Valve float? If the springs were getting weak, and you let a drunk buddy drive and he overrevved the motor in the air?

Valve loses contact with the rocker over the nose, and doesn't get the advantage of the cam's deceleration ramps and SMACKS the seat?

I lean away from reversion if his exhaust valves were fine. Same thing regarding detonation.
Valve guide too tight, maybe.

Was this motor ever overheated?

Hmm

I would go with valves being set to loose accelerating the closing speed.
Or:
Non-planar of the valve guide to the combustion chamber ( cylinder head, non-concentricity guide to seat set-up ).
Or:
Stresses generated by temperature or thermal fatigue failure. Looks like it got pretty hot by the picture.

Hello again, and thank you for your thoghts!!

Bob, what does this mean? --and excessively elevated contact stress-- (my poor language skills again, and poor knowledge of engines)

mcollinstn, I believe that i have overrevved atleast one time during som really rough seas.. have no idea how much, because i took the revlimiter out for a speedtest, and then forgot to put i back.. (my stupid idiot)
Today i got mail from Ralph att REV-valves.. he too think its related to valve float..
I´ll ask the builder about the valve guides
No i dont believe its ever overheated--

Throttle Fever, the spring load or what to call it, is set pretty loose, and that might have caused floating if i overrevved.. so ill take this up with the builder.
We have had discussions about valveguide.. but that seems right, but we will machine the seats now anyway..
Yep, well check that too!

I am really happy that you guys wants to help me!

My engine http://www.youtube.com/watch?v=GzzYNivZM6g

My boat http://www.youtube.com/watch?v=axvwhxi4wFw

http://www.youtube.com/watch?v=1doHXNm55Fk Maybe i should have posted the vids in another tread?

Why?

Video of engines and boats never get old.

However you damn well better post some pics or vids of chicks in fur bikinis. Preferably the Swedish Bikini Team!!!

Tomas_wallin; no while driving

But i admit it was stupid to dismount the rev-limiter

Finally, today we got everything together and fired it up! Thanks for all your input!

Ralph att Racing Engine Valves also says its valvefloat that causes the cracks in the valve!

http://youtu.be/QGdlYKLTKy4

buy a lottery ticket ! the pin was out....what brand of valve ? with all the fake junk parts all over you just never know..even though you think you are buying "brand name" parts...ck out this months issue of Hot Rod..scary story there