Trek 4500 / GP460 now twin belt jackshaft

[DetonatorTuning]

kerf,

there is potential in your proposal.

please define "your primary gear box" more closely. do you mean the 5:1 scooter tranny ?

you could only pull that off as a right hand drive because the tranny reverses the rotation. then you wouldn't have room for the pedal drive.

it would be totally do-able to; frame mount the 460 for standard left drive (which would be much narrower), hit a jackshaft for reduction advantage ,because the O.D. of standard V belt pulleys is not small enough to support a single step straight off the engine output shaft, THEN combine to a Whizzer sheave.

tensioning the final loop could be handled a number of ways, none particularly difficult. if done properly you could have the jackshaft outer plate be 1/4" and 1 piece with the engine mount, then use a square 4 bolt pattern to hold the inner bearing support plate and mount the pulley either between the plates or behind them like i've done on this one.

pedal clearance shouldn't be any more difficult than the 4strokes.

give me the "effective" Dia. of the Whizzer sheave or even the actual full O.D. and i will figure up the needed primary reduction.

got a frame in mind ? i can email you some sketches if you like.

thanks,
steve

 

[duivendyk]

I looked at your pics,it looks to me that the load on the jackshaft bearings will be rather high, due to the limited spacing between them,the momentarm of the chain forces will be acting on them.What is their spacing ?

 

[DetonatorTuning]

JJ,

i can always rely on you to be watching my "6".

the bearings have 1/4" support from the snapring down allowing 1/16" of the bearing casing to extend past the outside of the plates. inside the plates, the collar is a friction fit between the bearing centers so it's kind of one solid bearing and shaft totalling 1.5" from outside to outside.

the outer sprocket hub is fastened against the bearing center on the outside and a collar is fastened against the bearing center on the opposite end, then there is a 1/8" gap to the face of the inner sprocket hub. the total distance between the centerline of the sprocket teeth is 3-19/32".

thanks,
steve

 

[DetonatorTuning]

nearly a hundred new views in 24hrs. and only TWO comments ??

kerf loves a new twist and DUI see's a chance to make improvements.

BTW DUI, i can easily move the inner bearing support plate out 5/8" if that would help .

Brothers Graucho and Zomby, you guys do lots of jackshaft stuff, any comments or cautions about this setup ?

thanks,
steve

 

[kerf]

Relocate the JS so it passes over the upper aft portion of the wheel. This would allow the support bearings to to achieve the greatest spacing. Only suggestion I can come up with.

I'm "twisting" to mate a 12" sheave to an ACS LH freewheel. Total belt drive and a freewheel.

 

[duivendyk]

I looked at the structure a bit more closely and concluded that getting the jackshaft bearings close to the sprockets seems like a good idea.There is bound to be a certain amount of twisting of the jackshaft in the vertical plane,but that has to do with the torsional rigidity of the overall structure.Chain/sprocket alignment as such is not particularly sensitive to this I would think, however the chain slack could potentially be affected by this flexing.

 

[DetonatorTuning]

kerf,

sounds good on the freewheeled "sheave" keep us posted on the progress of the project.

i thought about putting the shaft in the position you mention and having the second bearing plate be over on the other leg of the rack but decided against it due to my experiences with trying to keep long chain loops under control.

PS............while it would work for chain, it would interfer with getting a wider belt past the tire. the beauty of this design is that it puts the inner sprocket or pulley in the narrowest part of the wheel and maximizes available space for belts.

DUI,

i concur on the tendency of the engine to exert 'lift" on the outboard end of the shaft and thereby introduce slack on both loops.

this very concept was part of my thinking in the design. knowing this force would act on the jackshaft in the verticle plane i thought giving it the shortes possible "lever" would play in my favor.

i can however see that moving the inner plate further out will increase the support of the total length of shaft. this should reduce the influence of the "lift" past the inner bearing, i'd think.

PS...........things didn't all go as planed on this as i was reworking some parts i'd intened for the twin belt.

now that i have the jackshft centerline established i could just cut another top plate that overhangs the outer edge of the rack leg, then cut another outer plate that fastens right against the lip, this would really cut the amount of possible "lift" since it wouldn't be working the bolts agaist the holes in the plates and arms.

thanks,
steve

 

[duivendyk]

That is quite true,if they were in the same plane that particular problem would completely disappear,the other parameter of interest is the ratio of the distance between the centerline of the sprockets and the centerlines of the bearings,the smaller this ratio the better the situation will be as far as bearing loads are concerned.(this may not be all that important) as long as they don't come from China!.It all depends on inherent mechanical constraints&tradeoffs.

 

[capturedbyrobots]

I really like the design.
Very simple......
My only worry is how the freewheel will hold up over time.
Besides that, Me likey.

 

[DetonatorTuning]

DUI,

duely noted, i have acces to lots of AL plate scrap i'll just make some up and do the spacing too.

CBR,

thanks for weighing in here, i appreciate it.

there are better hubs and freewheels to be sure, as this is a transitional build i figured i'd use what i had to start with.

since i'm still putting driving force thru the freewheel, enough tension for the chain and cogs and not too much thrust exerted against the freewheel and wheel bearings is a delicate balance.

when i trade sides and power the disk brake mount the drive thrust will be off the freewheel finally and fully on much better bearings.

thanks,
steve