Small Engines (Lawn Mowers, etc.): Bearing noise

Question
QUESTION: Hi Eric, I have a Kohler 10hp K241AS, the block says K301, Spec. 46766d, Ser. 9616725. I had it rebuilt about 5 years ago. Bored .010, new piston and rings. Lately after getting warmed up there has been a loud singing noise that sounds like it is coming from the flywheel side of the engine. Is there anything else it could be other than the bearing? If not and I can't find a new bearing will any K301 bearing from that side work? I have another engine that is a K301 but it is a 12hp,I don't have the model or spec numbers for it. Would it work?
Thanks, Carman.

ANSWER: Make sure there is nothing rubbing on the alternator.  I have seen flywheel magnets come loose but usually they make a lot of noise and break several parts.

I would is a fuel like tube, as a stethoscope, to help isolate the sound...just don't get too close to rotating parts with the end of the hose.  This trick has helped me pin point noises in the past.

As for a replacement bearing I'm not too sure what would work but the bearing should contain a part number on it...they all do.  You should be able to find a replacement on the internet.

Did you measure the crankshaft end play when you rebuilt the engine?

Eric

---------- FOLLOW-UP ----------

QUESTION: The noise started out faint and the last two months got louder. The engine was rebuilt at a repair shop so I hope they checked the end play.
Carman

ANSWER: What oil are you using?  Conventional?  Synthetic?

Have you tried changing to a different oil?

Eric

---------- FOLLOW-UP ----------

QUESTION: Conventional, the same oil I have been using in this engine since new in 1979. I don't know much about synthetic. Do you think it will help?

Answer
Many oils have changed since 1979.  I used to use Quaker State in the late 80's and early 90's but they changed their formula and I switched to another brand of conventional oil.

Many people like synthetic oil but I put some in my older motorcycle and the shifting became much rougher.  Switched by to the conventional and the shifting smoothed out.

My point is you could try a different brand of oil or try synthetic and see it makes a difference.  You could also try using an additive like Zmax.  We tested and older product called Duralube in the late 90's and it worked well as we ran an engine, after adding the additive, for almost 2 hours after draining both the oil and additive from the engine.  The engine finely seized but after disassembling we found minor wear on the front main bearing.

How often do you change the oil?

Eric