Solid cam damage diagnosis help
Looking at the first pic, I’m assuming this is a SBM cam...... based on how the two lobes are basically lined right up.
There is a(at least somewhat) unique feature of SBM cams(older hemi and poly motors might be the same) relating to the lobe taper.
Each pair of lobes for one cylinder have the lobes tapered in opposite directions.
So the wear pattern will be on the opposite side of the lobe.
This makes the lifters spin in opposite directions.
In the first pic, those four lobes are all tapered the same way.
The second pic they’re tapered the other way...... or the cam was flipped end for end before the pic was taken.
I don’t know if it “matters” which lobes are tapered which way....... but all the ones I’ve seen have it where the pair of lifters for each cylinder turn in opposite directions.
In the pic below, from left to right:
#7 I
#8 I
#7 E
#8 E
As seen by the wear pattern, the 1st and 3rd lobes are opposite each other, as are the 2nd and 4th.
Again...... what the OP has going on is not “wear”.
The lifter didn’t rub that chunk out of the nose of the lobe.
The piece broke away from high point loading.
This is why the lifters aren’t worn.
Assuming the lifter bores are square, my guess is you’d need to have .003 or more lobe taper to see the wear pattern that narrow and so far off the edge of the lobe.
Looking at the first pic, I’m assuming this is a SBM cam...... based on how the two lobes are basically lined right up.
There is a(at least somewhat) unique feature of SBM cams(older hemi and poly motors might be the same) relating to the lobe taper.
Each pair of lobes for one cylinder have the lobes tapered in opposite directions.
So the wear pattern will be on the opposite side of the lobe.
This makes the lifters spin in opposite directions.
In the first pic, those four lobes are all tapered the same way.
The second pic they’re tapered the other way...... or the cam was flipped end for end before the pic was taken.
I don’t know if it “matters” which lobes are tapered which way....... but all the ones I’ve seen have it where the pair of lifters for each cylinder turn in opposite directions.
In the pic below, from left to right:
#7 I
#8 I
#7 E
#8 E
As seen by the wear pattern, the 1st and 3rd lobes are opposite each other, as are the 2nd and 4th.
Again...... what the OP has going on is not “wear”.
The lifter didn’t rub that chunk out of the nose of the lobe.
The piece broke away from high point loading.
This is why the lifters aren’t worn.
Assuming the lifter bores are square, my guess is you’d need to have .003 or more lobe taper to see the wear pattern that narrow and so far off the edge of the lobe.
