Curing my rattling throttle bodies

[Pete.]

With my bike approaching 80k miles my throttle bodies have developed an embarrassingly loud rattle. I was aware that it's a common complaint and also aware of the 'ticker killer' fitting that's supposed to shut them up but I don't like the idea of pre-loading the throttle shaft axially nor the fact that it basically prevents the symptoms rather than curing the problem plus that thing only works on the right hand throttle body and my left hand one is just as noisy as the right.

This week one of my stick coils has failed (which of course has made the bike run rough, and rattle more) so whilst I wait for the replacement coil to turn up I thought I would take a look at the reason why the throttle bodies were so noisy, so I remove the left hand one and stripped it down.

It turns out that the cause is a worn out bearing bush. Each end of the shaft runs on a split oilite bush 8mm Id and 10mm OD. One is 12mm long the other 8.6mm, the shorter one being the TPS sensor end. I pulled out both of them by screwing in a M9 taper tap and drifting it out with a thin rod and small hammer.

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I measured the throttle shaft and found between 0.1 and 0.15mm wear in it - not a lot. The bushes however were much more worn. Actually the short one wasn't bad at all but the long one at the quadrant end was worse and a bit oval too. Removing the bushes essentially trashed them so I turned a couple of new ones from Acetal. This engineering plastic is very chemically inert and doesn't absorb moisture like for instance nylon. I turned the OD and reamed the ID, but I had to ream it again after I pressed in the bushes because the thin walls were too flexible.

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After that I re-assembled the throttle body and there's no discernible radial play plus the action is very smooth.

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After this I had my dinner and got to thinking that the bushes might be available as a standard part - and they are (at least the 12mm long one is). Cheap too so I have ordered some. I was intending to do the right hand throttle body with the same bushes but now I have found these off-the shelf parts I'm going to wait and use those instead.

https://www.bearingboys.co.uk/Split-Bea ... hes-1024-c

I'll report back when I have fitted the new bushes.

Pete.

[nab 301]

I remember replacing bearings on a set of DCOE Weber carbs I had in a Modified Imp back in the 80's.... , I don't think my skills then or now would match yours ! Eventually I saved up enough for a set of new ones.
I hope it all works out with the Tb's !

[Pete.]

Well, curiosity got the better of me plus I needed to know the sizes of the RH throttle body bushes so I've done the other throttle body and the noise is all gone. The RH bushes are both 12mm long so I'll order 3off 12mm and 1off 8mm bushes. The size I gave in the opening post was incorrect the short one is 8.6mm not 7.6 - so a 8mm bush will do just fine.

These are the four bushes that are required:

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If anyone is reading this and planning to do the same, you need the bushes above from bearing boys, a 9mm tap to pull the bushes out (you might get away with an easy-out but they tend to spread the part and since it's a split bush you might only make it tighter). I put the throttle blades back in with high strength threadlock. The originals are staked on the back and this would not be a bad idea but you need to be very careful not to drive the screws back through the brass threads and strip them.

[SP250]

Nice job that Pete and thanks for the bush details too.
Is it on an 11S or a 12S?

[Pete.]

It's my 1100S twin spark from 2004.

[KTM AL]

Hi Pete
Would it be ok to post this on the UKGSER.COM web site? It looks like the 1100S has the same throttle bodies as my 1150GS. I'm just about to make a order from Bearing Boys. Cheers

[Pete.]

Post away AL, if I didn't want people to know it I would not have put it here.

BTW take great care when staking those screws. I put them in with high-strength threadlock and staked them, you do not want those coming loose and getting sucked into the cylinders.

[KTM AL]

Cheers Pete
Did the end cap on the right hand throttle body come off easily? Any tips ? Cheers Al