Dewalt DW 758 Bench Grinder

[Kitt1993]

Hello everyone,


I got a DW758 at a yard sale. The owner said the bearings were making noise and needed to be replaced. I decided to purchase it and tear it apart at home. Upon inspection, I found the bearings to be in pretty bad shape and after some research on Google, I was able to find a set of Timken on Ebay, After installing them and assembling the housing back together, I plugged it in to make sure everything is ok. So far there is no noise, but the housing does get pretty warm. Using a laser thermometer, The bearing is 130 degree F with no load. The heat will make its way to the center of the base and is around 110F in the middle. Again, this is with nothing on the shafts (no load) running for just a few minutes.

Is this normal or maybe the bearings are not in place correctly. I can spin the shaft freely, but not fast. To be straight forward, the shaft seems a bit stiff.

I did pop the rubber seals off the bearing before installation and added more grease as there wasn't a lot in there. So I know there are getting the proper lubrication.


Appreciate any input,


Bryan

 

[matt_i]

Did you use -2RS bearings in place of -ZZ shielded?

If so the rubbing action of the seals on a 3600 rpm motor will generate a lot of heat. I recall working on a blower for a Powermatic 30 sander with an integral dust collector, the OE bearings were fried due to eating grit. I was all set with my shiny new -2RS bearings when I realized that they were limited to 3000 rpms and the fan shaft was overdriven from a 3450rpm 2 pole motor. After some more research these had to go due to same issue.

 

[Kitt1993]

Did you use -2RS bearings in place of -ZZ shielded?

If so the rubbing action of the seals on a 3600 rpm motor will generate a lot of heat.

Hi Matt,


Yes,

When I called Dewalt, they said it didn't matter for the rubber seals vs the shielded.

Whats your thoughts between the 2? Here is the ebay listing I purchased from

https://www.ebay.com/itm/Timken-620...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649


Bryan

 

[exmaxima1]

That is a relatively small bearing, and good for at least 10,000 rpm. I suspect the heating is from the actual motor guts: windings, core, rotor, etc

 

[Dagny]

Too much grease can make a high speed bearing overheat.

 

[Kitt1993]

That is a relatively small bearing, and good for at least 10,000 rpm. I suspect the heating is from the actual motor guts: windings, core, rotor, etc

But is that normal operating temp?

Bryan

 

[Kitt1993]

Too much grease can make a high speed bearing overheat.

I might go ahead and clean out all the grease and redo it got to be on the safe side. If I take the housing off the base that the bearing sit in, I can spin it way more freely than if its installed. I'm leaning towards that the bearings might not be seated correctly causing torsion and thus the friction when spinning by hand and heat when turned on.

I'm going to take it apart again and see if its something I might have done. Would you suggest that I use a metal shield bearing instead of a rubber seal?

Bryan