I’ve just noticed the tacho occasionally bounces wildly and then
it’ll settle down for a while before bouncing again. Throughout all
this the engine is fine - no misfires (I have elec ign off an S3
XJ6) etc
So this leads me to believe that it could be:
- a poor connection from the tacho to the coil
- a poor earth connection to the tacho
- a problem inside the tacho
I’m going to attach a spare tacho and see if that bounces at the
same time which would point towards an ign/coil problem
But with regard to the tacho itself, has anyone had problems with
the actual tacho ? and if you dismantle them are they cleanable ?–
Bill 71 S2 OTS 54 Sunbeam Alpine Honda CBR600
Southport, Merseyside, United Kingdom
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In reply to a message from Bill Molloy sent Thu 6 Sep 2007:
There is a fourth option Bill that could cause the bouncing rev
readings…
- Alloy flywheel and untreated Parkinson’s
Time to up the levodopa dose maybe, but be careful - it can cause
excessive libido and you wouldn’t want that at our age
Sounds like a connection problem rather than the instrument. A
watchmaker might be able to service the mechanical aspects of the
meter but I doubt it’s those. If there’s an internal electrical
issue it might be a dry joint somewhere on the coil or other
components or a broken wire that makes and breaks contact under
vibrations?–
66 2+2, 74 OTS, 76 DD6 Coup�, 84 DD6, 85 XJS 5sp convert
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Fri 7 Sep 2007:
Hi Pete
I’ve just checked all the coil connections and they seem ok.
Looking at the wiring diag maybe I also need to check out the ign
switch. I have noticed that it runs a bit warm but have always put
that down to conduction of heat from the engine compartment through
the steering column rather than the switch itself generating heat
due to poor contacts.
But I guess a poor connection there could cause the bounce although
I would also expect the engine to run erratically if that were the
case.–
Bill 71 S2 OTS 54 Sunbeam Alpine Honda CBR600
Southport, Merseyside, United Kingdom
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In reply to a message from Bill Molloy sent Fri 7 Sep 2007:
Sounds fishy Bill. FAR more likely to be electrical resistance IMHO
than radiant heat, or conducted heat along the column. Try to feel
the opposite side of the column from the switch, or a bit lower
down if you can get your fingers in there after a drive?
You may have two issues of course - a dodgy switch and a dry joint
or broken/breaking wire inside the tach. Not sure of the electircal
set-up (Ray or somebody could advise) but if you really can’t track
it down then maybe a temporary always-on bulb wired into the tach
power supply could show if there is a power flicker at the same
time the tach fluctuates, or if there seems to be no connection.
Make that ‘no relation’ :-)–
The original message included these comments:
I’ve just checked all the coil connections and they seem ok.
Looking at the wiring diag maybe I also need to check out the ign
switch. I have noticed that it runs a bit warm but have always put
that down to conduction of heat from the engine compartment through
the steering column rather than the switch itself generating heat
due to poor contacts.
–
66 2+2, 74 OTS, 76 DD6 Coup�, 84 DD6, 85 XJS 5sp convert
Cambridge, United Kingdom
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In reply to a message from PeterCrespin sent Fri 7 Sep 2007:
The temporary Tacho i’m going to connect up to check if it also
bounces is off a 4cyl car. I know the reading will be wrong … but
will it be higher … or lower
Anyone want to hazard a guess before I try it ?–
Bill 71 S2 OTS 54 Sunbeam Alpine Honda CBR600
Southport, Merseyside, United Kingdom
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In reply to a message from Bill Molloy sent Fri 7 Sep 2007:
Bill,
It should read 50% high. i.e. - 1000RPM will read as 1500RPM.–
Ray Livingston - '64 OTS Santa Cruz, CA
Santa Cruz, CA, United States
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In reply to a message from Bill Molloy sent Thu 6 Sep 2007:
I had the same problem in my '68 2+2 after installing a
Pertronics unit, combined with a low RPM reading. My tach
has a potentiometer (variable resistor) accessible through a
hole in the back of the steel case. I adjusted it for RPM
setting, and the bouncing stopped for a while but has now
returned. I believe the potentiometer is the problem, but
have not become motivated to try cleaning it or replacing it
on the circuit board. Many circuit board mount
potentiometers are not encased and simply consist of a metal
arm that is sprung against a circle of carbon resistance
compound. As you turn the metal arm, you change the length
of the electrical path through the resistance compound,
raising or lowering the resistance. If the metal arm
weakens or the carbon surface gets dirty (either is highly
probable after 40+ years), the electrical contact becomes
spotty, responding to vibration and variations in current
flow. I do not know if your tach is the same as mine since
there have been at least three different models used over
the years. Good luck,–
The original message included these comments:
But with regard to the tacho itself, has anyone had problems with
the actual tacho ? and if you dismantle them are they cleanable ?
–
Kent
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