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SU Throttle Spindles


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​I have some SU carbs that I would like to put in some new bushes,, or the larger spindles.

​Has anybody done this repair and where did you get the necessary reamers? The Moss one seems to be an eye watering amount!

​It seems an easy job to do if you have a couple of good reamers. Seen various Utube videos that make a lot of sense.

​I don't have a good machine shop that I would give this job too.

​Does anybody have these that I could either purchase or borrow please?

John

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Indeed its an easy job but requires some precision.

Anyway a not perfect job in most cases will be much better

than the carb was before overhaul.

 

I used an adjustable reamer.

It has a thread in the front for the adjusting nuts.

For that thread I made a shaft 10cm long with inside the thread of the reamer

and outside the diametre for the carb housing.

It must be fitted to the front of the reamer and acts as a guide

to bring both bearings for the shaft in line.

 

Quickly done, cheap and very helpfull..

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Just been to look and you are both right the spindles are pretty worn, and I was surprised to see that the non operating end is much more worn, but the good part of the spindle does still have a lot of play, the oversize spindle and ream would be a perfect repair. Anybody got a reamer to lend?

John

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I just measured the existing spindle and its 5/16" or 0.310" and the oversize spindles at 0.010" larger, so a reamer that is 0.320" I guess, or perhaps a little smaller to get a good air tight fit.

 

John

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Hi John.

 

Hi John,

5/16 is 0.3125" getting a standard reamer +0.010" on that would be difficult and expensive I would have thought.

Getting a nice airtight fit is not what you want as the spindle needs to be free to move (yet, let little air in)

 

Have you tried a NEW standard size spindle in the existing holes. There should be a very small amount of play. Maybe your old spindle is still worn at the good end.

 

Do/did you have extra springs on the butterfly to help return the throttle.

These springs cause considerable wear to one surface of the spindle and bore.

The original springs are radial and impart no or very little force onto the contact faces of the spindle/bore.

 

As mentioned it may be cheaper to get Burlen to do the job - give them a call.

 

Roger

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Just been to look and you are both right the spindles are pretty worn, and I was surprised to see that the non operating end is much more worn, but the good part of the spindle does still have a lot of play, the oversize spindle and ream would be a perfect repair. Anybody got a reamer to lend?

John

 

This is the reamer that might fit:

 

http://www.tracytools.com/straight-taper-reamers/5-16-11-32-adjustable-reamer

 

It is 8GBP, not worth to talk much longer.

 

The required tip as described above hopefully can be made by a clubmate

Looks like this:

 

post-13092-0-99015500-1512134303_thumb.jpg

 

post-13092-0-50436600-1512134319_thumb.jpg

 

1.) The bore is always a little bit our of round, so better fit a new standard spindle

than to do nothing! But that is always a "quick and dirty" job!

 

2.) A non adjustable reamer can not do the job because we need the bore

airtight and large enough that the spindle will not stick. That can be done best

by reaming to a smooth fit and try the spindle. If it sticks, a little bit more must be done.

This depends on how good the bores are in line and a fixed reamer never can give

that precise diametre to fulfill both requirements.

 

3.) Without the tip the reamer always will run into a wrong direction, although later you can guide

it with the second bore. But at that point most of the reaming is already done and the bore

points in the wrong direction.

 

Good luck with the work, did that several times and always ended with a happy TR owner!

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