Posted by Dennis Novotny (216.86.73.83) on 15:49:56 18/12/04
Penny:
By confining the wear to that of a line contact on the follower, wear can/will be a problem. If you can allow the follower to rotate about its axis, a slight geometry change could help immensely:
Grind the botton of the follower so that it has a spherical radius of 50" or so. This is something we do for automotive style flat tappets for pushrod activated valvetrains in the USA.
You then want to grind the lobe with a slight axial taper (0.001" over a 0.400" distance should suffice).
The spherical follower bottom will then be forced to rotate about its axis on the tapered lobe as the lifter goes through the lift cycle. It often helps if the lifter/follower C/L is offset slightly (~0.040" or so) from that of the cam lobe C/L.
If at all possible, you should try to provide for some replenishment of the lube. Frictional heat that develops after start-up can exacerbate the scuffing problem. A simple drip feed of 20W50 automotive racing oil or even APG 90-140 gear oil (race quality for sure) will probably help immensely whether or not you can modify the surface geometry as noted above.
The anti-friction/anti-wear agents in the lubes (usually zinc dialkyldithiophosphate) will do wonders for wear prevention.
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