I agree that the previous owner caused the damage. I disassembled the engine some time ago and carefully removed everything. I don't recall putting any kind of force on the camshaft when I pulled it out. The engine must of been rebuilt at some point which is when this happened? I received my Clevite bearings this weekend and taking them along with the block and cam to the machine shop. Will post when it's done.

I have another question related to crankshaft end play. It measured .003 in. while I was keeping leverage on the crankshaft which is a little tight. Haynes manual calls out .002 thru .006. Should I have my machine shop shave some of the thrust bearing or crankshaft, or just leave it as is?

Sorry I thought it was the front bearing that was scored. Agree with what lamb_daiquiri said - easy way to check is get a straight edge or ruler and place it on the journals - all the lobes should clear the straight edge. If not the lobes will score the bearings as you slide the cam down the cam tunnel. A bent cam would do this too but you would have issues getting it in and out if it were that bent. No doubt this damage was caused by a person and not the engine during running.

The damage looks like it was most likely cause during assembly or dis-assembly. i.e. the scores are in the direction the cam moves when it's removed or installed. It's possible they have been there all along, keep in mind a white metal bearing is there to "absorb" hard particles. The majority of the time the cam is spinning on a film of oil and not touching the bearing at all.

I think what Volodkovich is getting at is if the base circle of the lobe was too big it might have scored the bearing on the way in or out. Could be a number of things, debris during assembly, rough handling. If in doubt, measure everything and sit and think about what it's all supposed to do.

Not off the top of my head. You'll find the tolerance in a Datsun/Chilton/Clymer repair manual -- or at least journal diameter and bearing thickness. The proper clearance is achieved by line honing. Boring is not needed due to the tight manufacturing tolerance of Nissan, just the finish aligning hone. Some guys have skipped this step, if you fit the cam and it's easily turning and otherwise is in spec
* Cam bend limit
* Cam journal diameters
* Cam bearing diameter/thickness
* Cam thrust plate clearance

So your indicating that the front lobes not ground properly put stress on the camshaft towards the rear which is where the damaged cam bearing is? Why wouldn't the cam journal be damaged as well? If the cam has been reworked, I hope the journals were not turned. I ordered a standard size set of bearings and should be here early next week. Will have my machine shop make sure I have the right size. Any idea what the bearing/journal tolerance should be?

Almost looks like it is from a poorly reground cam, couple of front lobes base circle not ground to the correct size to clear the journal.

Yea this is a set back for me. Machine shop that I use here locally is highly recommended but super slow. I told him not to do anything with the cam bearings so he never did take a look. It must of been debris. Interesting though that the cam journal has no damage. It is the second bearing from the rear of the engine. One bit of good news though is that my crankshaft end play is within tolerance, .003. Well I'll be ordering bearings and dropping off the block and camshaft next week sometime. Thanks for the information.

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Yes, that is when you want to replace the cam bearings (when they are damaged). It's no big deal, just put the new bearings in and have a machine shop line-hone them

As long as the cam you sent them to regrind is STD size, yes

Ok thanks. Isky did a regrind for a mild performance cam. Journals should be the same diameter so I can stay with standard size bearings?