Hello John;
First of all thank you very much for your help.
I understand from your comments that the bearings should show a frosted appearance in the rolling elements. However we removed one of the noisy bearings (NU 240) and we did not see anything strange on it. We even sent it to the bearing manufacturer and he did not find anything on it either. We must also say that that bearing only worked for a month or less before removing it.
should frosted appearance appear since the beginnig or after a time?
In the following months we will remove other noisy bearings and we will check again.
It also sounds very extrange to me because we use shell alvania 2 an 3 in all our smaller motors and only this one make noise.
You are advising us to use a grease that slumps properly at operating temperature. As you know when starting the motor grease temperature is ambient temperature. Afterwards when running temperature increases. I do not understand well why when the grease is hot after running for a while the noise stands. Do you mean that the failure occurs when starting the first time and then nothing can be done (appart from using perma).That changing the grease after the first starting failure does not improve the situation?
Another question; what do tou mean by a slumping grease? a grease with an ISO VG oil with less viscosity? or you mean a grease with less consitency NLGI 1
Thank you in advance for your help.
Best regards;