Rotoflex couplings - Diameter

[Seveneer]

Hello
I tried to replace my Rotoflex with leaving the steel bad on, as recommended by the manual. But I find that the diam with the band is too small to fit the shaft. On Pegasus Racing, I see that the Rotoflex should have a diameter of 3.78" or 96mm. But when I measure the distance between two bolts on the Rotoflex, I find only 81mm, which, if my geometry is right, means a diameter of 93mm. So, the Rotoflex with steel band does not match the shaft. I have to relieve the steel band and use a hose clamp to adjust the Rotoflex to match the shaft. This makes the assembly process much more difficult. Can anyone explain this annoying difference ? Are my Rotoflex purchased from two different sources defective ?

[stugilmour]

Seveneer, have not done the job myself as I have CV's, but this recent thread in 'For Sale' looks relevant

elan-for-sale-f2/nearly-new-elan-driveshaft-doughnuts-and-bolts-t23439.html

HTH

[nebogipfel]

Hello
I tried to replace my Rotoflex with leaving the steel bad on, as recommended by the manual. But I find that the diam with the band is too small to fit the shaft. On Pegasus Racing, I see that the Rotoflex should have a diameter of 3.78" or 96mm. But when I measure the distance between two bolts on the Rotoflex, I find only 81mm, which, if my geometry is right, means a diameter of 93mm. So, the Rotoflex with steel band does not match the shaft. I have to relieve the steel band and use a hose clamp to adjust the Rotoflex to match the shaft. This makes the assembly process much more difficult. Can anyone explain this annoying difference ? Are my Rotoflex purchased from two different sources defective ?

It's quite a few years since I last fitted rotoflex coupling but I dont think the dimensions are partucularly accurate with the band on, it's just better than not having it on at all. The benefit of jubilee style clips is they give you some adjustment. It was never a job I enjoyed and often involved quite a bit of fiddling, levering and maneuvering

[reb53]

The last one I replaced didn't line up exactly either.

Having said that, all my bolts are half an inch longer than necessary with the extra length having a taper on it which makes it easy to tap the bolt home without destroying the thread.

Cheers
Ralph.

[billwill]

You don't really need those modified bolts; just fit the Rotoflexes by my technique.

See:
elan-f14/replacing-the-doughnuts-t16456.html

[65 Lotus]

Here's the deal with the diameter mis-match. I went through all this a while back when I got my Elan.

The early Elans (of which I have one) did have Rotoflex couplings with a larger diameter than the later ones. The large diameter couplings are no longer in production. It's been a while so the details are fuzzy, but I know that's the case.

Of course what you want is to have the coupling in compression most of the time and relieved to the point of zero stretch upon max flex. I contacted Trelleborg and discussed the issue and they confirmed the larger ones were out of production. When I brought up the issue that, now they were not in an optimal compressive state in service and were probably stretching and therefore subject to premature cracking, his response was, "Well, you don't really have much of a choice now, do you?" That pretty much ended the conversation.

I do the same thing you're doing with the adjustable steel bands. A benefit of doing it that way is that it allows you to fine tune the diameter so the bolts just slip in perfectly. Just keep the couplings inspected for cracks and replace on condition. It's all you can do unless you want to make some drastic changes.