380 ci sbc bending exhaust valve

[gsbrown83]

380 ci sbc. Circle track engine.
Long story short. Ran this engine four years. Zero problems. Same guy freshend it. Rings and bearings in the bottom. All new valve train up top. Same parts just new. Right out of the gate bends #7 exhaust valve. Four times now. Will run 30- 60 laps before it does it. Have changed everything including new heads all new valve train again. Also changed almost everything down to the carb and fuel. Have checked everything possible I can think of including looking for restrictions in the exhaust. Looking for new ideas or things to check.

[swampbuggy]

30 to 60 laps all together at full song ? Mark H.

[gsbrown83]

On average it will run 40 laps. The first three times it did it under caution after a long green run. This last time it did it under green.

[F-BIRD'88]

Ex valve guide clearance a hair too tight.
Exhaust valve seals doing a too good of a job.
Lack of oil getting in the guide.
A engine that runs WOT like that needs slightly more ex valve guide clearance and needs to use seals that do not starve the ex guide of oil lube or it will heat up and grab the exhaust valve stem. The valve hangs and bends instantly. Many of the aftermarket valve seals are TOO good.

[F-BIRD'88]

Late ignition timing even under caution will heat up the exhaust valves. Guide grabs the hot ex stem.
Excessive timing or poor fuel even slight detonation running wot will overheat the valves too.
What ever timing it likes on the dyno take out 2 degress.
Wrong spark plug heat range. Same same.

[swampbuggy]

F-Bird.....my thoughts exactly. Mark H.

[gsbrown83]

I'm not entirely sure on clearance on valve guide. Builder is very very reputable in this area. Prior to the freshen job this winter it was his motor built new four years prior with zero issues. So it has me and him stumped. Friday night it bent #7 for the fourth time in a row. We pulled the valve cover off took the pushrod and rocker off #7 exhaust fired it up to move it across the pits to our trailer and it in that short time it bent #1. This is the first time it had bent another valve. So before we go through it again we are just looking for ideas to check. Thanks guys

[JoePorting]

Change the cam.

[gsbrown83]

I have wondered about camshaft myself. He swears it's not the camshaft. The only mechanical parts that haven't been changed are the camshaft and the rods. Crank. And Piston which all rods have been taken out and checked for stretched or twisted. All are spot on

[gsbrown83]

Also the intake is still the same. Have had multiple guys at the track tell us to check the intake / vacuum leak. Multiple distributors. Plugs. Wires. Carbs. Runs flawlessly no warning signs

[travis]

How much piston to valve clearance? Is it bending the pushrod as well?

What intake? Could it possibly be a distribution issue on that cylinder?

[JoePorting]

Your #7 exhaust valve cam lobe is probably damaged.

[Sparksalot]

This is likely a lubrication problem. With what and how do you lubricate those valve stems?

[Biteme]

I’m wondering whether the engine is building up heat at the back of the head and either the guide clearance lessens, or the valve seat is getting buckled out of shape.
Is the valve kissing the piston?

[Biteme]

This is likely a lubrication problem. With what and how do you lubricate those valve stems?

But it’s doing it even with a different set of heads. Same valve. Same scenario.