I can't find a narrow rear axle with a 3.1 to 3.3 ratio, so I'm trying to figure out how to "overdrive" the 3.89:1 rear end I already have. What I've come up with is sketched below - an 11 tooth sprocket driving a 9 tooth sprocket (connected by a chain, of course) for an overall ratio of 3.18:1.

Is there any better, cheaper, lighter weight way of "overdriving" my differential? Power would be from a 50 hp CX500 engine so I don't need a lot of strength.

If the sketch doesn't show, it's at http://www.carcentric.com/trikeoverdrive.gif

How do you tension the chain?

And I *think* you will be going backwards.

[Edited on 6/4/04 by gjn200]

It would only work with an irs setup on live axle the chain will jump off because the diff moves fore and aft as it goes up and down and steers slightly in roll.

Much easier just to switch to an irs or de Dion and get a diif from a 2.8 Granada.
If you want stay with a live axle it is quite common to "narrow" Rover V8 SD1 axles to fit MGBs

i've been lookin into this option in my plans to make a twin bike engined middy. My stumpling block was the bearing that holds the ends of the various propshafts. just couldnt find a supplier of good bearings. The chains and cogs are a piece of pisss to find.

and as already said, it wont be happy with a live axle.

this is for the trike, isnt it?

britishtrident - The differential is a swing axle Triumph Spitfire unit bolted securely to the bike/trike subframe (i.e., it would not move relative to the engine/trans). The Spitfire is the smallest/lightest diff with axles available over here - no, we don't got no Reliants . . .

gjn200 - Tensioning the chain would be done by moving the pillowblock bearing (lime green) for left or right - it has elongated mounting holes for this purpose - or shimming under the pillowblock for up and down. Also, an idler sprocket tensioner could be added. As to 5-speeds in reverse, I'm pretty sure I've figured that out - the rule of thumb seems to be if a bike has the shaft drive on the right side of the rear wheel (viewed from the rear, e.g., a Honda CX500), it turns the same direction as the car's propshaft; if the bike drive is on the left (e.g., a Yamaha XS1100), it turns the opposite direction.

JoelP - Yes, it's for the CX500 Trike. The pillowblock bearing at the end of the propshaft is a 1" axle bearing designed for "high powered" racing go karts. I suppose I could bodge a front wheel bearing into something beefier if that would be necessary.

I'm trying to avoid costs and extra weight associated with narrowing a live axle. Of course, if I had a 3.27:1 gearset from a non-OD Triumph GT6, I'd be set, but they run > US$375.

Can't you use an overdrive unit, my old spit had one operated from a slider switch on top of the gear lever

I never realised the maggots drive shaft was on the other side, how odd. Not sure on the pillow block bearing though, most bearings that run at that speed (for any length of time) are normally immersed in oil,not the odd squirt of grease. Berk(e?)ley replicas use them engines so that may be of some use if you can find out about them.

i have always liked the cx500 - shame its called the plastic maggot!

cheap as chips now....


atb

steve

quote:

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Can't you use an overdrive unit, my old spit had one operated from a slider switch on top of the gear lever

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I know they add a little length, but being ally and small I cannot imagine the weight penalty would be much different than a chain and cog assy

I thought of using a similar idea on a trike but the engine had to be mounted over or alongside the diff so the sprockets would line up. Oval engine mount holes would allow some chain adjustment but it wouldn't be a problem like on a bike as there is less stretch due to the diff being fixed. An adaptor to fasten the second sprocket to the diff would be simple enough to make.

how well would a diffs input bearings withstand the pull of a chain? cos obviously a chain isnt an even twist, its more a pull from one side. Would make my life easier, if it could be done without having to add a short prop to hold the cog.

I don't think it would put any different stresses on the bearing to the ones it already endures. It is in a lighter vehicle which will make it even less stressed setting off and under engine braking.