ORIGINAL: KLF1292
Similar question, how do you tell if either the front or rear bearing set needs to be replaced?
Also, I have a Saito 72. I recently took the backplate off and noticed what appears to be wear from the connecting rod rubbing against the backplate in a pattern of slightly more than a half circle. What would be the likely cause? Bent connecting rod? Worn bearing?
If you can feel any side to side motion of the front of the crankshaft, your bearings are worn. How much wear is acceptable to you is probably personal preference. If I can feel play, I think it is time to replace them. Bearings are cheap to replace, when compared to the damage that can be caused by loose metal particles finding their way into critical areas.
The swirling pattern on the front of the backplate wouldn't concern me. When you push against the spinner to use an electric starter, the crank can brush up against the backplate a little. It might happen when the engine is idling down, and acting like a brake as well. Now, if metal is actually being REMOVED from the backplate, that is a different matter.
It isn't unusual for oil to leak through your front bearing. The seals aren't 100% oil tight.