Dead on blkford, as you well know, most other older engine designs the lobe on the cam
is ground slightly off square to cause the lifter to spin, necessary for proper wear pattern
and durability. Festiva style cams with followers do not have lifters to spin, but followers
track the lobe different than a roller because of the geometry necessary for the follower
to lubricate and not bridge the the ramps. The ramps and rate of acceleration - deceleration
of the lobe are a lot different between festivas and aspires. When degreeing
an engine during cam change or rebuild this difference will make degreeing meaningless
without factoring in an educated guess. The difference in lobe diameter would have to
be set during valve grind by changing stem height. Bottom line as said above, keep
roller cams and lifters together and in other engines they have to be in castings designed
for them. The little graph that comes with a cam that is shaped like a cam lobe but actually
shows the valve open time in lift and degrees..with mix matched followers the
measured valve open will not quite look like the graph. You have to change the grind for
a roller set up to reproduce the old cam and follower setup...as measured at the valve.
heat treating and metal type have more to do with quality than durability and do no vary very much.
Oil meeting specification and staying in specification, temperature of the oil, chemical
and physical contaminates and spring pressure specifications have more to do with
the durability of a cam than hardness variations as long as it was hardened. A cam
that skipped the hardening process will fail shortly as well.
is ground slightly off square to cause the lifter to spin, necessary for proper wear pattern
and durability. Festiva style cams with followers do not have lifters to spin, but followers
track the lobe different than a roller because of the geometry necessary for the follower
to lubricate and not bridge the the ramps. The ramps and rate of acceleration - deceleration
of the lobe are a lot different between festivas and aspires. When degreeing
an engine during cam change or rebuild this difference will make degreeing meaningless
without factoring in an educated guess. The difference in lobe diameter would have to
be set during valve grind by changing stem height. Bottom line as said above, keep
roller cams and lifters together and in other engines they have to be in castings designed
for them. The little graph that comes with a cam that is shaped like a cam lobe but actually
shows the valve open time in lift and degrees..with mix matched followers the
measured valve open will not quite look like the graph. You have to change the grind for
a roller set up to reproduce the old cam and follower setup...as measured at the valve.
heat treating and metal type have more to do with quality than durability and do no vary very much.
Oil meeting specification and staying in specification, temperature of the oil, chemical
and physical contaminates and spring pressure specifications have more to do with
the durability of a cam than hardness variations as long as it was hardened. A cam
that skipped the hardening process will fail shortly as well.
Comment