Lotus Elan

Prop orientation

PostPost by: worzel » Wed May 02, 2012 11:38 am

Hi

Possibly an obscure question but here goes.

How critical is the prop alignment on a car? By alignment I mean does any difference in height matter (measured from the ground/flat surface) between the nose of the diff and the output of the box? If I'm not clear as to what I'm asking suppose the prop to ground distance at the gearbox end was say 12 inch and at the diff end was 13 inch ie the prop was running upwards would it matter or would the uj's take care of that?

John
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PostPost by: garyeanderson » Wed May 02, 2012 12:54 pm

The basics are that the crankshaft (transmission output shaft) and pinion of the differential should be in parallel planes. That is the angles output and input equal. There is so much writen do yourself a favor and read what has been written before.
http://www.google.com/search?q=u+joint+ ... sxL7-9W2Eg

http://www.google.com/images?q=u%20join ... sult_group

Its better written and said than I can.

Gary
Last edited by Guest on Wed May 02, 2012 3:14 pm, edited 1 time in total.
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PostPost by: elj221c » Wed May 02, 2012 12:57 pm

I see now that Gary has beaten me to it!

The post I wrote before I realised:-

I can't remember where exactly but this has been discussed before.

Props are seldom in perfect alighnment and I believe it is not disirable either although I can't remember why. This picture shows that mine was and will be out horizontally as well as vertically.
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PostPost by: stugilmour » Wed May 02, 2012 1:10 pm

Wow, two guys beat me!

John, I am not an expert on this one, but when we discussed prop shafts a while ago my understanding was that it is OK for the shaft to be at an angle. The issue is to make sure the flange faces at each end are parallel to one another, i.e. the transmission and diff are both level and the flange faces are vertical or at the same angle to vertical. With this configuration the input and output of the shaft rotate at the same angular velocities with the two universals 90 degrees out of phase, although the rotational speed of the prop shaft is actually not constant.

Here is a reference to the Hooke Joint math I found interesting...

http://en.wikipedia.org/wiki/Universal_joint

I set mine up with a slight angle to the drive shaft but modified the height of my MT75 transmission mount to make sure the flanges were both the same angle, and no vibration issues. In my case, the Spyder supplied mounts (both engine mounts & transmission mount) required slight adjustment so the bonnet clearance could be sorted.

I think this is the thread where I got clued in to the Hooke joint by Gary, Gerry M and others...

elan-plus-f13/spyder-chassis-body-spacing-again-t21419.html

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PostPost by: ardee_selby » Wed May 02, 2012 3:03 pm

elj221c wrote: Props are seldom in perfect alighnment and I believe it is not disirable either although I can't remember why


stugilmour wrote: John, I am not an expert on this one, but when we discussed prop shafts a while ago my understanding was that it is OK for the shaft to be at an angle.


As I understand it you need a "degree" of articulation to induce rotation of the U/J bearings, whereas if the same axis is shared the bearings would be static.

Cheers - Richard
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PostPost by: worzel » Wed May 02, 2012 3:16 pm

Hi

Thanks to all the quick respondents- I take the point about the "offset" of a prop being essential but just wondered if an offset in a different plane would matter- I'm trying to track down an elusive noise and am reaching the "desperate" stage.

Regards

John
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PostPost by: frearther » Wed May 02, 2012 10:00 pm

worzel wrote:Hi

Thanks to all the quick respondents- I take the point about the "offset" of a prop being essential but just wondered if an offset in a different plane would matter- I'm trying to track down an elusive noise and am reaching the "desperate" stage.

Regards

John


I solved that by getting a louder muffler (I THINK that was a joke). :) :)

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