How it works

[DieselFly]

Here is a nice video link that will halp answer how a CVT works. Ridley uses a Vtwin lawn mower engine dressed up for motorcycle use (I think its a Briggs Vangard might be wrong) They claim a 75mph top end which jibs with the 20-25 hp
http://www.youtube.com/watch?v=XpO1wrEN ... PL&index=2

[coachgeo]

actually their video page site has alot of info including how to rebuild the CVT.

Their parts page has GREAT items too. You could nearly build a whole CVT diesel bike (chopper or old old school type, not counting engine) from parts available on their site.

[Dan J]

Good catch coachgeo - I'd never heard of these guys before.

I note with interest from the specs of the bikes they build:

RPM @ 85 MPH : 3600 RPM

Now there's a thought!

[Sphere]

For that kind of money I had hoped the parts are GREAT. 1000 bucks US for clutch and driven, no belt included

[DieselFly]

Remeber these are Comet Clutches and may not be availabe just yet. The good thing about a CVT is the fact that you can set you shift RPM to max torque to get the best from your engine. Being most of our engines are ment for constant speed use the CVT is ideal. When you read of Pusuns breaking cases it probably has to do with lugging the engine at low speed where it shakes and vibrates like crazy as it is not ballance for these speeds. Punsun says stable no load speed is 1400 rpm so you clutch should not engage until a higher RPM. I have been in the SAEbaja.net site where the have alot of good clutch tuning info. I'm looking for an engaement speed of 1800rpm and a shift speed of 2500 which should keep it from shaking itself to death.

[Sphere]

Do you think this applies to ordinary clutches as well, i.e. have them slip until 1800rpm otherwise you might end up ruining the engine?

[albertaphil]

I don't think setting an ordinary clutch to slip until a specific RPM would work because most of these small diesels make max torque in the 2400-2500 rpm range. Above and below that the torque will be less. So if you loosened your clutch, it will hold steady at lower rpms when things are really shaking, and then start slipping in the mid 2000's when you need it to hold, especially when you're running an enfield 4spd transmission. Maybe you'll have to put a CVT on your Hatz enfield, sphere:-)

Incidentally, why do so many people not like the MZ Variomatics? They are just another belt-drive CVT, aren't they? Is it just because many mechanical types are control freaks and just like to be able to control RPM and gear selection? Having said that, there seems to be quite few Variomatics around with Ruggerini twins, and some with sidecars, so obviously not everyone hates them.

Phil

[Sphere]

I cannot put a CVT in; or risk being disowned. Or evicted

My personal reason for using the Enfield 4-speeder is that obtaining a decent CVT for a fair price is nigh impossible here. And CVT is arguably less efficient than ordinary drive, because of belt slip.

[albertaphil]

Ahhh, peer (or spousal) pressure...the great motivator.

As for efficiency, I've always figured that whatever efficiency loss there is in the CVT belt due to heat, it is more than made up for by the fact that the engine itself is working in its most efficient (and powerful) rpm range at all times, or close to it, at least. Also, you don't drag gears through grease or oil constantly without some sort of efficiency penalty. A CVT has none of those lubrication issues...just two pulleys and a shaft with a sprocket on it. And this is coming from a guy who is now putting a gear box on his bike...too bad Comet didn't make a primary pulley to fit my oddball crankshaft. That's okay, it's cheaper this way. I'm just glad my little honda came with a 6spd box.

[Sphere]

Actually more like peer pressure by someone I won't name since this is a public forum he attends (lets call him Nanko).

Oops

I work with computers 9 hours a day, and I'm not much of a mechanic, so he's helping me overcome all the hard bits. Indispensable really. But I digress. Point in case: CVT is hard to come by, and if you import one from across the pond, you can roughly add 25% taxes to the price+shipping.

[albertaphil]

Yeah, I know, I have $400CAD wrapped up in a CVT that I can't use. However, around here, old brit-bike gearboxes (or ultimas or trik-shifts etc) are hard to come by, or expensive, respectively. You have more, better engines over there, too.

[coachgeo]

Yeah, I know, I have $400CAD wrapped up in a CVT that I can't use. ...

Tell me about the CVT you have.. I might be interested in it. I have an Ultima 6speed and 3" belt drive that I now will not be using.

[coachgeo]

... CVT is hard to come by, and if you import one from across the pond, you can roughly add 25% taxes to the price+shipping.

Holland? Is my geography way off... dosn't it snow there alot? No snowmobiles out there? Heicko got his out of a small diesel car. Would think ya'll have more of those little auto's than USA. We have NONE. The Track built in Holland is using a CVT. that is built in Holland right?

[Sphere]

Longitudinally, Amsterdam is between Calgary and Edmonton. Yet, because of the sea climate and gulftsream, two weeks of snow a year is excessive. Although this winter was an exception to the rule, owning a snowmobile is pointless in Holland. I think the biggest amount of snow on the ground this year was about a foot high, but usually it's a few inches.

[Crazymanneil]

Any of these left in Holland?

http://en.wikipedia.org/wiki/DAF_55

Coach, so are you selling the Ultima box and clutch then?.... (although I may also get disowned and evicted)

N

[coachgeo]

...Coach, so are you selling the Ultima box and clutch then?.... (although I may also get disowned and evicted)

N

yes

[DieselFly]

Do you think this applies to ordinary clutches as well, i.e. have them slip until 1800rpm otherwise you might end up ruining the engine?

The idea if you are using a gearbox would be to get away from low RPMs as fast as posible. In the case of the Punsun's they rate the engine at 3000rpm for contiuous and have a max governor speed pf 3600rpm. So if you wind it out to the governor speed then shift you should be okay. What will kill the engine is making it operate at say 1500rpm or lower which sounds cool but is kicking the crap out of the engine. Yes it will idle very low and sound like a Harley but again you are way outside its design limits. Are CVTs the answer yes and no use what you have. I'm using CVTech IBC CVTs because I can tune it to make the engine function 95% of the time between 2500 and 3600 rpm. If it is properly tuned you will loose very little power from friction remeber gearboxs are not 100% efficent either and what you gain form running the engine at almost constant speed will more than make up for the loses. If your CVT runs very hot and eats belts it is out of tune as a belt should last all season. I will upload a booklet on how to tune CVTs when I get home tonight that will take away alot of questions about CVTs. I have worked for many years in the aircraft industry and the advantages of a constant speed propeller over fixed pitch are well know for there increase in performance by allowing the engine to run at a fixed rpm for best power or economy as needed.

Sean

[arnaud]

Can you give an estimate, as far for the small single diesel engines, what gives the most output,(sa'; highest cruising speed) a conventional gearbox or a well adjusted CVT drive?