[TR] SU H6 throttle shaft bushing replacement

[John Reed]

> Date: Wed, 13 May 2009 22:39:31 -0700
> From: "Randall" <tr3driver at ca.rr.com>
> Subject: Re: [TR] SU H6 throttle shaft bushing replacement
>
> > 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.



I started having a problem with idle speed too high last summer.  I could get
it down when the throttle shafts were not connected and I adjusted them
independently and synced them (using hose to the ear and also a uni-syn).  I
had backed the idle adjust screw almost all the way out.  After clamping the
shafts together and driving idle speed was too high again.  I looked at the
throttle plates last year and looked like they would close all the way.  I
didn't check tightness on the throttle plate screws but they were in place --
nothing appeared out of place.  I lubricated the all of the throttle linkages
(back to the pedal) and checked the springs on the carbs.  I forgot about the
problem during the Michigan winter and then when I started driving this season
I decided it needed to be fixed.  I sprayed some starting fluid around the
shaft bushings and the idle changed when I sprayed the rear bushing on both
carbs.  Idle speed didn't increase.  I think it actually dropped -- maybe like
loading up.


>
> > 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.



Shafts and bushings arrived yesterday.


>
> > 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.



I ordered an extra set.  I'll either be able to recover from a mistake or have
some on hand for next time.


>
> > 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.



Actually now that I think more about it a few years ago I had to replace the
seals that go on top and bottom of the float bowl connection to the carb body.
Had a very small leak there, but it was such a small fix that I forgot about
it.   At least once a year I lift the piston by hand to make sure the needle
is aligned with the jet and that it drops nicely.


>
> > 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.



Really???  That's bad news for me.  Why wouldn't I be able to press out the
old bushings and press in new ones?  Assuming the bushing ODs are the same.
Or do you mean the ID of bush is going to need to be reamed after they are
pressed in?  I haven't tried sliding the shafts into the new bushings yet.  I
think I would need to have someone else do the reaming.  I don't know how I
would make sure the reamer is parallel with the carb mounting surface and also
perfectly horizontal.
>
> Randall
>

Thanks for the tips, Randall.  I'm on digest.  If you send a response could
you also copy me directly.

/John