mechanical tacho drive

[gino1]

Hi all,
I'm looking into installing a mechanical tacho drive and would like to hear from someone that has installed one and where to fit and eventually buy the parts..
Thanks
Gino
Milano - Italy

[rgh0]

Hi Gino

I have seen the mechanical tacho drive in twin cams in a number of possible places.

1. On the back of modified dynamos.
2. Using a Europa style longer cam shaft, coming out the back of the cam cover
3. The most popular is to bore the front cover through the raised section in front of the original ford camshaft and pick up the drive from there. James Lambert in one of his posts on his Cosworth twin cam engine showed milling the cover for this and can probably provide more details on the parts he is using.

cheers
Rohan

[gino1]

Hi Rohan,
Thanks for the tip....I'll have to investigate further and se what is available in Europ with regards to the drive and how it couples with the jackshaft.
Thanks
Gino

[Chancer]

I had one that was run from a 5 port dry sump pump which I believe was originally fitted to a Formula Ford, it was made by Pace Products who I think are still making pumps.

If you are dry sumped this might just save a lot of custom machining.

[gino1]

Hi Chancer,
Unforunately no dry sump.....I work for a company who has an amazing toolroom though with cnc machines so no fuss regarding the machining...i'll try this Pace company and see what they have.
I tried another source this morning and apparently they have a drive and coupling made from Billet steel at nearly 300 quid !! Or did he say Gold ??

Gino
Milano....

I'll post this on the wanted list ..maybe someone's got one lying around doing nothing

[EdHolly]

This is the way I ran a 2:1 tacho drive to a chronometric tacho in a Brabham BT21 replica I had some time back.

Admittedly the Hart cam cover helped, with its top cut-out. but I think it would still be achievable with a standard cam cover. The beauty of this arrangement is that the cam runs half engine speed of course.

I used the allen key cavity in the back of the camshaft that plugs its internals to drive a quill to which a simple MGB / many other sports cars, angle drive was screwed after making a suitable adapter. Getting a small tapped hole into the head itself to retain the adapter was the only difficult part - this was required to stop the adapter turning, but with modern glues you could probably do it that way, and of course once removed no evidence of ever being there unlike the little threaded screw hole..

This worked perfectly and was on the car when I sold it. Chrono are so much nicer than electric tach's. I have done something similar on the rear of the camshaft / cam-cover for the Climax going into the Elite.

Ed

.

[gino1]

Thanks Ed,
I prefer to go the jackshaft route as I've already seen this although now i'm not sure on the rev ratio, is it 4:1 ?
Gino
Milano
italy

[billwill]

I think jackshaft has same size sprockets as camshafts, hence half the engine RPM.

[gino1]

Thanks Bill...
Gino
Milano
italy

[gino1]

I just received a very helpful e mail from Alex at QED and he has come up with the following that fits the twin cam:

http://qedmotorsport.co.uk/qed-shop/lot ... rown/black

http://qedmotorsport.co.uk/qed-shop/lot ... earbox-key

Not cheap but at least I know it will fit without messing around. All I need to do now is machine a hole in the front cover.

Gino
Milano
italy

[SJ Lambert]

Gino, we centered it from behind, pilot drilled it and then milled it copying the Cosworth arrangement on our existing one. Will make a boss for the gearbox and have fabricated a gearbox key to match.

The boss can be drilled off centre if needed in order to get a good centralized mesh on gear box shaft & key. (Though it's not super critical as there's typically a generous clearance on shaft & key).

The boss needs a flat on the water pump belt side for belt clearance & the timing chest has a clean up cut taken off the mounting pad for trueness.

By the way, our milling machine is Italian!!!!

I'd post more pics but have laptop problems at the moment!

[gino1]

Hi SJ...
Yes I thought of doing the same by fitting a pointer onto the end of the jackshaft then marking the back of the front cover to be able to run a pilot drill through to the front and then pick it up as you have..seems great minds think alike
Have you got a picture on how to route the tacho cable around the engine ...mine's a LHD so i'll need to route the cable around the engine and into the cockpit with a little more difficulty that a RHD version

Gino
Milano
Italy

[SJ Lambert]

You'll also need an extended jackshaft dowel to accommodate the key & longer sprocket bolts.

We're routing ours into a monocoque open wheeler, so can't help with the specifics for an Elan instillation, but with a long enough cable so as to avoid tight radius direction change you ought to be able to sort it. Our engine is behind the instrument panel, so the cable has to make a 180 degree turn at the panel end.

[gino1]

Hi SJ....
I thought about picking up the external diameter of the jackshaft instead of dowelling it and use two bolts to hold it on.
Dowelling it may mean I lose that little "adjustment" I need to align it correctly.
Anyway still early days yet ..still have to purchase the parts.
Thanks for your help and the pics as they have been very useful to me.

Gino
Milano
Italy

[SJ Lambert]

Managed to obtain a length of magnesium to turn the boss from!