Lotus Elan

Elan drive shaft coupling PCD for S1

PostPost by: rgh0 » Mon Nov 03, 2008 9:07 am

The S1 Elan - at least the early ones had a different pitch circle diameter (PCD) for the donut coupling spider bolts from the later S2/S3/S4 cars.

I am having a discussion with a friend on what the difference was. The only reference I can find in in the Robinshaw and Ross book "The original Lotus Elan" which is a little vague but implies it was about 1/4 inch larger.

The later cars PCD was 95mm which implies the S1 PCD was around 100mm.

Does anyone have a early S1 with original drive shafts and have they ever measured the donut spider PCD ?

cheers
Rohan
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PostPost by: paddy » Mon Nov 03, 2008 10:48 am

Hi,

I have some I can measure tonight.

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PostPost by: 65 Lotus » Mon Nov 03, 2008 12:23 pm

The PCD of the early Elan's rotoflex coupling is 4 inches, which unfortunately doesn't give the proper preload using the current batch of manufactured rotoflex couplings, but as an engineer at the factory told me a few years ago, "You don't really have much of a choice, now do you?"
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PostPost by: cocky » Mon Nov 03, 2008 1:04 pm

I'm just at the end of the process of converting my donuts to CVs. I had a problem when I put my S1 together years ago as I bought some heavy duty diff output shafts which had the later dimension so I had to mix the two sizes (late and early) when fitting the inner donuts (which made a difficult job even more difficult). I searched for an answer to the early PCD question but I couldn't find one. For the CV conversion I had to make adaptor plates with two different dimensions. I used the 96mm dimension for the late type diff output shaft. I found through a little bit of trial and error on the mill that 100.2mm fitted my early type spiders. I tried 100mm but it wasn't right. The mill was accurate as the 96mm drillings fitted the later type spiders perfectly.
Not sure when the change came about. I had a set of drive shafts from my 1967 +2 and they were the later dimension.
Hope this helps. I'll post the full story of the conversion when it is completed (hopefully later this week).
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PostPost by: Bill » Mon Nov 03, 2008 6:32 pm

The smaller dia. was on 26/0538 - late 63.

During the restro 11 years back I converted to the later larger size. I have a doner car - 65 S2. The front disk brake assembly was a smaller dia. than later cars as well, I also changed those to the larger dia disks and calipers. I suspect both changes were done simutaniously at the factory.

The origional factory shop manual does not address the change or differences in any way.

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PostPost by: types26/36 » Mon Nov 03, 2008 9:20 pm

The S1 discs/shafts were fitted into the early S2 cars (S1.5) at least untill 26/3944 and a probably quite a few later.
Here is a pic of some new S1/S2 (early) disc's which I bought to fit to my early S2 although I also made up CV shafts to suit
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S1 AND EARLY S2 DISC.jpg and
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PostPost by: paddy » Mon Nov 03, 2008 11:32 pm

Hi,

Some measurements with a micrometer, centre-to-centre between holes in the spider:

"standard" (ie late) spider: 83.0 mm
early spider: 86.8 mm

PCD = centre-centre distance / sin(60) gives

standard: 95.84 mm
early: 100.23 mm

which matches the empirical 100.2 reported above and means it is *not* 4" (101.6 mm).

On the subject of preload and compatibility with later-type donuts, I had always assumed that in fact the nominal donut PCD didn't change, but the smaller diameter was adopted to increase the preload - but that's just a guess.

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PostPost by: rgh0 » Tue Nov 04, 2008 5:03 am

Thanks guys for the quick responses - It never ceases to amaze me that such an obscure question can be answered so quickly

My summary of the data is

late PCD 95.8 +/- 0.2mm
early PCD 100.2 +/- 0.2 mm

The tolerancing is my estimate from measuring up the 4 spare shafts and 4 spare disks I have plus the data given.

The change over from early to late was during the early S2 production and after chassis number 26 / 3944

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PostPost by: jpt » Sun Dec 18, 2011 10:25 pm

In a recent post, Gary noted that the early PCD driveshafts were supplied for the first 1000 or so Elans, up to around 26/4027.
http://www.lotuselan.net/forums/elan-f14/rear-axle-t24218.html

I just measured the driveshafts that were on my Elan, 26/4203, when I bought it in 1981 and confirmed that they are the late (95.8 mm) ones, so this provides more definition about the changeover point.

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PostPost by: garyeanderson » Sun Dec 18, 2011 11:01 pm

4027 is Peter's phone number, oops 4109 is the change point according to the Ross and Robinshaw book. Oh well, more misinformation as it becomes available :)

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PostPost by: Bill » Mon Dec 19, 2011 2:25 am

Rohan

If I were to order a set of your driveshafts for 26/0538 (late 63 production) which I intend to do in the near future, and considering the fact that I may have installed later shafts from my doner car during the last rebuild many years ago which made it work ay the time - I assume that you will need the PCD measurements to confirm correct supply. It has been so long that I am not sure of the spider size except that I changed the shafts to my S2 spares.

I will be lifting it thu the winter (new MaxJax 2 post) for maintenance and can check it out.

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PostPost by: bob_rich » Tue Feb 14, 2012 9:10 pm

Hi Rohan

Looks like you have enough info but I did a scan on a 5mm square grid on the disc of my car
+2 Dec 1973 +2S130. Hope it helps and not adds 2 confusion!!

cheers

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rear_disk_+2S130.jpg and
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