Perkins Cam Follower Tappets

[lifeofreilly57]

I'm currently rebuilding my Perkins 4108.
I have two cam follower tappets that have flaking on the wear surface, the rest look fine. The camshaft itself is also within spec and has no signs of damage or surface wear.
The engine has about 4000 hours on it.
Can I replace just the ones showing the surface flaking issue or should I replace them all?

[DougR]

Short answer: sure you can replace just the pitted tappets, but inasmuch as you are in there you might as well do all of them.

Pitting is a common problem with cams and followers. Sometimes if it's just minor, the parts can be reused, but once the pitting begins it usually continues to spread. Sometimes it can be caused by low quality oil usage, or perhaps heat treatment issues on the tappet. Another thing that can cause high wear on tappets is if they are unable to rotate for some reason. Normally tappets such as these do not sit directly centered on the cam lobe, but are offset a bit along the axis of the cam. This offset causes the tappet to rotate a bit each time the cam lifts the tappet. This rotation allows the wear on the base of the tappet to be spread out over a greater surface area on the bottom of the tappet. You can tell if the tappet is rotating, as the wear pattern will be circular. If the tappet is not rotating the wear pattern will be rectangular. If it's not rotating you need to find why not. Gum, varnish, etc can be among the causes.

DougR

[lifeofreilly57]

Thanks for the feedback, I figured as much.
Years ago Chevy had an issue with improperly hardened camshafts, which led to premature engine performance degradation.
TO fix it required replacing all the lifters as well as the camshaft, which is a bit easier on those blocks than on the Perkins.
The engine has been completely broken down, spent time at a machine shop and is now being reassembled, so any carbon or gum build up has been removed.
Don't know how well the previous owner maintained the engine but it had minimal wear when I pulled it apart, as for oil residue buildup that's a strong possibility. Now that everything is going to be new it's up to me to maintain it properly.
I'll be ordering the tappets today.