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I was helping my neighbors friend look at his 500 that he nuked. He already has the jugs done and new pistons (they thought it was just a top end before I looked at it and pointed out the crank wasn't spinning very well...) Now he plans to have the crank done too, but after pulling the motor we noticed the rotary valve surface on the case is scored from the meltdown. Can this be fixed, or is it ok to run it with a few grooves in it if you clean it up? What's involved in getting it fixed, can they just machine it down and then run a thicker plate or something?
 

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if the gouges are not too deep you can smooth them out and run it. it can be repaired by machining or by putting in a brass insert. try www.crankshop-vt.com. they do the repairs and have prices and info on their website-
 

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Discussion Starter · #3 ·
what does the brass insert look like, and where does it go?

The grooves aren't that deep, maybe he should just run it. What happens if it does leak air through the scratches, will it just cause poor performance, or a lean condition. or what?
 

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I don't know how bad your grooves are, but, usually grooves are OK on the carb side, RV cover, but not on the case side.

Any good machine shop should be able to clean it up by bolting the empty case halves back together (no crank or RV shaft) and resurfacing the valve area with a mill.

The brass wear pads that were mentioned by someone, are small discs that are put into the case halves in a few locations around the port openings, to help keep the aluminum case halves from wearing. Brass wears tougher than aluminum.
If you take a good look at an RV style engine that has a bunch of miles on it, you will see that the aluminum is worn around the port openings. This is from the RV spinning by the port while the piston is going up and creating a vacuum in the case. It sucks the valve up tight to the case, and over time it will show wear. How much wear will depend on lots of factors; oil, typical RPM's, number of miles of usage.......
Racers used to put the brass pucks in to ensure that over the life of the race engine the case wouldn't wear to the point where it may effect the performance.
I've seen trail sleds with over 10,000 miles on them that showed wear, but were still acceptable.

Hope this helped to answer your question.

Now I have a question,
Where's all the snow?
 

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Thanks for the info. We didn't split the cases, because it is a friend of my neighbor who I don't really know, I'm helping for free, and I didn't want to do the motor work for free and then get blamed if something goes wrong... After it's back together they're selling the sled to someone else they know. They talked to the machine shop guy and he said small grooves (even on the case side) are acceptable as long as you clean up the rough spots. I'm going to have them take the whole motor to the shop, have them put it all back together, then I'll help them put it back in. I just wanted to know what the machine shop might do to fix this..

If they machine down the case, do they have to take the same amount off the outside edge of the cover and the end of the shaft so the RV plate still has the same clearance?
 

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My Sea doo had the same problem this summer. Part of the ring jammed between the RV valve and case. Inspect the rotary shaft very closely for trueness. When those things jam there is a lot of lateral force on the shaft. It bent the shaft on mine just a little. That is going to cause the brass gear to wear out in no time which means another rebuild. The brass gear probably needs to be replaced as well.

My crank was fine it was just the jammed gear.

BTW I left the grooves in mine and it ran fine.(20 hours so far) I just cleaned up the burs.

Make sure you clean the cases real well if you don't split them. You don't want any metal in the bottom end. I used a lot of spray lube and shop towels to flush them out.
 
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