replacing lathe bearings on 9729

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John R
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Joined: Mon Oct 26, 2015 8:43 am
Location: Sour Lake, Texas

replacing lathe bearings on 9729

Post by John R »

Has anyone done this? Any tips? I read somewhere (I think?) that someone found some sealed bearings that fit instead of buying replacement bearings from Grizzly. If this is so does anyone know the brand and part # of those bearings?
Torch
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Re: replacing lathe bearings on 9729

Post by Torch »

The parts list shows the bearings as a 7112 and a 7110. Those are not sealed, but are angular contact bearings and you could get the dimensions from an on-line catalog.

I believe the manual is downloadable from Grizzly, and documents the correct pre-load procedures for the lathe bearings.
John R
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Joined: Mon Oct 26, 2015 8:43 am
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Re: replacing lathe bearings on 9729

Post by John R »

Torch the online Grizzly parts list shows the bearings to be p9729227 $38.50 and p9729250 $39, I have the manual that came with my machine and don't recall any instructions re bearing preload but will look again perhaps I missed it. Do you know if I will need to buy anything other than the two bearings and then the gaskets items 223 and 228? Have you ever actually replaced your bearings?
John R
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Joined: Mon Oct 26, 2015 8:43 am
Location: Sour Lake, Texas

Re: replacing lathe bearings on 9729

Post by John R »

I just looked at the manual again and didn't see any mention of bearing preload.
Torch
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Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: replacing lathe bearings on 9729

Post by Torch »

Ooops, sorry. I was thinking of the G4791 for some reason. My bad. The spindle bore on that one is bigger so the bearings will be too.

However, the preload procedure is probably similar.
Torch
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Joined: Wed Mar 17, 2010 7:58 am
Location: Muskoka

Re: replacing lathe bearings on 9729

Post by Torch »

I wonder if the bearings are 2007109 and 2007108.

That is what is used on a nearly identical Chinese-branded machine. They are all made in the same factory. But don't bet the farm on those numbers, they do make changes on the fly!
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NP317
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Re: replacing lathe bearings on 9729

Post by NP317 »

Grizzly maintains a good Technical Support team. I suggest contacting them will get you the info you need.
RussN
John R
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Re: replacing lathe bearings on 9729

Post by John R »

OK I called Grizzly tech support and he said to put the same preload that you would put on a car's front wheel bearings; when you start to feel a slight resistance stop. There are spanner nuts on the rear of the shaft that are used to apply the preload. These are clearly shown on the schematic in the manual. The bearings are open and will be oiled from the gearbox so do not require packing before installation but I will apply grease on them anyway to make sure they have lubrication until the splash oiling from the gearbox saturates them. The manual shows external ports where you can add oil from a squirt can and recommends that you do that, but my gearbox does not have those ports. I confirmed that the bearings are p9729227 and 250 which is what I stated above. The only other items that may be needed are front and rear gaskets p9729228 and 249. The cost before tax and shipping for both bearings and the two gaskets is $82.23.
John R
Posts: 37
Joined: Mon Oct 26, 2015 8:43 am
Location: Sour Lake, Texas

Re: replacing lathe bearings on 9729

Post by John R »

I just ordered both bearings and gaskets and the total with regular shipping and tax was $106.08. The fact that these were in current stock tells me I am not the first to be putting new ones in. This machine is 12-18 years old on my watch and dk how many more before I bought it from a commercial concern and it had had obvious use by them. I've turned aluminum, brass, and mild steel with it and milled those plus cast iron. It has been a darn good little machine but there is nothing made that doesn't require maintenance and replacement parts at some point.
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NP317
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Re: replacing lathe bearings on 9729

Post by NP317 »

Glad you can get the correct bearings and gaskets.
Price for all 4 items and shipping sounds reasonable, and a relatively inexpensive fix for a well used machine.
RussN
Rwilliams
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Re: replacing lathe bearings on 9729

Post by Rwilliams »

Replacing headstock bearings can be more important than we often realize.

Long ago a friend had a used home shop lathe with plenty of hours on it but never abused. He began to notice a minor vibration in the machine and soon the part being cut began to show some minor irregular micro chatter marks. He checked all of the gibs to make sure they were not at fault. He finally used a stick on the headstock bearings and when in operation, could hear a slight rumbling from the bearings. He took the headstock apart and found the bearings showing no signs of distress or major wear issues. He still suspected the bearings and replaced them with new bearings. Once installed, the machine tool performed better than it ever had and the rumbling from the headstock bearings had vanished. He only wished he had listened to the headstock sooner.
John R
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Joined: Mon Oct 26, 2015 8:43 am
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Re: replacing lathe bearings on 9729

Post by John R »

The new bearings are in and the lathe is running smoother than it ever has with no more rumble. There is no runout and I have been cutting chips and turnings on mild steel with no problems. At the start of this thread I asked if anyone had replaced the bearings on a 9729 and if they had any tips, and got no responses, so I will share what I learned while replacing the bearings on my machine. This may help someone in the future. There are no instructions for replacing the bearings in the owners manual that comes with these things but there are schematics at the rear of the manual, and a person can get a general idea of how to proceed by looking at them.

Here are my tips.

- My machine is close to the wall behind it and I have no casters on the stand it sits on to roll it out on. This makes it really tight to get to and see inside the rear cover on the lathe gear case. The schematics indicate that the gear case has a hole machined in the top of the case under the post which the mill head sits on, which would allow access to the gears through the top. I removed my mill head and the post it sits on from the top of my case to have this access, but there is no hole. My machine is a version one and perhaps later versions have this hole, but mine did not, so doing this was a waste of time for me. And I had to reinstall the post and mill head, and reconnect all of the wiring I’d disconnected.

- The keys, bearings, and gear A that were in/on the main shaft were so tight that I had to drive them off/out. I used a small punch on the ends of the keys and just kept tapping on them until the end rose up and I could get that key out. I then used a whetstone to take a little off of the sides of each key so they weren’t quite as tight and I could reinstall and remove them without a punch. The main shaft has three steps on it to accommodate the two bearings and gear A. I left the front flange on and drove the main shaft out of the bearings and gear A, using a block of wood and a bfh to do it. Then I took some material off of the main shaft using 320 grit crocus cloth, until It became possible to reinstall gear A and the new bearings by hand without driving them on.

- The schematic shows a lubrication channel from the face of the main case leading to both the front and rear bearings. My machine does not have these, thus my bearings were getting splash oiling only. I also had a very small leak in my main case, even though I had replaced the gasket on the rear cover. The leak was not the oil level sight hole so I think it may have been a casting flaw somewhere. I rarely used my power feeds so I just left gear A out during reassembly and packed the new bearings with axle grease, and did not refill the gear case with oil. I thus no longer have power feeds. I may reinstall gear A at some point or may leave that up to the next owner of this thing.

- The Grizzley tech people told me to set the bearing preload as you would the bearings on the front spindle of a car or truck. This is wrong; the preload must be set much tighter than that. I did not have a spanner wrench that fit the two spanner nuts at the rear of the main shaft so I used a punch and brass hammer to tighten the first nut until I got the preload where I wanted it, and then installed the special washer and second nut. The schematic shows the special washer going on first and then the two nuts one after the other, but actually the washer goes on between the two nuts. Set the preload until the chatter stops. The shaft will be pretty hard to turn when you get to this point, easier when the three or four jaw chuck is on there, but still hard. It will get a little easier after you’ve run the lathe awhile. You can adjust the preload with everything back together so just set it, then run the lathe and listen, and then tighten it a little more, run it again, listen, tighten, run it again, etc. etc. until the chatter is gone. Mine is now where it was in terms of difficulty in turning the chuck by hand before I took it apart, but much quieter. Yes it is quieter because the gears inside the main case are no longer turning but mainly because the new bearings are not making any noise.

I’ll post several pictures showing some of the above as it was done. I was half dreading this whole deal before I started but once you've done it it is no big thing.
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