Tach drive dog on inlet camshaft ’56 Mk1

I discovered the wrong mechanical tach drive adapter and drive dog, was attached to the inlet cam when the engine was rebuilt by the previous owner.

My question: how do I remove the drive dog on the inlet camshaft with the engine in the car? I have a long, 6 point socket that will fit on the drive dog but, will the inlet camshaft turn or be mis-adjusted when I turn the wrench to loosen the drive dog? Do I need to prevent the camshaft from turning, how would I do this?

On the other hand, I can leave the drive dog on the camshaft but, will have to buy a new $200+ angle drive.

I’m assuming, by changing the drive dog, I can avoid replacing the angle drive and use a cable from the clockwise sweep, 4:1, tachometer to the generator on the camshaft.

Thanks in advance for any comments.

Bruce, as the cam is connected to the crankshaft via the timing chains there is no way in this life or the next that the cam is going to move while turning the wrench.

The only way I can see it moving is if Bruce’s surname is Banner and he gets really angry…

1 Like

Thanks for the info.

As I understand it, you want to remove part 33.
If you have clearance to the scuttle (firewall) you can first remove 38 and 36 to give you some more wrenching room. You are unlikely to disturb the camshaft, and even if it moves a bit you won’t hurt anything else. I wouldn’t think you could jump a tooth on the timing chain just by turning the camshaft the wrong way.

I would remove the cam cover and rear bearing cap , so 34 and the oil slinger 28 is it , don’t fall in the head !
Like said , timing will not be affected at all !

Yes, #33 is to be removed but, I’ve been fitting the early Mk 1 generator (in drawing above) and the later generator (doesn’t use the gearbox, cable attaches from tachometer to drive dog on end of cam.) There is not much room and the cable has only a 6" radius bend. I might have to buy a new #38 generator or switch to an electric set-up. Thanks.

Could you not modify something like this !

I’ll look into something like that. I don’t know if there is enough room to fit that drive and the adapter and if it will work with the Smiths Tachometer. It’s very tight, maybe 1" to the firewall from back of tach drive.

I came across a photo of a '56 Mk1 on eBay, it appears they changed to an electronic tach drive.

I might have to go that route.

1 Like

You can always remove the camshaft. If you leave the sprocket undisturbed it will only go back 2 ways and you can see the timing notch to know you got it right.

That’s what I had to do Rob , when I converted the XJ6 Cam shaft to a dog drive !

Is the reason you suggest possibly removing the camshaft to get better access to the drive or, is there another reason? Thanks

No, that was the only reason. I’m not totally familiar with the Mark 1, so maybe my suggestion is not viable, but I thought if you can get those two allen socket head screws out with a shortened hex key, then the camshaft and tach drive will lift out together.

I was able to remove the drive dog with the cam shaft in place. Only thing I removed was the heater box and a water pipe. I decided, after talking with drive rebuilders, to spend the time/money elsewhere. The plan is to add a oil thrower and bolt to the intake cam shaft then, add a cover like on the exhaust side. I’ll probably run the tach off of the coil.

Q. What is the torque spec for the bolt holding the oil thrower at the end of the cam shaft? I started to tighten but, wanted to see if there was a spec.


I just did mine up tight after adding some thread lock !