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Bob Gervais - Cam Analysis

new 11/12/03

This is meant to be an FYI at this point, I have some pics that I will post later on this issue.

Kirk was generous enough to donate a camshaft for me to cut apart, which I did last night. I will summarize what I found, some of this is most likely old news, some of it may be new. I'd like to share it with the list anyhow, just in case.

My observations:

Cam Tube: 1. The hardness appears to be about Rc 30 or less, I was able to cut it with a regular carbon steel band saw blade.

2. The lobe and sprocket mounting areas are straight knurled, to raise the diameter of the shaft, allowing an interference fit for the lobes and sprockets.


1. The actual contact surface seems like it is Rc 50 or higher, my best guess would be about Rc 62 or so. I needed to cut the lobes with an abrasive wheel, and even then it was difficult.

2. There is a separate inner ring, that is pressed into the lobe. This ring seemed to be softer than the rest of the lobe, but harder than the tube. My best guess is about Rc 50 or so.

3. The inner ring has splines machined into the ID, parallel with the lobe centerline. IMO these are there to aid in ease of assembly (less contact area), and to increase the integrity of the assembly.


1. Appears to be Rc 50 or below, I cut it with an abrasive wheel fairly easily.

2. It does not have an inner ring like the lobes, but it does have splines machined into it like the lobes. Again, IMO for ease and integrity of assembly.

Timing chain sprocket flange:

1. This is a solid plug, splined and pressed into the camshaft tube. It has a straight knurl parallel to the centerline of the plug, again IMO to aid in ease of assembly and integrity of the assembled cam.

2. This will show in the pictures I will post later, but I am concerned about the amount of interference fit this flange has. There was hardly any material displaced in the camshaft bore where the plug is pressed in, and looks like another potential weak spot. I'll attach a pic here that Kirk sent me, so you all know the area I'm talking about.

I'd like to thank Kirk for the cam, hopefully working together as a group, we can learn more about these cams, potential failure causes, and general construction of the unit. IMO, it's the sharing of information that makes Kirk a real asset to the group, unlike some vendors who seem to think they have some sort of corner on the market.

A word about my estimations on Rockwell hardness:

I do not have a hardness tester available to me, so I've estimated based on experience and how the material cut. I know John Hamilton has tested all these components for hardness, and once I'm sure Kirk and I have all the info we need from these cut pieces, I'd like to send them John's way for more testing, if he's willing.

Comments? Suggestions?

I'll be posting pics later on tonight, I need to get some shuteye and resize them for emailing.



V8 SHO cam sprkt cut.jpg (38316 bytes) These images show the cam tube and sprocket, still assembled, in a cutaway view, as well as the sprocket only, again in a cutaway view.

Note how the cam tube cutaway shows the straight knurl perpendicular to the cam tube centerline.

Also note the machined splines in the sprocket ID.


V8 SHO cam sprocket.jpg (45399 bytes)
V8 SHO cam timing bore.jpg (40511 bytes) Tim, these images show one of the lobes in a cutaway view. Note the inner ring that is pressed in, and the splines that are machined into the ID of the ring.
V8 SHO timing plug 2.jpg (44161 bytes)
V8 SHO timing plug.jpg (33131 bytes) Tthese views show the bore that the timing sprocket flange gets pressed into, and the minimal amount of material displacement. This worries me also, and IMO, is another potential problem.

Also shown is the actual plug (2 different photos) that gets pressed into that bore.

V8 SHO cam lobe id 2.jpg (37964 bytes)
V8 SHO cam lobe id.jpg (26282 bytes)

V8 SHO camshaft 016a.jpg (123933 bytes) V8 SHO camshaft 015a.jpg (104711 bytes)
OK, let me try to summarize and see if we can all agree how the cam sprocket is attached to the cam tube.

Cam lobes aside, we have 3 major pieces. A hollow cam tube, a snout plug and the sprocket itself.

The tube seems to have a set of annular rings or threads cut or rolled onto the end.

The internal plug has splines knurled or rolled onto its surface.

The sprocket has splines as part of a bronze insert.

To assemble the sprocket is placed over the cam tube with the timing mark "in time" then the plug is pressed into the hollow cam tube expanding it slightly which is supposed to hold the sprocket in place?

A blow up of the contact between the sprocket and the cam tube in cross section seems to show some adhesive in use.

However much the outside diameter of the cam tube increases when the snout plug was pressed in, it is insufficient to keep the sprocket in place.

The one photo showing the plug looks like a parting line, if you get a good photo of it I can tell you if it is a casting or a forging. I would guess it is a forging. - Buford



Thanks for your thoughts and efforts. I am still bothered by the "knurling" process you mention.

By "straight" knurled, which direction do the grooves go that you think were put in before assembly?

Since there is NO doubt, none whatsoever, that the ID of the lobes and sprocket are a slight interference fit on the main cam tube as they slide on, then any "raised" portion would have to fit into the horizontal (along the long axis of the cam) grooves in the underside of the lobes and sprocket.

These raised areas can't touch the inner ID of the lobes and sprocket upon assembly or you will get metal chips in those areas that will be virtually impossible to clean out before assembly, so it is hard to see the benefit of this raised area or than any engineer would make it that way.

When you post pictures, please post good ones of the underside (ID) of the lobes and sprocket, to compare them to the marks on the cam itself.


Don Mallinson

My only suggestion would be to see if Larry, Tim, or Scott can host them, and then just post a link to all of the pictures. I'd assume that you have probably a dozen or more pictures, and it would probably be in the interests of list bandwidth and everyone's inbox sanity if they were just put on the net where people could look at them at their leisure. even if you get them under 200k each, a dozen pictures at a meager 20k will run over 240k, and make for an annoyingly long e-mail.

IMHO, it would be better, neater, easier, whatever, to build a page and caption all of the pictures. A little extra time (not too much), and you could do it with low-res thumbnails and hi-res picture links for people that want more detail.

Just a suggestion.

-John Breen III

Bob, Kirk,

I am, at this point, willing to admit that Kirk was right about the Knurling on the cam he had. But what bugs me, is that the underside of this sprocket does not jive with the spun cam that I had in my hands a couple of years ago.

When it spun, it cut grooves in the shaft, these pictures are posted on the V8SHO.com web site. The straight across fins or splines on the underside of this sprocket don't seem likely to have cut that pattern. And the pattern on the shaft that was posted isn't the same as the grooves on the earlier cam.

Is it possible that this is a newer cam with a different design?

Also, I would still like to see better pictures of the pattern on the shaft, because how these cams go together originally, still is baffling.

Thanks to Kirk and Bob for their efforts, I guess that the new cam I gave to Kirk, can be considered the "donor" for this project, although I hope that new cam got put in a car, and an old unusable cam got cut apart, in any case, at least the cam shouldn't have been an expense for Kirk.

Don Mallinson

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