What diff for a bike engined kart Cross

[cerberarno]

Hello
I want to put a Gilera GP 800 V2 engine in a Kart cross chassis
I'd like to install it transversal on back of seat
Transmition would go straight back with a shaft to a diff IRS
This engine has already a U joint underneeath the sprocket & a bearing on the outside bolted on frame
I could bolt dirctly a flange / shaft on the joint wich allows me to let go the shaft side ways to catch up the misalignment due to the lenght of the engine
There are plenty of kit cars using bike engine mounted in line , What are they using for diff ?
I'm not talking chain diff , I'd need a shaft diff ...

GOPRO chassis

I'd get rid of chain & main shaft

Engine

This is a pics of an Aprillia mana 850 , sprocket is different on the GP 800

Thanks for help
Cheers

[Furyblade_Lee]

Most kitcars use Ford Sierra or Landrover Freelander , but Mazda MX5 is a other choice, much cheaper and comes with an LSD for free of you like. Freelander is very light, and a Quaife LSD is available. BMW has been used too. But you really need to work out your gearing of your engine, wheel size and predicted top speed you will need to choos a diff with the right ratio. Looks a good fun project, keep us updated!

[cerberarno]

But those car's diff are very big !! is there any smaller ones ?

[cerberarno]

Would be easyer to put engine in line @ go with a chain diff , but lenght & weight would be on bad distribution

[Smart roadster]

You could try the diff from a shaft drive quad. It might struggle with the power but that'll be the smallest diff you can get.
I think you will struggle with the length of the diff and engine fitting behind the seat but good luck.

[Paul Drawmer]

Why use a diff?

With plenty of power, unless the diff is lsd, it will spin the unloaded wheel anyway. A diff makes it easier to park, but I don't expect that is an important consideration.

[Furyblade_Lee]

See if you can find out anything about the Fisher Fury "menace". it used a mid mounted Fireblade engine, tiny propshaft into a sierra diff. Somebody might be able to tell you the space reqd.

How about something like a Suzuki Cappucino diff? Not sure what it used, but that car was tiny with front engine RWD.

And I would not dismiss a chain drive, look up Sylva R1ot which uses a bike engine, chain drive and an Escort RS turbo LSD (modified) in a very compact configuration.

Or Blitz type buggies use similar bike engine setups inbuggies, maybe they can advise you?

[Steve_D]

Again I see no need for a diff.
I also doubt you will have the space for engine, prop shaft, diff.

Steve

[Furyblade_Lee]

On closer inspection of the picture, I agree there is not a lot of room for anything......

[trackerjack]

Fords 4x4 Sierra has a front diff in an alloy casing with 3.6 ratio and is bolted to the side of the engine sump. It is not LSD though.

[cerberarno]

SO here is the engine & its output shaft





If I mount it transversal , shaft going on back , i can fix it on honda 650 NTV "axle"




I would bolt on it , a home made flange , with 2 shaft going sideways , with ujoint, on both wheels
No diff , but a sort of axle .... with integrated disc brake ... like an e type !!
Ratio of 3,09 , shorter than GP 800 2,75 , should give better abillity in off road
I'm aiming a 150 kg short wheelbase kart cross with 80 HP variomatic & long travel smooth suspension
This vehicule doesn't exist yet !!

[cerberarno]

Well.. let's start

Off the stock chain transmition
Before

After


Engine fitment




Doesn't seem bad , stays not a lot of room for the shaft & NTV axle but should be ok hanging out a bit...

[Hunky Dory]

I might be able to help with a suitable diff - I know of a very similar vehicle using an Aprilla 850 bike engine. Probably a different unit to yours, but layout etc is very similar and significantly more power than you are using. I'll have a word tomorrow and let you know.

Failing that as others have said, big capacity ATV diffs are handling upwards of 60-70hp these days so should be able to cope with what you are doing. I also agree with the comments about not needing an open diff, it's not needed for what you are doing and 80hp will just get lost through one wheel spinning on loose ground.

Couple of questions though - you mention long travel suspension, so I am guessing you are changing the geometry from what you've shown in the pictures?
Also the position of the output shaft seems a long way off the centre of the vehicle, which will make the rear driveshafts you are planning to use quite difficult, (or the propshaft from engine to differential will be at an extreme angle)

It is also possible I've misunderstood your plans, in which case feel free to tell me I'm talking rubbish!

[cerberarno]

Hi Thanks for help !

Mana gets same engine / same power
only change is variator power control giving ability of changing gear or staying in gear on press of a button
GP 800 is a basic variator
Mana has a fixed bolted sprocket since engine is bolted in the frame
GP has this wierd mounting because the engine is mounted on links & silent bloc & is able to move a bit from the arm
in my case I couldn't use the mana as a chain drive would be hard to find a solution for transmition

About the diff off center , is it a problem not to have both final shaft the same lenght ...?
Sorry !! I was talking long travel instead of quite enough travel for what I will do with the bug....
& shocks are planned to be swapped for better ones.

[Steve_D]

In order for your diff and drive shafts to work they need to sit as close to perfect alignment with the centre line through the wheel centres in all planes.

In order for the drive shafts to deal with the amount of suspension travel they will:-
First need to be as long as possible so the diff cannot be off centre.
Second they will most likely need to have CV joints to deal with the angles.

With the engine positioned as per your photos there is no way the output is going to mate with the position you require for the diff.

Steve

[Hunky Dory]

OK - I've asked about the diff I thought may be suitable, but unfortunately it will be no use to you as it is a very low volume bespoke part and over specification for what you need (So very expensive!)

Try finding diffs from any of the products below on Ebay or somewhere and you may get lucky but, In relation to the position of the diff vs the centre of the vehicle, Steve_D has answered you comprehensively and there's little for me to add, I'm afraid. The position you have the output shaft in will make driveshafts impossible, given your aim to have long travel suspension


Bombardier Commander
Polaris RZR / Ranger
Yamaha Rhino
Kawasaki Teryx

The top two are the highest power vehicles in those markets, so would be most likely to be useable for you.

[cerberarno]

Found that

Bombardier 400 max



Nice but maybe a bit weak for my purpose ?

[Hunky Dory]

I think the 400cc Bombardier ATVs use Rotax engines and they are only about 35-40hp IIRC, so probably not strong enough for your kart, I'm afraid.

[cerberarno]

But they are 300 kgs , made for heavy duty with loads capacity & trailling ability ...
& known to be very strong

[cerberarno]

Found that thing 300 €
I Will start with & see