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prop angles
flak monkey - 23/1/10 at 12:35 PM

What are the general rules on prop angles?

The outtput shaft of the gearbox is around 25mm lower than the diff, but is aligned lrft to righ. is this likely to be an issue?

Thanks,
David

blakep82 - 23/1/10 at 12:38 PM

as long as the gearbox output and diff input shafts/flanges are parallel then you should be fine

i think thats the general thing

[Edited on 23/1/10 by blakep82]

matt_claydon - 23/1/10 at 12:53 PM

They must be parallel, that's very important. It's desirable to have an offset though as it distributes wear in the joints.

aitch - 23/1/10 at 01:20 PM

parallel and offset at the same time ??
how does that work?

surely either perfectly in line with no misalignment and the uj's are just there to take up movement in bushes etc, or its beneficial to have an angle in each uj for even wear?

and if its with a small angle in each uj why would it matter if the were in the same plane, i,e, diff and output shafts parallell?

aitch

blakep82 - 23/1/10 at 03:06 PM

quote:
Originally posted by aitch
parallel and offset at the same time ??
how does that work?

surely either perfectly in line with no misalignment and the uj's are just there to take up movement in bushes etc, or its beneficial to have an angle in each uj for even wear?

and if its with a small angle in each uj why would it matter if the were in the same plane, i,e, diff and output shafts parallell?

aitch


it works perfectly well,
l
..........l
^ the 2 lines are parallel and offset at the same time (ignore the dots)

if the output and inputs are not parallel you can get some kind of cyclic vibration which destroys everything, and there's something about UJ wearing faster if they are perfectly inline. i can't remember how it works, but if you look at capri axles, you'll see the input is never in the centre of the axle. this means there's ALWAYS and offset, no matter where the axle is in its travel

[Edited on 23/1/10 by blakep82]

matt_claydon - 23/1/10 at 03:17 PM

Prop angles
Prop angles

Top shows a good installation, with shaftes parallel but offset. Middle is OK as well, but bottom is really bad and will cause bad vibration.

Basically, if a UJ is angled and the input speed is constant, the output speed will fluctuate during each revolution. By having an equal and opposite angle at the other end of the prop you cancel this effect out. If making your own prop be careful how you fit the UJs as they have to be phased correctly with respect to each other for this to work (90 deg out if I remember correctly).

If the shaft is perfectly straight, the same point on the UJ bearings will always be loaded. If you have an angle in the UJs then throughout each rotation the bearings are constantly moving and spreading the wear over more of their surfaces.

[Edited on 23/1/10 by matt_claydon]

Richard Quinn - 23/1/10 at 03:18 PM

Why?
Sorry - That wasn't very clear. Why is it such an issue on cars that only cover a couple of k miles per year and are normally stripped and checked every couple of weeks.
I have a 2 piece prop but the faces on the joints are not quite parallel (engine mounted on a slight angle). There is no noticeable vibration even though my engine is solidly mounted.

[Edited on 23/1/10 by Richard Quinn]

Peteff - 23/1/10 at 03:20 PM

If the bearings are in line the rollers stay static and wear a flat on them instead of rotating and evening out any wear. It will probably not matter too much in a low mileage situation like a kit car but it does happen.

matt_claydon - 23/1/10 at 03:22 PM

This video has some good backgound info to understand how UJs operate.

http://www.youtube.com/watch?v=xgQgm3GwaFs

3:15 onwards specifically


[Edited on 23/1/10 by matt_claydon]

matt_claydon - 23/1/10 at 03:30 PM

quote:
Originally posted by Richard Quinn
Why?
Sorry - That wasn't very clear. Why is it such an issue on cars that only cover a couple of k miles per year and are normally stripped and checked every couple of weeks.
I have a 2 piece prop but the faces on the joints are not quite parallel (engine mounted on a slight angle). There is no noticeable vibration even though my engine is solidly mounted.

[Edited on 23/1/10 by Richard Quinn]


Prop failures are very rare on production cars. They seem quite common on kit cars. Coincidence?

The amount of vibration is related to how mismatched the angles are. If you're only a bit out the effect is probably very small.

Richard Quinn - 23/1/10 at 03:37 PM

Possibly, but there are also a lot of cut & shut propshafts used on kits.
Don't get me wrong, I'm not saying that it doesn't matter but it's not ideal. There again, a lot of the things we do , use, make fit etc are not ideal either.

omega 24 v6 - 23/1/10 at 03:48 PM

good video BUT given the home made nature of our cars how close do we think we can get to parrallel. Especially cars that are already built and may be out of line. I'm currently looking at mine for this very reason as I have a slight vibration ( could be from not using hubcentric wheel spacers though)
How many mm over say 600 of parrallel length would be acceptable
i.e. in the car a vertical staight edge on the prop flange and the gearbox tailshaft face 300mm above and below the centreline of each.
So how far out would be acceptable???
If you have a live axle it will to some degree possibly rotate as it rises and falls
so again an imbalance.
If you need to rotate your axle to align it parralel the the shock mounts will also be rotated ( bolts running from front to rear) and hence a strain on the bolts/bushes.

Wish I had really taken more care of this during the build

So what's the group collective on how far out is acceptable.??

aitch - 23/1/10 at 03:49 PM

quote:
Originally posted by matt_claydon
Prop angles
Prop angles

Top shows a good installation, with shaftes parallel but offset. Middle is OK as well, but bottom is really bad and will cause bad vibration.

Basically, if a UJ is angled and the input speed is constant, the output speed will fluctuate during each revolution. By having an equal and opposite angle at the other end of the prop you cancel this effect out. If making your own prop be careful how you fit the UJs as they have to be phased correctly with respect to each other for this to work (90 deg out if I remember correctly).

If the shaft is perfectly straight, the same point on the UJ bearings will always be loaded. If you have an angle in the UJs then throughout each rotation the bearings are constantly moving and spreading the wear over more of their surfaces.

[Edited on 23/1/10 by matt_claydon]


thanks it now makes sense to me, its not that i wint take on board the knowledge of those who know more (of which there are many) but just to be told "do it this way" i want and need to know why, i then remmber what and why and to apply the same lessons elsewhere.

in essence there should be 2 angled uj's with the same angle and phased so that the fluctuating speed created by the first is then cancelled out by the second

simples "click"

and thanks

aitch

omega 24 v6 - 23/1/10 at 03:54 PM

So we are also now saying ( from pic2) that the faces do not need to be parrallel as long as the 2 angle are the same??
YES or NO

TGR-ECOSSE - 23/1/10 at 04:04 PM

You should find all the info you need here Linky

Btw flak monkey if you type propshaft angles into the search box you will find more info

[Edited on 23/1/10 by TGR-ECOSSE]

aitch - 23/1/10 at 04:06 PM

quote:
Originally posted by omega 24 v6
So we are also now saying ( from pic2) that the faces do not need to be parrallel as long as the 2 angle are the same??
YES or NO


YES and the UJ's whould be rotated on the shaft so that the input and output speeds are the same

but just looked at the youtube and maybe we should all have thompson couplings on prop shafts and drive shafts

aitch

Bluemoon - 23/1/10 at 05:19 PM

From memory best keep diff flange and gearbox flange parrell. The prop should be run at slight angle (keeping flanges parrell, both horizontally and verticaly), the maxium angle is 1degree (I think It maybe 0.5)... A slight angle is required to work the UJ bearings slightly. The angle gives you some idea on how accurately we should align the flanges up to (<0.1degree???) I did the best I could.

It is possible to run without the flanges parrell (can't remember the details) but this needs to bet set up carefully to use the correct angles. I assume this is what the BEC two piece props are setup like?

Do your home work on this and don't assume we all know what we are talking about! The low-millage get out is not the answer with a prop, it may let go with no warning, and consequences don't bear thinking about.

Dan

PS double check, don't assume my angles are correct (U2U if you want me to check my build notebook).


[Edited on 23/1/10 by Bluemoon]

flak monkey - 23/1/10 at 05:50 PM

Thanks for the replies guys. I have made sure the gearbox and diff are as parallel as I can make them.

When the pinto was installed the engine was at an angle to clear the nose and there wasnt any noticable vibration, though ibviously it was far from perfect. The new install should be much better I hope.

Now I need to speak to Bailey Morris about shortening my existing prop by about 2.25"

David

Breaker - 24/1/10 at 08:11 PM

My MK kit was also supplied with BEC-cradle. But the engine is also not parallel to the diff when I will install it and I'm also afraid this will cause vibration.

Apparently (Linky Linky) if it is not possible to get the gearbox and diff parallel you can compensate this with rotating one of the UJ's. The angle of rotating this UJ is defined by the "misalignment".

I think I will put my bike engine in the car with the supplied cradle and do some measurements which I will send to Bailey Morris. If they can compensate this misalignment I will keep the cradle. If not, I will have to rebuild the cradle and engine supports.