Oliver H. et al.,
I have a Onan model MDKAL, vintage 2000, so twenty years old now. My Operator's Manual, which has the maintenance schedule, says:
Outer race rotation is the probable result of a frozen or damaged bearing. Deteriorating grease is the likely precursor to a frozen or damaged bearing. But you can't inspect the grease, since this is a sealed bearing, so the only thing you can look for is evidence that the bearing is failing.
That said, this thread suggests to me that failure of this bearing is very rare. If it was common, you'd expect the factory engineers to be quicker with explainations, you'd think Onan techs would be familiar with replacing it; and you'd expect the Amel community to have some war stories about it (like we have for the outhaul gearbox or raw water hydrant plumbing).
Based on all this, I suspect the maintenance schedule on this part is too frequent. My manual says to change every five years, the Onan tech in Panama City who adjusted the valve lash (and wouldn't do the bearing) said every 2000 hours, which for me would stretch that to eight years.
My Onan is at just over 5000 hours. I will replace the bearing this year and, if the off bearing shows no evidence of damage or excessive wear, will increase the interval to 3000 hours. It's possible that the original bearing is still in the genset (I've no maintenance logs from the first two owners).
With an upgrade in solar panels (and decrease in genset use), it'll last the rest of my natural life. If not, I'll let you know.
S/V Hanalei SMM266