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Mounting a chain diff in single seater
prawnabie - 23/8/15 at 09:15 PM

Hi all,

I have a long term single seater project that is in the planning/ideas stage at the moment. I am currently envisioning a terrapin like front end with a widened haynes like inner rear end (the box that the wishbones mount to).

At the moment I am looking at ideas to mount the chain diff - most of the ones I have see entail bolting the assembly to the rear of the chassis but from seeing a few failures and doing some research I can see some possible problems (if indeed they exist at all!)

A. Any movement between the engine and the diff will cause a"kangaroo" effect by pulling the chain when on/off the power

B. The chassis would have to be beefed up where the diff mounts as the engine would be trying to pull the assembly towards it when pulling off.

As I see it, if the diff and the engine were mounted together, the above forces would the above forces be contained within the unit and there would be no need to beef up any mounting points, saving weight.

Is this an idea I should give some thought to?, if so, does anyone have any photos or thoughts on it?

Thanks,
Shaun

Sam_68 - 23/8/15 at 09:31 PM

Your idea is fundamentally sound, for sure.

Most bike engined race cars rigidly mount the engine, so it's not a huge deal, but...

DJ Racecars stressed sump installation:



And even closer to what you're describing, the 'transaxle' arrangement on an American Stohr sports racer:


HowardB - 24/8/15 at 05:47 AM

The Stohr setup is pure porn...

Neville Jones - 7/11/15 at 11:25 AM

quote:
Originally posted by prawnabie
Hi all,

I have a long term single seater project that is in the planning/ideas stage at the moment. I am currently envisioning a terrapin like front end with a widened haynes like inner rear end (the box that the wishbones mount to).

At the moment I am looking at ideas to mount the chain diff - most of the ones I have see entail bolting the assembly to the rear of the chassis but from seeing a few failures and doing some research I can see some possible problems (if indeed they exist at all!)

A. Any movement between the engine and the diff will cause a"kangaroo" effect by pulling the chain when on/off the power

B. The chassis would have to be beefed up where the diff mounts as the engine would be trying to pull the assembly towards it when pulling off.

As I see it, if the diff and the engine were mounted together, the above forces would the above forces be contained within the unit and there would be no need to beef up any mounting points, saving weight.

Is this an idea I should give some thought to?, if so, does anyone have any photos or thoughts on it?

Thanks,
Shaun


I'll be doing just this in a few weeks. Doing the numbers, it's easy to see why a lot of rear engined bec's end up with problems in engine and diff mounts.

I've got a cbr1000rr, and in first gear, chain tension works out to be in excess of 11kN(~2500lb Force in my old units). This is the force of the diff and engine pushing against each other, so no 3/4" x1.5mm shs erw tubes in here! Unlike some.

Turn that into a full blooded drop the clutch launch, and that figure could be multiplied by a few times. I'm putting strain gauges on this thing, and that is one area that will be monitored.

Cheers,
Nev.

daniel mason - 7/11/15 at 11:33 AM

We make loads of full-bore starts on the stickiest Avons made! If anything chains and driveshafts will fail first, (although up to now I've never had either fail in over 2 years)
The setup on my Jedi seems spot on although not as complex of the stohr or dj.

Neville Jones - 7/11/15 at 02:33 PM

What chains are you using? What driveshafts? I'm thinking Fiesta shafts and hubs?

Cheers,
Nev.

daniel mason - 7/11/15 at 03:02 PM

In the radical I had the standard radical shafts and a spare set of the (unbreakable) radical shafts which I never used!
The force had dayson shafts which are as good as you can get
And my Jedi has rally spec mini shafts
Not sure what part number of chain is but it's a 530 did drag bike chain i think. I have a spare in the garage so can check, but again Ian dayson can supply them

[Edited on 7/11/15 by daniel mason]

Neville Jones - 9/11/15 at 12:09 PM

quote:
Originally posted by daniel mason
In the radical I had the standard radical shafts and a spare set of the (unbreakable) radical shafts which I never used!
The force had dayson shafts which are as good as you can get
And my Jedi has rally spec mini shafts
Not sure what part number of chain is but it's a 530 did drag bike chain i think. I have a spare in the garage so can check, but again Ian dayson can supply them

[Edited on 7/11/15 by daniel mason]


Thanks for that.

Seems the Fiesta shafts might do the job, if a bit wider than the mini's.

I was going to use Metro axles and hubs, same as Mini, but felt they might be a bit tender.

I was also going to run 10" diam wheels, quad bike items which are ultra light and cheap, but the only people who make decent tyres are Hoosier, and charge like a herd of wounded bulls. I've got access to used tyres from two F3 teams to start off with, then get new items when I can drive the thing properly.

Cheers,
Nev.

daniel mason - 9/11/15 at 12:30 PM

If your sprinting and hillclimbing you'll never get enough heat into an f3 tyre!
You'll pick up a used set of crossplies from a jedi or similar in a15 or a92 Avon compound for a reasonable price