Rev counter/ tachometer

zefarelly · 13 Apr 2004, 13:25 (Ref:938287)

I fitted the std smiths rev counter to my car . . . .and it was all over the place . . . .I found a cheap but new autometer gauge and fitted that . . . .its not much better, before I go and shell out £150 on an elliot one . . . .does anyone know why they go haywire . . .its fine when you start up, but goes nuts after a few minutes. . . .its wired up right, to the neg side of the coil as it says on the instructions, and has a power supply from the voltage stabiliser behind the dash, nd a good earth . . . .any ideas ?

**Peter Mallett** · 13 Apr 2004, 14:47 (Ref:938386)

I had a problem once resulting from a light switch connection. Every time the headlights came on my rev counter went to zero. But then again the engine stopped too so I guess it can't be that.

zefarelly · 13 Apr 2004, 14:48 (Ref:938389)

ha ha . . . .if the alternator overpowers the engine then I'd suggest a bit of fine tuning

**Tim Falce** · 13 Apr 2004, 14:52 (Ref:938395)

Have you tried connecting the power feed to somewhere that is not supplied by the voltage stabiliser?

graham blackwell · 13 Apr 2004, 15:29 (Ref:938442)

Is the feed wire from the coil screened? Do you have a supressor on the system? Could be stray RF that's creeping in. Have you tried routing the +12V wire away from other cables?

Dave Brand · 14 Apr 2004, 07:28 (Ref:939105)

Check the voltage at the supply! Have you taken a feed from the instrument voltage stabiliser? From (distant!) memory of MK1s the instruments use a lower voltage (9?) to ensure correct readings whatever the state of the charging system.

zefarelly · 14 Apr 2004, 08:06 (Ref:939122)

good point Dave, I could try it straight from the ignition circuit, and the main feed from the coil isnt screened, I cloud try that . . .I'll have a play before parting with more cash !

KC · 14 Apr 2004, 12:58 (Ref:939413)

We had similar trouble with an Autometer tach on the race boat and a better ground connection solved it.

1200Datto27 · 14 Apr 2004, 13:24 (Ref:939436)

Also make sure that you are not getting any stray pulses into the tacho signal, try and get hold of a graphing multimeter that can display the trace from the coil to ensure that under load you are not getting any extra feedback. Will also help you detect any misfiring/earth issues with the ignition system.

zefarelly · 14 Apr 2004, 15:24 (Ref:939527)

thanks guys . ..I'll go fettling the wiring and see how it goes

eclectic · 17 Apr 2004, 09:12 (Ref:942397)

You know about the Lucas smoke box theory?

Perhaps someone has a copy they can post here?

Rubinho · 17 Apr 2004, 16:18 (Ref:942673)

http://www.powroll.com/tech_smoke_th...ic_circuit.htm

zefarelly · 19 Apr 2004, 15:15 (Ref:944261)

quality . . .that explains it all.

I'd hazard a guess that article comes free with evert TVR ?

Rubinho · 19 Apr 2004, 15:53 (Ref:944301)

Quote:

Originally posted by zefarelly
quality . . .that explains it all.

I'd hazard a guess that article comes free with evert TVR ?

Probably, but it was my Alfa dealer that gave me the link!

zefarelly · 20 Apr 2004, 10:48 (Ref:945262)

ha ha . . .another manufacturer noted for its quality electrical hardware !

I was wondering (after last nights rolling road session) whether the fact that I have to run on points, and they bounce over 5500 or so and or dont close properly, has anything to do with it being erratic ?

Dave Brand · 20 Apr 2004, 11:01 (Ref:945279)

Quote:

Originally posted by zefarelly
I was wondering (after last nights rolling road session) whether the fact that I have to run on points, and they bounce over 5500 or so and or dont close properly, has anything to do with it being erratic ?

That would explain it - the tacho is reading ignition pulses, so if the points are bouncing, the direct relationship between ignition pulses & engine RPM is lost. The tweak used to be to fit six-cylinder points - physically identical but with a stronger spring.

StephenRae · 21 Apr 2004, 09:17 (Ref:946438)

Why do you think the points are bouncing at 5500? FF1600s easily rev to 6800 with standard one piece points.
I have had a life long war, first with mechanical rev counters and then with electronic ones...which I seem to have sorted with an SPA shiftlight/rev counter..although thinking on the first one I had of those.. gave up!!

zefarelly · 21 Apr 2004, 11:21 (Ref:946544)

well I dont notice them bouncing but the guy with the rolling road said they always do . . . .and the strobe gun showed varying RPM once over 5000 . . . . . V6 points as in Essex ones Dave ? I'll try that, could be a cheap fix, I know the FiA Lotus Cortinas rev to 8k and on points . . . .although theyre as good as dead after a few hours apparently

Dave Brand · 21 Apr 2004, 16:26 (Ref:946847)

Quote:

Originally posted by zefarelly
V6 points as in Essex ones Dave ?

Probably.......although nowadays it's possible that nobody makes two different springs.

zefarelly · 22 Apr 2004, 08:31 (Ref:947598)

I have a set of twin cam points and the spring is noticably stronger . . .I will investigate more . . .I know 'heavy duty' ones are available from certain outlets, but knocking on £20 for a set of points is what I'd call expensive, me being me will find an economic way of doing it if at all possible!

Dave Brand · 22 Apr 2004, 10:30 (Ref:947684)

Quote:

Originally posted by zefarelly
but knocking on £20 for a set of points is what I'd call expensive, me being me will find an economic way of doing it if at all possible!

Try a big rubber band!

Revracing · 22 Apr 2004, 10:41 (Ref:947691)

I would be very surprised if the Points manufacturer actually made the springs they fitted, for me it seems more likely they out sourced them.
If anyone has the dimensions of the spring. i.e overall length wire diameter and closed coil lengths, then check Lee Springs www.Leespring.co.uk they make all maner of springs with varying spring rates. You may find one more suited to you needs....

Dave Brand · 22 Apr 2004, 10:59 (Ref:947705)

Quote:

Originally posted by Revracing
If anyone has the dimensions of the spring. i.e overall length wire diameter and closed coil lengths, then check Lee Springs www.Leespring.co.uk they make all maner of springs with varying spring rates. You may find one more suited to you needs....

Points don't use coil springs!

Revracing · 22 Apr 2004, 12:19 (Ref:947788)

That is not a problem! Lee spring manufacture torsion springs aswell..

zefarelly · 22 Apr 2004, 15:18 (Ref:947975)

maybe I'll just break the rules and use lumenition

I have some 350lb strut springs but they wont fit inside the distributor cap

I wondered about trashing an old set and using 2 springs together ?

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