[Fot] Oversize lifter bore

[Enquiries Road & Track]

the problem is mostly the acceleration rate (profile) of the cam, not the
max lift per-se. as the cam rotates, the shape of cam lobe is designed not
to dig into the edge of the lifter (or vice versa). this is called
edge-riding and is a very common problem when upgrading modern OHC engines
where everything is designed to work perfectly, with zero room for change.

to check this out, put some engineers blue on the face of the lifter and
rotate the cam. it is OK, if a thin blue edge remains around the
circumference of the lifter. if the cam wipes it off totally, thats not
right. the cam and the lifter are scraping (not riding). eventually, the cam
wears the sharp edge off the lifter and/or the cam lobe wears away; neither
being good

the cam designer can mathematically determine the profile from the lifter
diameter, thats why its his first question

Terry O'Beirne