mikey ,my guess is the same as iains ,also if youve oil in those cylinders my guess is either the rings and the barrels are worn ,youll get the info back i expect from whoever is checking it out for you ,ie rebore and new rings
best of luck mate

900 engines start with z1e

nothing quite like it mike is there,firing them up for the first time ,esp that zed of yours ,you had much intrest in it ?

nice one jack ,they are supposed to be very good at crankshafts so ive been told

think youre right there davy it looks very much like a H****a item 500x4 or 550
garn hope this of some help mate

nice one steve ,learnt summat new today ,thanks

i too had a prob like this with a yoshi motor ,i like chris found the starter clutch was worn ,banged on a new one and end of prob,at the time i was unsure if it was that but it worked great.

garn ,ive seen this before on a z1a over here about 15 years ago ,like you ive no idea why ,but yeah if you can get to the bottom of how and why ,im sure there would be a lot of zed heads interested .

i'll go and have a look davy

could be a milling mark from the factory and wasnt spotted before stamping as theres little chance of the numbers being changed by some dodgy person if the borders are still there