From: NAME: Mike Jeffreys [DAT31 ]
FUNC: DAT31
TEL: 0473-645609 <JEFFREYS M J AT WEB AT WEBCS>
To: british-cars@hoosier.utah.edu@unet
Having read the various mailings on dealing with leaking over-run valves in
the butterfly by just soldering them shut I offer my tuppence worth:-
Bit of background from the interesting mailing on 'TR-7 and TR-8 history'
which is applicable to most newish SUs.
>On both engine types the SU carburettor spindles wear and may cause
>sticking throttles, while TR7s with an over-run valve in the butterfly
>can also suffer slow throttle closing action; the first requires a
>rebuild, the second can also be solved by soldering the valve closed.
Addressing the the first problem is fairly easy:-
a) if only the spindle is worn, buy a new one (cheap and easy to
fit),
b) if the SU casing is worn, have it rebushed (30 pounds in UK).
What this means is that an SU has an indefinite lifetime if you pay a
fairly small reconditioning charge (I assume there are SU reconditioners
over the 'pond') every 10 years or so.
The second problem can be addressed as said, i.e., soldering. My opinion is
that it is easier, safer, more efficient (and can release more power to the
car) if one just buys a new valveless butterfly. I have done this to all my
SU carbs and, in the UK, the butterflies cost about 5 pounds each. Why is my
method better?
a) easier, because only a screwdriver is needed (no military spec
soldering iron needed),
b) safer, because I wouldn't fancy a lump of solder falling into
the engine if the soldering was suspect (dry),
c) efficient, a large lump of solder on the surface of the butterfly
must cause unwanted turbulence in the inlet manifold,
d) more power, on full throttle a smoother passage for the air
past the butterfly will exist *without* the solder lump.
The downside of either soldering or fitting a valveless butterfly must be
the over-run emissions problem (which is probably due to the inlet vacuum
drawing oil down the inlet valve stem) plus increased carbon on the tops of
the inlet vavles (again due to oil being drawn down the stem).
Any thoughts on power losses due to carbon on the inlet valves?
Regards,
Mike.
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