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1990 indy 500 trouble

5K views 36 replies 9 participants last post by  Marc.gagnon 
#1 ·
Went thru the carbs today and one cylinder will not run properly. I have checked compression and both are at 118 or so. The cylinder that will not fire properly seems to blow mist out of the carb. I put my hand in front of both and the trouble one is blowing back. I didn't think these engines had reed valves, but I am no expert. I'd like to get it running so my kids could ride a little this year. :dunno:

Thanks for any help.
 
#2 ·
You are right, that version of the 500 is piston-ported. Pull the carbs and see if part of the piston skirt has broken off, that could account for too much blow back. Most piston-ported engines spit back some, but both sides should be about the same amount.
 
#4 ·
Try switching the spark plug wires from side to side to see if the problem follows the plug. That can rule out a wire issue. You can also try moving the carbs from side to side to see if the problem follows the carb. Do one thing at a time to rule out problems. Have you tried new plugs?
 
#6 ·
And the winner is......broken piston skirt. Dang...now do I spend the money to fix or go buy the old Phaser down the road for the kids.

Funny, this morning I tried to turn the clutch and wouldn't go, was hitting something. must be the chunk of piston.
 
#7 ·
#8 ·
Should I worry about the bottom end with that piece that was floating around? It does have 11,000 miles on it. I mean i will look at it when it is opened up, but does the bottom end really need work ever?
 
#9 ·
Bearings do go from time to time. If you disassemble the case, (I would) you can check for foreign objects and any damage, and also roll the bearings by hand. They should be smooth as glass. If they are rough at all, consider replacing bearings. That's something that most guys can't handle, it takes special presses to get the crank apart and back together properly.
 
#10 ·
I hear what your saying BC Dan. I'm now deeper than I have been in any engine. I am confident I can do the pistons and such, but not too thrilled about thinking of splitting the case. Part of me says do it and the other says to find a way to flush the bottom and put it together. There were not alot of big pieces in the bottom and there were some smaller ones in the oil holes which I was able to pull out. I knew that the top end was redone before I bought it 13 years ago, but the pistons were different from each other so I assume they only did one, which to me is the unbroken one in the picture.

 
#12 ·
I'm not sure when Polaris started using Nikasil cylinders, but I'm thinking yours are sleeved.

If the sled has iron sleeves, it's pretty evident. If it's Nikasil coated aluminum, there won't be a sleeve; the coating (which is really tough stuff) takes the wear. You don't hone nikasil the same way as iron, the coating is relatively thin and tough as nails. It takes a special hone to break through. If the coating has been gouged through, you can have the cylinder repaired, but it would probably be cheaper to find used ones in good shape. Running a hone through the nikasil is a good idea to break up any oil glaze and to re-establish the cross hatch.

Splitting the case involves removing the flywheel and stator, then the bolts that hold the case halves together. There aren't many moving parts inside. The crank and the water pump drive are about the only things that move in there. I wouldn't hesitate at taking the case apart, as much damage that was done to the piston, there's a strong liklihood that there are parts of piston in the crank and bearings. Some of that left behind will tear up the bottom end if you don't' get it all out.

When taking the cases apart, avoid using anything sharp to separate the top from the bottom. You will need both crank seals and an anerobic sealer to seal the case halves. I use Threebond 1104, or 1194. Yamabond also works well. Don't use a lot; just one side usually does great.

Getting a good manual, such as the Clymer Polaris Snowmobile Shop Manual, is also a good idea. It will have step by step directions as well as all the tech specs for torquing the case, cylinder, and head.

For the most part, 500 Indy engines are known for durability. There are also a bunch of 'em out there, so you may be able to find a pretty good used engine to pop in the sled to keep it on the snow without having to do the engine work. Your call. There is always a point of diminishing returns when throwing money into an old sled. At some point, you will be better off getting something newer for your cash.

Good luck!
 
#13 ·
Thanks for the tips. I have a Polaris Service Manual for my 04 which seems to have information for the Fugi 500 as well. We were pulling parts out of the bottom of the case and the oiler holes. I have to think alot of what is missing may have been blown out the exhaust, but who knows. I am going to use the sled as a starter sled for the kids, I don't really want to throw too much $ at it.
 
#19 ·
Saw that last night, thanks. I am a little nervous with the stator screws. I don't wan t to round them out, but they are in there good. Any tricks? I have an imact screwdriver, but that isn't working like I thought it would. Just nervous...
 
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