That's what I'd do: Is it in spec and is it close to the others?
And like Dan suggests: it may even be possible to save that lifter by polishing it out, depending on depth of damage. If you have access to a surface plate there's a couple of ways you couid measure that. Plastigauge or a DTI mounted on a height gauge perhaps. Most people can detect a difference of about 0.001" with a finger, so if you can't feel it then it may not be as bad as it looks in the photo.
Misters Torch, North Idaho Wolfman, Old Hokie, Runs With Scissors and hagrid I'm sorry for not getting back with you but I didn't get notification or your responses in my email account. Don't know what's up with that!
I've read all of your responses as well as reading on-line regarding cams and lifters and I have contacted (4) machine shops that specialize in regrinding cams and refacing the lifters. I only heard back from one shop and I'm waiting to hear back from them with a price for polishing the cam and replacing the lifters. They do reface lifters but they thought it would be cheaper to just buy new lifters but they weren't aware of Kubotas price for lifters. Here's what I have noticed about the cam and lifters:
The base of #3 lifter is scored and I polished the face with 400, 800 and 1,200 grit but the scoring is still there.
The lifter bores were already cleaned with some fine grit paper but I don't remember what grit.
The block is still on my bench and I lubed and reinstalled the cam in the block. I then lubed the #3 and #5 (random choice) lifters and started them in their bores. Both lifters slowly settled under their own weight and seated on the cam.
I put two identical 3/8" sockets into the cups of the lifters to keep a bit of weight on them and slowly spun the cam with a drill motor. Both lifters have a dot of yellow paint at the top of the cup and they both rotated 360 deg. and at about the same rate.
All of the cam lobes are well within spec and the lift of all six lobes is similar so I don't think there is any damage to the cam. The cam lobes all look fine with no scratches.
The scoring on the #3 lifter can barely be felt with a fingernail after my attempt at polishing but I'm pretty sure I could remove the scoring with a coarser grit paper.
My first thought is to continue sanding the lifter until the scoring is mostly gone (Torch, I liked your idea about checking the depth of the scratches with Plastigauge). Then polish the cam and reassemble the engine and forget about it!
I've verified that #3 lifter can rotate and maybe twice yearly oil changes will alert me if something is wrong with the engine internals.
Thanks in advance,
Larry
