SAH cam identification

[thescrapman]

I have had a Mk1/2 Spitfire engine for quite a few years now that I suspected has an SAH cam in it.

The car came with an SAH timing disc in with other bits.

I took the rocker cover off today for the first time and the rocker pedestals are shimmed, so I still suspect the cam isn't original, so I have tried to work out what it might be.

I lined up the timing disc TDC with the small hole in the crank pulley and then noted the following

The push rods go up 8mm (.31")

Valve no.1
Starts to open at 55 BBDC
Fully open at 65ABDC
closes at 45ATDC
280 degrees

Valve no.2
Starts to open at 25BTDC
Fully open at 65BBDC
closes at 70ABDC
290 degrees

Valve no.3
Starts to open at 15 BBDC
Fully open at 60BTDC
closes at 90ATDC
285 degrees

Valve no.4
Starts to open at 60 BTDC
Fully open at 80ATDC
closes at 50ABDC
290 degrees

Then I ran out of light.

Has my measuring been too vague??

I have spent ages looking at James's compar-o-meter and am none the wiser.

Any clues anyone??

Cheers

Colin

[TedTaylor]

If it's any help I have just gone through a couple of my SAH catalogues - the Herald one that Steph and her first husband used when they had their 12/50 given the full treatment for rallying in 1965, and one for a six cyinder (Vitesse and 2000).

Herald
Stage 1
Inlet open        22
Inlet Closed      62
Exhaust open   62
Exhault closed  22
Lift an extra 45 thou

Stage 2
45/70-70/45
Lift an extra 50 thou

For the six cylinder (no iift given)
Stage 1
Same as Herald

Stage 2
30/70-70/30

Full race
44/76-76/44

Hope this helps

MUT

[thescrapman]

Thanks TEd.

Figures do not seem to fit the numbers I cae up wth.

Went back again this afternoon and tried again

Valve no.1
Starts to open at 60 BBDC
Fully open at 75ABDC
closes at 35ATDC
275 degrees

Valve no.2
Starts to open at 20BTDC
Fully open at 75BBDC
closes at 80ABDC
280 degrees

Different enough to make me  think my method is not accurate enough.

Perhaps I will have to remove the cam to see what is stamped on it.

Cheers

Colin

[GT6 M]

Col, ye need to re set the  deg wheel to O, and also re set TDC on that piston,
that what ye been dooing,or just kept turning owa.

Pull the rockers off, a 3/8th extension usually fits into cam folloer.
so then ye can put dial gauge on that

rgds M

[Nick Jones]

Problem may lie in how the figures are originally quoted.  Unfortunately cam makers vary in the way that they do this.  Most report timing figures than run from a specific (small) amount of lift after actual start to same figure before actual finish.  Problem is what that lift figure is for a particular cam maker.  Some quote it - most don't.

I'd say you have the 30/70 there.

Nick