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Prop angle (again, but with a twist)?
Nickp - 14/7/15 at 03:00 PM

Hi,

I'm looking to finalise my engine position now I've got the bodywork to clear the BMW 6 pot. I've currently got the engine and box in line with the chassis but offset to the passenger side slightly (15-20mm) to clear the tunnel on the drivers side. I've read a few posts on here and it seems this is a good scenario and makes the UJs work and prevent premature wear (brinelling?). Thing is though, I'll be using the original rubber donut between the BMW gearbox and the prop and then a Ford UJ at the back. So question is should I angle the engine/box so the front donut runs straight and the rear UJ at a slight angle? Seems to make sense to me but I'm happy to take any advice/experience on board. Or are the amounts I'm talking about too small to make a difference?

Thanks in advance
Nick

Ivan - 14/7/15 at 03:17 PM

I am no expert on this but is it common practice to use UJ and Donuts at opposing ends of a prop-shaft - I would think that the variable speed that the UJ gives would cause all sorts of problems to the donut.

Having the one aligned with the engine and the other out of alignment would I think exacerbate vibration issues.

I think you need to seriously research what you intend (I know that this is what you are doing and I hope you find an expert on here - but if you don't then take the issue further with some professionals in the field)

Nickp - 14/7/15 at 03:23 PM

quote:
Originally posted by Ivan
I am no expert on this but is it common practice to use UJ and Donuts at opposing ends of a prop-shaft - I would think that the variable speed that the UJ gives would cause all sorts of problems to the donut.

Having the one aligned with the engine and the other out of alignment would I think exacerbate vibration issues.

I think you need to seriously research what you intend (I know that this is what you are doing and I hope you find an expert on here - but if you don't then take the issue further with some professionals in the field)


Donut front and UJ rear is what the BMW had as std I believe. But it did have a bearing carrier in the centre IIRC, which would make a difference I guess?

These guys are just down the road from me, I think I'll pop in for a chat - http://www.propshafts-greno.co.uk/


[Edited on 14/7/15 by Nickp]

blakep82 - 14/7/15 at 03:47 PM

Bmw props have a donut at the gearbox, straight to a a centre bearing, then 2 offset UJs don't they?

I wonder why no one uses CV joints on prop shafts?

SteveWallace - 14/7/15 at 04:10 PM

I did away with the BMW rubber donut on mine and got a purpose made prop shaft and adaptor plate for the BMW gear box from D&F in Leeds. It cost about £200 delivered, which was a lot cheaper than getting a new left leg if something that wasn't designed to be there had failed and come through the transmission tunnel.

This one is someone elses on here, but is exactly what I have. The three countersunk allen bolts attach to the output of the gearbox and the 6 bolts to the propshaft. If you already have a propshaft then D&F will probably sell you an adaptor separately

propshaft not mine
propshaft not mine

Nickp - 14/7/15 at 04:30 PM

quote:
Originally posted by SteveWallace
I did away with the BMW rubber donut on mine and got a purpose made prop shaft and adaptor plate for the BMW gear box from D&F in Leeds. It cost about £200 delivered, which was a lot cheaper than getting a new left leg if something that wasn't designed to be there had failed and come through the transmission tunnel.

This one is someone elses on here, but is exactly what I have. The three countersunk allen bolts attach to the output of the gearbox and the 6 bolts to the propshaft. If you already have a propshaft then D&F will probably sell you an adaptor separately

propshaft not mine
propshaft not mine


That looks just the job Steve

Ivan - 14/7/15 at 04:30 PM

quote:
Originally posted by blakep82

I wonder why no one uses CV joints on prop shafts?


A good question - a friend of mine used CV joints on his Cobra prop shaft (about 400 HP) and said it made a noticeable improvement to vibration. Never had any problems with it either.

Could well be the answer to the OP's problem.

[Edited on 14/7/15 by Ivan]

Nickp - 14/7/15 at 05:03 PM

Ok, so it looks like the best bet is to do away with the rubber, get an adaptor and a 2 UJ prop made up.
I'll carry on with the plan of running the engine in-line but offset by about 20mm. With a prop length of about 80cm this should give me a prop angle of about 1.5deg, this sound OK?

feckn7 - 14/7/15 at 09:33 PM

the rubber donuts don't like running at angles - keep the shaft straight. Use a centre bearing cv joint and then to a uj at the rear.

I'm running a uj front to centre cv to uj rear with quite a marked change in direction and angle between the front and rear shafts (with the uj's phased correctly) and have no noticeable vibration - as far as the uj's are concerned the shaft(s) between them is straight.

I used a Holden Commodore centre CV - Opel/Vauxhall Omega in UK?

I think Audis use CV joints in their drive shafts (on the quattros)

David