I am still having vibration problems between 5-6000RPM guys. I am stumped! I found cracks in the moving sheave of my clutch and changed the part (Thanks Bill Cudney).

I have checked runout of the crank, clutch, sheaves and alignment of everything. I have done timming and track tension and still cannot pin point the problem. The crank is not bent and I checked it for twisting. Everything checks out fine.

The dam thing vibrates violently between 5-6000RPM while cruising in this RPM range and on DE-celleration. If I hit the gas it goes away immediatly.

I cant find ANY loose in anything that I have looked at. I am really stumped. The engine does have a 501 rotary valve in it. I dont know if that can make any difference? It runs, idles and revs high great. Just 5-6000RPM I have vibration. I am getting sick of this. It looks like I am going to loose another weekend if I cant fix it.

If I free run it with the track in the air, I barely hear it. It seems to be comming out of the clutch. The clutch is aligned, and has been taken apart 4 times for this problem. EVERYTHING checks out fine. The ramps are 228. It doesnt make the noise when I accelerate. Just when I decelerate.

ANY IDEAS?

I have some more info.


When I ordered a new TRA clutch spring, My dealer gave me a new spring that was shorter then the one that I originaly had in it. The new one measures 98-100mm free length.

The one its replacing is about 148mm long. Its a green/pink spring. The dealer told me that Ski Doo superceded the old spring design to a newer shorter one.

In my manual it says the 1993 spring should be what it now is with the new spring. The one that was in it comes up in the manual as a 1992 Mach-1 X. Mine is a 1993 with a 670 RAVE.

Should I question this? I dunno anymore. The clutch seems to shift fine.

I dont know if this helps or not but i recently tore my chaincase apart cleaned it and put a shorter chain and different gears. this was the only thing i changed and mine has the same problem now, but mine does it just when crusing 5000-6000grand. I havent taken it back apart yet i'm pretty sure its something in the chaincase. You might want to check there if you haven't. Andy

I thought it might be in the chain case but I have put my finger on it while running the machine and she runs smooooth. I havent done this while driving it. Just while free running it in the driveway. Would it do it only under a riding situation?

What was your problem in the chain case? I will look into mine. I gotta look at everything at this point.

Just curious, but do you have a buddy with the same type sled that you can swap some parts with? I know it sounds mickey mouse, but there are times when it's a last alternative. I was thinking in regards to the clutches. Might be the cheapest way to eliminate possibilities.
Good Luck.

A guy I work with had a similar problem, tore everything apart, couldn't find the problem. Turned out it was a slight bend in the jack shaft .... not saying that's what's wrong with yours, just giving you something more to look for!

Hope you figure it out ...

Hey DrZOOM,

Here are a few things I need to know to try to help you.

What model/year is your sled ?.
What kind of pins are you running in the tra (Long Hollow?)
What model TRA governor cup are you running on the 670 ? (should be a cushion drive with a rubber dampener)
What clicker setting are you at 1~6
What recent changes did you do to the power train ?

I have experienced some intermittent decel vibration on my '98 MXz 670 and found it to be belt related. The vibration happens when you are going corner to corner then decelerate through 5500 rpm. I found the OEM belt is prone to flap laterally at that speed. Check the belt width for parallel. I have found a good comprimize using a Ultimax 3 belt, but find it grabby when launching. PM me if you want some Known good parts to try.

T.D.

Ok guys (and Thumbdoctor), Here goes for my sleds specs:

Its originally a 1989 Formula MX PRS chassis. It was completely converted to a Mach-1 using a 1993 Mach for parts. Has Fast racing front wide suspension.

Even the drive axle has been converted to Mach-1 for internal tooth drive. Its just a shorter track lighter weight Mach-1 now. Even has the hood with custom paint. This is my first year out and the dam sled took me 2 1/2 years to build. EVERYTHING IS NEW.

Engine: Has Cudney pistons in it and a 501 rotary valve. The entire exhaust was ceramic coated too. Timmed right and running tip top. Crank checked for twisting. Its as straight as a board. Runs to 8000 RPM without vibrating as long as its free spinning in the driveway. It does however growl a bit on once off the gas as the engine decelerates between 6000-5000 RPM. The growl seems to come from the clutch. Its very hard to tell because without actually driving the sled, I cannot feel the vibration. The vibration is bad enough to make me want to stop. I can feel it in my foot rests, handle bars and its LOUD. It gives off a loud resonance growl. Always comes into play when between 5-6000RPM and goes away the second I hit the gas. It comes back as I slow down or if I try to cruise in that RPM/speed range.


TRA clutch: 228 ramps. The pins are stock and solid from 93 Mach. Arms are stock too. The TRA head does not have that rubber damper on it. It never did. The dealer doulble checked this for me and found that in 1993 they did not come with a rubber damper. The inner sheave with the shaft was changed, the head was changed too (loose on the shafts teeth). The moving sheave was changed this week because the orig had cracks. The spring that came out of it was a green/pink 148mm long (like Mach-1 from 1992 X model with 670cc and 44mm carbs)((mine is a 1993 with the 40mm carbs). The new spring that I got from the dealer ended up being shorter. Its 100mm and I think blue/blue. Its part number is 414689400. The bushings are like new. No loose in this clutch. The clickers are on #3.

Belt is new. Its a Bombardier belt. I forget the number but I know its the right one.

Spaced at 27mm and aligned perfectly with,....

Secondary clutch: Its set up to 1993 stock Mach-1 for now. Cam shoes are perfect. Helix is not cracked or binding. Mach-1 stock spring is in position-1.

Goes to a free spinning jackshaft. Jackshaft is nice and tight. No bends. I am using my 1989 Formula MX jackshaft. They looked the same to me. Goes too,...

1993 Mach-1 chain case. Top bearing and jackshaft spins perfect. No bindind. No axial play. Top sproket is a 26 tooth. Top sproket shows signs of typical wear (7000kms on it) but nothing that can vibrate like this in my opinion. Chain looks pretty good too. Also with 7000kms. Lower sproket is a 44 tooth. Looks pretty much like the top. 7000kms on it too. Not eaten up just typical wear marks were the chain grabs it.

Drive axle. The drive axle has 1mm of axial play in it. Not bent. All 4 sprockets look fine and mesh up to the internal track lugs perfectly. Both bearings run nice and smooth.


The track is a Kimpex Vantage. Its the only track that fits with the short MX C7 Suspension. It clears the rads fine and is brand new. Its 15X116". Track tension is just over 1 1/2 inches with a 14lbs pull on it.


I will post pictures once I get some. You can eat off any part of this sled. Its in museum condition. You just cant drive the friggin thing! :cussing: It vibrates like MAD between 5-6000RPM. About the RPM, it can also be a speed issue. I just dont keep a good eye on the speedo. I always notice the RPM and that the vibration is in that range.

Need help.

I hope these specs help you come up with some ideas Thumbdoctor.

tighten your chain case chain takes 5 minutes and every thing will be beautiful...

What a mess but I think I got it.

I really hope this info I post here will help someone out one day.

The clutchs inner sheave with the shaft WAS bent. Bent in the middle of the dam shaft. Now I know why it only happend between 5-6000RPM. The guy that sold it to me must have got it off a accidented sled that was hit right on the head of the TRA!!!!!!!!

I started the engine again to check crank run out with the TRA off. Then I decided to check it with only the inner sheave on. Lucky I did it this way. Theres run out in the middle of the shaft. It was bowed.

I called the store that sold it to me and the ars wouldnt do anything about it. He swears it was never accidented and that it was straight. He sugested that I straighten it with a hammer! Yah right! Since I bought it 2 months ago, he says I could have done all kinds of things to bend it even though I only started my sled for the first time just over a week ago. He said he would have exchanged (after 20 minutes of arguing) it buuuut conveniantly, he didnt have another for exchange. Yah thanks alot guy. What a jerk! I will NEVER deal with this screwball frenchmen again.

It was late but I didnt want to give up. I called another sled parts guy. He had one for $150.00. I drove out to go get it and I am glad I did. This guy knows his stuff. he told me a story about how Bombardier changed clutch manufacturers in the 90`s. All of my clutch is made in Austria except for that bent inner sheave/shaft I had in it. This guy spotted it right away and told the story. Bombardier stopped getting their clutchs made in Austria in the late 90`s. They switched over to Powerblock parts that are made in Canada. He also told me to NEVER mix the Canada parts with the Austrian parts. The inner sheaves from Canada are heavier and meant to run with the rubber bound TRA caps. The Austrian ones are made for the metal TRA caps. Since the clutch is a crank damper, the total wieght of the damper is very important. Ok fine. I learnt something.

My new Austrian made inner sheave/shaft has been tested and it perfectly straight all the way through. This made my day. Its too late to start her up tonight (midnight). Tomorrow morning will be the big test but I am very confident that after the bend I saw and what I learnt about the manufacturers that now I should be fine with no more vibration woes.

Thanks for the help and I hope this helps the next poor sap that buys a second hand inner sheave. Test it first and make sure not to mix the Canadian and Austrian part together.