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Camshaft


Mint
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My Mk2 GT6 is running triple dellorto carbs , there are double springs on the rocker valves , i think there might be a none standard camshaft is there any way of finding out without dismantling the engine . I have no history of work carried out on the engine and need to set the valve clearances .

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It's  fairly straightforward to measure valve lift with a dial gauge on top of exhaust and inlet rockers, and this may give a clue to the type of cam fitted. Checking valve opening and closing degrees is more difficult but with the radiator removed,  it may be possible to attach a 360deg protractor to the crank pulley and deduce approximate valve timing. 

Nigel

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Mint,

I agree with Nigel!

I'd add that measuring lift at the valve end of the rocker will increase the cam lift by the rocker ratio (1.45:1?)

But just knowing the lift will be a very guesstimate way of knowing what sort of cam you have.    HP cams do tend to have more lift, but the marker is a longer duration.     You're not timing the cam, so high accuracy isn't required.     Could you mark the pulley damper, perhaps on a strip of white gaffer tape on the edge of the pulley. with degree markings, all around?     The diameter of the damper part, the inertia ring, will give you the circumference (Circ = Pi x D!) divide that by 36 and mark the strip before you wrap it round the pulley.   That will give you 10 degree resolution, and probably 2 degree by eye, enough to determine the duration.       Or else a degree wheel held on by the nose bolt, and a mirror on a stick to read it??

Tabulating your valve height measurements on Excel will let you visualise the cam design, like this:

image.png.298a671343ee2ca05507a5cbed01336c.png

You can then smooth out any irregularities by hand, and get a good picture of the cam's dimension.     The above was taken on the bench, and shows a 300 degree, hilift cam.

The standard GT6 cam has a duration of 230 degrees, an early TR5/6 one 250,  'Fast Road' cams are about 280, 'Full race' 300. 

Good luck!

John

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