TR4/4A Camshaft oddity has me concerned

[Sarastro]

Recently installed the camshaft in the TR4A engine I'm rebuilding. Looking down through the holes where the tappets go, I noticed something odd about the location of the cam lobes. In every pair of holes, the lobe toward the front of the engine is offset quite far from the center, so the edge of the lobe is about at the center of the tappet. In the other, the offset is not so great, about what I'd expect. Pictures below.

Is something wrong here? Could I have an incorrect camshaft? It doesn't seem possible, but I'm still disturbed by the large offset, which is more than I've seen on other engines.

 

[bobhustead]

This is designed to rotate the lifter to even out wear.
Bob

 

[Sarastro]

Yes, I'm aware of that. As I said, the one with the smaller offset seems reasonable to me. I am surprised by the large offset of the other one (right picture), and I don't understand why they would be different. I'm hoping someone can illuminate me.

 

[bobhustead]

One of our engineers could enumerate more, but engineering choices about valve head diameter and depth/volume of combustion chamber would be involved.
Bob

 

[CJD]

Interesting. If I pulled a head and noticed either orientation I wouldn't even think twice about it. It does seem odd the orientation would be different between the 2 lifters, though.

We need one of the long term Triumph guys, like Randall to clarify if the cam was ever changed in production.

 

[Sarastro]

Duh!

Gee, do I feel dumb.

Turns out I had the camshaft too far toward the back of the engine. If you install the plate and front bearing, it locates the camshaft and all is well.

I had mounted the engine block high on the stand so I could access the plug that covers the camshaft in the rear of the engine. I didn't want to turn the block over, as it was top-heavy and difficult to handle. As soon as I turned it over, though, I saw that the journals were not centered in the bearings, and it became obvious.

When correct, both lobes are offset slightly toward each other, and it all looks like I'd expect.

 

[TR3driver]

Sorry, I've had very limited Inet access for the past week or so.

There was one very early change, to beef up the shaft at the distributor drive. I'm not sure offhand when that happened, might have been preproduction.

Otherwise, AFAIK, the camshaft remained the same until the TR4A.