[TR] SU H6 throttle shaft bushing replacement

[Randall]

> It's time for me to replace the throttle shaft bushes in the SU H6 carbs
> on my
> TR3.  They're leaking a bit and I can't get my idle speed below 1200 RPM.

Have you checked to see what is holding the throttles open?  I wouldn't
expect the leak itself to be the problem; and there can be many other things
that hold them open a bit.  Including having the screws that hold the plates
to the shaft work loose.

> Should I just get four new bushes from Moss and not replace anything more?
> Hoping the wear is in the bushes and not the shafts.

Seems unlikely to me.  One way to tell is after you've stripped the carbs,
reinsert the shafts so the bushings ride on the unworn area and compare the
side play to the normal position.

> Should I put in new shafts also?

I would.  In fact, I would expect the shafts to have most of the wear, this
time around.

>   Will I be able to use micrometers to
> tell if there is wear on my shafts?

Yes, but the test above is easier.  A micrometer isn't really required, even
calipers are plenty to measure any significant wear.  A few .0001" doesn't
matter here.

>   My concern with replacing the shafts is
> drilling
> them for the pin to locate the throttle stops.  Any tips for doing that?

Sorry, I'm no help here.  I did mine "by eye"; goofed the first one up but
fortunately was able to correct my mistake by turning the shaft end-for-end
and trying again.

> Should I install a complete rebuilt kit even though I have no other
> problems?
> I've only got about 25000 miles since the rebuild.  But is 17 years
> getting
> near the end of the life expectancy for seals?

I would like to know how the heck you got that much out of them!  Mine only
seem to last a few years at most.  As far as needles, jets, float valves,
etc.; I'd probably leave them alone if no problems are evident.  That said,
one of the most frustrating (and damaging) TR problems I've ever fought was
caused by jets that were internally worn (presumably from poorly centered
needles by a DPO).  Changing them might turn out to be cheap insurance.

> The shafts that are installed measure 5/16" (.3125").  I'm hoping that is
> the
> standard shaft size

I believe it is.

> and the OD of the bushes Moss sells now is the same as
> those sold 17 years ago.

Sorry, no idea there.  But I doubt you can just drive them out anyway, most
likely they will have to be reamed again.

Randall