Engine: Cam Grind For Flat Tappet Versus Roller Lifters

[JoeHall]

Just wondering, is anyone here familiar with the difference in grinding procedures for flat tappet versus roller lifter cams? I am talking about "straight" versus "tapered" lobe grind.

I understand: all 1950s-1960s flat tappet motors (except Buick nail heads) had tapered lobe grinds. The taper was in minutes (versus degrees); drop was measured at 3/8" width, and was usually .0005" to .003", dependent on the motor's spec. The tapered lobes mate with the slightly offset, convex lifter ends, to spin the lifters. Roller lifters are flat, are not offset, and mate to a straight ground cam.

In talking to several cam grinders, I find some do not have a clue about the above, but others pick right up on the conversation. So I believe this is a perishing skill, yet critical to differentiate. Obviously, a straight ground cam, used with convex tappets, is a disaster in short order.

If anyone is familiar with the above, do you know the spec for Stude V8s?

Thanks

[Pop's Chariot]

Excellent Question!!....It does seem some specific knowledge in various topics is not being retained as it is becoming obsolete. Sadly Time marches on

[PackardV8]

[Skybolt]

Thanks for the info. I always wondered how the valves rotated but never got into it in depth.

Now I know more than I did.

Len

[wittsend]

The valves themselves generally don't rotate but on a flathead (or specific design) I'd assume they likely do.

Also, it is just not roller cams that need to be flat. A lot of the OHC engines have what are called "finger followers" where the cam presses directly on the rocker arm. With similar aspects to a non-rotating lifter I'm left to wonder how they prevent wear? The rubbing surface on the rocker is an insert so perhaps it is a quality metal thing.
There are also inverted "buckets" that ride in a cylinder on top of the valve on OHC engines. I'd assume they likely have a taper for rotation also. These can be a pain to adjust because you need to check the clearance, remove the cam and install (often hard to find) shims under the buckets. I have a Mazda that is .0005-.001 out of spec and I've chosen to not lose any sleep over it.
Some engines easily transfer over the roller aspects. The 2.3 Ford Lima (Pinto) engine came in later years with a roller cam. $25 worth of Pick a Part cam and roller rockers gets the job done.

Ironic that a "flat tappet" actually has a taper ground into it. So much for words accurately representing the part.

[JoeHall]

Glad others are familiar.
Jack, glad you posted. Maybe I shoulda specified cam grinder v. re-grinder. I'm sure grinders, with new cam blanks, MUST have the subject data. However, not sure every re-grinder of old cams has it. I know of at least two who do not have it for Packard V8s.

As for, "data card", sitting here reading a paper one, returned with a 56J cam I had reground 13 years ago. It lists: duration at .050 as 184/184; lobe lift as .250; lobe separation as 110; timing events at .050 (-14 18/26 -22); seat duration at .006" (245/245); gross valve lift (.375/.375); valve lash hot (000/000), and "degree intake lobe to ATDC" as 106. There is no mention of lobe taper. Fortunately, that cam worked great, and the lifters spun like tops.

I'd like to, "trust but verify" cam lobe taper before installation, similar to plasti-gage of rod & main bearings, verifying piston ring end & side gap, etc.. Currently, I can only install a reground cam, with new lifters, and hope they spin. They usually do, but sometimes do not. Some will say the cam & lifters were not correctly broken in, not enough ZDDP, off-shore lifters, etc. But if the cam lobes are not tapered, the lifters are never gonna spin, simple as that.

As you recall, Jack, I once had a newly reground 56J cam that would not spin the lifters, from the get-go. Problem is, I had the guy regrind three of them. Two are still in boxes on the shelf. I strongly suspect they were straight ground.

To verify at least some taper, I think a 12" machinist ruler should tilt a wee bit, if stood on its end, across a lobe, with the cam laying flat. Has anyone ever tried that?

[wittsend]

I'd assume that the taper must run across the base circle too - especially with a hydraulic cam lifter staying in constant contact. Perhaps that would show easier since the base circle can often have adjacent lobes with some degrees in common. Hence, you should see the taper getting a straight edge across any two side by side base circles - where you can. That being that the high edges should be parallel and the taper should show though using a flashlight would help. I'd think trying to eyeball a possible .0005 taper over the nose of a single lobe might be hard to see.

[JoeHall]

I'd assume that the taper must run across the base circle too - especially with a hydraulic cam lifter staying in constant contact. Perhaps that would show easier since the base circle can often have adjacent lobes with some degrees in common. Hence, you should see the taper getting a straight edge across any two side by side base circles - where you can. That being that the high edges should be parallel and the taper should show though using a flashlight would help. I'd think trying to eyeball a possible .0005 taper over the nose of a single lobe might be hard to see.

With the two suspect cams, mentioned above, if I stand a straight edge on the lobe, it positions same as when stood on the bearing surface. If tapered, I'd think it would lean a wee bit, when stood on the lobe.

Still learning. I am challenged by this kinda stuff, and hope to get to the bottom f it sooner or later.