SBC sticking valves
 

Guys, I have a fresh 383 that keep sticking exhaust valves...The heads are Summit vortec units with SS valves. It stuck 4 &8 and bent two valves and nicked the pistons...Reamed the guides and replaced the valves...Now #2 has done it...Is this a clearance issue in the guide or SS valve? ...I ran SS exhaust valves all last season with no issue...Thank you

Too much cam overlap causing water reversion that lets water sit on the back of your exhaust valves and rust to the heads. First starter turn and they are done.

It's a comp 270 marine...Nothing crazy..It's sticking while running...I ran it like 5 minutes at 2700 RPMs yesterday and next thing you know it starts making all kinda of noise....Removed bank 2 valve cover and I have another bent valve...They are sticking in the guides...You could see the scoring when I had the issue with 4 and 8....Do I need regular valves and not SS or do I need to hone my exhaust guides some?

Clearance to tight? What is the current valve to guide clearance?

Marine valve guide clearances is larger than auto. If you bought the heads already assembled. The machinist might have made them too tight.

I had this issue when I went to Merlin heads years ago. Only thing that solved it was using the water passages on the back of the intake. Within 5 minutes of idling and then getting on plane it would take a valve out. (3 times) This was on a BBC cylinders 6 and 8. My cylinder head guy clearanced the guides to larger than optimal tolerance and still took out a valve. Bad cooling/water flow with that head was the issue. Only 1 out of the 4 heads did it.

^^^Who woulda’ figured. That must have been a tough one to figure out. ^^^

I believe the OP’s Summit’s cast iron heads are Darts. Well, used to be anyway.

Seizing exhaust guides, as mentioned, are typically from not enough clearance, not enough oiling, or very hot cyl head temperatures.

I got the heads off this AM and the valve is bent on #2 and you can see some scoring on the stem..I kinda 1/2 ass measured it with a dial indicator and it looks like .002 clearance..I'm sending them to my machine shop...Would some bronze liners in the exhaust guides help my cause? I'm getting sick of pulling heads..I'm getting fast at it and that isn't a good thing...Thanks..

On my twin turbo street car, the exhaust valves were tight in the guide after it ran on 2 different times I pulled the heads off. Nothing broke and the valves weren't bent but I had to tap them out gently with a rubber mallet to remove them. I forget what the clearance was than, but it's at .0018 now. I have thousands of miles on it with a ton of boosted runs, some at 30 psi. All valves are free now. 😀

Its almost certainly the guides. The Chevy Vortec heads had problems when they first came out and if the aftermarket heads are made the same then they will have issues too. I think a lot of engine builders are so stuck up on tight clearances that they dont take into account how hard a marine engine is on things. I prefer them a little loose rather than too tight. I try to get them at .002" and have never had an issue that way.