Throttle shaft

Russell Reay

Russell Reay

Well-known member
The red book cautions the need to install a new bushing to prevent air leakage if there is wear on the throttle shaft. I can't attach a video, but the free end of this shaft can be moved about 1/16 of an inch--maybe a hair more. Is that enough to cause air leakage of an amount that will affect performance?
 

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Russell Reay said:
The red book cautions the need to install a new bushing to prevent air leakage if there is wear on the throttle shaft. I can't attach a video, but the free end of this shaft can be moved about 1/16 of an inch--maybe a hair more. Is that enough to cause air leakage of an amount that will affect performance?
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I'll say no, but you could solder the shaft and file to fit if it bothers you.
 

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Y-Blockhead said:
Are you having idling issue? How much does the shaft move when in normal position? 1/16" seems excessive to me.
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This is a core I am rebuilding. With the shaft inserted all the way the slop is maybe 0.003-0.005" My only fear about a new shaft or new bushing is that the casting will be very hard to hold tight in a drill press, or hold tight in a vise for free-hand drilling.
 
Oversized replacement shaft if the bore is enlarged. Sideways not so much, have seen Teflon tape used there. Or try some EZ-turn.
 
Why not install the carb and see if it idles OK? - I've come across carbs where there was definitely slop but idled well nevertheless. Solder as Gary WA suggests is one option but if there's an air leak then the oversized shafts mentioned above are available and better than soldering, and they straightforward and easier to fit that trying to rebush
 
If you are rebuilding the core then add a new bushing and possibly a new shaft. Why not do the best job you can? To hold it tight in a drill press, you can use hot glue and then peal it off later. One trick is adding masking tape to the part to make removing the hot glue easier. Just peal off the masking tape later.
 
In which direction does the shaft move? If it is radially, that will leak and needs to be fixed. If the motion is axially (in/out) 1/16" motion is not likely to be a problem.
 
Bob Bidonde said:
In which direction does the shaft move? If it is radially, that will leak and needs to be fixed. If the motion is axially (in/out) 1/16" motion is not likely to be a problem.
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The movement is radially. I was hoping to be able to post a short video so the amount of slop was evident, but can't do it. Will try to add a film of solder --report to follow. The carb I am currently running does not respond at all to changes in the idle air mixture, and I suspect the throttle shaft is the culprit there, also.
 
Bob Bidonde said:
In which direction does the shaft move? If it is radially, that will leak and needs to be fixed. If the motion is axially (in/out) 1/16" motion is not likely to be a problem.
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I think it would be a problem if the shaft was moving axially. How would the throttle butterfly seal when there is 1/16" movement side to side?
 
Y-Blockhead said:
I think it would be a problem if the shaft was moving axially. How would the throttle butterfly seal when there is 1/16" movement side to side?
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You are correct. The photo would be of no value if I had slid the shaft all the way in, and I tried to avoid a long essay describing the movement, preferring to post a video. Working on it now--will keep you posted
 
Success !! I added a film of solder, filed it down , and it fits with ZERO slop. Thanks for the help.
 

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Russell Reay said:
My only fear about a new shaft or new bushing is that the casting will be very hard to hold tight in a drill press,
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For future reference: To hold the body secure in a drill press: Bolt the mounting flange to a piece of angle iron, then bolt the angle iron to the drill press table. Use a piece of 1/4" rod in the drill chuck to align the throttle body. Simples
 
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I have never been very successful at soldering with an iron, but I have done my own plumbing for 50 yrs. I shined up the shaft with plumber's sandpaper, clamped it gently in a vise, added flux, heated the shaft with a propane torch, and touched some lead-free solder to the target area. Naturally, the solder flowed over the shaft and collected in a bulb on the underside. I quenched the hot item, and used a ******* file to file down the bulb. Am very happy with the result.
 
Reference message #16. I need to to learn how to do this with some old throttle shafts from Simmons Model-A replacement carbs. Thanks for the "how to" Russel Reay!:cool:


Bob-A:D
 
I would be afraid to drill it. I can never get the drill angle just exactly correct. Plus drill bits always seem to cut just barely bigger than what the drill size is.

I don't know if I have a reamer that size of not. Pretty small.

I think you made the right choice with the solder. Esp. since it is a spare. You'd be surprised how much slop makes zero difference (that can not be adjusted out) and no one will ever notice.
 
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