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BJ8 rev counter showing double rev.

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N

NIB

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Just bought myself a Healey 3000 BJ8.
The rev counter shows twice the actual revs, what can be wrong?
Also on the rev counter there is 4 cyl written, is that correct? It looks like the original rev counter.

Niels,
Denmark
 
Just bought a Healey 3000 BJ8.
The rev counter shows twice the actual revs, what can be wrong?
---Wrong Rev counter???

Also on the rev counter there is 4 cyl written, is that correct?----Nope!!!, and that is the probable cause the Tach is for a 4 cyl engine not a 6.----Fwiw---Keoke



It looks like the original rev counter.Prolly is but for a 4 cyl engine.

Niels,
 
The Tach for a BJ8 should have a black face and be numbered
"RVI 2602/00". Mine also states "6 cyl, positive earth".
That, however, is for a 1964 phase 1, BJ8 Healey that was exported to the United States. I am not sure that for a car exported to European countries would be identical.
 
I have also found the tachs on Healeys somewhat inaccurate, more so if a pertronix ignition is used. Some of the internal capacitors, resistors, etc. can deteriorate and may need replacing. However, if yours states it is for a 4 cyl, it is not the correct one to begin with.
 
Something fishy here: the 4-cyl Healeys--and earlier 6-cyl Healeys--have mechanical tachs; the BJ8s have electronic tachs.

You can calibrate the electronic tachs. I've done this and my BJ8's tach agrees precisely with my dwell/tach meter. I used the tach to calibrate my speedo, which agrees with a GPS (FWIW, I'm using a Pertronix Ignitor).
 
Something fishy here: the 4-cyl Healeys--and earlier 6-cyl Healeys--have mechanical tachs; the BJ8s have electronic tachs

Yep BOB,
But there is a fella here in the US that is well known for converting Tachs [Mechanical / original Electronic] to his specific Electronic configuration. I forget his name at the moment,but he is also well known in Europe. Consequently, that Rev counter could be one of those--Fwiw--Keoke
 
Finally bought a correct RVI2602 6 cyl tachometer from a dealer. I installed it, but it still seems to show too much. When driving 60-70 mph in 4th and overdrive it shows around 4500 rpm. I believe thats too high?

Not really sure what can be wrong, but perhaps I can check the rpm with some other instrument? What about the wiring on the back, is the white wire supposed just to be twisted aroung a bracket and then continue on in the wiring harness?

Niels
 
FWIW cos they are never that acurate, mine reads 2500 RPM at 65mph or thereabouts. If it has been rebuilt at some time there is probably a pot (variable resistor inside to calibrate it. There are lots of articles available on the net about rebuilding anc particularly calibrating the smiths tacho. Try here https://www.classictiger.com/techtips/motach.html
Ian Irving
 
I believe the tacho works, I just bought it from ahspares.co.uk, it seems strange if they sell tachos that arent calibrated, it looks completely new. What strikes me is that it shows around the same as the previous MG 4 cyl tacho that was in the car, thats why i was thinking of the wiring could be wrong. Or a long shot, is the engine running that fast, atleast it makes alot of noise when going at that speed.
I better find a tool to check the ignition, I believe they can measure the revs. too. That should make it somewhat easier to solve the problem.

Niels
 
There should be a loop (white wire going through the "terminal" twice)with no copper exposed. Are you using electronic ignition or points? Get a external tack and compare the readings. I got one that is an Ohm/volt meter. It will also tell you if the points are good. Nice tool to have. I carry it in the boot along with a timing light. Check the swap-meets and flee markets for a used one. Can be had for 5 to 20 bucks.
My dash tack is spot on. Wish I could say the same for the speedo.
 
My '65 BJ8 tach does everything just fine except being heat sensitive, when heated up it is about 20% too high. On mine there is an adjuster on back. took it out of dash, set in on passenger seat with extension wires, steered with knees and based upon reverse math from road speed (so many mph in certain gear should be X RPM)reset it while hot, okay for a while then same thing, overestimate when hot.
 
Why, Does an external tach also read high? Something is wrong somewhere. This is a simple device. Could your tach may have been oiled improperly and when the oil gets hot it moves more freely than when cold?
 
Interesting point why has, so today I had a look at my tachometer. When cold it shows app. 3000 rpm at 60 mph, thats close to normal I guess, when warm its almost 4000 rpm at 60 mph. So I guess something in my system is heat sensitive too, dont know if its the tachometer or something else.

Could it be the ignition coil, I have a Mallory coil in the car, I know it should be a Lucas originally.
 
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