This has been quite an interesting thread.
I am both a designer/manufacturer of model products, and a diesel aficionado. From the information in this thread, it appears that Jens' engine has been assembled with the wrong head, or the head was mis-machined (did someone at the factory mistake 21.0mm for 20.1mm?)
My questions now, in view of the spate of autocongratulation in this thread, which more or less drowns the opinion of those who are happy with the engine :
Has anyone fed this information back to the factory, with sufficient detail that the mistake will not happen again?
Has anyone asked Enya what the design head size is?
I mean that, in Jens' position, having fully ascertained the cause of the problem, I would certainly already have contacted the manufacturer.
I for one at least sent an email to Enya with the URL to this thread.
As a designer, prompt and proper feedback is something I seek avidly, especially when a new product is launched (By the way, my "day" job is about technical support for maintenance engineers, repairing printing machines).
This is how any mistake can be corrected early in the product life.

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