Tach conversion

Tachometer no longer works. Have checked with a meter and their is no sign of activity at the Tach generator. Have read the archives about conversions as this seems easier than taking the Tach generator off. I have a retro air alternator fitted. Assuming I can find someone in New Zealand to convert the tachometer does anyone know if the alternator will be compatible? Electricity is not my thing!!

63 MK 2 3.4.

Has the drive dog expired? Common failure point.

Also, the armature bearing can back into the case, withdrawing the tang from the drive dog.

Hi Stewart, I have a generator off my ‘S’ that might be a fit but as Wiggs says the tang can become divorced from the cam. Check back on some recent threads, I think Erica had one that she repaired?

your alternator conversion has no impact on the tach.

I took my generator off a few months back to stop a oil leak , it’s not too bad of a job , removing the battery helped a lot , 2 of the Allan headed bolts you can see , but the 3rd middle one at the bottom is a pain , why Jaguar never fitted ordinary bolts I never now , would be much easier with a socket !
Any way , you would have to take it off to check the drive dog .
I would say about as much work as removing a Tacho from the dash .
You don’t have to take the cam cover off , I did as well as the rear cam bearing cap , as it is a xj6 engine , that never had a generator on the back of the cam , just wanted to seal it up oil tight !


Yes, that happened to me many decades ago. I fixed it with a small pin inserted from the groove that holds the O ring. Been working fine ever since.

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Thanks for the advice everyone . I’m going to give it a go today at removing the generator.

Actually started yesterday but didn’t have the right size Allen key…,

Pro tip: I never reinstalled the muthaf%#€!ing bottom one: the two on the side keep it in, just fine.

My Mk1 had the old cable drive which would leak oil like crazy… Ended up buying a brand X tach that had the same rev range and installing it behind the “Smiths” face. Worked perfect and no oil leaks. Only real electrical connection was a wire to the coil. JS

Jeff Smith
Atlanta, GA

Wasn’t to bad a job. Greatly added by removing battery and air cleaner and laying on top of engine with legs out the front.

Visually everything looks ok. Using my iPhone camera I can see drive dog is in one piece.

The bearing on the generator sticks out about five mm and doesn’t move back or forward. If you rotate the bearing it is a notchy movement not smooth at all? Could this be the culprit?


The notch movement is normal its the magnets which create the output.
Stewart, did you ever have the E on Pukekohe way back when we had the Lotus BMW Jaguar race days?

Update!! Just had a look at the tach generator image on SNG Barratts and the circlip sits flush with the lip of the barrel - mine is recessed into the barrel by a few mm, so mine has recessed. further tested it by refitting to cam and it fits flush regardless of angle of bearing (hope this make sense).

Robin- that probably was me with E Type - Golden Sand OTS, used to race a fair bit…

Hook a drill up to the tach gen: if it works, you’ve found your problem.

Fixed! For now at least. Took the back cover off the generator and hit it with a hammer till it was flush. Then refitted everything and works like a charm. If it happens again I’ll investigate one of the permanent solutions.

Appreciate everyone’s help.


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Found a pic of the drive dog , this is a old one , worn , I replaced it with a new one before refitting the gen !

Basically anything can be fixed with a big enough hammer! :slight_smile:

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More properly known as a percussive adjustment tool.


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