Hi All

So I took the MK Indy to Le Mans last week, except I got to about 20K outside Alencon and my propshaft snapped!!! Thankfully I still have legs, but sadly my car is still in France and will be for a few weeks waiting for repatriation. I didn't get a great deal of chance to look at it at the side of the Autoroute but it's basically snapped along a weld on the front section of the prop I think. My conjecture is that the prop adaptor bolt worked its way loose (but not off) for reasons below, which induced significant vibration and the prop decided it wanted out.

So, to the issue. My car has a Fireblade engine, and as we all know they are installed at an angle. This however means that the prop installation is far from perfect: -


Prop Current

Basically I know you want a small angle at the diff to stop the rear UJ brinneling, and you also want the gearbox output and diff input to be in the same plane. However, because of the engine installation the input and output are out by quite a few degrees (can't measure at the moment, car's in France etc etc...)

What it should be like for ideal prop installation I believe is this: -


Prop-osed

So basically the engine and diff are parallel to each other (horizontally and vertically), the UJ's counter each other and everything runs smoothly.

It's always been a concern of mine that it's not ideal, and now I've seen the full consequences of what happens I'd like to look to how it can be improved. The misalignment is noticeable on part-throttle where you get the rattle ("they all do that sir".

Has anyone else engineered this problem out? Either by re-mounting the engine (will it fit? I guess there's a reason it's at an angle. Obviously cradle, manifold etc etc would need work), or even by re-mounting the diff to be in the same plane as the engine???

I'm not an engineer so all the above is just what I've read and learned, but would like to hear any suggestions - I can't be the only one that's not happy with how this is designed???

Thanks

I built my bec as in your second picture not an indy though. I've never been a fan of the angled engine.

It baffles me how more secondary locking devices are not used In the assembly of these parts. Maybe it's because in my line of work most critical parts are safetied. Along with the loctite and the lock washer I wirelocked every single bolt and nut from the engine output to the diff. These engines are high revving and usually rigid mounted. All this activity and vibration is a recipe for stuff coming loose.

Glad the legs are in one piece these failures can be incredibly nasty.

In reality you have to be a long way out before it causes any noticable problems, especially if you have a TRT prop (which is highly recommended). Also remember that it is quite feasible to have non-parallel drive faces and still have the propshaft in phase as long as the sum of the angles is 0 degrees.

More likely cause of the prop adaptor coming loose is the sprocket adaptor being too thick. The nut shouldn't be torqued onto the adaptor, but onto the shoulder on the shaft, stopping any torque transfer into the nut.

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Originally posted by sdh2903
I built my bec as in your second picture not an indy though. I've never been a fan of the angled engine.

It baffles me how more secondary locking devices are not used In the assembly of these parts. Maybe it's because in my line of work most critical parts are safetied. Along with the loctite and the lock washer I wirelocked every single bolt and nut from the engine output to the diff. These engines are high revving and usually rigid mounted. All this activity and vibration is a recipe for stuff coming loose.

Glad the legs are in one piece these failures can be incredibly nasty.

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Originally posted by gingerprince
So basically the engine and diff are parallel to each other (horizontally and vertically), the UJ's counter each other and everything runs smoothly.

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I'll just leave this here...

Thats a very interesting video! Never realised you get elliptical rotation when they are angled. Scary!

Guess why they invented constant velocity joints

Thank you for posting that video. I learnt alot.

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especially if you have a TRT prop (which is highly recommended)

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More likely cause of the prop adaptor coming loose is the sprocket adaptor being too thick. The nut shouldn't be torqued onto the adaptor, but onto the shoulder on the shaft, stopping any torque transfer into the nut.

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Also remember that it is quite feasible to have non-parallel drive faces and still have the propshaft in phase as long as the sum of the angles is 0 degrees

and

You don't have to have the angles equal and opposite, i.e. so engine and diff are parallel. The UJ velocity cancellation still works if the angles are equal and not opposite e.g. if you needed a total angle of 10 degrees, and you had two UJs working at 5 degrees each they would cancel. This might be easier to arrange in your case.

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I'll just leave this here...

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Originally posted by gingerprince
Are these 2 saying the same thing? I've read a little about "broken-back" configurations, which generally talk about vertical alignment but is this essentially the same thing. So in theory if I move my centre bearing to the right and try to make the angle between centre and rear be the same as between centre and front then this will cancel out?

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UJ angles

The full consequencies of what can happen, quite amply demonstrated with my reverse gearbox failure at Combe, with the output shaft shearing off. The car was destroyed, the scars on my legs are still there after 8 years. The combination of a Hayabusa, 10" slicks and all that goes with it, not a happy one.

All bike engines are at an angle, the Hayabusa moreso than others, it's a size thing. With the smaller engines and their stacked gearbox units, the sprocket output is now becoming less of an offset problem. The R1 went in the Westfield, with the engine gearbox output pretty much in a straight line.

Many hours racing were 'safely' carried out with a Bailey TRT, Centre Bearing, no reversing sprocketry (etc.), despite the angles on the engines not being ideal. This is what I'd recommend.

So I believe my car is based on an early Indy chassis. My centre bearing is floor-mounted, whilst I see photos of newer Indy's with the centre bearing mounted sideways on to the passenger tunnel. Was this a design change to improve alignment?