Flat Face Cam Follower Spin
Flat Face Cam Follower Spin
(OP)
I understand that flat tappets have a slight spherical crown that mates with tapered cam lobes to induce spin and spread wear evenly. Question is: How much spin is typical? It seems to me that it really doesn't matter how much spin as long as it's greater than zero. Any thoughts or experience here?





RE: Flat Face Cam Follower Spin
Rod
RE: Flat Face Cam Follower Spin
RE: Flat Face Cam Follower Spin
Rod, I too remember the GM camshaft fiasco. The shop I was affiliated with had at one time, 32 5.0 and 5.7 camshaft jobs waiting in line, and almost all were the #6 exhaust lobe and all were in the 35K to 50K mile range. We had to analyze the failures for any possible warranty issues and GM stated that they had not had any complaints from other locations that the problem was localized, probably due to owner neglect (HAH!) One thing of interest, once we changed the cams, they did not fail again. I don’t recall any change in lifter diameter though.
Franz
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RE: Flat Face Cam Follower Spin
Back to the original post...I do recall watching my pushrods rotate...pretty slowly at idle...maybe 2, 3 turns a minute...a guess. Actually I think the taper on the cam lobe is responsible for the tappet rotation and the convex finish to the tappet is more for break in purposes.
Rod
RE: Flat Face Cam Follower Spin
Chev had more than their fair share of engine problems in the late 70's and early to mid 80's. Too many exhaust valves tuliped into the heads, flat camshafts, and #1 and 2 rod bearings spinning. Toss in the aforementioned flexplates, AC compressors and evaporator coils, PS pulleys, cracked fan blades, diode trios, and lousey engine and transmission designs, its a real miracle they survived even that. More than one company switched to Fords, and many to Toyota PU's too.
As for the OT, the lifter convex surface mates with the cam taper for the lifter rotation. Only a portion of the lifter face actually contacted the cam lobe. When the taper is interfered with by a small piece of debris and the lifter quits rotating, its only a matter of time until the bottom is wiped out.
Franz
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RE: Flat Face Cam Follower Spin
Block and camshaft manufacturing machining is slightly more critical with this setup.
Will
RE: Flat Face Cam Follower Spin
I don't understand the configuration you state. I'm visualizing a convex tappet running on a straight (not tapered) lobe will result in edge loading of the lobe and not tappet spin. What am I missing?
RE: Flat Face Cam Follower Spin
If the lifter is offset and run against a flat lobe, contact will be in the center of the lifter regardless of the offset. A flat surface has no idea where the offset is.
Another purpose of the crown and taper is to allow for misalignment. A crowned lifter on a flat surface would not have edge loading, but without the taper there is nothing to make it rotate.
RE: Flat Face Cam Follower Spin
Franz
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Flat Face Cam Follower Spin
RE: Flat Face Cam Follower Spin
Rod
RE: Flat Face Cam Follower Spin
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Flat Face Cam Follower Spin
Somehow OHC engines with lobes running directly on tappet shims seem to work flawlessly. When I peek in the oil filler hole the lobes appear to bear on the tappet shim full width, but the shime removed to have a faint circular wear pattern. Maybe it helps that they live in oil.
I think you'd find that even though they look centered, they are slightly offset (not anywhere near 5mm though)
RE: Flat Face Cam Follower Spin
There must be some difference in hydrodynamic conditions, sliding velocity profile across the lobe, wear life, and I'm sure others. Any thoughts? Is the tappet rotation effect linear with engine speed? With applied force? Cam ramp slope?