ZBox Series 4 Needle Bearing Failure


New Member
Mar 3, 2009

Needle bearing in my 2800km Zbox S4 66cc engine has broken up. I have no idea when the first needle shattered but it stayed in the cage for quite a while as it has eaten a small chunk out of the wrist pin.

Then, at some point a chunk of roller has - somehow - made it up the transfer port where it embedded itself into the top of the piston. It was like this for roughly 600kms before finally coming loose and hitting a shallow spot in the cylinder. Apparently anything heavy that gets trapped in these motors rarely falls out because of the angle it bounces off the piston. The only indication that anything was wrong was a very dull clunk every now and then.

Two of the rollers had seized up and ovalised, two others were just shattered.

It's not like this engine was thrashed, it only does daily riding at nominal speed and has always had correct oil. It's my hope that most of the metal lining lost from the cylinder has come out with the piston, so I've ordered a rebuild kit.

I thought I'd share to see if anyone else is having issues with these new motors. I know the block studs on mine are oversize and you can barely fit the head on without getting shavings in the engine or filing the holes out. The CDI also gives up as soon as the spark plug gets a little dirty, so not the most reliable of engines in any case.
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