Lotus Elan

Diff Position

PostPost by: William2 » Wed Jan 08, 2014 3:58 pm

I have just started dismantling my S4 chassis and noticed that the diff unit seems to be off centre to the right of the chassis by about 1". Any ideas why?? Also, having removed both Lotocones I noticed that the bolts holding them to the turrets have very shallow heads. Is there a reason for this?
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Elan Chassis Stripdown 022.JPG and
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PostPost by: TroonSprint » Wed Jan 08, 2014 5:28 pm

Not knowing anything about Elans when I started the rebuild, it surprised me too. My Spyder chassis shows exactly the same offset. It isn't in fact that the diff casing that is off centre, it's the drive flange is not central on the casing, due to the position of the crown wheel and pinion. I was going to post a photo but realised I have no idea how to do it, and there seem to be no help files. I pressed the Img button but that didn't help me at all. Anyone let me in on the secret?
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PostPost by: oldelanman » Wed Jan 08, 2014 5:55 pm

TroonSprint wrote:I was going to post a photo but realised I have no idea how to do it, and there seem to be no help files. I pressed the Img button but that didn't help me at all. Anyone let me in on the secret?
Mike


announcements-f32/tutorial-how-upload-photos-t27816.html?hilit=tutorial#p186541
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PostPost by: TroonSprint » Wed Jan 08, 2014 7:26 pm

Thanks Roger. I still don't know how to find those help articles. I tried searching suitable words but got nothing. Anyway, here's the photo I meant to show William. The camera is looking up the Spyder chassis from the engine bay.
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Offset Diff.jpg and
Offset drive flange in Spyder chassis.
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PostPost by: AHM » Wed Jan 08, 2014 7:49 pm

The diff is in the centre, so that the drive shafts are of equal length, angle etc. This means that the pinion and hence input shaft must be offset.

It is supposed to be like that - you would have a big problem if it was in the middle!

The output from the gearbox is also offset.
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PostPost by: oldelanman » Wed Jan 08, 2014 7:56 pm

William2 wrote:having removed both Lotocones I noticed that the bolts holding them to the turrets have very shallow heads. Is there a reason for this?


I can't see why thin bolt heads are necessary there - at least not with the original chassis set-up and standard diameter springs. Maybe it was thought necessary to avoid contact with the spring top plate as the rubber mount compressed but the plate will make contact with the vertical flanges of the seatbelt mounting plate before it gets to the bolt heads. This flange is around 13mm deep so even with a standard bolt head at around 7mm plus the lotocone baseplate at around 3mm thick the bolt head would not stand proud of the flange.
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Lotocone mount 015.jpg and
Standard bolt head
Lotocone mount 017.jpg and
Standard bolt head
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PostPost by: types26/36 » Wed Jan 08, 2014 8:13 pm

oldelanman wrote:
William2 wrote: the plate will make contact with the vertical flanges of the seatbelt mounting plate before it gets to the bolt heads.

Not sure it is relevant but I remember machining the heads thinner on standard bolts when I rebuilt my S2, its a long time ago but I'm sure there was a reason at the time :? ..... also the early cars did not have the seat belt mounting plate which came later so maybe that had something to do with it.
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PostPost by: robertverhey » Wed Jan 08, 2014 9:08 pm

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PostPost by: William2 » Thu Jan 09, 2014 10:48 am

Very interesting. This also means that various chassis drawings in books such as Brian's Bible are incorrect when showing from above that the diff flange is in the middle.
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PostPost by: oldelanman » Thu Jan 09, 2014 11:54 am

William2 wrote:Very interesting. This also means that various chassis drawings in books such as Brian's Bible are incorrect when showing from above that the diff flange is in the middle.


Which page in B B 's book is that incorrect drawing ?
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PostPost by: elj221c » Thu Jan 09, 2014 1:16 pm

Page 306 in the rear suspension chapter. It as Lotus drawing which appears in the same chapter of my manual, 36T327, Section D, page 2.

I've never noticed the incorrect drawing either in all those years.....

You could also look here. It seems that the shaft centres should be parellel but not on the same plane.

lotus-elan-f19/prop-orientation-t25151.html#p163497
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PostPost by: oldelanman » Thu Jan 09, 2014 1:46 pm

Aha thanks.....I was looking in the Chassis and Final Drive sections ! I've never noticed that before either.
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PostPost by: AHM » Thu Jan 09, 2014 2:16 pm

elj221c wrote: It seems that the shaft centres should be parellel but not on the same plane


If they are parallel the articulation angles will be equal and it is possible to balance the sine waves.

They aren't parallel, you wouldn't notice the difference, and there is little that can be adjusted even if for some strange reason someone might think they needed to.
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PostPost by: ricarbo » Fri Jan 24, 2014 9:07 pm

I always understood that prop shafts should never run in a straight line, but be arranged so that the joints work a little as they spin. This is because if they are perfectly straight they will vibrate more. If you look at other installations on cars and boats, you will find this is the universal arrangement. I imagine it is better for the joints to do a little work to spread the wear on them, too. So what you have is correct.
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