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Old 03-24-2008, 12:56 PM   #1
162Whiskey
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Default Thoughts on the 550 Fan Engine

In physical appearance the "new" 550 Fuji block is very much like the older 440 block. In many ways the new one has been improved in several small ways which I like.

So, what's not to like? Well, there are the obvious problems that have been rather well documented here and elsewhere. But aside from those and the adjustments which have been made in the carburetors, timing, etc to correct them, and the likely fact that heat appears to be related to most failures....is it possible that the engine just doesn't breathe well sometimes?

One of the most significant differences, physically, is that the 550 has reeds, while the older fans did not. That is a really noticeable difference in how they run, especially noticeable when you have ridden one of the older ones for awhile. Yet you never, or almost never, hear anyone mention reeds as a possible cause of the problems the engine has. And I wonder.....those reeds are one of the things that have stayed the same throughout the ten year history of the engine: part # 3085715.

I wonder how and whether the 550s would run sans reeds or with different or modified reeds? And what changes one might have to make in carburetion in order to get things right. Has anyone heard of pioneering souls who have played with this?
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Formerly known as 63November, and before that as Golsovia.

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Last edited by 162Whiskey; 03-24-2008 at 01:08 PM. Reason: minor grammaticals
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Old 03-25-2008, 04:16 PM   #2
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Hmmmmm. Reeds. I never thought of that being part of the problem. But I've also not heard of any problems with the '07 or '08s. My wifes '08 has a little over a thousand miles now with no problems at all.
One theory I've read on here is that a 550 cc engine is just too big to air cool. Nothing could be further from the truth. I've seen a lot of motorcycle engines a lot bigger that are free air cooled, in the summer, with no problems. Deutz tractors used to be exclusively fan cooled. Those are diesel engines up to about 6.5 litres, and turbocharged. If an engine like that can be fan cooled, a 550 should be no problem. Once they figure out how, that is.
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Old 03-25-2008, 05:53 PM   #3
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Ski-Doo has a 550 Fan with no problems cooling it. Same with Cat. If the problem were Reeds, I think Polaris would have figured it out a long time ago...
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Old 03-25-2008, 10:20 PM   #4
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Obviously bigger air cooled motors can work. The question I have is whether their (Polaris') specific design can and in this particular application. As for the reeds and Polaris figuring it out; well, perhaps they've looked into that (probably I'm sure). However, their history of solving the 550's problems effectively leaves something to be desired. I guess I have a hard time believing they really understand the engine as well as we'd like to hope they would. I'm also rather surprised that they have never altered that part (reeds) over the entire history of the engine.

And again, while I don't know a lot about reed technology or design, I guess I wonder if allowing the reeds to "breathe" a bit more at lower rpms might make it be just a bit more tolerant of more range of use.
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Formerly known as 63November, and before that as Golsovia.

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-Scorpion Whip
-Ski-Doo Skandic
-Yamaha Enticer LTs
-Polaris Trails

Current:
-99 Arctic Cat 550 Panther 14,000+ miles
-08 Ski-Doo 550 Backcountry
-340 eBay Edge from AK, and 10+ other states
-'11 AC T570 brand new...4000 miles
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Old 03-26-2008, 09:54 AM   #5
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I wouldn't rule out their engineer(s) having tunnel vision on this issue. I have no idea how many people Polaris has in R&D, or many of those work on the 550. We can tell that they are trying by the fact that they have gone to the nicasil cylinders, but it's entirely possible that they haven't thought of getting in more air in first place. That in it self is a disappointing thought!
Now, if getting in more air is the key, maybe a turbo........(kidding)
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Old 03-26-2008, 04:17 PM   #6
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What I find interesting, is that even though all of the manufacturers have had engine issues over the years, they are usually resolved by the following year. This 550 thing seems to be ongoing. Also, the fix seems to be multiple updates, and not just one or two defective flaws...
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Old 03-26-2008, 09:24 PM   #7
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It's going to be interesting to see what the 07/08 models show us. 'Cat used NiCaSil right from the start on their big fan; I'm not sure about 'Doo. I'm sure that will help with the heat transfer. How much and if enough is the question that begs and answer.

One think I know for sure, if they do finally get the engine figured out, it's one I'm going to like from a mechanical standpoint since the block retains the simplicity of the original 340 and 440 engines, while making some nice improvements in some of the details - other than the difficult to access hex socket screws they use on the six-screw exhaust manifold.
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Formerly known as 63November, and before that as Golsovia.

Riding since 1983.

-Scorpion Whip
-Ski-Doo Skandic
-Yamaha Enticer LTs
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Current:
-99 Arctic Cat 550 Panther 14,000+ miles
-08 Ski-Doo 550 Backcountry
-340 eBay Edge from AK, and 10+ other states
-'11 AC T570 brand new...4000 miles
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Old 03-27-2008, 10:24 AM   #8
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162, I don't think reeds are the problem. Reeds have been around for a long time, originally developed by McCullouch, the chain saw guys, back in the early 60's. On a 2 sroke, after combustion, as the piston goes down, the exhaust port first oppens, and most of the spent exhaust goes out this way. Unforunately, a few millimeters down the cylinder, either the carb piston port, or the tranfer ports open up and some of the exhaust gas gets forced back into the carb , which pulls gas up in the carb . The gas sits around for the intake cycle, maybe droplets form by then, and when the intake happens those droplets of gas, not a nice mist of air and gas, can cause problems, like low speed stumble, and other things. The reed valve is just a one way valve, that stops this, and make the engine a little more efficient.

Been awhile since I had a fan cooled, 88 340 Sport was the last one in our fleet, but I'm going to maybe blame some accountants, maybe, for the 550 problems. Heat in a 2 stroke is always a problem, especially as the power goes up. Air cooled 4 stoke diesels probably run a less than 3,000 rpm. 2 stroke sled engines turn 8,000+ rpm, with a power stroke every revolution. Run your air cooled diesel at 15,000-16,000 rpms, and see how they deal with heat extraction. I have not really looked hard at the 550, but you say it looks a lot like the 440/488 fans of the past. Back to my accountant problem, any chance the fan rotor , and housing, is the same size on the 550 as on the 488. My guess, and it's just a guess, is that someone at Polaris said, sure we can make more power with the 550, and keep the same engine case casting and fan, and not tool up ( meaning major $) for new engine parts. Looks like the real world may have proved that wrong. Maybe. The real problem has to be getting heat out of the engine, under all conditions. NicaSil cylinders will help, timing changes can be effective too. Was it the fan size, or something else? We may never know, but somebody in Medina knows, that we can be sure of. My $.02 worth.
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Old 03-28-2008, 12:34 AM   #9
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SF, While the newer cases share the same basic design as the older ones, it is in their construction that they differ. There are some nice improvements including the way the magneto end is constructed. Overall it seems like a more solid, somewhat beefier case. The one piece head seems like a good thing too.

As far as function goes though, the case is pressurized as the transfer ports are opened so the air/fuel mixture comes up (and probably helps flush the exhaust at the expense of some efficiency) rather than exhaust being pushed into the case. There is really no way exhaust can find it's way back toward the carbs if the engine tolerances are up to spec.

The reeds probably help some in preventing any back and forth air fuel movement between the case and the carbs. However, I think their function in this engine has a lot more to do with performance than anything else. The 550 in the SuperSport, even in a geared down version, does not like to putt along at lower speeds and actually tries to climb out of the low end. I thin that has to do with the reeds being on the verge of opening fully or not. I could be wrong about that but that is what it seems like to me. Anyhow, that has never been a problem with the smaller, reedless Fuji fans I've run. They tend to have a much smoother useful power band which, I think, indicates that they aspirate better at all ranges.

I kind of wonder if perhaps the 550 might work better for some applications - especially sled pulling and other work applications, if it had no reeds. Then again, perhaps a modified reed with a small hole or other low speed "breather" was there. I suppose if my 550 goes one more time I might play around with testing these ideas. However, it would be much simpler (and less expensive) if someone else had already done some of the work.
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Formerly known as 63November, and before that as Golsovia.

Riding since 1983.

-Scorpion Whip
-Ski-Doo Skandic
-Yamaha Enticer LTs
-Polaris Trails

Current:
-99 Arctic Cat 550 Panther 14,000+ miles
-08 Ski-Doo 550 Backcountry
-340 eBay Edge from AK, and 10+ other states
-'11 AC T570 brand new...4000 miles
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Old 03-29-2008, 05:35 PM   #10
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126 tell me what happens when your engine goes down. What do the pistons look like??
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