Non-rotating tappets

[High Hopes]

How essential is it that the valve tappets rotate? About half of them do not.

[Don Moyer]

Steve,

This is a really good question and I'm afraid I don't have a good authorative answer.

In my experience, tappets tend to rotate in either direction and will stop and start somewhat randomly. I suspect this movement is from the top of the cam lobe imparting a very slight difference in contact pressure on one side or the other on the bottom of the tappet. Other than to confirm that the tappet is completely free to rotate with all pressure from the cam removed (as when that particular cylinder is at TDC), I wouldn't know of anything else to do to affect tappet rotation.

Hopefully others will weigh in to confirm this experience, or to add additional light on the subject.

Don

[baileyem]

My understanding of tappet rotation in the old Ford flathead engines is that the tappets rotated because the cam lobes were slightly canted to one side on their 'lifting' surfaces. The purpose was to keep the valves rotating, which was supposed to prevent the valves and seats from burning. I have no idea how effective it was, but I can remember watching the valves slowly turn while cranking engines with the heads off.

[Don Moyer]

Are you sure it was the valves that you saw turning, or just the tappets? I would think that the valve springs would prevent the valves themselves from turning.

Don

[baileyem]

Boy, Don,
You got me....It has been so long that I can't say for sure. Even if I saw it, I don't think that it kept the valves from burning or pitting. It seemed that valves were always a problem... If I can ever get the answer I sure will let you know.

Mike