Lotus Elan

Tried a search, tach question

PostPost by: TypeRboy » Thu Sep 29, 2005 6:30 am

Hi Folks. New member here, great forum! I searched and read quite a bit about Tachometer issues, but found nothing to help me really ( unless I want to buy a computer program to produce a tach signal off my home computer to calibrate..)

My tach is a NOS original for my 66 S2 with the looped wire connection ( inductive I guess ) for the signal. My ign is point type with a Lucas sport coil ( no external resistor provided with the new coil, so I assume internal resistance if it matters..).

The tach reads about double the actual revs. I have heard that these older tachs are externally adjustable for calibration, is that true?

Any other suggestions?
66 Elan tall block Alfa 5 speed
63 Cortina Cosworth BDA
Very understanding wife!
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PostPost by: curly type 26 » Thu Sep 29, 2005 7:56 am

Hi noticed your description if you have 5spd fitted could you let me know what you had to do ect i am busy rebuilding my 65s2 with a TTR chassis ect and would love to update to 5gears there is nothing worse than watching your rev counter needle trying to escape at motorway speeds thanks Colin. :D
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PostPost by: gjz30075 » Thu Sep 29, 2005 1:30 pm

TypeRboy wrote: I have heard that these older tachs are externally adjustable for calibration, is that true?

Any other suggestions?


True. There's a hole in the back of the tach that allows access to a potentiameter (sp?). A small, flat bladed screwdriver will do the trick for you. Pretty tough to access while in the car, though. I used a mirror to help get the screwdriver to the hole.

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PostPost by: tonycharente » Thu Sep 29, 2005 7:21 pm

I recently did mine (on a '69). Certainly much much easier with the gauge pulled out from the dash. There was a little rubber plug on the rear of the unit, which I removed, and then as suggested above a small flat blade screwdriver poked through this hole accesses the adjuster.
[In my case the Tach had been "all over the place" because (I think) I have electronic ignition fitted, so in fact I took the Tach right out in order to be able to reduce the (internal) "loop" from two turns to one to reduce the sensitivity. I then wired it up again and calibrated it against a digital multimeter. I set it dead on at 4000 rpm - it now slightly over reads at 2000 and slightly under reads at 6000 rpm but is pretty accurate thoughout. And it's no longer "all over the place". Hope this helps. Tony.
1969 Elan FHC S4 SE
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PostPost by: TypeRboy » Fri Sep 30, 2005 2:06 am

Hey great, that's good news. I'll pull the car into the garage and pop out the tach and give it a whirl.. I have been basically running without a tach for three years now, and hate to think how high I have been actually reving the poor thing..

The 5 speed is out of a Spyder Veloce ( pretty much any year will do..).
A friend of mine designed and manufactured 4 adapter plates to mate it up with the stock ford bellhousing. I'm sure that I have the specs for the plate around here somewhere if you wanted to duplicate another one. He sold one, used one, gave one to me, and still has the last one ( but I am going to use it..) The tranny is a bit taller than the Ford unit, so it tilts the motor down slightly at the back, and up at the front. ( no way to tell by just looking at it, but with the tall block it reduces my hood clearance to less than 1 mm, with the carbs sitting on the foot well..)

I machined off the tranny yolk and welded on the Ford yolk, and had to slightly shorten the input shaft for crank clearance. The pilot bush is custom ( just machined brass ) and the pressure plate is stock Ford, the disc stock Alfa.. same diameter..)

The shifter comes out about 1 inch or so further back than the Ford, so a tiny bit of frame material had to be removed. The shifter is cut down to 1 inch, and a short extension is slipped over it ( adjustable shifter length, cool. Except that this tranny normally has a 17 inch long shifter, so the mechanical advantage of a 2 inch long shifter is not so good, mine is about 6 inches long, and still a bit hard to move around.)

The tranny mount is custom, and the speedo cable is kind of jury rigged up with the Lotus elbow, which worked fine at first but has since stopped. I'm sure it's something simple, but i'm not removing the body just for that.

The advantage of the Alfa tranny is lightness, a better first gear ratio, with pretty good ratios all around, and of course the 5th gear ( just heaven let me tell you..)

The disadvantages are a harder pull on the shifter and not a very quick shifting tranny at any rate. They are also a somewhat weak syncro, and not strong enough for any 200 hp monsters ( I've had no problems yet with my 1750 motor, which must be about 130 hp anyway..)

Overall I like it so much that I'm going to put another one in my Cortina, I know the Ford T5 will fit the Cosworth block, but it won't fit in the tranny tunnel of my Mk1. We'll see how that holds up.. :shock:
66 Elan tall block Alfa 5 speed
63 Cortina Cosworth BDA
Very understanding wife!
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