Yellow Bullet Forums banner

1 - 12 of 12 Posts

·
Registered
Joined
·
116 Posts
Discussion Starter #1 (Edited)
Didn't realize how low traffic was in the valvetrain forum, so reposting here, hoping someone has seen this before.

Found an issue with my cam a few years back when I had the intake off, at this point it had a few thousand miles on it. It was broken in properly, and I always used either Brad Penn or VR1, 10W30 or 20W50. The lobes were smooth, and the lifters still had a crown. You can not "feel" any of what you can see.

I wound up replacing, and i'm happy because the new cam makes more power. But it looks like its beginning to happen again. Spring pressures are 125 on the seat and 350 open, cams are not very big, mid .500s lift solid flat tappets.

Has anyone ever seen this bullseye pattern on a lobe before, and do they have any idea what might contribute to it?
206671
206672
206682
206684
206686
206688
206689
206691
 

·
Registered
Joined
·
246 Posts
The dark spots on the lobes are spots the lifter does not contact. The lifter contacts the shiny spots. The lobes are cut with a taper. This taper makes the lifters spin. Looks like normal wear to me for a flat tappet cam. The bottom of the lifters also look normal and indicate the lifters were spinning.
 
  • Like
Reactions: desoto30

·
Registered
Joined
·
1,589 Posts
Not that there is no one looking, it is just such an odd pattern. I have been around various engines for 40+ yrs and have never seen anything like it.
 

·
Registered
Joined
·
865 Posts
Looks like inconsistent machining, looking at the lifters. The wear pattern varies too much. Radius on lifters not correct &/or taper on the lobes.
 

·
Registered
Joined
·
95 Posts
Not an expert by any means here, and knowing lifters don't sit center to center on lobe to lifter base. BUT some of those lifters do not look like wear is avial on rotation.
1. I think I would look at cam depth into block to see if lobes end up over lifter bores correctly.
2. This old dinosaur's brain has an ancient file in it that is hard to recall, however something about cam blanks and lobe width correction in the manufacturing process.
3. Also double check for valve seal to retainer bind.
 

·
Registered
Joined
·
116 Posts
Discussion Starter #10
Not an expert by any means here, and knowing lifters don't sit center to center on lobe to lifter base. BUT some of those lifters do not look like wear is avial on rotation.
1. I think I would look at cam depth into block to see if lobes end up over lifter bores correctly.
2. This old dinosaur's brain has an ancient file in it that is hard to recall, however something about cam blanks and lobe width correction in the manufacturing process.
3. Also double check for valve seal to retainer bind.
What do you mean by avial, is that a typo? What are you seeing that suggests that?

The cam does sit in the block all the way and the back of the timing gear seats up against the block, so it couldn't fit any deeper without modification, but I will take a closer look at lifter alignment over the lobe.
.
Retainer clearance and coil bind are both good.
 

·
Registered
Joined
·
95 Posts
Yes, axial.
One of the lifter pics looked odd to me.
Maybe just the pic.
Back some 20 or so years ago, a machinist suggested to me that the edge of the cam lobes need addressed with some type of debur. And location of lobe under the lifter is a concern, overlooked.
If the lifter is overhanging the high side of lobe taper, then the result is less contact area, as the radii of lifter foot creates only half lifter contact to lobe.
Clear as mud?
 

·
Registered
Joined
·
5,215 Posts
3rd picture down from the top it looks like the center lifter is out of line with the cam lobe enough to be on the lobe next to it. Is this just an optical illusion because of camera angle?
 
1 - 12 of 12 Posts
Top