Snowmobile RPM's

[Dman]

I got a 1988 Indy 400 for FREE! Here's the only problem so far.<br />At full throttle operation the RPM's are about 7000. According to specs it should be about 7900 +/- 200. I can only get about 75 mph out of it. While I don't really care about the speed, I just want it to be running at top performance. The engine runs perfect. <br />Clutch? Any tips. <br /><br />Thanks<br /><br />Dman

 

[JasonJ]

Re: Snowmobile RPM's

Bear in mind I don't know much about snowmobiles, but it still has an engine, so the rules should still apply. Check to make sure it is in good tune, that it has good compression. Make sure there isn't undue drag on the variable transmission, make sure it has good gas in it, that the carbs are clean and properly adjusted, the usual maintenance items. Good luck...

 

[walleyehed]

Re: Snowmobile RPM's

Check secondary clutch spring...If it has many miles, the secondary most likely needs a new spring or set-up one more notch. That's what controls your RPM in general during any running conditions.<br /><br />Edit: A new drive belt will ride higher in the secondary, and give more rpm as well...make sure belt is not worn more than 1/8" from new specs.

 

[Dman]

Re: Snowmobile RPM's

Thanks. It has 4100 miles. Now to the spring question....<br />How do I fix it? I really have no knowledge of clutches on sleds. Special tools? Ect....<br />D

 

[walleyehed]

Re: Snowmobile RPM's

Set of snap-ring pliers and you should be set....Do you have a Polaris dealer around???<br />When you take the 2 halves apart, you must index the starting point so you know where to rewind to when you go back together.....

 

[Topmason]

Re: Snowmobile RPM's

I'd be checking the primary clutch as well.<br />One is only as good as the other as they work in harmony.<br />Engagement ramp bushings are probably shot, as well as the ramps themselves with that many miles.<br />Also check the slider buttons on the secondary. They slide on the helix and if worn or uneven to each other, will slow your ride.<br />When I was riding sleds, both clutches were removed after each outing, completely disassembled, cleaned with a tooth brush and solvent, then all the parts were put into the dishwasher and washed clean.<br />For reassembly, I wore white cotton gloves so as to not get ANYTHING on the belt sheaves.<br />Minute amount of white lithium grease on slide areas being especially careful NOT to get any on or near the belt sheaves.<br />Prior to installing a belt, I start engine at let idle for a few minutes to throw off any possible excess lithium or moisture.<br />On new belts, I use a wire brush on the taper (drive) areas to remove the factory release agent from it, run it through the dishwasher separately from clutch parts and install with new cotton gloves.<br />I learned all this from a very serious race sled tuner whom told me, "It's 1/4 MPH's and 1/4 HP's that wins races"<br />Those clutches are just as important as the engine.<br />Cheers.

 

[walleyehed]

Re: Snowmobile RPM's

Only problem I have with your theory on the primary clutch is that as the weights wear it takes MORE RPM to get the belt to the outer reaches of the clutch.....Lack of RPM is a sign of too loose of secondary, or severe belt wear. The primary only deals with engagement and shifting in the first sequence of acceleration.<br />Again, you need to be looking into secondary, and drive belt thinkness.

 

[Topmason]

Re: Snowmobile RPM's

The primary clutch ramps wear where the pins they hinge on go through them. I've seen them worn far enough that they no longer contact the roller in which they actuate upon, and bind up and stay bound at the clutch tower's.<br />The clutch system is only as good as the lesser of the two allows it to be.<br />Kinda like a chain, only as strong as it's weakest link.

 

[BRIAN03]

Re: Snowmobile RPM's

Befor you go after the clutch. Try a new belt a good one not an aftermarket one. I run a Thundercat with a big bore kit. I put a new belt on it every thousand miles. some times sooner. A drive chain every 500 miles.

 

[walleyehed]

Re: Snowmobile RPM's

Topmason, I've ran snowmobiles for alota years and even spent 6 winters racing for team Yamaha, and have done more clutch work than most sledders do in a lifetime, and I can tell ya right now, if the spring is weak or not set up properly, THAT is the reason for low RPM...Primary clutches wear, yes....weights wear, yes.....Full engagement of the primary does not control RPM at Wide open throttle....the secondary does....<br />Hole-shot, yes, the primary is the single most important factor at hole-shot and shift, but WOT RPM is controlled by the SECONDARY....the TIGHTER the spring, the more RPM it takes to shift and hold, hence higher RPM....the looser the spring, or thinner the belt, the lower the RPM and shift hold.<br />If the primary clutch is worn to the point of flats on the weights, the was plenty of indication before it wears the rollers out for someone that understands the clutch operation.<br />If you want more RPM for hole shot, or higher engagement, you install lighter weights and stiffer spring, with added shims-again, this is HOLE-SHOT...after this, the secondary begins it's purpose of clog-drive acceleration and RPM control......

 

[Topmason]

Re: Snowmobile RPM's

Kenny,<br />I've not disagreed with you once here.<br />However, with 4100 miles, who the he11 would just do a secondary spring and not check the primary?<br />Also, what about the slider buttons in the secondary, what about the condition of the helix?<br />Too many variables to contend with.<br />Ya know, dwell before timing, etc., etc.<br />It'd be like changin the oil, but not the filter.<br />BTW, there's only two kinds of sleds, "Cats" and dogs.

 

[walleyehed]

Re: Snowmobile RPM's

Topmason you are right......about the sleds...I ride Green, Black and Purple. Tim Bender and I both jumped ship on Yammy and went with "PRIDE"...."CAT'S PRIDE" that is.....<br />The helix is what I was trying to get him to have checked....a thou low on R's is a big gap...but you're right, maybe the primary is about to launch....Comet 108C, change the secondary and have it over with.....1200 dollars will fix'er up!

 

[Dman]

Re: Snowmobile RPM's

To settle the debate, I took it to my relatives who have been working on sled for 20 years. <br />The problem was the primary clutch. The whole thing was shot and needed to be replaced. <br />I picked up an new used clutch for $200 with new weights and new spring.<br />Runs great now....except for a odd thumping noise all the time. I can feel it on my feet pretty good when going slow. <br />I checked the secondary clutch bearing and it seems good. I also checked the speedo bearing and that was decent as well.<br />I think it's a bearing but I'm not sure.<br />Thanks for everything.<br />D

 

[walleyehed]

Re: Snowmobile RPM's

OK, Topmason, Beers on me.........

 

[Topmason]

Re: Snowmobile RPM's

Kenny,<br />We was both on the right track, I just got lucky. <br /><br />Dman, <br />Did you put a new belt on the sled?<br />I had that odd thumping one time, turned out someone had smoked my belt a good one and it created a small "narrow" spot on the belt.<br />As the belt would rotate on the clutches, it would make that thumping feeling as the spot passed over the primary. If memory serves me, I think I could even hear it.<br />Just a thought.

 

[Dman]

Re: Snowmobile RPM's

The sled quit going the other day. Pulled off the chaincase and the top gear just fell off. No bolt holding it on!! Replaced the bolt and tightened it and works fine again....except for the thumping noise, it really sounds like it's coming from down by the track.<br /> <br />Havn't figured it out yet. I put a new belt on but might try another new one.<br />D

 

[Topmason]

Re: Snowmobile RPM's

It's sounding as if you may have a bad driveshaft bearing.<br />This shaft has the plastic drive cogs on it and actually turns the track.<br />If you could, loosen your track and reach up to the shaft and try wiggling it. You can have a bad bearing and not feel movement, however, if you're hearing thumping noises, you should be able to wiggle the shaft.<br />If this is your problem, fix it ASAP, otherwise you'll be repairing your tunnel soon and possibly your chain case as well.