Cam

[Alex Myall]

Hi John

The Pigsty cam you have must be a very old grind. We have used the same lift on inlet and exhaust for about 25 years now.
I wouldn't recommend using it.

[John L]

Ok thank you for that Alex. When is the best time to call you guys?

[Charles Levien]

I'd agree with Ian,the only way to check a modified cam is to set it up in an engine, (Timing disk and drop clock on the valves).even then how it is likely to perform is another matter.I have a box full of them ,some have been fitted and quickly taken out again ( Done by well known regrinders).Most have too much duration to give any power low down,and one brand new one  £330 absolutely useless.
I personally prefer a good standard cam with reprofiled followers the best compromise for power and torque for a road engine.There is also an advantage of being able to up the compression ratio a bit.

This seems good advice though the Jack French cam I have in my special has a bit ground off the bases and works well in conjunction with JF cam followers which are gently profiled i.e. not over flattened.  
( but remember to shorten the guides) This combination gives good torque at low revs which is important in a road car.
It occurs to me that we have an advantage these days with strong cranks available and electronic ignition. Given a good carb ( I have an inch and quarter SU using a no 6 needle) your road car should be a lot of fun to drive.

Charles

[Bob Culver]

Reference is often made to flattened followers, which encourages newcomers to rush off and do the same. A completely flat follower produces theoretical infinite accel/decel, something Herbert , Stanley or whoever actually  did the arithmetic would have astutely avoided! Increased radius to ¾ “ is less severe.

Referring to modified std camshafts, if the tangent or near form is retained even quite severe grinds do not hugely extend the duration. I suspect persons get obsessed with duration as the object rather than by product of extended lift and obtain by departing from the tangent form. The valve lifts as soon as the cam departs from the base circle and so cams refinished other than as tangents to  or near the small radius or well up the flank can produce absurd durations unaccompanied by much initial or late lift. (ie the diag in Williams book with about 300 deg crank duration). Good camshafts are rare and it is annoying that the best are carefully selected then reground in a manner which often renders them useless for almost anything, and short lived in mileage terms

The Seven inlet timing is somewhat staid but the exh is reasonable.  .020 off the radius, which will likely retain some hardening,  extends cam duration about 3 deg, 6 crank degrees, a negligible increase for the inlets but a mod which makes a noticeable difference applied to them alone..050 off extends about 7 deg cam, 15 crank.
 
  0 40 45 15 gives crank durations of 220, 240 deg and with tangent cams included angles about 180 less 110, and 180 less 120 , both less a surprising  10 cam deg to take up the clearance ie inlet 60 deg, exh 50deg. If tangent cams have been retained and grind is moderate and symmetrical about the original as is usual, a fair idea of the timing can be figured from the included angles, established with cardboard cut outs or a builders angle gauge and a protractor. 
 
I reground the cam on my car by mounting in a the lathe and using a B and D drill traversed across above it on tangents as grinder. It did 3000 stirring miles before the crank destroyed it and most of the rest of the motor....

For those who enjoy diy, followers can be reradiussed by clamping to a faceplate or chuck accurately on axis and rocking back and forth by hand before a grinder. (note angle grinder wheels  are not
for hardened steel and run dangerously fast for unreinforced wheels).

[Bob Culver]

As a matter of interest, what tining is usually attained with a stock camshaft in place? Seems to me valves unlikely to be lifted free of seats at 0 40 45 15 timing claimed. Clearance accounts for a remarkable amount of rotation, and unless my 4th form trig is rusty 10deg of cam rotation seems indaquate to cover both lift and close, unless clearance just .002.

[Alan]

No idea, Bob, and it's not useful to know. What you need to do is dial your cam in to a point where it's just starting to open , say when it's 10 thou open
, thats far more accurate.

[Bob Culver]

In making comparison with other cars the 0 40 45 15 is usually taken as gospel. Most other cars understate as often taken with extra clearance, although often not made clear. (The SAE standard used to be plus .006 over normal settings.) Even if achieved, the Seven timing 0 40 45 15, esp the inlet, is relatively staid, but is even this actually achieved?
Unless it is maker’s recommendation, setting timing from a single opening point is fraught, although accurately repeatable. One good datum is mid overlap equal lift point, 7.5 deg ATDC for stock Seven, or, for symmetric cams, mid lift determined as midway between same lift on flanks.
(On standard cars, whenever the head is off an unfamiliar engine the 7.5 point is worth a rough check to ensure no gross timing errors.)