Should I replace the bearings in my “new” PM 65 arbor assembly before installing?

[David Traster]

I just acquired a “new” arbor assembly for my Powermatic Model 65 Table Saw on eBay. The threads on the existing arbor are badly worn. The nut will loosen if I don’t use an extra spacer and make sure that the nut is very tight. (It’s only happened twice when I was switching back and forth between a regular blade and a dado stack, but it was scarry.)

Powermatic produced the Model 65 until about 1965 so both the existing and the “new” assembly are at least 58 years old.

I haven’t inspected the existing arbor assembly since I first acquired the saw several years ago. The new assembly does not appear to have much wear and there’s no “play” in the bearings that I can detect by hand. When I remove the existing assembly, I’ll carefully inspect and compare them both.

I could replace the existing arbor assembly with the new one without replacing the bearings. Or I could disassemble both and use the new arbor in the best of the two housings. In that case, I would replace the bearings but I don’t own a bearing press so I’d have to take it someone who does or put the housing in the oven and the bearings in the freezer...

I can’t visually inspect the bearings without at least some disassembly and probably not even then. I would have to install the new assembly and put them under a load to find out if they heat up or vibrate. Even then, I won’t be able to tell if they make noise.

I’d rather work on the project I’m using the saw for than on the saw itself... but if I should replace the bearings, now’s the time to do it.

Is there a way to test/inspect the bearings without installing the assembly? What “should” I do?

[John Lanciani]

In the history of reparing used machinery, I don't think one person has ever said "I sure am glad that I didn't bother replacing those inexpensive 50 year old bearings with dried out grease in them".

[Jimmy Harris]

Do whatever you feel like. On one hand, swapping the bearings now would be the prudent thing to do. On the other, it's not like pulling the motor on these is that hard. So if you left them and found out you need to replace them anyway, it won't take, what? An hour to get it back out now that you've broken the rust off the bolts?

[Bill Dufour]

Old bearings are probably shielded so the grease has dried out. Put in new sealed bearings with fresh grease from the bay. They should last for your remaining lifetime. I would guess cost will be $20-25. Now is a good time to buy a bearing splitter.
Bill D.

[Earl McLain]

I'm in the "replace them now" camp. Better than even chance that they need to be done, as Bill pointed out. I just put the top back on my new (to me) 1988 PM66 after bringing it home. Between the weight of the table, realigning the wings, miter slot, etc., the reassembly was 2-3 hours. If you reassemble, put it under load and find you need to do bearings, you get to do that exercise twice. (granted, i was slow, and i'd be faster the second time, but i'd rather do it once)

Arbor bearing come off & on easier than motor bearings (usually), but even if you have to take the arbor & bearings to a machine shop to do the bearing swap--labor should be relatively inexpensive (guessing $25-$30). Last time i did motor bearings, i took the motor to a guy from our church along with a root beer and some Utz's cheese balls. Retired machinists mostly like doing that stuff!!

[Patrick Kane]

In agreement with everyone else. Bearings begin to get slightly pricy when you get into the bigger machines, but a 10" saw bearing is like $10 for top shelf stuff.

Yanking the arbor in the future will involve taking your fence rails and table top off, and then putting them back on and aligning everything. These steps will take an hour or two versus the 15 minutes to swap the bearings.

[David Traster]

Well, darn... I already knew the answer to my question; I was just hoping for a different answer.
After seeing Mr. Lanciani's response, I thought, "Well, this my one chance to make history." But then I realized that I probably won't remember to say that on my death bed. Oh well.
Thanks so much for the great advice.

[Bill Dufour]

Note that the two bearings may be different sizes. Do not pull one and order two of that size. There are probably online notes about what size those bearings are. Any nuts etc are most likely LH thread if they rotate.
Bill D

[Lee Schierer]

I would do it now while I have the assembly in my hand. As others have said, bearings don't cost a lot. Having to do it down the line will obviously take time and you already have to take the saw apart to take out the old assembly and the align your saw.

[Bill Dufour]

A quick search says two 6204 bearings. It also says older saws have a shorter spacer and use thinner bearings? Unclear if 65 and 66 are the same arbor or not.
USA Sellers on ebay have them for under $4.00 each. At that price it is a no brainer to change them out.
The Horrible Fright digital caliper is plenty good enough to measure your old ones if needed.
Link to NTN bearing search, just in case.
Bill D

https://bearingfinder.ntnamericas.com/

[Jerry Bruette]

A quick search says two 6204 bearings. It also says older saws have a shorter spacer and use thinner bearings? Unclear if 65 and 66 are the same arbor or not.
USA Sellers on ebay have them for under $4.00 each. At that price it is a no brainer to change them out.
The Horrible Fright digital caliper is plenty good enough to measure your old ones if needed.
Link to NTN bearing search, just in case.
Bill D
https://bearingfinder.ntnamericas.com/

Those "thicker" bearings are probably double row 5xxx series.

[Bill Dufour]

For most users single row is good enough to replace old school double row. bearings have improved a lot since 1930's. yes they may have little shorter life but single row should last as long as you in home shop use.
Bill D

[David Traster]

Thank you for all of the excellent advice.

FWIW, there are two bearings separated by a 0.625”wide spacer. There are actually two spacers, one inside the other.

Assuming that I measured correctly—which is a pretty big assumption—both bearings are 0.810” wide with an ID of 0.787” and on OD of 1.850”. The first one had a single row of ball bearings. (I had to cut it off because I couldn't get the bearing splitter between the first bearing and the outside spacer... probably because of "operator error.")

Wearing three pairs of reading glasses, it appears that the bearing is stamped with “MRC 204 SZZ C.”

6204 is as close as I can come to an exact match. It's 0.551" wide while mine are 0.810" wide. Not sure that I need a wider spacer... or that I even need the spacers.

Ordered two bearings from eBay

Dave

[Bill Dufour]

Measure in metric to reduce confusion. All ball bearings are metric. There are a few old odd ball bearings with inch bores. You machine is too new for that.
Sounds like you need the longer spacer.
Width of the new bearings is 14mm the old ones are 20.5mm. The spacer could be an English length. I would assume the bearing closet to the blade is fixed in place the one at the other end may float a tiny amount. The spacer can be off length a good bit before it is an issue. A few washers might do the trick for a test.
Bill D

[Jerry Bruette]

You definitely need both spacers. Without them your bearings may not be in the proper placement on the arbor after mounting or they could be side loaded without both.

I'm assuming the bearing closest to the flange is mounted tight to a shoulder, then your spacers and then the other bearing is mounted tight to the spacers. Everything should be tight after mounting the bearings and spacers on the arbor.

No need to put the arbor in a freezer when mounting the bearings. Don't heat the bearings over 240*F to mount them. Put some oil on the arbor and the bearings should slip right on. Let the first bearing cool before putting the spacers and second bearing on or you'll have a gap between the spacers and bearings. If you have access to a bearing driver I'd use that instead of heating the bearings, it's actually easier and faster mounting bearings with a driver.