CVT trouble - back wheel locks up

[Peter the blacksmith]

Hi guys, I have a problem with the newly bought little Honda with Yanmar 418cc clone. When I ride and if the gas is turned off too quickly, the back wheel locks up and it is hard to stay on the road I have no experience at all of CVT:s, what is wrong ? The cvt is from a micro-car, only one wire goes to the gas on the engine, no visible brakewires from the gas-handle to the cvt. Confusing, and a bit dangerous...
Thanks for any inputs.

[coachgeo]

what rpm does your cvt activate and deactivate enough for the front pulley to free wheel not moving the belt?

Did you change any weights or springs in the clutches/pulleys? They are tune able?

Also though I don't have much experience yet beside conceptual based on tons of reading....... it seems to me you drive little different with a cvt on a home built rig. You dont decelerate as fast cause cvt gears down so fast thus you end up with engine braking (and in your case locking up of rear wheel cause rpm's /gearing is so low the wheel looses traction). When you drive you will want to manage the fuel down. Not fully releasing throttle to decelerate but to manage braking. AKA- You do not just drop fuel to nothing as you brake with foot (and hand like you would a normal car (or) bike; you manage it down......... In fact Im wondering if you would manage it down and use mostly only front brake lightly. You may not need rear brake much at all. think of it as your hand throttle is not so much lowering fuel to the engine....... and more of like...... it is your down shifter and reducing throttle is more like shifting down thru the gears as fast as your twisting down the throttle.

Now a consumer built rig they tune the CVT not as much for best over all balance of performance and or efficiency....... but tune it to match closer to how a user expects the average rig to drive. Unfortunately this is means the rig is no where near it's true efficiency. Unfortunate cause if user struggles thru the learning curve to get the nuance of a CVT tuned for mechanical efficiency....... it will all truly work better once driver is use to it.

Again though changing weights and springs in the clutches you will find a point your more comfortable with. Especially clutches not tuned to the parameters of the engine in the first place.

[Peter the blacksmith]

Thanks for a quick and most interesting answer ! I have no idea what rpms I use, a wild guess would be between 1500 and 3000, perhaps...And I have no idea how to tune the cvt, don't even know if it is possible, have to find out that. But it might very well be that what is causing the wheel to brake is that I'm "gearing down" all too fast when shutting the throttle. A change in driving style is obviously what is needed here. You explained it really well, thanks a lot ! Most of the snow is gone now from the road, so I'll make a new attempt as soon as possible

[gilburton]

Is your CVT from a diesel car or petrol??

[Peter the blacksmith]

It is made for microcars, I think. And they run all on petrol, don't they ? Is there any significant difference in the function of a cvt for petrolengines vs diesels ?
Here, I found a link: http://www.ebay.nl/itm/1-GO-KART-TORQUE ... 4d17063ef9

[gilburton]

That could be your problem as the petrol versions spin up to 5000 revs.
The diesel versions(Aixam Kubota) and early microcar (lombardini diesel) only spin up to app 3000 revs so all the weights etc are different.
Having said that mine never locked up so possibly you have a problem?
If you can send pics or do you know if your bike was built by someone who was possibly on this forum??

[Peter the blacksmith]

Here is a picture. No, not built by anyone in this forum.

[pietenpol2002]

That CVT looks suspisciously like a Comet Torq-A-Verter which is only rated to 9 hp, or about what your engine is producing. If so, tuning would be a bit different than the Aixam. Additionally, it would be interesting to know how it stands up to the grunt of the diesel's torque. Just to satisfy my curiosity, does this unit not require a jackshaft, using instead a stub shaft with the driven pulley and sprocket on opposite sides of the backing plate?

http://www.bulletlines.com/ProductDetai ... 025_a_7c52

[pietenpol2002]

The diesel versions(Aixam Kubota) and early microcar (lombardini diesel) only spin up to app 3000 revs so all the weights etc are different.

And now with Polaris' purchase of Axiam we may have the world's repository of CVT knowledge located right here in the frozen north of Minnesota. They only now need to aquire CVTech and they'd pretty well have it wrapped up. One might hope that with the Polaris history in snowmobiles, ATVs (including a diesel ATV), Victory (and now Indian) motorcycles coupled with the aquisition of Axiam, we might see a production diesel motorcycle here in the states. And please don't deprive me of my fantasies!!

http://www.polaris.com/en-us/company/ne ... icleID=129

[Peter the blacksmith]

well, today I scrutinized the little beauty - it seems the gas wire moves only within a rather short distance - I'm of course used to a bigger register with lots of more rpm. Checked the rpm, btw from the owner's manual of the engine, and it is only 1500 - 3000 rpm, so no wonder one must be rather careful when turning off the throttle . Guess it is here that the dilemma is from. I must try to adjust the gas wire a little, maybe that helps too, added to a more modest use of the throttle Well, soon the snow and ice will be gone from the village road so I can test

[gilburton]

That is a Comet type unit so any info from microcars is useless as they are NOT from microcars.
I say Comet TYPE as there are a lot of copies out there so if you could find any markings on it it would help with parts.

http://www.geminikarts.co.uk/shop/ProductList.asp?GID=7

I'm not sure of your throttle linkage but possibly you could put a longer actuating lever on it which would give more movement at the twistgrip??
Or maybe a secondary lever linked to the original lever in such a way as to give more movement?

[albertaphil]

I have the same cvt setup on an old minibike. The back plate of the cvt supports everything and there is a little sprocket right behind the secondary pulley. My bike had 4hp...

[Peter the blacksmith]

.....
I'm not sure of your throttle linkage but possibly you could put a longer actuating lever on it which would give more movement at the twistgrip??
Or maybe a secondary lever linked to the original lever in such a way as to give more movement?

Yes, that is what I think I have to do. Thanks for the input !

[gilburton]

Personally I would leave it until you can get some feel for it in the dry weather.
There is not a lot of movement on these engines anyway and using a CVT means the engine is generally around full throttle all the time.
Instead of just instantly closing the throttle try rolling it off in anticipation of stopping a bit further away from your actual stopping point.
Things happen slowly in the diesel bike world so try to adapt to it first.
Nice looking bike, by the way, so might be worth posting a few more pics/details

[Peter the blacksmith]

Thanks gilburton, that was good advice I intend to do what you suggest
The bike is a 418cc (China-made) diesel in a Honda CMX Rebel (former 250cc) frame.
Found it when I randomly surfed on the net on a Dutch site, Autoscout or something like that.
Called my Dutch friend Ruud and asked him to go and take a look, so he bought it and shipped it here to Sweden in his van - he has a summerhouse in this village. Convenient

[Peter the blacksmith]

Another picture...
No. Unable to load a picture, even if it is small

[gilburton]

Most of the 10hp engines get around 80kph(50mph) so if it pulls well but does less than that it may be worth playing around with the final drive sprocket

[Peter the blacksmith]

Good tip, thanks ! The chap who sold it claimed it does 90 kmh, time will tell....

[gilburton]

That is about all you will get out of it but it will probably lose a bit on hills.
No problem in The Netherlands though
There is a CVT section in the forum so plenty of advice if you need it

[Peter the blacksmith]

Well today the problem solved itself.
I went for a ride in the wonderful weather, and thought well today I'll try the top speed. Lo and behold - 90 km/h
But in a long uphill there was a funny buzzing sound, and the bike lost the drive, but engine was running smoothly.
sh*t, I thought, must be the cvt-belt that broke. And indeed it was. There was not much left of the belt, in fact
How could this happen - new engine, new cvt...??? Ahaa ! I discovered the disks in the cvt were not in line, not at all
The difference is more than 5mm, take a look on the photo. That must be why the belt got hot and sticky and did not function well.
Or what do you think guys ?

[gilburton]

Well it looks to me as if the final drive sprocket is in the wrong place??
Shouldn't it be behind the backplate?
If that is the case you might be in for some serious re alignment of the engine as you can't move the chain alignment.

[Peter the blacksmith]

So - is it not possible to move the front sprocket out 5 - 6 mm with a spacer ??

[gilburton]

I'm not familiar with the Comet CVT but if you can do that go ahead
Only other comment I'll make is if the rear chain is a standard chain needing oil I would try to make up some sort of splash guard to stop it getting on the belt/pulley.
If it's sealed chain it shouldn't be a problem
If you still have belt problems after you correct alignment have a look at this post.
Does your drive pulley have a bearing/bush like this for the belt to rest on at idle??


https://www.dieselbikeforum.com/view ... 670#p14670

[Peter the blacksmith]

No, it doesn't
But thanks a lot, it was really a good tip what you wrote about keeping the oildrops from the chain apart from the discs !
I really appreciate that

[pietenpol2002]

I think too this design is to have the sprocket on the backside of the backing plate. Looks like the chain's been nibbling at the inside of the driven pulley. I don't think they were ever intended to be sleeping that close to one another. As it is, the driven shaft is cantilevered off the bearings with all forces excertd outboard of the backing plate. All a recipe for a short life. If the drive pulley can't be moved outboard a sufficient distance to align with the driven, another option would be to replace the stub shaft with one long enought to reach to the other side of the bike, flip the rear wheel over and move your drive sprocket to the right side. All in all it would be a fairly simple process. It would also include mounting a bearing on the right side and re-routing the brake mechanism. Probably easier than moving the engine that much to the left.

[coachgeo]

Believe comet sells a tool for setting the distances left and right properly between the two clutches. Since one clutch has one sheave that moves inward and the other has one that moves outward as they expand/contract thru their ratios; they do have to be aligned properly to keep the belt from being tweaked. The secondary I do believe is the one whose sheave moves inward so if your sprocket is there it may also be conflicting with its travel; thus the marks your found on the secondary sheave.

Another idea is for you to NOT use the comet mounting plate your using. Get rid of it and mount a jackshaft for the secondary to ride on with pillow blocks. Might give you a tid bit more options that way and prevent you from having to swap it all to the other side.

[pietenpol2002]

I think too this design is to have the sprocket on the backside of the backing plate.

I was wrong. The sprocket is outboard of the backing plate. But, that's good news in that no major mods are thus required. Still a bit puzzling why the chain is turning down the driven pulley. Especially since it's the outer half that moves (Sorry George, I think we're arguing on the internet over this one. I believe that's something we're never supposed to do).

[coachgeo]

I think too this design is to have the sprocket on the backside of the backing plate.

I was wrong. The sprocket is outboard of the backing plate. But, that's good news in that no major mods are thus required. Still a bit puzzling why the chain is turning down the driven pulley. Especially since it's the outer half that moves (Sorry George, I think we're arguing on the internet over this one. I believe that's something we're never supposed to do).

CVT.jpg

hmm. interesting on sprocket location. Different designs apparently do it opposite of one another. It appears some manufactures set inner as movable sheave while others set the opposite. In the following video the Team Industry set up has the secondary's movable sheave as the inner one
http://www.youtube.com/watch?v=uCEvBGT8twM

while the comet; like used on his bike in video below has the outer as the Movable.
http://www.youtube.com/watch?v=DNzFTxTvajg

doing some looking at CVTech units and apparently they too have the inner sheave of the secondary moving inward as well.
http://www.youtube.com/watch?v=xeQITB_H2wM
note this video has a bent or flexing jackshaft holding the secondary. Threw me for a second too

So back to topic... could the torque of the diesel be flexing the shaft the secondary is mounted too?

[Bj-torb]

So - is it not possible to move the front sprocket out 5 - 6 mm with a spacer ??

Hi Peter
I moved the front sprocket on my bike with a spacer I made. On my engine it was not a problem. Took some measurement and turned a spacer on my lathe

[pietenpol2002]

could the torque of the diesel be flexing the shaft the secondary is mounted too?

Seems a reasonable hypothesis. While it's rated as taking 9 hp, the torque from the diesel would be considerably greater than a petrol engine. Additionally, as this unit is designed for a #35, 40 or 41 chain, could the wider #530 chain also be contributing?