So after replacing the entire valvetrain to get rid of lifter noise, upon removing engines this year for transom work; the rear exhaust valves are toasted. Heavily corroded looks like reversion. Engine has to come apart for the 3rd time. Anyone have issues with reversion on stock 500efi setup? Exhaust is cmi e top headers. They have been Pressure tested numerous times. No issues.

Before the rebuilds there was a lot of carbon build up but valves did not look like they look now. It's a stock cam, Johnson lifters, isky springs, scorpion 1.7 rockers, and trend push rods. Any help is appreciated. Thinking we may have to go dry to prevent this happening again. Going on 20k for top end rebuilds...should have left them alone.

Are you running mufflers ??

No

Switchable exhaust?
Picture of your exhaust angles and tips may help.

No switchabke exhaust. I'll take picture of tailpipe but there is nothing fancy about it. It's the standard cmi e-top. Termination of water into exhaust is 16-20" down pipe.

Check your tail pipes for cracks

I looked. Tails and headers are in mint condition. No rust, no corrosion, etc.

Cylinder #8
https://i.imgur.com/qS4uLE7.jpg

Cylinder #2
https://i.imgur.com/uhJB95q.jpg

I think it's reversion because both motors are identical in terms of pattern. Rear cylinders are bad. Front of engine appear good.

#8 is horrible. Yuk.

Rear cylinders primary tubes are the 'bottom' ones. Could be water leaks,,,,could be just the ignition timing. You pulled heads to get redone right ? Anything else touched other than removing heads, intake, dist, and exhaust ?

I didn't do the work...paid someone to do it. but I am only aware of heads, intake, exhaust, and dist coming off. Heads don't appear to be rotted.

Lower end was not touched