On 27 Jun 2002 at 19:18, Graham McMicken wrote:
> It seems as though my advance is not working.
One has to ask, how do you know? :-)
> The engine can Idle, and slowly start to rev, if I am manually
> turning the distributor.
That's because more advance generally gives more power, up to point
where the timing is too early. This behavior is entirely normal. It
also means that setting idle speed and idle timing is an iterative
process. You might consider setting timing statically first, i.e.
with the engine off.
> Now, I need to know how to fix this, I have a TR6 with a Lucas #41219D
> Distributor. I was wondering if there is a way to check the advance?
The weights work like this. When centrifugal force throws them
outward, they move the cams and the rotor more forward (i.e. in the
same direction that the rotor normally spins, which is
counterclockwise, if I remember). The springs pull the weights back
in when the spinning slows down or stops.
Systems often have two slightly different springs, and they won't
necessarily become active at the same time, meaning that one may seem
to have some free play. This is also normal. The idea is that you
get two different behaviors, a large advance vs. rpm increase at
lower rpm's, then less advance increase as rpm's go higher.
If you grab the rotor (with the engine stopped! :-) and try to rotate
it in its normal spinning direction, you should be able to turn it
easily enough to see it move, perhaps 5 to 10 degrees depending on
the spec'ed total advance. You should also be able feel the spring
pressure working against you. If you then release it, it should
return back to its starting position. (There may be a small bit of
play in the at-rest position before the springs become active.)
In most cases this will work perfectly, more or less. There are two
possible failure modes. The mechanism could have siezed, meaning
that you can't turn it and you get no centrifugal advance when it is
running. (This happened to me with a Chevy 305 once.) Or one or
both spring could have weakened or broken so that whenever the engine
is running the mechanism advances to its fullest. In either case you
should be able to observe it with this simple test.
The toughest case is one of weak springs. You usually can't tell by
feel whether a spring is as stiff as it ought to be. But it also
isn't a fatal problem. If a spring is too weak, you will get a bit
too more advance than you are supposed to as rpm's climb. You may
notice this as pinging or similar sign at higher rpm's even though
you set the timing to spec at idle. You can correct this by moving
the timing backwards a bit. In the worst case, you'll have good
timing at some rpm's but less than ideal timing at others. Given
that timing is a mushy compromise anyway, especially at higher rpm's,
this isn't a so bad.
If you really suspect the springs or any part of the centrifugal
advance mechansim, you can use a timing light and simply observe the
timing at different rpm's. You'll need some way to rev the engine to
various higher rpm's. A spouse or friend sitting in the driver's
seat and watching the tach while reving the accelerator with a steady
foot is one way. You then observe the timing with your timing light
while the engine is roaring in your face. Check it at, say, 1000,
2000, 3000, and 4000 rpm's. You can compare this to various
published curves.
Most likely you will have no problem. Setting the timing will then
be your next task. There are several ways to start. I like to start
with the static setting. Also with your idle advance (which should
actually be a retard) disconnected (but plugged to
prevent extra air from entering the carb) and the idle under 1000,
the timing should
be similar to the static timing. So another technique is to pull and
plug the retard line and then use the static timing (then reconnect
the retard line and set your idle speed). Or if you trust that the
vacuum unit works, just set it to the spec'ed idle timing. When
you're done, rev it a bit and watch the timing climb with rpm.
Hope this helps.
--
Jim Muller
jimmuller@pop.rcn.com
'80 Spitfire, '70 GT6+
/// triumphs@autox.team.net mailing list
/// To unsubscribe send a plain text message to majordomo@autox.team.net
/// with nothing in it but
///
/// unsubscribe triumphs
///
/// or try http://www.team.net/cgi-bin/majorcool
|