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Discussion Starter #1
I got a couple quick questions about general rebuilding. First off there is nothing wrong with the engine what so ever, good compression strong runner etc. This is a 97 mxz 670. I ordered a wiseco piston kit with all gaskets, pins, pistons. I am looking to rebuild the engine as preventative maintenance. Is this a good idea? It has around 4000 miles. Also what else should be replaced at rebuild to eliminate future problems? I have ordered the needle bearings. What about a thermostat, carbs, etc. I just want to keep this strong and not be out mid season. Any opinions greatly appreciated..
 

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I got a couple quick questions about general rebuilding. First off there is nothing wrong with the engine what so ever, good compression strong runner etc. This is a 97 mxz 670. I ordered a wiseco piston kit with all gaskets, pins, pistons. I am looking to rebuild the engine as preventative maintenance. Is this a good idea? It has around 4000 miles. Also what else should be replaced at rebuild to eliminate future problems? I have ordered the needle bearings. What about a thermostat, carbs, etc. I just want to keep this strong and not be out mid season. Any opinions greatly appreciated..[/b]
1) 4000 Miles on a 97, split the bottom and replace the PTO bearings.
2) Check condition of the brass R/V drive gear and coolant pump / oil reservoir seals
3) Check connecting rod big end side clearance 1.2 MM (.0742") maximum
4) Check condition of rotary valve face on crankcase (if tapered around tunnels get it machined)
5) Select a choice of cylinder base gaskets to achieve a squeeze band of.065" (87 ~ 89 octane gas)
6) Adjust ignition timing to .086" before top dead centre (.076" Stock)
7) Cut rotary valve plate to achieve 169 degrees opening (or procure a Ski Doo 420924501 plate)
8) Time above plate to 146 degrees opening & 76 degrees closing.
9) Remove 13 MM (.5") off the -pipe just behind the ball flange and ahead of the spring perches the move move the perches back same amount.
10) Open carb side of R/V cover to 43 MM Install short rubber boots off 1990 Formula Plus 521 P/N 57001600 rubber flange (also available from Kimpex)
11) Update needle jets to 224-AA-3 and main jets to 310 MAG and 290 PTO
 

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Discussion Starter #3
Thanks for your input, that is a lot of stuff to do does the replacing of the rotary valve help out a lot? Is it fairly easy to install and time? Once again thanks a lot..




1) 4000 Miles on a 97, split the bottom and replace the PTO bearings.
2) Check condition of the brass R/V drive gear and coolant pump / oil reservoir seals
3) Check connecting rod big end side clearance 1.2 MM (.0742") maximum
4) Check condition of rotary valve face on crankcase (if tapered around tunnels get it machined)
5) Select a choice of cylinder base gaskets to achieve a squeeze band of.065" (87 ~ 89 octane gas)
6) Adjust ignition timing to .086" before top dead centre (.076" Stock)
7) Cut rotary valve plate to achieve 169 degrees opening (or procure a Ski Doo 420924501 plate)
8) Time above plate to 146 degrees opening & 76 degrees closing.
9) Remove 13 MM (.5") off the -pipe just behind the ball flange and ahead of the spring perches the move move the perches back same amount.
10) Open carb side of R/V cover to 43 MM Install short rubber boots off 1990 Formula Plus 521 P/N 57001600 rubber flange (also available from Kimpex)
11) Update needle jets to 224-AA-3 and main jets to 310 MAG and 290 PTO[/b]
 

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The rotary valve will not help unless the other steps are performed. That valve was designed for the twin piped Mach 1.
 

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Discussion Starter #5
Will changing the jets require quite a bit of tuning? What about the elevation I am in IL and there is very minimal elevation to contend with. I am very scared of carbs even though I am an auto mechanic. I dont know if I want to switch things unless it will be a noticable change in performance, without sacrificing reliability. Where do I need to go to get the jets If I decide to go through with this. Sounds like a lot of fun when I am done but I am very worried I might be getting in over my head, and causing headaches in the future. All opinions on this matter will be very informative. Is there a website or book on these upgrades or is this just tried and proven.
 

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Will changing the jets require quite a bit of tuning? What about the elevation I am in IL and there is very minimal elevation to contend with. I am very scared of carbs even though I am an auto mechanic. I dont know if I want to switch things unless it will be a noticable change in performance, without sacrificing reliability. Where do I need to go to get the jets If I decide to go through with this. Sounds like a lot of fun when I am done but I am very worried I might be getting in over my head, and causing headaches in the future. All opinions on this matter will be very informative. Is there a website or book on these upgrades or is this just tried and proven.[/b]
where at in IL? those mods will work. the change will be noticable. reliabilty will not be an issue.
 

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Discussion Starter #7
In northern IL Richmond to be exact. What about the carbs once you change the jets dont you also have to tune them?
 

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The carb changes are so that your new top end will not burn down the first time you load the motor. 670s build heat fast under excessive load and the pistons expand fast, sometimes squeaking the cylinder and spoiling your day. This was a big problem on 1997 MXz 670s on first oversize (most notably on after market twin pipes) The carb specs are for the 1998 MXz 670 which had no big burn down issues. Messing with the air box will also create mid range lean bog and seizure and pod filters will give you a big headache. The specs printed on the Wiseco piston boxes need to be adhered to..bettter to run them .001" looser than tight. Make sure the guy on the boring bar and hone knows exactly what he's doing.
 

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In northern IL Richmond to be exact. What about the carbs once you change the jets dont you also have to tune them?[/b]
not sure what you are asking :confused: . jetting is tuning it, with exception of sync'ing the carbs and cables, which an auto mechanic should be able to handle. the stuff doc has here should make it run a tad better than a 99 ho. yeah I always say leave the air box stock. not worth any hassles. there are a couple of us with-in a few hundred miles and might help if asked :whistling: . I would follow Docs advice you will be very happy, and the miles it has just seals the deal.
 

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Discussion Starter #10
I have decided to keep the motor stock for the season and make this a summer task for the off season. However I am going to take off the head and jugs and check pistons specs. Most likely I will swap for the wisecos I have, standard bore. The sled has a lot of miles and I dont want piston deteroriation to occur. Since these are wisecos and I have heard mixed responses on them is there anything I need to watch out for or change. I am also installing new needle bearings but that is about it. I am going to clutch it but Do I need to worry about anything with these pistons. If the pistons specs are fine I will most likely keep them in but I have a feeling that they will be out of tolerance. For the season I just want to keep it running fine with no engine mods.
 

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Discussion Starter #11
After I put the engine back together can I ran it with my regular oil which is amsoil? Or should I run some mineral oil it. Thanks also is there a secret to putting the new bearings in I believe they are not sealed?
 

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If you are not reboring the cylinders and replacing with over sized pistons there's no need to run mineral oil. Having said that you are installing Wiseco pistons, you should be OK running loose wall clearances as long as the piston ring end gap is within spec. Generally Wisecos can run up to a 7 thou skirt clearance on bores over 3 inches seeing as they are forged & dual ring design.

Best way to replace PTO bearings is to first measure the space between them and make a spacer that size out of a block of wood in a horse shoe shape. Note the old bearing alignment pin / ring orientation. Use a puller with a bearing guilotine and remove the old bearings (DO NOT RESORT TO USING A HAMMER !!!). With the old bearings removed, polish the crankshaft stub with 600 wet or dry paper. Take about 1/4 litre of motor oil and pour it into a cooking pot (do this without women folk around !). Place new bearings in the pot and heat them to about 150 degrees F. Place the crankshaft PTO side upright in a vise using softjaws or a 2 blocks of wood. slide first bearing on observing orientation (as previously noted), then install the distance ring. Now install your wooden bearing spacer (previously measured and fabricated). Lastly, install the outer PTO bearing. Allow everything to cool to room temperature and clean oil from outer bearing races and install new seals being sure to lube the seal lips with Lithium grease. DO NOT REFRIGERATE CRANKSHAFT TO SHRINK IT ! as condensation will form on the bearings and pit them.
 

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Discussion Starter #13
Sorry I should have specified what bearings I was talking about. Not the main but the needle bearings in the connecting rod. I got them from skidoo and from past experience I believe they are not sealed.
 

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Just stick them in the rod small end using synthetic grease and use a 13 mm socket as a pilot to hold them in place when you slide the tight fitting wrist pin into the piston. Always double check the bottom end in case you dropped a needle. Take extreme care installing the piston pin retainers, don't over tweak them or they'll exit after some miles. Make sure the clip opening is pointed North or South.
 

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hey ryan its kyle, anyways i think that with your wiesecos you got caged didnt you? i was looking around as well because i know that mine are cageless for sure, but i found this thread about it...

http://www.snowmobileworld.com/forum/index...bearing+install

and many other threads that all said to use a socket coated with grease so the needles stick to the socket.....sounds tough but i dont think it will be too bad, as long as none are dropped. most guys say a 14 or 13mm socket works good from what ive read. thinking about it, the needles would slide through the rod with the socket.....so you would actually need two sockets one with the needles on it and one on the other side (deep socket) that the needles would hit but the pin could slide into.

it makes sense to me....ill be home this weekend and ill show you, actually mine should come with a plastic guide, you could use it.
 
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