On Thu, 26 May 2011 00:13:55 +0000 (UTC), Jules Richardson
wrote:

On Wed, 25 May 2011 08:38:56 -0500, dpb wrote:

On 5/25/2011 7:55 AM, Jules Richardson wrote: ...

Yeah, it's getting pretty bad on both the old B+S engines that I have,
which are around 25 years old now. They use tiny grub screws to hold
the throttle stop onto the shaft too, and there's no chance of getting
those out after so many years - removing the stop is the only way of
removing the shaft.

Maybe I'll motivate myself to cut the stop off one sometime (and make
myself a replacement) if I can plan a way of adding bushes to the carb
body (which I expect is what's worn; the shaft's probably not too bad)
...

It's pretty trivial to grind off the throttle plate screws then remove
them and replace.

Ahh, this is just the screw holding the stop / idle speed adjustment
which sits externally to the carb - whether the throttle plate screws
(although I think it might only have one, without going to look) are also
snafu is another matter :-) I don't think I could get the stop off
without completely trashing it, but it shouldn't be too hard to make
something functionally equivalent anyway.

The trick is the machining for bushing in the carb body to accurately
bush the shaft.

Yes, that'd be my worry, too, getting it all aligned properly.

I've wondered if one of the JB Weld or similar products
would be hard enough but figured unlikely so haven't ever tried it. It
wouldn't be bad if one had a milling machine setup (or very, very good
drill press, even) but my press is ok for farm repair heavy stuff but
not up to the task for such precise work.

Yep, same deal here. Maybe drilling slightly larger than needed and then
epoxying the new sleeves in place (using some kind of rig to keep it
aligned while drying) might work. Modern epoxies seem to be pretty robust
- I even filled some quite serious scoring in the cylinder bore of my
"junk" engine with the stuff, and so far it's taking the oil and heat and
having piston rings sliding past it just fine (I tried it more for
chuckles than anything, but it's really surprised me how well it's
holding up). If it can take that kind of abuse, it'd likely last in a
carb body, too.


Indeed, it is the carb body casting that wears; I've mic'ed the shaft on
a couple and they're barely discernible as to wear--it's all in hogging
out the body from the longterm vibration.

Yeah, I don't think that whatever metal they're cast from is particularly
hard, so I'm not surprised that they wear long before the shafts do. But
then 25 years isn't bad for something that was probably only designed to
last a fraction of that, either.

cheers

Jules
The carb bodies are "generally" die cast zinc. The best way to
re-bush one is to take a good one and fixture it on the mill, using an
end-mill, reamer, or transfer punch as a locator, then put the old
carb in the fixture with a larger end mill or reamer, then press in
new bushings and mill/ream back to proper size , again in the fixture.