Rear sprocket offsets?

[Crazymanneil]

Hey all,

Getting geared up to do my build now (Smart CDI engine, Harley gearbox, enclosed chain primary, custom made adventure trailbike style frame).

Need to skim the flywheel because otherwise the primary will stick out too far. On the subject of primary sticking out too far, I have measured my Yamaha TDM850 for comparison and the offset of the rear sprocket from centre-line of the wheel is approx 10cm. This affects the alignment of my gearbox output sprocket and hence the gearbox -> primary drive -> engine. With this setup the engine would be approx 3cm to the right of centre at the top. (its actually more than this at the bottom of the engine, but the fuel pump is attached to the left at the top and so offsets it back in again) I don't think there is much I could do about this and would probably have to live with it. I think weight distribution will be ok because the clutch, primary housing etc will be hanging out the left hand side.

Is there somewhere you can get a list of the rear sprocket offsets of various bikes? I measured my dad's Suzuki Bandit 600 and it was about 11cm. I'd need 14 or so cm to get the engine centred although don't know if it would be worth the hassle of finding the right wheel/swingarm combo anyway. I've seen a rolling TDM chassis for sale and might go with that for simplicity sake (will need new frame obviously but can keep wheels, suspension etc).

Cheers,

Neil

[oldbmw]

Dont worry about the engine being off centre. So long as the sprockets line up it will be ok.

BMW's are the most cockeyed bike you wiill ever come across. The motor is ofset, the footpedals are offset even the wheels are offset. ( they do not run one behind the other. Despite this they work reasonably well

[Crazymanneil]

Thanks for that - very re-assuring. Missed out on the rolling frame, have to keep looking for bits. Hopefully get this engine running pretty soon.

Neil

[jdaftra]

I'm not sure I understand this post. I assumed that the bike needed to be in balance so that it was neutral when it was upright. Otherwise wouldn't a guy have to constantly counter-steer a bit to make the bike track straight? I wanted to to a similar swap but my engine is too long and would stick out to far to match up to the rear sprocket if it was balanced but might work if it were offset. -JD

[oldbmw]

I'm not sure I understand this post. I assumed that the bike needed to be in balance so that it was neutral when it was upright. Otherwise wouldn't a guy have to constantly counter-steer a bit to make the bike track straight? I wanted to to a similar swap but my engine is too long and would stick out to far to match up to the rear sprocket if it was balanced but might work if it were offset. -JD

At first thought you would think a bike has to be perfectly balanced, but it is not so. The rider will compensate for it . Just hang 20-30 lbs over one side (fill one pannier) and you wont really notice the difference.

The bmw 's are not only odly balanced but the rider sits with one leg out further than the other. this forces a slight twist in the body for your hands to reach the bars. Mine at least hates wet grass or any other slippery surface.

[Crazymanneil]

Interesting opinions. I would have thought the bike would need to be balanced also, but I am now realising that the weight should be relatively low down in my case and hopefully therefore closer to the centre of gravity. Also in my case although the engine will be offset, the flywheel and clutch will be on the other side so will hopefully balance it out slightly. Failing that I'll put a toolbox or something on the light side to help further.

Neil

[Fiddler]

Hi Niel,

Don't worry too much about weight distribution at this stage. Its easy to get too distracted and forget you still have the exhaust to route and hang also a 5 to 10kg battery to help balance things up once you get the sprockets aligned.
I've heard oldbm's advice before from various sources and reckon its sound. You'd have to grossly get it wrong to notice it when riding.

Cheers, Mark