Roller Barrels - Help for an Elise S1 owner

[I reply to every thread]

Request over on SELOC

 

"Late last year I bought an S1 Elise race car. The car has a Rover K series engine in what is basically the original Caterham R500 specification, including fancy looking roller barrel throttle bodies.

 

Since buying the car due to various reasons I've had little running in it. The most common problem with the car itself has been the throttle sticking open. This of course is "interesting" on track.

 

First time this happened, I examined the throttle cable, and it turned out that there were in fact 2 cables joined together within a heat shielded sheath and it appeared that they had separated, which I believed was causing the binding. I replaced these cables, and in my garage testing all performed as expected. Next time on track, end of session one and the sticking throttle returned. On examining my new cable installation, I found a tiny squeeze in the cable outer which I concluded could have been the problem, and this led to my purchase of a super duper teflon lined pre stretched high temp resistant cable. I duly fitted this with extreme care to avoid any chance of pinching the sheath and ensured the routing was as good as possible. The cable essentially turns through 2 gentle 90 degree bends, and that is it. With this third cable in place I managed 1 session on this recent Saturday with no problem, and then each subsequent session for the rest of the weekend I ended with a sticking throttle despite believing the problem was fixed before going out each time.

 

The other relevant details are:

 

The return spring on the throttles is strong, and when cold the throttles snap shut instantly.

The return spring on the throttle pedal is strong.

The problem occurs both with revs being held at WOT and with revs being held in the 2000-4000 range at 0% throttle.

The problem appears mid to late on the track session.

The problem goes away when the engine has cooled down.

 

These last two characteristics suggest the problem is heat related.

 

I think I was wrong initially and that this is not cable related. I think I must have separated the two parts of the first cable when removing them, and the squeeze I found in the second cable I would now say was irrelevant. With the routing and the spec of the current cable I cannot understand how there is a problem with it (it did stretch somewhat more than you'd think a pre-streched cable would, but that is now fixed and is not causing the problem). The pedal box end is also all good.

 

So, my conclusion following some thought and useful discussion with the brains trust is that my problem is actually in the throttle bodies themselves where something is binding only when hot. Maybe a bush, maybe a worn guide. Who knows.

 

A bit of internet research this morning confirms that these very throttle bodies DO have a habit of binding, but I have yet to find any suggestions on what, if anything, can be done about it.

 

So, my question is, do any of you have any experience of whether there is an effective long term fix for such binding on roller barrels (replacement of bearings, worn parts, etc etc)? Is it maybe possible to strip them and grind down the barrel if that is the part that's binding? Or is it actually a design flaw and am I better off thinking about a different induction solution such as Jenveys?

 

Thanks for any suggestions and thoughts."

 

Thanks on his behalf

 

 

[RogNeedham]

AVES

 

I had a similar problem last year. Like your friend I looked at cables etc to no avail. About a week before the problem manifested itself I had over-filled the engine oil. In talking the problem through with local club members, I investigated how the roller barrels operated and noted that on opening the throttle (engine off) a black, sticky residue could be see on the roller.

 

It was suggested that this could be as a result of oil blowing back through the head. Whatever the cause, I cleaned it all up and car has been fine ever since

 

hope this is of use

Rog

[Tony Whitley]

+1

 

[simonpa]

I too had a sticky set.

Make sure they are clean and don't oil them - this can cause binding...

 

Graphite powder may help with non-sticking lubrication.

 

Cheers - Simon