Throttle Shaft Bushing Questions
 

Yesterday, I pulled apart my "previously unmolested" carb from my 126. I knew the shaft was way sloppy, like 20 thousandths or more.

I found that both brass screws were loose, but still riveted enough to keep them from coming completely out. Scary. I cut the riveted parts off and backed them out. They were so worn from constant wiggling that the 3-48 threads were no longer there on the screws. The shaft still has decent 3-48 threads.

I noticed that the recessed area where everyone puts the bronze bushing still had what looked like a fine foam black gasket. It crumbled when I touched it though. Was that some sort of OEM seal to keep it from sucking air or dirt?

I went to the local hardware store, McGuckin's, to see if I could find 3-48 brass screws and the Hillman bushing mentioned here on the forums. McG's is a HUGE hardware store. They have everything! Except 3-48 x 1/4 brass round head screws and Hillman bushings that is. I bought some stainless 3-48 screws and some zinc plated steel of the same.

Should I use the stainless steel screws with Loctite, or should I keep searching for brass screws instead? I don't think I could effectively rivet the SS, and if I did, someone might hate me in 25 years when they try to tear it down.

I also bought a bronze oil-lite bushing that was 1/4 ID, 7/16 OD, but 1" long. I can part that off in the lathe and be home free.

But I got to thinking. What if I were to make the shaft bushing out of Teflon? I have some Teflon rod stock, 1/2". Would a bushing made of that last longer or work better? It seems like wear would be minimal. Fuel resistance is excellent. I can make it 0.247 to fit the shaft unlike the bronze bushing .250, and make it a nice snug fit in the 7/16 bore of the carb.

Does the Teflon bushing sound like a good idea to any of you? Has anyone tried it with success or failure? All comments are welcome!

Space age material in an old cub tractor? Hmmmm?

Thanks,

Jim

I've used zinc-plated screws with lock washers and blue locktite with good results. I'm not sure where you'd get the brass screws. I doubt you could even
get them through Kohler anymore.

has anyone tried hard nylon screws, easy to find,install then hit back side with hot soldiering iron to lock in place??? but that sounds tomuch like the junk they are selling today, sorry, guess I should think agin!!
GIG
BIG
PAC
Daduke of Earl

I'm thinking the nylon screws just don't seem strong enough being that small a dia.
I used button heads (allen) on my throttle shaft one day when the butterfly divorced the shaft and caught in the venturi. it was all I had in stock without running in to town and trying to find brass.
I never did find the broken screw heads but I'm glad they didn't marry the piston head.
Using the button heads kind of made me nervous if they wanted to leave home,but so far,the locktight seems to hold and it's been 2 years or
about 3-400 hours.
the shaft was worn way bad, but I just wanted a quick fix to finish the mowing.
well you know how that goes-- yea is wobbles & wiggles and does a little jig when it is idling.
it runs well,so I'll let er go till it needs a total rebuild.
that little 10 H.P. Kohler has been problem free for 30 years, I sure can't complain.

I would not recommend a teflon bushing. I made one out of nylon and it would swell when the engine was hot and the throttle would stick. Teflon may work better than nylon but why not use bronze. It has been tried and proven and is about as cheap as dirt.

You know why those are brass screws, don't you? That's so when they fall out of the shaft and go into the engine, they don't mess everything up, because they are softer than everything else in there. I would not advise the use of steel screws on a throttle shaft. Why don't you try looking at other kinds of carbs, say, in a wrecking yard. My guess is that they are probably pretty commonly used in carbs for other uses, like maybe even some smaller automotive carbs. chain saws, weed whackers, lawn mowers, etc. Every carburetor with a butterfly valve has one or two. It is unlikely there are a large number of different sizes, since carb manufacturers don't actually manufacture the screws. They design with what is available. No need to reinvent the wheel...I mean screw. I would be very surprised if you could not get them from any small engine shop

Thanks guys!
No teflon bushing duly noted. I didn't think of the heat causing it to swell, but now I've learned that Teflon is bad for thermal expansion. I was just thinking if Teflon would last forever, not wear itself or the shaft, and maintain a good seal, why wouldn't it be a good thing. I've got 2 feet of 1/2 rod, which was very reasonable in cost.
I did find some 4-40 brass screws, and I will probably use them and re-tap the shaft to fit. 3-48 is an odd size for brass apparently, although I didn't try McMaster. I'd hate to pay more for shipping than the screws themselves.
Good point on the brass being softer. Mine were so loose I almost tested that theory!