How does one know if engine bearings are bad?
 

I have a Zenoah G45cc engine I haven't used for a few years. I had problems starting it so I put a new carburetor kit in it, and tried to hand start it to no avail. With the new kit installed, fuel began leaking from the two tiny holes(fuel pump)on the back of the cab. I was not successful stopping the leak, and the engine wouldn't start, so I purchased a new carburetor. After installing the new cab, I still was unable to hand start it so I used a drill with enough RPM's to turn the propeller and the engine started(after several tries)I let it run for awhile and noticed black oil coming from the exhaust. I shut it down and was unable to start it again. Could this mean that the bearings are bad?

Most likely. In some cases it might sound like something is loose, high vibration, runs hot, lack of power, but the black oil is a good indication of bad bearings.

Regards

Thanks for the reply, I was afraid that could be the problem.

Can you please advice me if I should change the ball bearings on a propdrive 42-58 500kv 60w engine after it hit the ground. The engine still works fine, shaft
straight, lots of power, everything ok but when I hand spin the prop some slight noises are heard. You can barely hear it.. I think it's the front bearing, what could had happened inside it? should I change it? The rear one I
couldn't find on my local store or hk. What could happen if I don't change it? How can a bearing go wrong? What happens to them? And what can happen if I oil them and let them there?
Thank you!

Not sure about bearings, it's unlikely, but from what you're describing, I would first check your plug (if you havent already done so), then take off the head and check the ring and sleeve. Problems with both of these could cause black oil, and are more likely the culprit, especially on an engine that hasn't been used in a while. If the engine has been stored properly, those issues are rare, but they CAN happen. Also, you don't mention if you changed your reed valves when you changed the carb. Those things are delicate, and even a tiny chip or crack can cause serious problems of your engine, especially if bits of them made it into the cylinder, causing black oil. If it were bearings going bad, you would know for sure. While turning with your hand, it would be rough, and there would be an unmistakeable vibration sound as. From what you describe, something is affecting your fuel flow and burn which would indicate a blockage or leak somewhere. The black oil leaking from your stacks? Check it closely for tiny metal bits. Might be bearings, but most likely piston/sleeve shavings if present.

Just my 2 cents and experience