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.

What int/exh seals do you have? What is your all in ign timing adv? Late timing really heats up the exh valves.

What is the exh seat contact width? If they're not wide enough..the stem ends up trying to shed more than its share of the valve heat.

They were your standard positive type...I was only running about 22 degrees as I don't want to detonate the thing..I was only turning 2700 rpms...I don't remember my seat width, but when I lapped the valves I do remember thinking the width was on the thin side...The heads are at the machine shop now...I think I'm gonna have them add another .001" to my exhaust guide clearance and get the seats out to like .085" plus go one jet size richer on my secondary metering rod(quadrajet) to get the EGT lower...How does that sound? thank you

Holy crap.
when you set the total timing to say 30* you’ll swear you installed a whole ‘nother motor.

Good luck, sounds like you are on the right track.

Oh, i thought those heads came with umbrella seals. Did you buy them bare ?

Here is what happened..I set it at 30 initially and it ended up sticking 2 valves and it blew the headgasket...So I assumed it was detonaing..It had a good bit of blow-by before it stuck the valves..That is why I set it at 22....I know it needs more timing, but I figured I would work my way up as I didn't want to tear up anymore stuff..This time the blow-by was low and it ran much longer, but stuck #2 and the headgaskets are fine...I think the blow-by cam from the detonation...The engine has 160 PSI compression and the leak down is great....These were fully assembled Vortec heads from Summit.....

Did the head gasket blow between 4&6 or ???

This says those heads come umbrella seals (which are fine) , just wantvto make sure your valves are getting plenty of oil:
https://www.summitracing.com/parts/s...Zsoc-#overview

They are this one.https://www.summitracing.com/parts/sum-151120
They are not umbrella seals..that is incorrect..They are viton with a spring...I couldn't really see where they were blown, but I ended up with water in the oil...I know were you are going with the 4&6...No they are not warped and the block was just decked to get my quench correct..It didn't blow headgaskets this time and there is no water in the oil...Just the exhaust valve sticking in the guide..You can see and feel the scoring on the valve stem...The thing is pissing me off.I'm an exotic car tech. by trade and I did everything right on this thing..I setup the TDC, measured valve train geometry, set up CR and quench etc, filed the ring gaps and now I have had the heads off twice...It sucks!