larry stein sez, re a '72 gt6:
> 1. the vacuum lines for distributor etc are all messed up. first there is no
> vacuum line on the distributor (lucas). also there are no vacuum lines on the
> thermostatic vacuum switch on top of the radiator.
Can't help with this unless I do some research. I have no idea why there
should be vacuum to a thermostatic switch on top of the radiator unless you
have a vacuum-controlled fan!
> 2. ...someone has taken the vacuum line coming from
> the bottom of the rear carburetor and attached it to some small device that is
> mounted next to the radiator. i do not know what this thing is but i know it
> is not original or factory.
I think it may be original. Read on.
> it has two wires on it as well as this vacuum
> line. one wire goes to the oil pressure sending unit...
> does anyone have any clue what the heck this thing is and what it is
> doing ???
This sounds like the anti-run-on valve. When it is engaged it opens up
vacuum to someplace in the carb (the float bowl perhaps?) so that no fuel
can be drawn through the jets. It opens only when you turn *off* the
ignition and when there is also oil pressure. If you check the voltage on
the lines to your oil pressure sender you should find that one of them has
voltage only when the ignition is off, not on. The reason for the oil
pressure switch is so that it will turn off once the engine stops turning
over. Otherwise it would drain the battery by being engaged whenever the
ignition is turned off. More on this below. (On my Spitfire I replaced the
oil pressure sender with a VDO unit that powers both the idiot light and a
gauge, but it didn't have the terminal to feed the anti-run-on valve. So I
installed a spring-loaded momentary-on switch somewhere under the dash so I
could engage it manually if necessary. However with the removal of the non-
functional air pump and EGR, the anti-run-on capability is not necessary.)
> i am amazed that the car ran so well with no vacuum line on the
> distributor.
The vacuum line on the distributor is probably an idle-only vacuum retard
for reduced idle emissions. Note which way the application of vacuum would
move the base plate. I'll betcha' it pulls the timing late. (I can't
comment about where on the carbs the vacuum tap oughta' be because my GT6
has SU's and I haven't even had time to sort them out yet.) The only things
you have to worry about if the vacuum line is missing are (1) that you set
the timing closer to the static timing rather than idle timing (probably
about 10 degrees difference), and (2) that the carb end is plugged. (We
recently had a round of discussion on this subject.) Technically you don't
need a vacuum advance at all, though some people claim to notice its absence
when they disconnect it, assuming they re-timed everything appropriately, of
course. At least some versions of the TR6 had both the vacuum retard and a
vacuum advance.
If I understood it and remember correctly, according to one manual I have
for my '70 GT6, that same vacuum line attached to a small valve on the carb
linkage someplace. It opened on decceleration, leaning-out the mixture just
a bit. It is probably unnecessary for normal operation.
If your car had Exhaust Gas Re-circulation it would also have used this
vacuum or a similar one to opearte the EGR valve. It too would unnecessary.
> 3. oil pressure sending unit. the book shows only one lead coming from it and
> going to the idiot line on the dashboard. but this unit has 3 wires on it.
> any clues as to why and what ???
As I described above, this is probably the anti-run-on version. (Until I
wrote the paragraph above I hadn't throught about it for a decade!) If I
had to guess, I'd predict this: One terminal grounds when you have no oil
pressure, thereby lighting the idiot light. The other two terminals connect
together when you *do* have oil pressure, thereby allowing current to
energize the anti-run-on valve. You should be able to trace those lines,
one to the valve and the other getting power only when the ignition switch
is turned off. Thus the valve operates only in the oxymoronic state that
the ignition switch is turned off but you have oil pressure anyway!
> 4. i did a compression test on all cylinders. the book says 130-145lbs. but
> mine read 200 lbs on all cylinders.
Set all the valves first (set them cold) then repeat the compression test.
Then for yucks warm up the engine and try it again. (My engine reads about
180 warm.) If the compression is still high you may have to spend money for
octane booster additives. But first, if it pings badly just try more
conservative ignition timing.
> 5. i wanted to adjust the valve clearances (or at least check them)...
> and worse yet, the book says to see the spec on the clearance (.007 ????)
> are they the same for intake and exhaust ?
That valve-setting procedure does seem a bit odd but I've never stared at a
6-cyl camshaft with that question in mind! What's odd about it is that it
seems overly complex compared to how easy it is. (Was that a Chilton's
manual, by chance? The Haynes manuals are usually pretty good.)
You can tell when a valve is fully open just by watching the rocker arm.
Put the car in gear and roll it forwards (or backwards) and watch. You
don't have to be real close. On the premise that a camshaft is round
everywhere except on the lobe part itself, all you need to be certain of is
that you aren't on or too near the lobe when you set it. As you turn the
engine forward you'll see an exhaust valve open then close, then its
corresponding intake valve open. When that intake valve has closed again
you can be certain that its exhaust valve is "definitely" closed, and thus a
candidate for setting. The reason you know the exhaust valve is closed is
that it must be closed for the compression stroke to happen and that the
piston must now go through a full power cycle before the exhaust valve opens
again. Similarly, just prior to a pair's operation, you can be certain that
before an exhaust valve starts opening its corresponding intake valve is
still "definitely" closed to prevent burning gasses from backing out through
the carb. If you are concerned about being too close to a lobe (or non-
roundness of your cam), you can always rotate the engine a dozen degrees or
more one way or the other and check the clearance again.
Here is another way to do it. Any valve can be set when its symmetric valve
is fully open, the symmetry seen across the center of the engine. Counting
from the front, when valve 1 is fully open you can set valve 12; when valve
2 is fully open you can set valve 11, etc. Of course, they don't operate in
a straight line front to back so the exact sequence will jump around!
As for clearance, every engine spec I've ever seen for the SC engine,
including both the 4's and the 6's, was .010 inches cold. Would Triumph
have changed the spec from '70 to '72 for the 6 but not the 4? I doubt it.
Does anyone with a '72 TR6 want to verify this? The .007 setting may have
been a warm setting (which is not advisable), or perhaps a reference to
James Bond (who drove a Stag briefly in Diamonds Are Forever).
A good source for info is Spitfire & GT6 Magazine's website:
http://www.triumphspitfire.com
Sorry about the length. Hope this helps.
Jim Muller
jimmuller@pop.rcn.com
'80 Spitfire (Percy)
'70 GT6+ (Nigel)
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