CVT Belt Size Restrictions? By jomama0867 (Read 1,074 times)

[jomama0867]

First, let me start by thanking all of you "geniuses" for my continued "schooling" in the fine art of Chinese scooter modifications/repairs! I decided before I bought one that I would take care of all the maintenance/repairs myself, rather than trust the ONLY local scooter repair shop (or GOD FORBID the local HONDA dealers)! This would have never been possible without you guys (and gals). Now for my question; I've got a 2013 Taotao ATM150-A with the 157QMJ GY6 engine and 13" wheels. The CVT belt that is installed is a 835-20-30 (I acquired the scooter pre-owned, so I do not know if it is the original). Upon recently installing a 115mm variator, I noticed that the fan doesn't fit completely over the splines of the shaft (because the width of the belt ext tends past the boss?) and when I tighten the nut the pressure actually moves the belt up the face of the variator. I have revisited the stock variator/boss and they are the same dimensions as the new ones, so it must have been experiencing the same conditions. Does this sound "normal" or familiar to any of you out there? Currently my belt doesn't travel to the top of either variator, and I can't seem to accelerate past 6,000 rpm's (started with 13g rollers, currently running 7g's)! I know there are dozens of variables involved, but I'm just wondering if the installed belt is too short to physically reach the top (I've noticed that some 150cc's run an 842-20-30 belt).

[Bashan]

The 835 and 842 are interchangeable. First, your outer pulley must fit up against the boss. If it doesn't something is wrong. Sometimes the belt will move up a little on the pulley and not sit on the boss as you tighten up the outer pulley (fan). The clutch should compensate for that once the bike starts. The belt usually will not make it all the way out on the pulley, especially with a 115mm outer pulley. You are right, the shorter belt will give you different ratios than the 842 so try them both and see which one you like. However, top end 6K on the tach is way outta normal range, I don't think that's your belt doing that. That sounds like a mechanical problem in the engine or carb.

[jomama0867]

Thanks Bashan! Yes, the outer pulley DOES fit tight against the boss when it's torqued (but not without the belt sliding up). I'll try the longer belt and see what happens. As far as the rpms, I thought 7,000 - 7,500 was the typical power band. I tried lighter weights (down to 7g's) but never got past 6,000! Mechanically, the engine seems and sounds fine, could this be the result of a restriction somewhere (everything except the variator is stock)? I've checked the CVT, carb., and bypassed the PAIR, maybe the CDI? I'll try to get some pics.

[Bashan]

Yes, 7 to 7.5K is the ideal running RPM but you should be able to touch 8K or even a little higher. How fast are you going at 6K and you should clock that with a GPS or have somebody follow you. Your Chinometer is probably way off. Most 150s do not have rev limiters on the CDI but I guess it's possible. But even so they wouldn't hold it down to 6K. Yeah, try the other belt and see what happens.

[jomama0867]

Okay, still waiting on the "842" belt! Meanwhile, I run an average top speed of 60 MPH (GPS verified) at around 6K RPM's (have made it to 65 MPH at 6.5 RPM's on occasion)! I've discussed this with other scooter dudes, and they all say "leave it alone", but I'm still curious about the low RPM's. When I get the "842" belt, I'll update this.  THANX AGAIN BASHAN!

[rks]

Your tach is no good.... if the speed numbers you posted are not misprints

[jomama0867]

Thank you rks, I didn't even consider that but it explains ALOT (like why I have to set my idle at 2k or more)! I'll hook up another tach and see what I get.

[jomama0867]

UPDATE: I changed to the 842-20-30 belt and re-installed 7 gram rollers (the lightest I could find so far). The result . . . NOTHING! Although I've managed to reach 6,500 rpm's on occasion, this scooter seems to prefer 5,000 to 6,000 rpm's as it's "normal" range. RKS suggested a faulty tach which would make sense, I just don't know how often that occurs, or even how a fault could exist (engineering not exactly my strong suit)?!? I've ordered a digital tach that should arrive in about a week. Meanwhile for all of you master mechanics, engineers and gear-heads out there, my question is this: What are the hazards (or benefits) of continuing to run the engine as-is (with the exception of the missing rpm's, the scooter seems to be performing great)?

[rks]

My scoot has pretty much the same drivetrain as yours......157QMJ with a 835-20-30 belt, but I run on 12" wheels. I switched from 12 to 14 gram sliders last spring, just to knock the rpms down some. I don't have any idea of what this scoot's top end is (really don't care), for I am totally happy cruising along at 40 or so. Rpms at this speed are 5400 + or -, depending on wind direction and such. At 6000, speeds are in the 46/47 mph range.

I very rarely exceed 6000 rpm....even climbing hills with a 12% grade, (common where I ride), 5500 rpm produces plenty of torque to do the job. Lower rpms = cooler operating temps, increased fuel economy, increased engine life.

There is no way your scoot is only turning 6000 at 60mph, with seven gram rollers.....still say your tach is no good

[jomama0867]

Thanks for the feedback rks. I'm still waiting on the digital tach I ordered. Meanwhile I'm leaning towards taking the advice of the majority of opinions I have gotten: "If it's working fine, DON'T FIX IT!" Now it's become more of a curiousity than anything, but from your last post it seems that my "normal" rpm range isn't that far off from yours, and that's a relief! I'll post an update after the digital tach arrives, just for any curious minds out there. Thanks again, rks, and safe scooting!