Carb rebuild, bronz or brass?

[Speedy]

I will attempt to rebuild my carb since parts are not available.

I need to make a bushing for the throttle shaft (pics soon) what should it be made of?
will brass work? or is bronz the way to go.

this is the first part of many questions :big:

 

[joeby]

Speedy,

I would assume that this would be the carb from your Case tractor, the Kohler engine?

I used to get replacement bushings for some of the small engines, I think most, if not all, were brass.

I think brass should do fine, bronze is a better choice for bushing material, but you aren't dealing with a constantly rotating shaft here.

If brass is what ya got, I'd use it.

Kevin

 

[Speedy]

I actually dont have any, but I can get brass easier then bronz.
it is for my kohler, I think I will do a type of proto type then move to bronz in the next rebuild.

so I will get some brass bar then move onto my next question

 

[Speedy]

took a picture of the elongated hole.

the previous bushing was plastic and it deteriorated. the bushing would be quite thin in this area.
not sure if I should reem the body out on the carb slightly deeper?

or I could reem the entire carb body and make a fancy bushing with a shoulder..... nah thats to much work for a novice.

 

[ozzie46]

If it was me, I would drill the hole oversize to get rid of the elongation and make a bushing to fit the oversize hole and lock tight it in. Then i would drill the bushing for a very close fit for the shaft. The fit must be tight enough for no air to bleed by but still allow the shaft to turn free.

Back in the old days ( early 1970s) I was a mechanic and some Ford Autolite carbs I worked on would have the throttle plate holes in the carb body wore like yours. Air would bleed by and cause problems in the running of the engine.


Ron

 

[Speedy]

so if I understand this correctly.

drill out the hole.
make an appropriate bushing, lock tight it in. and let sit to harden.
now this part I am not sure what to do, when the bushing is in, how would you get the center? would you drill a guide whole first befor you loctight it in the carb?

need to figure out a fixture to hold the carb! ahhhh :big:

 

[joeby]

Drill and ream the carb body first. Easier to turn a bushing to fit a hole that to size a hole to fit a bushing. You should be able to use the float bowl gasket surface as a reference, set it up on parallels. Drill the bushing in the same setup as turning the OD to make sure the hole is concentric with the OD. Install bushing, return carb body to the same setup as you had when you drilled it, pick up the pre-drilled hole and ream to size......done.

Kevin

 

[ozzie46]

Kevins post beat what I was going to post by a mile. Yes; what he said. :big: :big:

Ron

 

[vlmarshall]

The throttle shaft is parallel to the carb mounting flange, no? Can you bolt it to the crosslide of your Taig , and drill and ream it there?

 

[Speedy]

The throttle shaft is parallel to the carb mounting flange, no? Can you bolt it to the crosslide of your Taig , and drill and ream it there?

!!! you are right! never thought about the lathe for this. will look it over tomorrow. ;D

 

[Ed T]

I have rebushed several dozen carb bodies which developed loose holes. The ones I did had brass shafts and that would be a consideration for your bushings since brass on brass is not a good plan as it will tend to gall and the shaft will stick. As suggested, I would bore the body out to a size larger than it is now. Then make a simple bushing with the ID around .015" smaller than the required finish diameter and the OD sized to fit the holes. If theres room, you may want to putba small flange on the bushing to control how far into the body you can press it. As I recall, I did not run the new bore all the way into the throat of the carb, but stopped just shy of breaking through. If you look at how the butterfly interfaces with the walls of the carb bore, you'll see that if the new bushings extend far enough to fill the new bore all the way, they will jam the butterfly. If the bushings extend only far enough to touch the butterfly, there is a big air leak path which is what you're trying to fix. If the carb is arranged appropriately, you might be able to pres the bushings in all the way and shape the protruding part of the bushing to conform to the throttle bore. I found it easier to make the hole not go through. Once that's all done, press the bushings in with some loctite and, after it hardens, ream the holes in the bushings to the correct diameter for the shaft going through both holes from one side so that the holes line up with each other. Ithink I ended up using valve guide reamer because it has an undersize pilot diameter that would reach across from one bushing to the other before it started to cut metal. That's my 2 cents worth. Good luck.

 

[1Kenny]

Hi Speedy,

Are you sure you can't get a throttle shaft re build kit? I have found that when the bushing is worn, the shaft is worn too. With out both being in good shape the engine will be hard to start and have a poor idle. Check with these guys. if you look towards the bottom of the page they have shaft kits.

http://www.psep.biz/store/kohler_carburetor_parts.htm

Kenny

 

[Speedy]

ED T. so are you saying make a bushing for both holes? the top one and the one that continues into the carb?
could you make a picture of what you mean :big: I read it but pictures help me allot.

1Kenny I have been looking at those I am not sure if they are for my application, seems 2 of them might be.
humm more investigating.

if the shafts need to be perfect I could sand them down with a very fine grit? emery cloth maybe? then make the bushing to match.

 

[Ed T]

Sorry, I don't have a good way to get pics onto this site. We're both dealing with mental images of the carbs we've worked on. The ones I have done have a shaft that goes all the way through and comes out both sides. I assume, perhaps incorrectly, that yours is the same, but maybe one of the holes is blind. In any case, yes, two bushings with slightly undersize holes that are line-reamed to the diameter of the shaft after installation. This ensures that the bores are in line and that the shaft can fit tightly w/o binding. I would stay away from sanding the shaft. You'll end up with various diameters and, probably, not round even if you use a block, you'll probably end up with taper one or both directions. That is, fat on one end or the other or in the middle. The shafts I dealt with were, miraculously, not worn to any meaningfull degree so that was not a problem. If the shaft is worn out and the holes in the body are egg shaped you have twice the fun and, as much fun as it is, you may want to find an unworn carb. Making a new shaft is doable and, if made a little oversize, you might be able to avoid bushing the carb body altogether. Since, I surmise, this is not a race car engine the slight additional restriction to airflow probably doesn't matter.

 

[Speedy]

hi Ed.
(ahh that is the word I was looking for, bare with me im still a newb.)
yes the other hole is blind it does not go all the way through, but its not nearly worn like the top is.
and the shaft doesn't seem to be worn.

maybe its best I just do the top for this one.

but another question for everyone.
how can I drill the hole out so that its flat on the bottom?
originally I wanted to use a drill bit but then that would leave a taper at the end.

 

[jack.39]

Did anybody mention that if the old holes are drilled, or whatever, if the finished hole/bushing(s) are off-location by a bit, which is pretty likely, the throttle plate(s) may bind and lock-up when closing or nearly closed?

If yes, strike this passage........................jack

 

[Russel]

To repair an eccentric hole with a bushing you should use a small boring head. That will allow you to correctly center the oversized bore for a bushing, as well as allowing you to machine a flat bottom. Of course, it would have to be a very small boring head.

A Sherline boring head might be small enough.

 

[Alan J. Richer]

Re: Eccentric hole:

If you don't have a boring head the other thing you can do is pilot the hole.

I've done this in situations where it was impossible to align a hole any other way.

Drill a slightly undersize square-to-the-mounting-point hole in a piece of waste material, aligned so you can bolt it up to your mounting flange for the carb or whatever is close and convenient. Then run a reamer through that hole and the hole in the casting. The pilot bit of metal will keep the reamer square and counteract the tendency for it to drift because of the eccentric shape of the hole.

Personally, I'd much rather go after something like this with a 2-flute end mill, chucked up really short in a collet and used to bore the hole straight and clean with the piece mounted to the cross-slide of a lathe.

There are a thousand ways to skin a cat - the trick is choosing the one that is the least hassle.

Alan