kz1000j

I heard that the kz1000j engine is more less reliable than the pre 1980 engine,
by looking at the engine parts list I can see that the same crankshaft on the J engine used by kz1000-p24(2005),the bushing,camshft is use by pre 1980 engine and kz1000 p till 2005,the cylinder head and the cylinder is use only by j1-j3 and ELR engine,so what is realy go wrong with J engine? is the cylinder head and its components.
Im asking this question because I own one 1981 that did 120000km, little bit smoking and no service history.
tnx

Bigger, stronger trans, improved lighter cases, better flowing head, modern cam chain design... Cons; a crank that may twist easier than 73-80 models and an aluminum clutch basket. Welded crank and an earlier clutch basket yield you a better breathing higher power package stock to stock, quite the solid motor

My 96 KZP has a J in it.

any prob?/do you happy with the engine?

at that milage it could be a couple things causing the bike to smoke. I would do a compression test and go from there.

Mine went to 48000 and now its getting a top end go thru included a 1075 bore. The transmission is a rock and is G2G. I hope to get another 50k after since I won't ride it like the PD did.

Stop listening to people who have no idea what they are talking about. The KZ1000J is as good and reliable as the older ones.