Classic cars forum & vehicle restoration.

[1935Hillman]

Hi all,

Further to my travails over a rev counter drive I have decided that the best way is to go with a C40T dynamo with rear tacho drive. However, my next decision is whether to go for an original NOS item offered to me at £120 or an off-the-peg reproduction item at £83. It seems that while I type this I am thinking " whats 30-odd quid for the sake of originality?" but I'll ask the question anyway. Does anyone have experience of the widely available repro dynamos, and if so what do you think ?

Many thanks,

Tim

[kevin2306]

I looked at these a while back but decided to stick with the dynamo, Keeps things simple and they work well enough for me.

[Bitumen Boy]

No direct experience of my own, but there is a school of thought which says that the repro stuff, even brand new, just doesn't match original Lucas gear for quality, and that overhauled original tends to be a better bet. Also, I get the impression, going by the tone of your question, the non-original part might well niggle you into replacing it before too long...

[ukdave2002]

I'd stick with an original if you can; the repro stuff can be better than original in some cases but also far worse!

The challenge is that it's difficult to identify who actualy makes the repro stuff as it's often branded with whatever the importer wants.

One thing that I would be concerned about on this particular Dynamo is the quality of the tachometer take off; the Triumph stag has something similar in the form of 90 degree speedo take off that fits on the gearbox, they are available as repo but have a reputation for failing after only a few thousand miles, whereas the original ones rarely fail.

Cheers

Dave

[Penman]

Hi
What strikes me about the dynamo driven rev counter is how many variables there are to get a correct reading.
First there is the difference in diameter between the dynamo pulley and the crankshaft pulley, then if there is a gearbox at the back of the dynamo there is another gearing change unless it is 1/1.
Whereas a distributor driven electric rev counter presumably works by counting sparks.

Or am I missing something.
_________________
Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10

[Ashley]

My advice to anyone wanting to fit a revcounter to a car without a drive is to obtain a mechanical one that suits and send it to JDO, John Ostick to convert it to electronic. It's not expensive and they need three wires, Earth, positive and a wire to the points side of the coil

http://www.jdo1.com

[1935Hillman]

Thanks for all of your replies. Yes, I was kind of wanting to be persuaded to go with the original part and I think that this is what I will do. The part I am offered is NOS but will be checked and reconditioned if required so should be good.
Originally the rev counter on my car would have been mechanically driven off the distributor but I can find no-one with any experience of these types pre-war. Most dizzy experts seem to know of the ones that came with certain TR's but nothing earlier. My choice has really come down to (1) Use an adapted TR distributor with tacho drive which would not be original or (2) Use a C40T dynamo with rear tacho drive which would also not be original but easy to fit and in my opinion a more robust arrangement.
I am mindful of the potential for rev count error but will be working with Speedograph Richfield to try to get this right. Of course the gauge will be to some extent cosmetic and I am confident of my own abilities in feeling / hearing the revs of the car when driving !

[goneps]

[Penman]

hi
Yes, that is yet another variable.
_________________
Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10

[Ashley]

Wasn't it the six cylinder TRs only. that had a Delco distributor with a Tacho drive.

[1935Hillman]

Of course if anyone knows of ANY prewar cars that employed a distributor tacho drive I would be very interested to hear of it.

[Bitumen Boy]

[1935Hillman]

Revisiting this dynamo issue again.
I am going for the recon Lucas with the rear tacho drive just delayed doing it while more pressing things were being done
My next question is: As I am making this system up effectively from scratch how will I be able to get the correct reading when I get back to the rev counter itself ?
Presumably it will be a case of measuring pulley diameters etc. and perhaps creating and/or modifying the rear drive gearing.
If anyone has done this before I would be grateful to hear about it
Many thanks

[MVPeters]

Two thoughts:

A dwell meter will show you engine revs.

If you know how the car is geared - mph per 1,000 revs in top gear - expressed as "15MPH /1,000 RPM" & often in older handbooks, then at 30 MPH the tach should show 2,000 RPM. 45 MPH = 3,000 RPM & so on.

Neither will be especially accurate, but might be a starting point, or even 'close enough'.
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

[petelang]

You can always get a gearbox made up in line to get the speed correct. Any tachograph workshop should be able to are one to suit.
Peter