yeah something seriously wrong with the setup here i think..
only problem iv heard from these engines are the kick starter gears. havent heard of a cracked cases issue for well over 12months with these engines and the model before it.
the new z160's are factory fitted with a de-comp cam so im guessing all the stock head guys running these engines wont have a problem..
DHZ_XR8cing you fitted a V2 head and more comp but no de-comp cam. problem number 1.
buy your self the takegawa s35 de-comp cam plus the special cam gear adapter.
or get the TB de-comp option fitted to your V2 head.
aitken your running a de-comp cam (which must be the takegawa one) are you running this special adapter? im guessing no..
id say the cam has already spat the circlip of the de-comp mech on the cam gear which would make the de-comp not work, and not to mention have a circlip floating around in the bottom end..
4 motors same mechanic...thats gotta be telling you something.. sounds like your not doing something or what i have said above is correct...
your second problem is your running an IRK.. man p!ss this off ASAP, its half your problem cause they spit out what every timing curve they want. not to mention theres many batch's of these that the magneto has the magnets in the wrong location..
id be sending your engine to DHZ and get then to fit all the TB parts, then if it fails again theres definitely an issue.
also a bad carb tune can result is a cracked case or broken gears.
and most importantly too tight of chain.
a lot of people dont realize that as the rear shock compresses (swing arm travels up) the chain gets tighter. guess what this does?
it distorts the engines cases and the counter shaft so something have to give..
the new 175's are the same motor as the z160 but with a 63mm bore kit and im pretty sure they deleted the de-comp cam out of them, because there are reports of these killing kick start gears too..
aitken you only have 1 option left for an engine... DAYTONA 150 (good luck with that $$$$$$)