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Well, the seat is missing from the dropped exhaust valve. I haven't taken off the oil pan to see if it is in there, but I don't think this will tell us much even if it is.

A few years ago I had an overheating problem (due to a clogged radiator) perhaps that is the ultimate source of this failure, i.e greater thermal expansion of aluminum vs. steel.

Yep , I believe that wasvthe cause of failure . Even when valves break the seats still remain in . Just really unlucky

Good observation!

You may be able to tell from the bits of seat you'll recover if it has come out before or after the valve failure. If there are signs of scoring on the outside of the seat, it must have been moving by itself before it came out. If it's just shattered but no scoring, it's probably busted by flying bits of metal.

Forensics is mighty interesting if it's not your own expensive bit of metal that just failed.

Now it happened to us. I was driving endurance race qualification session and everthing seemed to be just right, but then engine sayd snap crackle pop and lost power as a smoke seen on rear mirror. The failure is 1:1 to Maldis pictures. Engine was rebuilt and olny two dyno sessions were driven before the race.

Maldi,

Did you check the cams and followers after the failure? Was the cam lobe and follower surface OK?

In my friends engine, the one I was driving, the exhaust cam lobes were gone really bad. Some of the lift was missing and followers were worn so that the valve lash was something like 3mm or alike. That's probably the reason why the valve broke. Valve hit the seat at full speed. Also 4 other exhaust lobes were ruined. Cams and all followers were new.. It's still unclear why the cam failure happened.

I think my engine is having early signs of possible sodium valve failure. All exhaust lobes were pitted and even the base circle showed signs of wear, suggesting the lash went to 0. Impossible that I set it at 0. It must have tightened up. Inlet lobes were in excellent shape. This means the cams themselves were great, but my (exhaust) valve train is not well.

Either the valve seats are receding or the sodium valves are starting to show signs of stretch before failing.

So I'm taking off the heads, shaving them 0.5mm to get 11:1 compression and installing steel valves.

I rev my engine to 7000 rpm regularly and was told the sodium filled exhaust valves do not like the high revs and it would just be a question of when it would fail, not if. If I stick to around 6000 rpm I should be fine. But why would I? This thing sounds so sweet at 7K rpm.

Anyway my motor was built around 2005, so after 6 years, it's not too bad to have minor work done.

In my experience, the value of the sodium valves is overstated. There are very many excellent alternate engine brands out there that don't rely on them all without any detriment.

If you want to spin the engine at high revs, I would be considering reducing the overall mass of your valves and forget about sodium filled units altogether.

MD,

my valves are stock. But new valves are gonna be regular steel valves. Need to check for seat recession too.

Z

TS sodium filled valves might be somewhat better I guess, or then I have had a good luck. Have to knock the wood, because I have been racing long runs since 2004 and still got two original exhaust valves.. Other two were replaced when got piston failure and the valves were slightly bent.