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Discussion Starter #1
Hello all, quick question for all you engine guru's. I just got done rebuilding a ski-doo 580 1996 gt engine, complete from bearings to pistons, the question i have is that the rotary valve is pooched, I have a new one off of a 670 ski-doo but it is a different cut would it work? I am not sure of the part number of the one off of the 670.

What would the difference be? Will it be harder to start, more power or less? I am looking for reliability and decent performance.

Any suggestions would be great.

thanks bruce
 

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Hello all, quick question for all you engine guru's. I just got done rebuilding a ski-doo 580 1996 gt engine, complete from bearings to pistons, the question i have is that the rotary valve is pooched, I have a new one off of a 670 ski-doo but it is a different cut would it work? I am not sure of the part number of the one off of the 670.

What would the difference be? Will it be harder to start, more power or less? I am looking for reliability and decent performance.

Any suggestions would be great.

thanks bruce[/b]
you do not know the timing of the new or 670 valve?
 

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Simon what is it?
 

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I'm going to take a stab in the dark (I wish I had my older Race Manuals @ home) :confused: . The 670 is pumping more air thru the motor than a 580 cc, so the RV probably is of a longer duration than the stock RV, so it'll probably lose some bottom end power & maybe & it's a big maybe, improve the top end slightly.

The 580 has VM38 carbs on it doesn't it. What's stock on a 670?

IMO, I'd get the proper RV for the 580.
 

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It's a standard MXZ 670 (type 669) 164 degree P/N 420 924 500. Timing is 145 degrees opening and 71 degrees closing. Since your 580 is not a RAVE motor and peak power will drop off quick. I would recommend running it 2 degrees advanced to close the ports earlier and give it a little more punch out the bottom. You will not notice any difference in starting or running except if the rotary cover or crankcases are deeply scored (gouged).
 

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well revrnd hit it. less bottom end, more top end. I would do like doc said and advance it a couple degrees. how much more peak hp you will get, is probaly not much.
 

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Discussion Starter #8
Well I got the sled running on the weekend, everything went well and a couple hours and a few whiskeys later it was done. The sled seems to pull hard throughout all the rpm's and runs smooth. Never realized how quite the gt 580's are.

Thanks for everyones help.

brew
 
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