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Thread: GMF grinder bearing replacement
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7th Dec 2018, 11:20 AM #1Member
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GMF grinder bearing replacement
I think I need to replace/regrease the bearings in a GMF 8" HD bench grinder that I recently bought. Anyone know if the bearings need to be pressed in/out or can they be knocked in/out with a drift.
I assume you take the end castings off and remove the bearings from the inside?
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7th Dec 2018, 12:01 PM #2Most Valued Member
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I'd say that they could be punched out with a drift, and assembled the same way. Hopefully Eric (Lamestllama) will come in shortly and confirm this, as he has recently rebuilt one.
KrynTo grow old is mandatory, growing up is optional.
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7th Dec 2018, 02:52 PM #3Golden Member
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Just remove the wheels and shields then the four screws holding on the left hand housing.
Use a dead blow hammer to knock the right hand end of the motor shaft. Don't do the reverse as this will damage the internal plastic fan.
The whole left hand housing and rotor should come out usually with the right hand bearing still in place.
Support the left hand housing and knock the rotor out then slide the fan off the rotor shaft.
Use a bearing puller to remove old bearings from rotor or whatever improvised method works for you, they can be stubborn but not particularly so.
Don't bother re-using the old bearings, just replace them.
All of the original bearings I've seen on GMF's only have a metal shield on one side, I replace these with dual rubber shielded bearings.
Assembly is pretty much the reverse of the above.
Good luck.
Cheers,
Greg.
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7th Dec 2018, 03:01 PM #4Member
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Excellent info, thanks. When assembling do you tap the bearings onto the rotor or into the housing then fit the rotor?
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7th Dec 2018, 03:11 PM #5Golden Member
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I put the bearings on the rotor then fit them back into the housing.
Cheers,
Greg.
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7th Dec 2018, 07:06 PM #6Most Valued Member
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If hitting the bearings onto the shaft use a tube so that you are only hitting the inner race.....not the outer.
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8th Dec 2018, 09:02 PM #7Senior Member
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hi when you have put it all back together and if the shafts a bit tight to turn , the end housings may be a tad out of alignment, i just tap around softly the end housings with a soft hammer and bingo, shafts free and just nip up all bolts again,
i have 3 gmf grinders and they are there great machines, new bearings should be less than $20 , well worth replacing cheers mate
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8th Dec 2018, 11:22 PM #8Golden Member
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Just realised I sad knock the rotor out of the left hand housing then remove the fan.
That's not quite correct, you need to remove the left hand bearing before you can slide the fan off.
It's also a good idea to mark the rotor so you know which end is which for reassembly.
The end of the rotor with the left hand thread must be on the left hand side when the grinder is back together.
This is very important in order to keep the wheels on.
Cheers,
Greg.
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10th Dec 2018, 09:53 AM #9Member
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So the fan is on the left hand side then? Does the fan need to come off if I'm just replacing the bearings?
Would the process be the same for GMF "Senior" 8" grinder. The Senior grinder looks the similar the "HD" but bigger in most dimensions.
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10th Dec 2018, 02:23 PM #10Golden Member
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The fan always seems to have a generous coating of crap so I give it a blow with the air compressor to clean it.
It's just a sliding fit on the shaft so I take it off because it's easier to clean that way, but no, it doesn't need to be removed.
I can't comment on the Senior 8 in particular as I've not done one sorry.
Cheers,
Greg.
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18th Dec 2018, 11:32 AM #11Member
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Hi kwijibo99,
After taking the dust covers of the ends I noticed there's a circlip on the left hand side rotor shaft, I'm guessing to stop the rotor or bearing from moving? I was expecting to see a seat for the bearings to butt up against on the outer edge, but there doesn't appear to be one. It looks like the bearings could be press in from the outside, hard to tell without viewing the inside though. Does this grinder look like the ones you've repaired? Photos show both sides. One with the circlip is the LHS.
IMG_3865.JPGIMG_3867.JPGIMG_3868.JPG
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18th Dec 2018, 04:38 PM #12Golden Member
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That looks like an earlier GMF model and is a similar setup to the Brobo Waldown 8" grinders.
The GMF ones I've done have been the later type where the bearings are fitted into the end housings from the inner side. The end housings are one piece without a separate dust cover and the location of the bearing is set by a shoulder on the rotor shaft and the housing itself, there is no retaining circlip and the axial preload is fixed.
I would say that on your grinder the bearings are fitted into the end housings from the outside and the location set by a shoulder on the rotor shaft in the inwards direction and the dust cover in the outward direction, which means you may need to be careful not to load the bearings axially when tightening the dust cover.
Assuming the fan is still located on the left hand side of the rotor, I'd guess you can disassemble as follows:
Remove wheels and guards.
Remove left hand dust cover and circlip.
Temporarily replace left hand dust cover.
Remove right hand dust cover and circlip.
Remove nuts retaining left hand end housing.
Use a dead blow hammer to knock the right hand end of the rotor shaft which should make the whole left hand housing and rotor come out.
Remove left hand dust cover again.
Knock left hand end housing down to clear left hand bearing, look out for the fan if present.
Remove left hand bearing and slide off left hand end housing.
Remove right hand end housing and remove bearing from housing.
Assemble in reverse taking care not to load the bearings axially when tightening the dust covers.
Hopefully that makes sense, I've nearly confused myself now.
Cheers,
Greg.
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19th Dec 2018, 10:28 AM #13Member
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I've included some info for anyone else looking to replace bearings on GMF 8" HD mark 3 bench grinder.
The bearings are pressed on to the rotor shaft up against a shoulder.
The left hand bearing is retained by circlips but the right hand is just up against the shaft shoulder.
The bearing bore in the end castings have no bearing seat, the bearings can be pushed in from either side.
The left hand bearing is captured in the housing horizontally by an internal & external seal/waster, which I believe sets the position of the rotor & right hand bearing when everything is assembled.
There was no fan blade on this unit.
Because there is no seat for bearings in the end housings, I think the safest way to disassemble is knocking the housing ends outward, at the interface with the body, with a drift/screw driver. It wasn't that hard on my unit. The end housings are then easy to tap off the rotor leaving the rotor with bearings.
When re-assembling I think the left hand side should be done first. Put the housing onto the left hand side and secure the internal and external seal/washers with screws. It would be very hard to get the screws started on the internal retaining washers if the right hand side was done first. Put rotor with left hand housing back onto the body then install the right end housing and dust cover.
Second photo is the LH end, third photo is RH end
IMG_3871.JPGIMG_3872.JPGIMG_3873.JPGIMG_3874.JPG
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19th Dec 2018, 11:24 AM #14
Hi Ponchochos.
I think it is great you have taken the time and effort to document and photograph the bearing replacing of your GMF 8" HD mark 3 bench grinder for the benefit of the forum members.
Its is handy information to refer for those considering a repair or upgrade whether its now or in the future.
I am sure it will be checked out on a regular basis. I recall they were a staple when fitting out a workshop. The GMFs are lovely bits of gear.
Thanks
Grahame
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21st Dec 2018, 12:01 PM #15Senior Member
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Just to add a little to the thread, a Waldown 7 inch grinder which I suspect is quite old needed bearing replacement (6204) the originals were un-shielded and the housing under the wheel guard has a small hole for pumping in grease, of which plenty had been applied during its life. The spindle washer uses a labyrinth type seal which appeared to not work so well by the amount of grit in the old bearings. The end of the washer housing sits against the inner race of the bearing when the wheel is installed. New shielded bearings and it runs like a sewing machine. Alan.
grinder1.jpggrinder2.jpggrinder3.jpg
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