Has anyone heard of a 720 cc rotax using stock 700 poo pistons in a bored out 670 motor. I'm trying to make my old 97' push a 151x 2.25 16" wide track. Any gearing recommendations? Runnin 23-44 with 9 tooth drivers. Any help would be great. THANKS
670 Rotax to 720cc
- Thread starter SmithEngineering
- Start date
T
tinman800
New member
I'm sure it will work. I had a 750 done on the 700 series 3 motor with the stock polaris 700 pistons. Watch for the piston skirt clearing the bottom of the exhaust port. You may have to shim the cylinder height up a bit and make it up off the head or top of cylinder to get rid of it. Call Val Simmons of Simmons skis he has alot of experiance with both a 720 and 760 on the 670. I believe he uses wiesco pistons.
Could call Wiseco for the piston dimensions on both as well. Then its just a matter of seeing if they match up on paper. Don't know what the piston pin diameter is. DWHalverson on here has a lot of experience with this motor as well.
My 97 670 pushes my 151 (15" wide) with no problems and that's with my 300# azz on it.. You can mod the hell out of the 670's without getting too western and still have a very reliable motor. Port the track to free it up a bit.
I don't remember off the top of my head, but I'm pretty sure you will not have much jug left if you bore to 720 with stock liners. Wiseco used to make a kit with liners - my old one was a 740. But cylinder and case porting help the ol 670's a bunch, as well as recutting the rotary valve to 501 specs and using the port timing fromthe 96? Mach with twins. As far as gearing is concerned - I ran 20/44 or 19/44. Bear in mind I weigh about 235lbs with gear - also ran solid pins in primary with a purple/purple spring, cat roller with a 44 degree helix - can't remember spring color, but it opened at 15# using the spring scale. That sled with a drop and roll would beat the hell out of my buddies 01 and 02 Doo 800 almost everyplace but on the rough trail - those s-chassis rode like a stoneboat. Hope this helps you.
I have seen 740's run and good running 670's will be right with them. I was going to go to the 740 kit when my sled needed an overbore. 3 seasons later and still on the same stock bore I really don't think the 740 would be a wise investment unless your sleaves are shot and need to resleave.
There are some differnces between the 670 and the 670x or H.O. Port timing can be matched or made to be the same as a ported x engine, bore the 40's to 44's, case porting, get the squish to .058, good set of twins (jaws are my preference for altitude ), and the list goes on. You can doo all of this for what the sleaves are going to cost.
I run a 151 16 2 inch on my x and the sled can handle a bigger track but I can't. I like the 151. Best of both worlds imho. I installed a 144 16 2.25 on another x this year and it works well. drop and roll needs to be done to run the 9 tooth drivers and it is worth it.
gearing I use on my x is 18/43. Cool belts and my original belt after 600 miles is still within .002 of the spare that has only been broken in. Very cool clutches.
Depending on what you want out of the sled and altitude you run there are a lot of guys that still remember how to set up a 670 on this forum.
jon
There are some differnces between the 670 and the 670x or H.O. Port timing can be matched or made to be the same as a ported x engine, bore the 40's to 44's, case porting, get the squish to .058, good set of twins (jaws are my preference for altitude ), and the list goes on. You can doo all of this for what the sleaves are going to cost.
I run a 151 16 2 inch on my x and the sled can handle a bigger track but I can't. I like the 151. Best of both worlds imho. I installed a 144 16 2.25 on another x this year and it works well. drop and roll needs to be done to run the 9 tooth drivers and it is worth it.
gearing I use on my x is 18/43. Cool belts and my original belt after 600 miles is still within .002 of the spare that has only been broken in. Very cool clutches.
Depending on what you want out of the sled and altitude you run there are a lot of guys that still remember how to set up a 670 on this forum.
jon
I have a stock bore 670 that is swinging a 159x16x2 with no prob with 9 tooth drivers and 19-43 gearing.
For more--just ask.
H20SKE...
For more--just ask.
H20SKE...
I have a stock bore 670 that is swinging a 159x16x2 with no prob with 9 tooth drivers and 19-43 gearing.
For more--just ask.
H20SKE...
What's your clutching?
Thanks for the advise. Already have the drop & roll in and track is ported. changeing to anti-ratchet drivers today and have new hyper fax on a 01 zx 151 skid w/two wheel kit on it ready to bolt in. I'll probably try a 20-44 gear and go from there. ??what is the 501 rotory valve cut and mach 1 timing??
