but I don't get online near as much as I used to. I wish I had the time to spend on here ... Probably sell more mount kits..
Your failure looks typical of the, ahem, few I've seen. Definitely oil related, or lack thereof. The other side shows the blowby and symptoms of cylinders which are neither round, nor straight. I've seen way too many of these right out of the box that need to be resized and fixed. Are any of these engines using the nikasil kit like the new 550 engines?? Effective heat control and evacuation was a big problem with these sleds especially when driven at lower speeds as SuperDave stated. Sleds driven like they were stolen didnt seem to exhibit the problems. The newer nikasil engine addressed the oil issue in several ways. The non-iron lined cylinders transferred heat better to the atmosphere, the CDI module had a different timing curve to change heat generated in the engine, the exhaust had shields attached to not release as much heat into the engine compartment, jetting was changed, and the oil pump had a thermal barrier added between pump and case along with a self bleeding setup that would catch the air and return it to the oil tank each time the bottle was filled.
I do believe that these engines can be made to run trouble free (and many do) with careful setup and maintenance. Don't run too loose a piston clearance. This can cause problems especially in electric reverse engines. .004-.005" is plenty. If the auto-bleed kit is not installed on the oil pump then check and bleed it on a regular basis. An "air catcher" can be made in similar fashion to a water trap on a carburetor. It would consist of a fitting in place of the bleed screw with a short piece of hose extending upwards and a plug in the end. As air is accumulated in the pump it would rise into the hose instead of causing an issue inside the pump and could be released periodically. The auto-bleed does the same thing without user intervention ... probably a good thing anyway..
Try to jet proper and not dump fuel into it. It is generally not the issue and excess fuel only makes the oil situation worsen. If you expect the drivers are driving in the critical range run premix in the tank along with the injection. The ill effects of too much oil are way more long-term than lack of it.

I'm assuming these are round slide MIK carbs? Why not try a slide with less throttle valve cut-away?
Fan motors typically run richer to help cool them. You need to get those 1/4 throttle temps under control.

HMM, I really believe this is oil related not fuel.

16:1 A/F readings at part throttle doesnt bother me at all. It is not a issue of oil boiling it is a issue of an air bubble being created in the oil pump and not allowing the oil pump to work properly.

As Colin states it is only a issue of consant part throttle conditions that this happens. If the operator would (ride it like he stole it) occasionally it clears the oil bubble out and you dont have the problem.

Hard to believe that all these issues exist with a simple, fan cooled sled. Does Polaris test anything anymore before they release it? Seems like their quality control just keeps getting worse and worse.

Are the 550 engines made by Fuji or by Polaris? Here are links to some other threads
http://www.hardcoresledder.com/forums/index.php?showtopic=388191

http://www.hardcoresledder.com/forums/index.php?showtopic=356737

Interesting reading. Just lost the PTO cylinder on my 09 550 IQ. These issues are compounded in the 09 design by the lack of air flow into the fan shroud. The IQ design requires speed to force the air into a small inlet hole and down 90 degrees into the fan. I added an additional air intake port to help add more cooling air, but to no avail. The older Gen II and Edge designs had wide open engines, the IQ's engine is packed in tight. Here's where Ski-Doo's axial fan system would be much better -cooling air coming in high.

I traded my old 2000 550 in for the new and intended it to pull freight sleds and such. But slow pulling speeds minimize incoming cooling air adding heat and so on.

I was pushing my sled hard and when I smelled hot, I backed off the throttle and lost the cylinder. 30 mph was not enough to keep the engine cool. I believe now that the 550 IQ is only a short track runabout. Forget about pulling powder or freighting with this sled.

My engine was as delivered with 230 jets, and I thought it was too rich. By the way, the mag side plug had a perfect tan color, the PTO side was white. I have never been around a motor that was too engines in one and I have been a Polaris fanner since 84. Oh well if it ain't one thing its another and that is what makes it fun. Cheers.

Tom400CFI said:

They're made by Fuji. I wish they employed the same design principles and criteria as they had w/the old 440/488 fans.


Can you explain to me why/how air bubble is created...in the absence of air? Everything from the reservoir to the discharge nozzles should be oil, and oil filled. How does air magically appear inside the pump? Why isn't this an issue on ALL other Polaris, Ski Doo, Yamaha, and Arctic Cat's that use the same Mikuni Oil pumps?


These sleds get beat regularly. And putt-putted too. Mostly they're operated by kids who actually think that these sleds are "bad-assed" so they (try) to ride them that way. It's kind of pathetic.

We had three more machines go down today. On the upside, we've settled on new jetting specs: 240-250 mains, Q-4 Nozzles, #3 needle position, and 40 Pilots. All this at 7000' to 9000' elevation/25*F.

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hey tom, I dont know if you can try this or not with rentals..but if you want to eliminate the likelyness /or isolate this as an oil problem. can you oil the gas on 1-2 sleds where everytime it gets fueled up it can get oil put in the fuel tank? if you could it would either show it to be a oil problem or prove its not a oil problem....a polaris sled should basically burn 1 quart for 10 gallons..so even if you could just dump a 1/2 qt in it would keep a sled from burndown I think(leaving the stock oil system alone) also have you tried running polaris ves/gold oil(synthetic might just do a better lube job when these motors are going thru their burn down cycle) also I dont know if the 550 stator could handle the load but what about installing a small electric fan such as they run on the turbo intercoolers to aid low speed cooling?we do have an 08 550 rmk(daughters sled) and so far in 800 miles the only problem with it is it ate a belt first time out(clutches out of line)..I do run ves/gold in it since I run it in my sons (600 rmk) and my sled (800 dragon)..even when I have gotten on her sled and rode the dog snot out of it showing her what it will do in powder it has never acted up in any way...just some thoughts..I know how hair pulling nuts things like this get...mike

550 fan

Call Alan bender at Spirit Lake Polaris in Colorado., I think he has the 550 fans figured out.

Dan

AKrider said:

Hard to believe that all these issues exist with a simple, fan cooled sled. Does Polaris test anything anymore before they release it? Seems like their quality control just keeps getting worse and worse.

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LOL!!!!!! Isn't that the truth.

Tom, have you got any hair left at all? man I feel for you...the second one that hit deto for sure looks like it overheated.......the other 2 is harder to say since one piston does look pretty good on each motor...I agree doesnt look like fuel or oil problems...looks like it just keeps getting hotter and hotter till the pistons scuff..that one that lost the skirt looks just like it swelled the piston till it scuffed then it tore the skirt off...on the wisco motor that lost compression..whats the ring tension feel like compared to new rings? pistons sure look good for no compression..I have seen bad overheated motors with no ring tension left(ak low compression)and the pistons looked good but I think the reason why was they had good wall clearence and the piston didnt swell enough to scuff the piston ,just took the tension out of the rings....keep us posted..someone is gonna figure this out sooner then later I hope....

PM'ed you Tom

This is really unusual for me as I am normally a lurker BUT after reading your thread I just had to get involved.. I have been in your shoes MANY times and can share your frustrations brother!!!
OK, take a deep breath and a sip of coffee,, lets see here.. Were the ring end gaps checked before install?? Has there been any checking for air leaks? If nothing else, I would at least take a can of starting fluid and attach the little plasic tube in the nozzle and squirt it directly onto the crank seal behind the clutch while motor is running, if no change there I would test all seals on that side..
I have worked on a few fan melt downs and most of them were the result of mouse nests blocking the air flow under the motor shroud.
Maybe check that on your motors and see if there is a design flaw allowing the air flow to excape before it routes past the rear of that jug?
Just start one and feel around the shroud for airleaks that do this..
Next I would find out what the spec is for ignition timing, put a dial indicator on each pioston and make my own timing marks on the engine for each side - start her up and toss on a timing light and see how close each side is to the mark.. It is not impossible for a manufacturing flaw to create a timing flaw and create a mass problem like it sounds like is going on..
Remember that these are only machines!! They dont plot and plan to drive us insane (I KNOW you know what I am talking about!).
figure it out and YOU stand to gain a lot from Polaris - new engines or maybe a new fleet of sleds wouldnt be out of the question!!!
Best of luck
'Puc

Shouldn't the ring gaps be 180deg from each other on two-ring pistons? Seems like having them that close is just asking for blowby, possibly dumping a lot more heat into the cylinder walls. Are they pinned to force the placement as shown in your pictures?