Lotus Elan

POLYURETHANE rotoflex ( Donuts ) anyone heard of these ?

PostPost by: barrydoran » Fri Dec 09, 2005 10:15 am


there's a pair of POLYURETHANE donits on Ebay, the are supposed to be suitable for Lotus Elans.

I'v enever heard of them before, has anybody else ?

Would they flex enough ?

Here's the link.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... Track=true
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PostPost by: cliveyboy » Fri Dec 09, 2005 10:37 am

They look like industrial drive couplings used on large motors etc.
I would want to see the manufacturers specification for them before using them.
These type of couplings are designed for straight connection or very slight misalignments.
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PostPost by: rgh0 » Fri Dec 09, 2005 11:00 am

I agree with Clive. They will not accomodate the angular and axial deflections required in a suspension. They are designed for connecting motors to fixed and properly aligned loads and to accomodate only slight misalignment.

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PostPost by: iain.hamlton » Fri Dec 09, 2005 4:20 pm

It looks a bit like the coupling used on certain rangerovers and discoveries instead of back UJ on the propshaft

http://www.roversnorth.com/RRD04/RRD04_ ... page38.htm

(bottom picture)

agree with Clive and Rohan: different application altogether

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PostPost by: type26owner » Fri Dec 09, 2005 5:38 pm

I haven't done any polyurethane engineering in awhile but from what I can remember it's best to treat it like it's concrete. It's great for compressive loads but in tension and torque you can run into trouble right away. This the safest and most conservative approach.

Just because it's available does not mean it's a good idea. :(
Last edited by type26owner on Sat Dec 10, 2005 4:44 pm, edited 1 time in total.
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PostPost by: Rob_LaMoreaux » Sat Dec 10, 2005 4:08 pm

I suspect these are more for something like our Volvo with IRS, where there is a rubber donut to connect the transmission to the driveshaft. The only deflection in this instance is the twist of the engine mounts. I wouldn't want to risk these in my car. Polyurethane is too stiff and brittle for the rubber donuts in an Elan in my opinion.

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PostPost by: type26owner » Sat Dec 10, 2005 4:55 pm

Hey Rob,
Actually Monothane can be range from ShoreA 10 to 100 in hardness. Monothane was my favorite choice since it use to be cheap. Too bad their website sucks now and all the technical info has disappeared.

These donuts could very well possibly be an improvement from the rubber ones. There isn't data provided to make that determination though only vague claims.

It's the bonding strength of the urethane to the metal inserts that makes me nervous. Are those indentations for strain relief? Looks likely, in which case these might be well engineered. The bubble is suspect though as a stress riser.
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