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Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 11:11 am
by Eugen
It seems so easy to buy a new carburetor when you come across a Kohler K321 14 HP engine in rough shape that you want to restore. There are plenty of cheap carburetors available for this engine, but as some of you may already know, most that you find are cheaply made in China. Their threads are metric so you won't be able to use carburetor rebuild kits made for the real carburetor, and the choke shaft lever is strangely shaped so that the choke function is reversed.

If you're happy to just have the engine back in running shape, this may be a perfectly viable solution. But what if you want to restore the old carb?!

My preference is to not throw out old parts just because it's easier to get a new part, when possible. Therefore, I will attempt to restore this old Carter #30 carburetor.

tempImageiem2DW.gif
tempImageHhXxFT.gif

Re: Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 2:57 pm
by Timj
With the help of Smiley Green Wrench, it will be done. :smash:

Re: Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 3:46 pm
by Eugen
There are "rebuild" kits you can purchase but they won't include everything you need to restore the carb to its former glory. One of the first things that need to be checked is throttle shaft wear. You've heard @ssmewing mention this already. Here's the throttle shaft of this particular carburetor. It's most likely to be have wear in the area circled in yellow, where the shaft is brighter from touching the housing. There is no bronze bushing set in the carb housing, so the housing, which is probably a aluminium or magnesium based alloy can incur wear more readily than the shaft which is steel.

IMG_5690.jpg

For the record, the shaft measures 1/4" at the area of interest. It is supposed to be 1/4" too.


tempImage8JJnzt.gif


If either the shaft or the housing has excessive wear in that area, air will be sucked in and the air/fuel mix ratio will no longer be right. One way to test without disassembling the carburetor is to spray some starting fluid where the throttle shaft meets the housing while idling the engine. Safety first! Don't anything like that if you don't know how to handle very combustible gases.

In my case the shaft doesn't seem to have any significant wear. But what if the housing is worn out significantly where it meets the shaft? Here I try to move the shaft sideways to check for play.


https://vimeo.com/659102443






As you can see, there's very little play. Even so, if I want to improve the situation, what is the solution? The answer is bronze bushing.

Here's a view of where the shaft fits in the carb housing. Observe the recess area around the 1/4" hole where the shaft goes in. It is about 9/64" deep. Well, we can call it 1/8" though :D


tempImage4arptg.gif


The inner diameter of that recess area is 7/16"


tempImageDUmPvA.gif


One can find something called bronze thrust washers, made by Hillman. They are 1/16" thick, with 1/4" ID and 7/16" OD. Two of these inserted in the recess will give you the 1/8 thickness to fill the recess and provide a really nice bronze bushing bearing. Even more amazing is the fact that I found the item available in a pack of 10 on amazon and will be ordering it. I'm sure in the US it will be much cheaper and more readily available.


Screen Shot 2021-12-21 at 3.18.26 PM.png

But I found a bronze sleeve bushing at a "local" store and will try to get it from them.

Screen Shot 2021-12-21 at 3.56.12 PM.png

Re: Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 3:48 pm
by Eugen
Timj wrote: Tue Dec 21, 2021 2:57 pm With the help of Smiley Green Wrench, it will be done. :smash:
My wife insists that I use quality tools. My son reluctantly lent it to me :giggle:

Re: Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 5:18 pm
by DavidBarkey
What did you determine was the difference between the old carb and the new one to make the linkage askew ?

Dave

Re: Restoring a Kohler K321 carburetor

Posted: Tue Dec 21, 2021 6:31 pm
by Eugen
DavidBarkey wrote: Tue Dec 21, 2021 5:18 pm What did you determine was the difference between the old carb and the new one to make the linkage askew ?

Dave
Not yet Dave, that tractor is way in the back of the tent for now. Hopefully I get to it in the next few days. Will post an update then. :letmesee:

Re: Restoring a Kohler K321 carburetor

Posted: Wed Dec 22, 2021 10:06 pm
by Eugen
@DavidBarkey had a look today and no idea how but the link looks fine.


F783900E-56D2-4FA1-A71A-B423B62A949C.jpeg

Maybe it was skewed when I first assembled it.

Re: Restoring a Kohler K321 carburetor

Posted: Wed Dec 22, 2021 10:27 pm
by Eugen
Back to the old carburetor. Got the one inch long bronze bushing from a bearing place just north of Toronto and cut a 1/8 piece. Hacksaw guys, forgive me for not using the lathe but the wrong chuck jaws were on and I was in great hurry having a few chores for the family waiting for me. After a little filing and deburring the bronze sleeve went in with a few light hammer knocks. It's a tight fit so I've no concerns it goes loose.


6EEEA1F6-A53A-4ADD-8834-06A99C7C1E09.jpeg


Inserted the shaft with a little grease in all the right places. There is zero side movement now, and the rotation action is smooth and precise. I deserve a beer! :drink:


202181A7-3E6F-4FDC-B7EC-36B18E2739A8.jpeg


But the housing looks pretty shabby, wouldn't mind stripping it of gunk and paint and giving it a new finish.

I'd say it also needs new gaskets, a good cleaning of all tiny holes and jet, etc.

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 5:52 am
by Dave180
It looks like hole in governor arm is to big to work properly

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 7:02 am
by DavidBarkey
Eugen wrote: Wed Dec 22, 2021 10:06 pm @DavidBarkey had a look today and no idea how but the link looks fine.



F783900E-56D2-4FA1-A71A-B423B62A949C.jpeg


Maybe it was skewed when I first assembled it.
I wonder now if it was just the camera angle .

Dave

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 7:16 am
by DavidBarkey
Eugen wrote: Wed Dec 22, 2021 10:06 pm @DavidBarkey had a look today and no idea how but the link looks fine.



F783900E-56D2-4FA1-A71A-B423B62A949C.jpeg


Maybe it was skewed when I first assembled it.
As @Dave180 Said . The hole in the govenor is too big because it has the wrong linkage for that arm . There are 2 types , the one you have and this one you need .
image.png
or use a nylon bushing like what is used in car door linkage with the one you have .

Dave

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 9:02 am
by Eugen
I should be able to fix the governor arm guys. Not sure I can be so precise with the wire welder on that thin arm but I'll try, what's the worst that could happen?! :giggle:

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 11:33 am
by ssmewing
Eugen wrote: Wed Dec 22, 2021 10:27 pm Back to the old carburetor. Got the one inch long bronze bushing from a bearing place just north of Toronto and cut a 1/8 piece. Hacksaw guys, forgive me for not using the lathe but the wrong chuck jaws were on and I was in great hurry having a few chores for the family waiting for me. After a little filing and deburring the bronze sleeve went in with a few light hammer knocks. It's a tight fit so I've no concerns it goes loose.



6EEEA1F6-A53A-4ADD-8834-06A99C7C1E09.jpeg



Inserted the shaft with a little grease in all the right places. There is zero side movement now, and the rotation action is smooth and precise. I deserve a beer! :drink:



202181A7-3E6F-4FDC-B7EC-36B18E2739A8.jpeg



But the housing looks pretty shabby, wouldn't mind stripping it of gunk and paint and giving it a new finish.

I'd say it also needs new gaskets, a good cleaning of all tiny holes and jet, etc.
Nice work, as a smack my hand to my forehead. :40: :40: :40:

But, That is not where the new bushing goes. You are right the carb body is some alloy that is very soft. That is where the wear from the throttle shaft happens. Calipers are not used since there is no known spec for the acceptable wear which is actually the hole, not the shaft. You drill and add a bushing to the main hole.

The correct repair is all over the internet if you use Google, with pictures, and everything. Sorry if I seem harsh. I am the older guy and why I am the one who uses Google and has to tell young people to use Google kind of baffles me. Maybe I should try Google on that.

I recently replaced the rear brakes on my beater with a heater. A very easy job that I have done many times. But, the first thing I did even before ordering parts was to watch a YouTube by a professional that usually is hosted by the parts sellers. What this does for me is if there are special considerations I know them. The good videos that I look for I actually take notes from. The good videos tell you the wrench or socket sizes you will need. Then at the end, the good video tells you the torque specs for each fastener. If it does not then I Google the specs. It's all free and easy and should be your number one step.

Now it turns out I also have to the front ones. The price of owning a 20-year-old vehicle that lived a dirty life. The front bleeders were barely anything left. The rear calipers were completely not working. So, on to the fronts.

The rear disk had one of 2 pistons not frozen. All sliders were locked up.
Eugen wrote: Wed Dec 22, 2021 10:27 pm Back to the old carburetor. Got the one inch long bronze bushing from a bearing place just north of Toronto and cut a 1/8 piece. Hacksaw guys, forgive me for not using the lathe but the wrong chuck jaws were on and I was in great hurry having a few chores for the family waiting for me. After a little filing and deburring the bronze sleeve went in with a few light hammer knocks. It's a tight fit so I've no concerns it goes loose.



6EEEA1F6-A53A-4ADD-8834-06A99C7C1E09.jpeg



Inserted the shaft with a little grease in all the right places. There is zero side movement now, and the rotation action is smooth and precise. I deserve a beer! :drink:



202181A7-3E6F-4FDC-B7EC-36B18E2739A8.jpeg



But the housing looks pretty shabby, wouldn't mind stripping it of gunk and paint and giving it a new finish.

I'd say it also needs new gaskets, a good cleaning of all tiny holes and jet, etc.
Nice work, as a smack my hand to my forehead. :40: :40: :40:

But, That is not where the new bushing goes. You are right the carb body is some alloy that is very soft. That is where the wear from the throttle shaft happens. Calipers are not used since there is no known spec for the acceptable wear which is actually the hole, not the shaft. You drill and add a bushing to the main hole.

The correct repair is all over the internet if you use Google, with pictures, and everything. Sorry if I seem harsh. I am the older guy and why I am the one who uses Google and has to tell young people to use Google kind of baffles me. Maybe I should try Google on that.

I recently replaced the rear brakes on my beater with a heater. A very easy job that I have done many times. But, the first thing I did even before ordering parts was to watch a YouTube by a professional that usually is hosted by the parts sellers. What this does for me is if there are special considerations I know them. The good videos that I look for I actually take notes from. The good videos tell you the wrench or socket sizes you will need. Then at the end, the good video tells you the torque specs for each fastener. If it does not then I Google the specs. It's all free and easy and should be your number one step.

Now it turns out I also have to the front ones. The price of owning a 20-year-old vehicle that lived a dirty life. The front bleeders were barely anything left. The rear calipers were completely not working. So, on to the fronts.

The rear disk had one of 2 pistons not frozen. All sliders were locked up. It was making some noise in the rear end.

I seem to be blocked or not allowed from posting pictures or attachments.

https://photos.app.goo.gl/J68CBfJddUjpDdoz9

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 11:35 am
by ssmewing
Eugen wrote: Thu Dec 23, 2021 9:02 am I should be able to fix the governor arm guys. Not sure I can be so precise with the wire welder on that thin arm but I'll try, what's the worst that could happen?! :giggle:
It is fine to leave it alone. It does not affect much.

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 12:01 pm
by Eugen
I did google it :109:

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 12:08 pm
by Eugen
@ssmewing nothing should be blocked for you, what error did you get when trying to upload/post a picture?

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 3:53 pm
by DavidBarkey
I saw the rotor , worn down to the fins on the back side . The link did how ever take you to google photo ??

Dave

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 5:19 pm
by ssmewing
Eugen wrote: Thu Dec 23, 2021 12:08 pm @ssmewing nothing should be blocked for you, what error did you get when trying to upload/post a picture?
It just will not do it. I have spent years on this kind of forum and used the menu this one has. I do not get an error. I just cannot paste anything into the operators. I think it is just not enabled maybe? Drag and drop copy and paste, nothing works.

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 5:21 pm
by ssmewing
DavidBarkey wrote: Thu Dec 23, 2021 3:53 pm I saw the rotor , worn down to the fins on the back side . The link did how ever take you to google photo ??

Dave
Posting a link is not the correct method for this type of forum. It works, but what you would want is a photo or link to something appears in the post without the address showing.

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 8:41 pm
by Eugen
ssmewing wrote: Thu Dec 23, 2021 5:19 pm
Eugen wrote: Thu Dec 23, 2021 12:08 pm @ssmewing nothing should be blocked for you, what error did you get when trying to upload/post a picture?
It just will not do it. I have spent years on this kind of forum and used the menu this one has. I do not get an error. I just cannot paste anything into the operators. I think it is just not enabled maybe? Drag and drop copy and paste, nothing works.
Hm.. have you tried dragging the picture directly onto this text box? I'm going to record my screen as I do it, and post it below. Worked for me. I'll make sure it works for you too.

Re: Restoring a Kohler K321 carburetor

Posted: Thu Dec 23, 2021 10:16 pm
by Eugen
Here's a screen recording of how I just did it.


https://youtu.be/6zGsrza9fIA



Re: Restoring a Kohler K321 carburetor

Posted: Fri Dec 24, 2021 8:56 pm
by Eugen
ssmewing wrote: Thu Dec 23, 2021 11:33 am Nice work, as a smack my hand to my forehead. :40: :40: :40:
I'm really glad you approve! :D
But, That is not where the new bushing goes. You are right the carb body is some alloy that is very soft. That is where the wear from the throttle shaft happens. Calipers are not used since there is no known spec for the acceptable wear which is actually the hole, not the shaft. You drill and add a bushing to the main hole.
I'd like you to consider a few things though. Sure, normally you drill the entire area of contact and replace it with the bushing. That repair to make sense needs a straight hole true to the hole on the other side of the housing. It's quite a risk to attempt that with a drill press. You also need a good reamer. The other thing is there are quite a few people that only used a smaller bushing like I did and the repair was successful. If the original carburetor worked fine for many years, with only a soft material in that position, this small bushing solution should also work for many years, don't you think so?

I showed calliper measurements in part to highlight the right size for the bushing, and in part to show that there is no significant wear on the shaft. Notice that I did not measure the wear on the hole, rather I showed a little video clip with the side movement. I do have a nice set of Oldak small hole gages and an Etalon 0-1" micrometer, but what would be the point? I think I already mentioned above that the side movement was so small that most likely the carburetor was going to work just fine without the bushing, but I felt like doing this repair anyway and I'm pretty sure I can get many years out of it.
The correct repair is all over the internet if you use Google, with pictures, and everything. Sorry if I seem harsh. I am the older guy and why I am the one who uses Google and has to tell young people to use Google kind of baffles me. Maybe I should try Google on that.
I honestly want to know why you consider the repair I did incorrect.
I recently replaced the rear brakes on my beater with a heater. A very easy job that I have done many times. But, the first thing I did even before ordering parts was to watch a YouTube by a professional that usually is hosted by the parts sellers. What this does for me is if there are special considerations I know them. The good videos that I look for I actually take notes from. The good videos tell you the wrench or socket sizes you will need. Then at the end, the good video tells you the torque specs for each fastener. If it does not then I Google the specs. It's all free and easy and should be your number one step.

Now it turns out I also have to the front ones. The price of owning a 20-year-old vehicle that lived a dirty life. The front bleeders were barely anything left. The rear calipers were completely not working. So, on to the fronts.

The rear disk had one of 2 pistons not frozen. All sliders were locked up. It was making some noise in the rear end.

I seem to be blocked or not allowed from posting pictures or attachments.

https://photos.app.goo.gl/J68CBfJddUjpDdoz9

My truck is only 14 years old, but the previous owner didn't maintain it very well. I know what you're saying about getting good info on the internet. My default is to use the service manual for my truck which does have all the correct torques and procedures, but it does tend to be terse in places you need more details, so for one job (timing belt replacement) I did watch a good youtube video. This is the work I've done myself so far on it: replaced catalytic converters (major pain because of the tight area), oxygen sensors, valve adjustment, timing belt and everything that was in that area, like water pump, idling pulleys, tensioner, etc., serpentine belt, parts of the AC circuit piping, fuel injectors, fuel pump, radiator, xfer case fluid, transmission fluid, rear diff fluid, rear brake disks and pads, front pads, AC clutch, and most recently the alternator. From double digits long term fuel trim values I got it to near zero, and no more codes thrown. Now the power steering pump whines I think, and I'll probably replace it soon. My point here is that I think I know where you're coming from regarding life with an old car.

:cheers:

Re: Restoring a Kohler K321 carburetor

Posted: Sat Dec 25, 2021 7:19 am
by DavidBarkey
I personally do not like Utube videos as an instruction tool . There is no way to know if the information is correct , and if it is false or misleading the maker is not held accountable . There is no way to inter act with the maker if you are unsure about something . Most people assume if it is on the the internet it is correct . I prefer manuals, put out by the makers ,diagrams , tips and tricks from forums like this where you can bounce things of others back and forth . Now that been said , the internet is repository full of information both good and bad . Sifting through it can be the biggest challenge at times .
My 2 cents , you may keep the change

Dave

Re: Restoring a Kohler K321 carburetor

Posted: Sat Dec 25, 2021 9:26 am
by Timj
DavidBarkey wrote: Sat Dec 25, 2021 7:19 am I personally do not like Utube videos as an instruction tool . There is no way to know if the information is correct , and if it is false or misleading the maker is not held accountable . There is no way to inter act with the maker if you are unsure about something . Most people assume if it is on the the internet it is correct . I prefer manuals, put out by the makers ,diagrams , tips and tricks from forums like this where you can bounce things of others back and forth . Now that been said , the internet is repository full of information both good and bad . Sifting through it can be the biggest challenge at times .
My 2 cents , you may keep the change

Dave
I do use YouTube and other internet videos as a convenience thing, but I never go with the info from just one. It is generally a educational thing, then I decide if I'm comfortable with tackling it or do I go looking for more info. Manuals are always first. I've picked up some good tips, but some info is so off. :O

Sometimes for entertainment I sit and watch well and pump videos, as it's my business, but in the end I end up feeling so sorry for people that have received and followed so much bad information. :headbash: I don't comment, I should, but there are not enough hours in a day. :35:

Re: Restoring a Kohler K321 carburetor

Posted: Sat Dec 25, 2021 9:55 am
by Jancoe
There are many ways to skin a cat. Just because it's not your way dosent mean it's not gonna work. I think the repair will work just fine. I have a hard time trusting youtube guys also. Lots of mis information floating around out there.

Sent from my SM-G975U using Tapatalk



Re: Restoring a Kohler K321 carburetor

Posted: Sat Dec 25, 2021 11:29 am
by ssmewing
Eugen wrote: Fri Dec 24, 2021 8:56 pm
ssmewing wrote: Thu Dec 23, 2021 11:33 am Nice work, as a smack my hand to my forehead. :40: :40: :40:
I'm really glad you approve! :D
But, That is not where the new bushing goes. You are right the carb body is some alloy that is very soft. That is where the wear from the throttle shaft happens. Calipers are not used since there is no known spec for the acceptable wear which is actually the hole, not the shaft. You drill and add a bushing to the main hole.
I'd like you to consider a few things though. Sure, normally you drill the entire area of contact and replace it with the bushing. That repair to make sense needs a straight hole true to the hole on the other side of the housing. It's quite a risk to attempt that with a drill press. You also need a good reamer. The other thing is there are quite a few people that only used a smaller bushing like I did and the repair was successful. If the original carburetor worked fine for many years, with only a soft material in that position, this small bushing solution should also work for many years, don't you think so?

I showed calliper measurements in part to highlight the right size for the bushing, and in part to show that there is no significant wear on the shaft. Notice that I did not measure the wear on the hole, rather I showed a little video clip with the side movement. I do have a nice set of Oldak small hole gages and an Etalon 0-1" micrometer, but what would be the point? I think I already mentioned above that the side movement was so small that most likely the carburetor was going to work just fine without the bushing, but I felt like doing this repair anyway and I'm pretty sure I can get many years out of it.
The correct repair is all over the internet if you use Google, with pictures, and everything. Sorry if I seem harsh. I am the older guy and why I am the one who uses Google and has to tell young people to use Google kind of baffles me. Maybe I should try Google on that.
I honestly want to know why you consider the repair I did incorrect.
I recently replaced the rear brakes on my beater with a heater. A very easy job that I have done many times. But, the first thing I did even before ordering parts was to watch a YouTube by a professional that usually is hosted by the parts sellers. What this does for me is if there are special considerations I know them. The good videos that I look for I actually take notes from. The good videos tell you the wrench or socket sizes you will need. Then at the end, the good video tells you the torque specs for each fastener. If it does not then I Google the specs. It's all free and easy and should be your number one step.

Now it turns out I also have to the front ones. The price of owning a 20-year-old vehicle that lived a dirty life. The front bleeders were barely anything left. The rear calipers were completely not working. So, on to the fronts.

The rear disk had one of 2 pistons not frozen. All sliders were locked up. It was making some noise in the rear end.

I seem to be blocked or not allowed from posting pictures or attachments.

https://photos.app.goo.gl/J68CBfJddUjpDdoz9

My truck is only 14 years old, but the previous owner didn't maintain it very well. I know what you're saying about getting good info on the internet. My default is to use the service manual for my truck which does have all the correct torques and procedures, but it does tend to be terse in places you need more details, so for one job (timing belt replacement) I did watch a good youtube video. This is the work I've done myself so far on it: replaced catalytic converters (major pain because of the tight area), oxygen sensors, valve adjustment, timing belt and everything that was in that area, like water pump, idling pulleys, tensioner, etc., serpentine belt, parts of the AC circuit piping, fuel injectors, fuel pump, radiator, xfer case fluid, transmission fluid, rear diff fluid, rear brake disks and pads, front pads, AC clutch, and most recently the alternator. From double digits long term fuel trim values I got it to near zero, and no more codes thrown. Now the power steering pump whines I think, and I'll probably replace it soon. My point here is that I think I know where you're coming from regarding life with an old car.

:cheers:
I have been around the forums for some time and even read decades of posts that happened before I was on the forums. That is how I learn and that is all I needed to graduate with honors in college even. No notes, I read it understand it, and move on.

Yes, you must have a drill press and a drill press vice to open and set the carb on, and the drill press must be corrected squared. But, no you do not drill two holes, you only drill the top hole. The bottom hole is a blind hole. No, you do not need a reamer as the hole will get a bushing. So, it does not need a precision cut to the hole. Then you are now using a very small contact with the throttle shaft which is softer than a bronze bushing.

Once you put a full bushing in the hole where the throttle shaft originally makes contact you will never need another bushing. The only thing that will need eventual changing is now the throttle shaft. Yes, I have done this to a carb that came to me with a bushing but a worn shaft. But, I guess I do not know if the shaft was replaced during the bushing install.

I am not talking about theory. I repair these as a hobby that pays for my hobby. I have done at least 20 of these repairs and have seen on forum posts spanning many decades others doing the same repair. I have at least 2 bushings and 2 new shafts in my parts bin at all times. I advertise through Craigslist that I will do this repair.

This is the correct bushing. https://www.mcmaster.com/catalog/127/1303

Re: Restoring a Kohler K321 carburetor

Posted: Sat Dec 25, 2021 1:15 pm
by Eugen
The bushing from McMaster-Carr is indeed superior. I also agree that a larger contact surface area is desirable all things being equal. Not sure how you concluded that 841 bronze is harder than the shaft which must be some sort of mild steel. You could harden the shaft a little if you really wanted to.

That being said, if I did this repair for someone who paid me I'd probably aim for the best solution.

But what if the smaller surface area of a lesser quality bronze bushing allows it to wear faster than the shaft? It then becomes a maintenance item easily replaced every 2-3 years. Cheap too.

Re: Restoring a Kohler K321 carburetor

Posted: Sun Dec 26, 2021 1:06 pm
by ssmewing
Eugen wrote: Sat Dec 25, 2021 1:15 pm The bushing from McMaster-Carr is indeed superior. I also agree that a larger contact surface area is desirable all things being equal. Not sure how you concluded that 841 bronze is harder than the shaft which must be some sort of mild steel. You could harden the shaft a little if you really wanted to.

That being said, if I did this repair for someone who paid me I'd probably aim for the best solution.

But what if the smaller surface area of a lesser quality bronze bushing allows it to wear faster than the shaft? It then becomes a maintenance item easily replaced every 2-3 years. Cheap too.
I have replaced a couple of shafts in carbs that had the bushings. So, experience is the answer. The way that the vibration of the engine shakes against the governor set up I think is what starts the problem. I have seen Onan engines with 10 times the hours and the throttle shaft is just fine.