07-07-2019, 07:18 AM
(This post was last modified: 07-07-2019, 08:56 AM by Bob Culver.)
There was no answere to A in S enquiry; the following might bemuse some.
Assuming the original tangent flanks are retained, the method of regrinding camshafts is reasonably obvious. I presume French ground camshafts more or less as I did.
The obvious preliminaries; set in lathe between accurate centres, or between ind chuck and steady etc, and bump until all journals run absolutely true
Arrange a grinding wheel so that it can cross feed to directly above the camshaft (to a g clamp on slide or more refined reference) With some means of vertical feed height adj (setscrews etc)
When lowered the stone should cut equally across whole width. Arrange arms clamped on the camshaft to provide rotation stops.
Unless going racing increased overlap is not in itself the objective, it is the by product of more lift area. The final tangents should run out just before the crown radius starts. If tangents run out much earlier excessive duration likely. If cam is shaped convex as diag in Williams special book duration will prevent operation! The exh closing is already 15 deg atdc and duration is reasonable and probably little to be gained to normal 3,500-4,000 rpm by altering. Just .020 off the inlets seemed to perk up my car.
Cross Feed in at a tangent until above the exact centre line, turn the camshaft to the other tangent and feed on out. Progressively increase feed and adjust arms to suit. More than about .020 radius goes thru the hardening but seems not to much matter for modest mileages. Smooth with fine oil stone. The pre pump cams are most convenient as the shaft is smaller.
Cam durations in cam degrees is 180 minus the included angle, allowing about 10 cam degrees total to take up clearance. Assuming everybody has a science type calculator or kept their school trig tables or can draw to giant scale and measure, can deduce the half/full angle change from length of tangent and depth removed.
I find many camshafts have inconsistent base circle diameters. I dunno if have been reground or whether it due to wear of factory wheels. I have encountered cams with consistent reduced lift; presumably the result of some attempt to recondition.
Although often not clearly stated, many spec valve timings for other cars are for wide tappet clearances. Makes comparison difficult. The SAE standard was .006 extra. Cam timings after the 1970s are confusing as many designed to avoid emissions and depend on very rapid lift.
Please leave some good original cams undestroyed for those who want their restored cars to be true Austin Sevens.
The main problem with lathework is that it can easily become a hobby in itself and your Seven may never make the road. Console yourself that safer.
Assuming the original tangent flanks are retained, the method of regrinding camshafts is reasonably obvious. I presume French ground camshafts more or less as I did.
The obvious preliminaries; set in lathe between accurate centres, or between ind chuck and steady etc, and bump until all journals run absolutely true
Arrange a grinding wheel so that it can cross feed to directly above the camshaft (to a g clamp on slide or more refined reference) With some means of vertical feed height adj (setscrews etc)
When lowered the stone should cut equally across whole width. Arrange arms clamped on the camshaft to provide rotation stops.
Unless going racing increased overlap is not in itself the objective, it is the by product of more lift area. The final tangents should run out just before the crown radius starts. If tangents run out much earlier excessive duration likely. If cam is shaped convex as diag in Williams special book duration will prevent operation! The exh closing is already 15 deg atdc and duration is reasonable and probably little to be gained to normal 3,500-4,000 rpm by altering. Just .020 off the inlets seemed to perk up my car.
Cross Feed in at a tangent until above the exact centre line, turn the camshaft to the other tangent and feed on out. Progressively increase feed and adjust arms to suit. More than about .020 radius goes thru the hardening but seems not to much matter for modest mileages. Smooth with fine oil stone. The pre pump cams are most convenient as the shaft is smaller.
Cam durations in cam degrees is 180 minus the included angle, allowing about 10 cam degrees total to take up clearance. Assuming everybody has a science type calculator or kept their school trig tables or can draw to giant scale and measure, can deduce the half/full angle change from length of tangent and depth removed.
I find many camshafts have inconsistent base circle diameters. I dunno if have been reground or whether it due to wear of factory wheels. I have encountered cams with consistent reduced lift; presumably the result of some attempt to recondition.
Although often not clearly stated, many spec valve timings for other cars are for wide tappet clearances. Makes comparison difficult. The SAE standard was .006 extra. Cam timings after the 1970s are confusing as many designed to avoid emissions and depend on very rapid lift.
Please leave some good original cams undestroyed for those who want their restored cars to be true Austin Sevens.
The main problem with lathework is that it can easily become a hobby in itself and your Seven may never make the road. Console yourself that safer.