Very interesting. It has been a very long time since I have seen valve problems cnetered around quality. Is the machine fairly new? I would think if it was a metalurgy issue it would have shown up early in the life of the machine. Chances are the injectors are fine as if they were bad you would see piston and ring issues. Good luck solving this one. Keep us posted.

Bob - I have the entire Cat "library" of failure analysis books .. and I can supply any info you require from them. However, might I suggest, you probably need to take your question regarding a Komatsu problem from this BB (where you'll get very little serious response, I'd reckon .. and not without good reason, as these guys are 100% Cat) .. and take it over to the ACME BB, where we have a "Non-Cat machine" forum, for questions regarding all the Brand X's.
I have owned and run many Komatsu's and never encountered a valve failure problem with them .. but I did have plenty on my Cats. In essence, cracking is generally a heat-related problem, a "faulty batch" problem (I had this with Cat), or poor quality aftermarket parts.

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