Diesel motorcycles. Me want, me shall have.

[Christ]

I understand that, but that's what gearing does.

That bsa trans, I'm gonna have trouble finding parts for when (not if) it breaks, and the shipping alone is close to what I'd pay for a cvt unit. The belt in the cvt is about the size of a3 or 4 rib serp, so it should be capable of holding, I'd think?

[Varn]

My edit crossed over to your reply, Consider the enfield. They still are in production.

My 50cc scooter has a belt about 27mm wide. It gets punished when I upped the performance with porting carb and expansion chamber.

I would like to see what you come up with. If you can keep the bike aero you will have a super economy ride.

[skyl4rk]

I would give it a try with the centrifugal clutch. One challenge will be to adjust the weights/springs so the clutch engages at the right rpm, but that should be do-able.

You might try gearing it for a speed of 35 mph at top rpm, and see how that works. Then keep switching out different size sprockets so your top speed is faster, until you don't have enough torque to start on an uphill.

I messed up the motor on my 50cc gas 4 stroke by trying to go fast when it was geared low (too high rpms), so take it easy at first.

Diesels have a fairly low rpm range from idle to the top rpm, so I would start out with a gear that is geared pretty low and don't expect high speeds out of a single gear bike.

[Christ]

Right at this moment, since I just made another commute to work, I'm realizing that it only REALLY needs to go 45mph... I DWL the Golf all the way to work and seldom exceed 45mph, even though the PSL is 55 for a good section of the trip.

Interstate highway 86 is only 1000 feet at the further from my route, so everyone takes that. Funny, it takes me longer to get home on the interstate at 55 than it does on the rough road going avg 40 or so. I say rough road loosely, because must of that section of 86 is like a dirt road in terms of being smooth... Ask Wonderboy.

[dcb]

I'm with you on the cvt, get it working then worry about perfection.

FYI, an 83 yz 125 parts bike followed me home today I'll post the ratios and if it looks like the transmission/clutch is reasonably adaptable to an industrial engine (or a brushless etek in my case).

[Christ]

Let me know how that works for ya, Dave. Did you get the whole bike?

[dcb]

yup, got the caboodle too (plenty of broken bits though).

Here are the approximate ratios from the crankshaft to the rear wheel (just turning the wheel one rev and listening to the compression):
gear, crankshaft turns for one wheel turn
1, 33
2, 25
3, 20
4, 17
5, 15
6, 13.5

seems pretty close ratio (no surprise) with 1st gear being 2.44 times the ratio of 6th. My saturn is about 5.3. Ah well, I'll be different shifting my electric a lot It should still add up to better acceleration and climbing.

looks like a 49 tooth sprocket on the rear and probably a 12 on front.

jt sprockets lists commonly available options for 12-15 teeth for front and 40-52 on rear JT Sprockets: Catalogue (though I don't have any plans for the rear yet. It is about 12.75 inches radius to the outside of the knobby).

Will take the jug off soon and get a closer look at how to interface with the transmission.

edit: re 2.44 , it might not be too bad, I looked at a gs1100 and 1st to 5th was 2.6
Suzuki GS1000G, GS1000GL, GS1100G, GS1100GL, GS1100GK

edit 2: of course the yz transmission was designed for maybe 24.6 hp at 10500 RPM and I have a peak hp of 14hp and 3500 rpm redline, so if I drive the crank (or crank surrogate) directly I will need to gear up the speed on the tail end. I should really consider gearing up going into the transmission and keeping the torque demands low. If I drove the crankshaft directly with the etek on this bike I would have a top speed of 20mph So maybe 3:1 gear ratio going into the transmission. Though the peak hp torque difference is 1.68:1 (the etek has more torque). Dunno if the tranny can handle 68% more torque of direct drive (probably handles a lot more than that when you dump the clutch) but direct would seem to be a bit more efficient if I didn't need an extra chain.

edit, I cannot get much above 30mph using common sprockets and direct drive. for maybe 60mph and direct drive into the tranny, I would be looking at a custom rear sprocket with like 15 teeth!! (or use a standard 15 tooth on front and a custom 19 tooth on rear)

[Christ]

Any time you add or change gearing, closer to 1:1 is best. If you want to add interface gears that would end up being 3:1, maybe better to split the difference between the interface and the final?

Of course, you can also play with tire profile to fine tune.

[dcb]

I'm thinking about splitting them, having a chain/sprocket interface to the tranny should be straight forward.

maybe a 2:1 going into the tranny
then a yz compatible 14 tooth on the front and the existing 37 tooth on the gs250 on the rear.

@3500rpm that should give me 57mph on my gs.

speeding up the ratio into the trans to slow it down later seems a little weird though.

I'll have to take a closer look and keep re-evaluating the options (and list some spare parts on ebay ) I'm a looong way from fine tuning

our motors are relatively close in power/rpm range (and torque profile).

[Christ]

Re: spares... It didn't have the USD front end?