Re-profiling Cam Followers

[Zetomagneto]

Mark, I Hope the cam is on the shelf, not in the engine! These are real crankcase wreckers.

[Charles P]

Mark, I Hope the cam is on the shelf, not in the engine! These are real crankcase wreckers.

They have a reputation for that but the biggest crime in my book is overly strong valve springs. Always have the weakest spring that you can get away with. I've found Tony Betts' double springs, which are of lighter gauge material, are both gentle and don't bind at higher lifts

Charles

[Zetomagneto]

Yes Charles that's very true, and strong springs rob power

[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.

[Colin Reed]

Hi Bob.
You will find that a lot of cam timing is done with 20 to 50 Th  just for set up depending on the camshaft manufacture ,
then revert to recommended running clearance.
Your other comment on quick lift lobs a lot of these run roller followers and the tip of the lob has a bigger radius they also require stronger Valve Springs

Colin
NZ

[Rogerfrench]

No, Culver, my father didn't grind cams like you.
He abused an ancient lathe by mounting grindstones in the chuck. Camshafts were mounted in a rectangular frame that slid on a rod mounted parallel to the lathe bed, and rotated towards and away from the stone. Each Cam was presented to the stone by hand, measurements being taken by micrometer from time to time.

[JonE]

Old thread.
Having a bash at re-profiling some followers myself. I'd just be interested to know what are the DISadvantages, other than originality, of reprofiling? I've recently changed a head back over to LC as a better match for an old crank, twice ground.., on the basis that its extra strain on a baggy engine. Should cam follower efficiencies be viewed in the same way, or is it a win win?
Do some always resist doing such a thing, and if so why?

[Bob Culver]

Hi Rogerfrench
I used your fathers surname alone because I have no way of knowing the first name.

[Charles Levien]

Just google “ French Austin Seven”  — I’m old enough to have had several conversations with Jack French  who re profiled the cam followers still in use in my special. I remember him commenting about the best profile saying it’s important to avoid over flattening. I remember him for his true engineer’s approach — cautious, coupled with an open mind and enthusiastic.