26-09-2017, 04:09 AM
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).
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).