Topic: How would one modify a rear end

[KB02]

The bike's... not my own... I know how to modify that one (Lot's of McDonalds stops.  )

My question is this: How would you modify the drive spocket on the engine to handle an overized rear tire?
I did a quick search, but didn't really get what I was looking for.

Okay, here's my idea, tell me if you think I am completely nuts. When I was getting my bike inspected, the tech offered me a parts bike for it. He said it was "79, I think," but did say it was a SOHC, so probably a 78. Anyway, I started thinking it might be a nice project bike. My thought was that since I already have a Cafe racer, I might build a low, fat cruiser. I thinking really fat, too, like a 160 or 180 rear tire and appropirately as fat up front as well (although not quite as fat to keep it looking within poprortion) and slammed to the ground to keep it low (but tall enought to still have suspension - Too many bumps around where I live for a hard tail).

Now, obviously I know that this will effect handling and will take some major modifications to both ends, but in theory, it could be done, right?

Why would I do this, you might ask? Because I can. I'm not looking to build a chopper, just a nice, fat street cruiser.

Thoughts? Comments? Proposals for my commitment to phychological institution?

[Aaron J Williams]

I did a little measuring on mine and it looks like 3/4 in. between the swingarm and stock tire on the right side and 1 in. from the tire to the chain on the left. That gives you barely 2 in. to play with. It looks like you could spacer the sprocket over 1/2 in. but that still doesn't help much. If you were to make a new wider swingarm you could fit whatever size tire to it that you desire but then the problem becomes the engine sprocket alignment to the rear sprocket. You can't shim the engine sprocket over so now you are talking re-working the motor mounts to move the engine back into alignment. It could certainly be done, it just depends on how much work you want to do. Also, the engine can't move over too far or the pipes will hit the frame so maybe build some sort of stub shaft that fits to the transmission output shaft and brings the chain to the outside of the frame. You would lose your passenger footpeg and have to build a custom chain guard and remove your front sprocket cover to accommodate the extender shaft. You also would want to keep the tires in line with each other so the bike doesn't "dogtrack"  At this point, the mental institution is starting to make sense!

[KB02]

...the problem becomes the engine sprocket alignment to the rear sprocket.

...and remove your front sprocket cover to accommodate the extender shaft.

Yeah, my thoughts on the project involve a customer swing arm, so the alignment, like you said would be an issue. Also, speaking of an extender shaft, do you think there is enough meat on the shaft to accomodate an extender shaft? Baically, that is the one thing that puts the biggest kink in the works. If I could figure out a way around that, I'd be all set.

At this point, the mental institution is starting to make sense!

Well, that's been known for years. 

[Aaron J Williams]

My mental picture of the extender shaft is to take an old output shaft from a junk motor and cut it to the length you want and weld it to a collar that is splined on the inside to slide over your output shaft. Then you drill your output shaft and matching collar and pin them together. Of course the clearances and welding job need to be perfect so the extender shaft doesn't wobble but you probably knew that already. It will put more stress on your transmission unless you rig some sort of bearing to support the sprocket end of your extender shaft, but that wouldn't be too hard to make.

[xtalon]

You also have the issue that if you go wide on the swingarm, the shocks have to mate up above to something too.

--xTalon

[KB02]

True. But, the way I figure it, if I'm going to go low and fat, the rear of the frame would have to be altered anyway to accommodate the new tire. So, if I widen it out enough, the shock mounts should match up.

It look beautiful in my mind... but then again, so do a lot of things.

[nteek754]

Hy guys I really think they use a jack shaft not too too far back from the countershaft sprocket  a shoet chain back to the  shaft that is mounted solid with two  bearingd  then of coarse a  chain going back to the rear wheel I have seen  custom chopper frames with  250 rear tires and thats the only way   they  could  do this hope this helps  seven fifty four ever Craig in Maine

[eurban]

Check out Cycle Exchange's website www.cyclexchange.net   . 

[333]

The jack shaft idea seems best, but You must keep in mind that any of these ideas  will either take power away((The jack shaft idea) or never be strong enough to take the torque that engine makes(extending countershaft).  The rear sprocket could be extended out without being too weak, and then the engine could be moved to align.  The frame would need to be modified for the exhaust issues.  The rim would need to be replaced with a larger one to correctly fit the size tire you want.  Seems like a lot of work