I'm sure i've seen before, but a search hasn't thrown anything up, a BEC driven through 2 UJ's to a sierra diff. Does anyone know who this is or where the topic is? I can't remember whether this was thought of as good or whether it had any flaws!

Thanks in advance

What car are you planning installing into? If its a front engine'd RWD car such as a Locost then virtually everyone uses this method, although you'll need a centre bearing in the middle because the distance between the engine and diff is too much to use a single piece propshaft with a UJ either end

I'm sure the one it was mounted in was a middie with just 2 UJ's between the sprocket adaptor and the diff.....

Yeh, I remember that also.
Was a year ago (and a half?) I beleive ...

Cheers

In a middy a short prop is okay so this may be correct.

The length of the prop from sprocket to diff is quite long, a single prop will be liable to aggressive vibrations and will try and destroy itself unless balanced perfectly. You will be hard pushed to get someone to make a single piece prop from 2" tube, they would maybe if you are lucky make one from 3" tube as this would be stronger.

Not a good idea really, its a lot of metal at 5000 rpm threatening to take you leg out if it fails.

Regards Mark

dunno who's car it is tho Image deleted by owner

I think someone once calculated that to make a single piece prop that was suitable for a front engine'd RWD BEC, it would need to be something like 5" diameter. Its not the balancing as such, its the resonant frequency of a tube of that length thats the issue, so it will always be likely to fail at a certain RPM regardless of how well its balanced.

it was spunky.

from what i remember from seing it at newark, it was a bike engine, could well have been a blackbird, with a prop that was little more than 2 uj's, think they were bolted back to back, onto the sierra diff

afaik, he sold it some time last year, maybe the year before, but he still post pretty regularly

tom

[Edited on 22/1/07 by indykid]

pic is of a Honda VTR in a midtec Spyder

I found it, but just after someone had done it on here, thanks guys, that was the pic i was looking for. So is that configuration still in one piece and a suitable method for a BEC middie to avoid complication/cost of a chain drive?

Spire did something very similar with a ZX12 in the Spire Gt, I think theirs was a single U/J with a sliding joint IIRC.

to be honest you could do that in a variety of ways. If you want the engine that close then you could just make an adaptor to go onto the sierra pinion flange that takes a rubber drive donut, then get a sprocket manufacturer (Talon Engineering) to make you up a flange to bolt to the engine side of the donut, and which pushes onto the bike output spline as usual.

They quoted me £15 for that sort of item (basically a blank sprocket with 4 or 6 holes in it)

that 2 u/j method is fine IMHO, the middle piece essentially IS a prop. If you imagine the bolted flanges being a short piece of tubing etc...

And if it did fail, at least its not beside you!

If you could get your engine to one side of the diff flange or above it you could use sprockets and a short loop of chain. If you got used different size sprockets you could then vary the gearing so you don't depend on manufacturer ratios.

the problem can be / is balance..

because its centered on the bolts and thats never as perfect as a straight tube wich is balanced

TKs

I got mine manufactured with 2 UJ's and a sliding tube in the middle. Overall length between the engine sprocket and diff flange is about 8 inches.

Dave