The Kiwibiker site has a heap of info on it. Some really interesting rabbit holes to follow down too!
Incidentally I found something on there that I think may be of interest to CriCri owners. In this thread
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner there was some discussion about having four through bolts holding the head on, causing four corner seizures among other things. There was also reference to the flat four air cooled VW engines, in the that later engines used thinner studs to hold the heads on.
I had a good look through the thread but do you think I can find the posts again??


There is a brief mention of it here, but not about the VW engines.
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=2002552#post2002552
Anyhow, it turns out that with the higher heat in the more powerful engines was causing issues with the heads distorting and the gaskets leaking. The thermal expansion of aluminium is close to twice that of the steel head bolts and as the cylinder gets hotter the tension in the cylinder studs increases, distorting the head. By thinning down the studs, they would stretch as the cylinder heated up, maintaining the right tension in the studs holding the head down.
In this youtube video after the 2:55 mark they show a head gasket failure.
This has been a somewhat common issue with the JPX engines in the CriCri. Normally this has been attributed to the four studs holding the head on not clamping the head evenly enough. I suspect that the different rates of thermal expansion of the cylinder and thick steel studs also have something to do with it. Possibly thinned studs would help alleviate the problem?