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post #1 of 17 Old 08-11-2019, 01:20 PM Thread Starter
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Iron carb throttle shaft replacement & bushings

I am working on a '56 LI with cast iron carb and it has quite a bit of slop in the throttle shaft. Definite wear on shaft so that needs replacement and I believe some wear in the holes.

So a couple of questions:
1) What has anyone done for throttle shaft replacement? Yes, I know GT gravely has replacements for $125. As much as I like to support them, $125 for a brass shaft with a flat & a couple holes is out of line. No big deal to move the throttle stop from one shaft to another.

2) Any suggestions/advice on the bushings? Any tried and true procedures? I have a mill & lathe ... so have some thoughts as far as how to go about it, but always willing to listen to someone that has done it.
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post #2 of 17 Old 08-11-2019, 04:41 PM
Lnk
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Quote:
Originally Posted by Mister ED View Post
I am working on a '56 LI with cast iron carb and it has quite a bit of slop in the throttle shaft. Definite wear on shaft so that needs replacement and I believe some wear in the holes.

So a couple of questions:
1) What has anyone done for throttle shaft replacement? Yes, I know GT gravely has replacements for $125. As much as I like to support them, $125 for a brass shaft with a flat & a couple holes is out of line. No big deal to move the throttle stop from one shaft to another.

2) Any suggestions/advice on the bushings? Any tried and true procedures? I have a mill & lathe ... so have some thoughts as far as how to go about it, but always willing to listen to someone that has done it.
If I had a mill and a lathe, I would have already measures the old shaft and if buggered I would remove and clean up the ends with my lathe, and made bushings to fit my carb and the shaft. I probably would have made them out of brass or bronze and allowed for enough clearance to move freely. Most carb kits come with shaft seals, so I would account for them. Pretty sure if you have those things, you have enough talent to do this. I have not done this. Let is know how you make out, and we want pictures. ;')
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post #3 of 17 Old 08-11-2019, 11:47 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

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Originally Posted by Lnk View Post
If I had a mill and a lathe, I would have already measures the old shaft and if buggered I would remove and clean up the ends with my lathe, and made bushings to fit my carb and the shaft. I probably would have made them out of brass or bronze and allowed for enough clearance to move freely. Most carb kits come with shaft seals, so I would account for them. Pretty sure if you have those things, you have enough talent to do this. I have not done this. Let is know how you make out, and we want pictures. ;')
Zenith made this carb in a boatload of configurations and were used on a great many applications. That being said, if there is a shaft available that only requires a swap of the throttle linkage (which is pinned) and it is available for cheap (many are) that is the best and easiest way to go.

If I had tight tolerance .250 (+/- 0.0002) brass round laying around, I may have made one already. Then there is threading those puny threads, which is a PITA.

I would not consider the approach that you outlined on the shaft to be good one. Once you machine off the wear, are you going to have a matching reamer for the new size? And you will need to do more than just clean up the ends. You would need to turn the entire shaft to your new OD, else the shaft will not fit through your bushings.
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post #4 of 17 Old 08-12-2019, 07:24 AM
Lnk
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Originally Posted by Mister ED View Post
Quote:
Originally Posted by Lnk View Post
If I had a mill and a lathe, I would have already measures the old shaft and if buggered I would remove and clean up the ends with my lathe, and made bushings to fit my carb and the shaft. I probably would have made them out of brass or bronze and allowed for enough clearance to move freely. Most carb kits come with shaft seals, so I would account for them. Pretty sure if you have those things, you have enough talent to do this. I have not done this. Let is know how you make out, and we want pictures. ;')
Zenith made this carb in a boatload of configurations and were used on a great many applications. That being said, if there is a shaft available that only requires a swap of the throttle linkage (which is pinned) and it is available for cheap (many are) that is the best and easiest way to go.

If I had tight tolerance .250 (+/- 0.0002) brass round laying around, I may have made one already. Then there is threading those puny threads, which is a PITA.

I would not consider the approach that you outlined on the shaft to be good one. Once you machine off the wear, are you going to have a matching reamer for the new size? And you will need to do more than just clean up the ends. You would need to turn the entire shaft to your new OD, else the shaft will not fit through your bushings.
Unless you put the shaft in first, then pressed in the bushings from each end. Doesn't have to be that tight a fit to where you need to ream. I don't know if there is a shaft available, but decent used carbs are reasonable. Good luck and let us know how you make out.
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post #5 of 17 Old 08-12-2019, 06:12 PM
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Re: Iron carb throttle shaft replacement & bushings

A reamer is what I would use. The carb is too odd shaped to be able to hold it properly in the mill. And getting the holes in the carb casting in the proper place is important, but more important is getting both bushings on each side dead nuts square and even with each other. A extra long reamer is best to do that.

If the shaft is a standard size, I would find brass bushings at McMaster Carr that had the proper id for the throttle shaft, and had a reasonable OD. And then get a couple of reamers to ream it out to the OD of the bushings, either .0005 under or ream them to the same size and epoxy the bushings in place.

Then of course the butterfly is going to have to be fiddled with a reset so it fits the throttle bore nicely again.

If the new bushings are a little bit wider than the wear points on the old shaft, they should ride on a new part of the old shaft and might be ok as is.
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post #6 of 17 Old 08-12-2019, 10:59 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

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Originally Posted by franklin2 View Post
A reamer is what I would use. The carb is too odd shaped to be able to hold it properly in the mill. And getting the holes in the carb casting in the proper place is important, but more important is getting both bushings on each side dead nuts square and even with each other. A extra long reamer is best to do that.

If the shaft is a standard size, I would find brass bushings at McMaster Carr that had the proper id for the throttle shaft, and had a reasonable OD. And then get a couple of reamers to ream it out to the OD of the bushings, either .0005 under or ream them to the same size and epoxy the bushings in place.

Then of course the butterfly is going to have to be fiddled with a reset so it fits the throttle bore nicely again.

If the new bushings are a little bit wider than the wear points on the old shaft, they should ride on a new part of the old shaft and might be ok as is.
For the bushings, I was figuring on jigging the top of the carb up on an angle plate on the mill, using appropriate sized shaft to assure proper alignment. Drilling undersize, then reaming to final size. Then a final ream on the ID of the bushings once pressed into place.

For the shaft, I was hoping someone had a Zenith part # for an available shaft (for a different application) that the original Gravely linkage could be installed on. Alot of the rebuild kits for Zenith carbs actually include new throttle shafts and the shafts are available fairly cheaply. But, it looks like I am striking out there ... so time to order some stock and make a new shaft.
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post #7 of 17 Old 08-13-2019, 06:55 AM
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Re: Iron carb throttle shaft replacement & bushings

I didn't think about using a 90 degree plate, and bolting the carb mounting flange to it. I would assume the shaft is parallel to the carb mounting base.
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post #8 of 17 Old 08-13-2019, 09:39 AM
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Re: Iron carb throttle shaft replacement & bushings

Look up McDonald Carb on the internet.
All kinds of Zenith carb parts available; nice people.
Shafts, bushings, gaskets, floats, jets etc.

Also GT Tractor has parts for both the aluminum and the CI carbs.
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post #9 of 17 Old 08-13-2019, 01:49 PM
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Re: Iron carb throttle shaft replacement & bushings

Well, I finally found it. I have only made use of it on Kohler engines with a Carter carb. Hillman calls it a bronze thrust bushing. In this part of the country ACE hardware carries a Hillman section. It is 1/4" id and 7/16 od and is Hillman part # 58087-A.
Hope this helps.
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post #10 of 17 Old 08-13-2019, 02:57 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

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Originally Posted by nhgravely View Post
Look up McDonald Carb on the internet.
All kinds of Zenith carb parts available; nice people.
Shafts, bushings, gaskets, floats, jets etc.

Also GT Tractor has parts for both the aluminum and the CI carbs.
Yes, I know GT gravely has replacements for $125. As much as I like to support them, $125 for a brass shaft with a flat & a couple holes is out of line. No big deal to move the throttle stop from one shaft to another ... if I can figure out the best match (would be easy if I had a bunch sitting in front of me, LOL).

That being said, I'm trying to figure out which of the other Zenith shafts might fit (after swapping out the throttle stop/linkage). I'd think the only other shaft difference for the 161 carbs would maybe be the size of the butterfly (and the milled out section for it). Many are available for <$20 ... if I can find one that works at that price, it doesn't pay to create one from scratch.

Quote:
Originally Posted by TimWH View Post
Well, I finally found it. I have only made use of it on Kohler engines with a Carter carb. Hillman calls it a bronze thrust bushing. In this part of the country ACE hardware carries a Hillman section. It is 1/4" id and 7/16 od and is Hillman part # 58087-A.
Hope this helps.
Ok thanks for that. I will keep it in mind. There are also come readily available 5/16 OD bushings or the Zenith aluminum carb (68 series) that are .350" OD. When you machineed out for the bushings on the Carter carb, any special tricks or tips you can share from your experience?
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post #11 of 17 Old 08-18-2019, 02:22 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

Ended up not having to bush the carb. Made the shaft and installed. I still believe that there are other Zenith shafts out there that would only require minor modification, and would be cheaper in the long run.
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Old 08-21-2019, 02:49 PM
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post #12 of 17 Old 08-21-2019, 02:53 PM
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Re: Iron carb throttle shaft replacement & bushings

Wow,

Did you get the right angle on the milled surface, to the accuator arm hole pin, so that the throw from closed to open is in a working Gravely range, the governor range?

Faux Pas are my forte

Last edited by beaner2u; 08-21-2019 at 03:14 PM.
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post #13 of 17 Old 08-21-2019, 09:11 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

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Originally Posted by beaner2u View Post
Wow,

Did you get the right angle on the milled surface, to the accuator arm hole pin, so that the throw from closed to open is in a working Gravely range, the governor range?
Got it covered.

I milled the center first and then drilled the hole for the roll pin. To pick up the angle, I put the proper sized drill bit in the mill then put the bit through the old shaft with milled edge down. Then measured the angle from table to the milled flat. Removed the old shaft and clamped the new shaft using that same angle & reference. It should be spot on.

The toughest part for me was, working with such small stock, drill bits and taps, LOL. I'm used to seeing 1" or 2" stock in the lathe.
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post #14 of 17 Old 08-22-2019, 08:19 PM
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Re: Iron carb throttle shaft replacement & bushings

Excellent work, how the heck did you hold a piece of stock like that for milling?

Faux Pas are my forte
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post #15 of 17 Old 08-22-2019, 10:00 PM Thread Starter
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Re: Iron carb throttle shaft replacement & bushings

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Originally Posted by beaner2u View Post
Excellent work, how the heck did you hold a piece of stock like that for milling?
Excellent question, and one I struggled with for two days while I was waiting for the stock to arrive. Then it hit me ... toe clamp it right to the table.
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