Engine not turning over. Starter motor checked.

Hello fellow KZ folk.

Firstly - apologies if this seems like a reoccurring issue. I have searched the forum's and can't seem to find a similar issue.

I'll jump straight into it:

I have a KZ750b Twin from 79. I'm rebuilding it into a brat style tracker. Before i broke it down, the engine stopped turning over which i diagnosed as a start clutch/motor issue. I recently took the engine to a garage to get replaced with a donor motor/clutch which i already had as well as getting the valve clearances checked and a compression test done.

The outcome is that the start motor and clutch was fine and the clearances were fine. However. they told me that when a compression test was done there was an unequal reading (both within correct parameters). To make things even more confusing, they told me the engine was proving very difficult to turn over and the starter motor couldn't do it.

I obviously want to get the issue diagnosed before I rebuilt and feel like it could be either nothing or something major! I searched high and low, but doesn't look like anyone else is having this issue.

Any help or thoughts would be extremely gratefully received and apologies if i've missed a previous post or if it's too vague to diagnose.

Much appreciated,
Sam

You may have to look at the crank bearings.
Steve

Is your battery in good shape? I would be looking towards something that didn't change, as you've had the same issue with 2 diff motors?

2ND motor? Yeah battery.
Steve

The engine is difficult to turn on starter likely and electrics fault, does it turn freely on the kickstart?

And the compression test, the garage did a wet and dry test? I think you need a motorcycle mechanic, your garage don't seem too hot on the diagnostics.

I'm still stuck on this 2ND motor thing.
Steve

Pull the spark plugs out. Put the bike up on the center stand and stick the tranny in 3rd or 4th gear.
Try to turn the rear wheel over by hand and see if you can rotate the engine easily.
If you can... you either have a crap 2nd starter motor, a bad battery or corroded wiring.
If you can not turn the engine easily, you have a spun bearing or seized piston that broke loose... etc.