Lobe centre valve timing tips please

I'm trying to set the valve timing on my T140 engine. I have a dti set up directly on a pushrod on a cam follower.

I am having trouble deciding when to call the needle on the dti back at the +2mm starting point. The reason I'm having this trouble is that the needle flickers around when it gets back near the no-lift area, and therefore there are quite a few degrees during which it could be called opening/closing, or not (if anyone sees what I mean??).

OK, so what I'm thinking now is that using pushrod lift at TDC would be a better way of tackling this. I have a figure of around .176" for the inlet (standard Spitfire profile, 71-7016), but I don;t have any figure to aim for re. the exhaust (I'm using a 70-9989 cam, which is the same profile as E-3134, on the exhaust).

So this is my question: What should I be aiming for, clearance at TDC-wise, with this exhaust cam?

If anyone happens to have a concise explanation of how ti work the lobe centre method, and what figures I should be aiming for (with all relevant info relating to ATDC / BTDC / BBDC / ABDC etc, it would be very helpful. Thanks in advance.

Hello Tiger!

Here is the method I use to precisely locate the lobe center (it may be described on jsmotorsports site but not sure). You need a degree wheel mounted on the crank and a dial indicator.

1) Find the top dead center (TDC) and set the degree wheel to 0° at TDC.
2) Install the dial indicator at the tip of the Intake valve and set it to 0 at no lift of the intake valve.
3) Turn the engine forward until the intake valve is open of x thou. Record the value read on the degree wheel in that position (e.g. = 40 degrees after TDC)
4) Continue turning the engine forward until the valve is x thou (same value as in 3) from fully closing. Record the value read on the degree wheel in that position (e.g. = 80 degrees after TDC)
5) Use the degree wheel to locate the crank and camshaft et the intake lobe center which is right in the middle of the 2 values, e.g. 40 + 80 /2 = 60° after TDC

Doing it this way avoids the uncertainty linked to the few degrees when the dial indicator shows no movement of the cam.

Hope it helps;

L.

I believe there are two sets of timing figures given for E3134 cams. One of them uses a wide tappet clearance, that avoids the uncertainty about the opening point. The smart thing to do is set the timing where you believe it should be, then put the dial mike on the top of the pushrods, or the valve cap (with zero tappet clearance). Take readings at 5 degree intervals - then make a plot on graph paper of the lift of both cams versus degrees. You will be able to see the lift at TDC, and correct any errors. It is worth varying your valve timing and finding the optimum to suit your exhaust system, unless you are using the factory specified racing exhaust system which originated with the mid-fifties race kit.