As title says I've seen many "I've heard that", but no actual facts, and no explanation why changing cam bearings can go wrong. So is it a myth or not?

 

Sounds like a myth to me. If someone had a problem it was likely installer error or incorrect cam bearings.

 

measure the clearance, or else you're just guessing.

 

I changed mine when I was doing my swap and have a few thousand miles on it with no problems. Like someone said above just make sure you check the clearance.

 

Whoever said that either installed or had someone install them wrong, that is a myth. Like said above, check the clearances, otherwise is a guessing game.

 

clearance is .004-.0045" What I don't like is, front bearing is scored

 

That clearance is within spec, I'd run it depending on how deep the scratch is. You can also take some 2000# sandpaper and smooth out the scrtch.

If you do swap the bearings, I recommend getting the right tool and also measuring the clearance after installation.

 

For some reason it seems all are. It's been discussed a lot. I remember seeing several threads with engines with low miles from the factory look really bad.

Cam bearings can be a pain and easy to screw up if you've never done them before. It's easy to get one cocked.

One some engines the cam bearings are different sizes and must be installed into the corresponding hole.

It's a good idea to put a slight chamber on the bearing to ensure there are no rough spots on the edges and helps in the installation process.

As mentioned you can clean them up with a fine scotch brite pad or sander paper afterwards to ensure they are smooth.

 

I decided not to touch them. I believe circular gouges, while not very good, will not disrupt oil film, and thus I'd better not risk messing with that bearing (somehow it looks easy to screw up according to internet mind)