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Thread: Machining related: Lathe motor rebuild

  1. #1
    Join Date
    Mar 2001
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    Saranac Lake, NY
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    365

    Question Machining related: Lathe motor rebuild

    The 5hp 3-phase motor on my 1941 14" Hendey yokehead crapped out this week. At first I suspected my home-brewed add-a-phase, but it turned out to be a bad front bearing. The motor is an old cast iron No. 254 frame, and I guess I just assumed it would run forever. Took it apart, removed several colors of gunk that used to be grease. Now time to order new bearings.

    Bearing lubrication is by upward-pointing zerk fittings supplying grease to the exterior side of the bearings. Opposite the zerk fittings are two downward-facing drillings, apparently to allow excess grease to exit the motor.

    The front bearing (on the end with the shaft) is open -- no shields or seals. The rear bearing has one shield, oriented toward the outside of the motor.

    Question 1: Is one shield on the outside of the rear bearing the normal configuration for a motor of this size? If so, what is the reasoning behind this? I would have expected shields on the interior side of the bearings, to prevent excess grease from getting into the interior of the motor.

    Questions 2: The front bell housing has an annular groove about 1/8" wide and 1/8" deep just inside where the shaft emerges. Looks as if this was provided for a shaft seal of some kind, although none was present in this case. If the groove is for a seal, given the age of this motor, was it originally a felt seal? Could an o-ring be used? If so, should it be of any particular material? Round or square?

    Any & all information will be appreciated. I'm dead in the water without my lathe, and I'd like the rebuilt motor to last longer than I will.

  2. #2
    Join Date
    Mar 2009
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    Ohio
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    I would replace with sealed bearings front and back. No need to grease again. The front groove probably had felt. If replacing use felt again. Probably not necessary.
    Toolznthings

  3. #3
    Join Date
    Jan 2005
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    Ct
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    Only 78 years on a bearing?
    Cheap crap.
    Len

  4. #4
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    Jun 2009
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    san jose, ca. usa
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    I would agree with sealed bearings also, if it's an option.

  5. #5
    Join Date
    Aug 2018
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    Tai Tokerau - NZ
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    I would get sealed bearings... then pry the dust caps off and lube them warm and putt the caps back on before fitting.

    I wouldn't run a spinning shaft in an o-ring, unfortunately it's probably too small of a gap to fit a proper oil seal.

  6. #6
    Join Date
    Oct 2014
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    365

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    I would say you would want a seal on the motor side of a bearing to keep grease out of the motor. And if you use a bearing with one seal or one seal removed, on the end of the motor with the output shaft it wouldn't matter if a bit of grease leaked out to the outside of the motor. On the other end the space outboard of the bearing would make a nice grease reservoir. If the bearings have a fair amount of grease in them when you put them in you will not have to grease more than every few years and not much at that time. On large motors there is often a plug to remove when greasing aside from the grease fitting. You remove this plug, pump in a little grease, run the motor for a few minutes to allow excess grease to be purged out, then put the plug back. A well greased sealed bearing used in a home shop should last for 15 or 20 years or more with no additional grease I would think.

  7. #7
    Join Date
    Feb 2012
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    251

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    Well you won't get 78 years out of sealed bearings, because they never put enough grease in them! Also, they are not "seals" regardless of whether they are metal or metal rubber, they are dust covers, and that is all. Buy good quality non sealed bearings, pack them with grease, and refit to the motor, and give them two strokes of a grease gun every three months max! Yes, it is a good idea to not let grease go into the motor, but this most often happens when the motors are over greased, which is a very common cause of failure, NOT because there is too much grease in the bearing, but because the grease has got into the motor, and this can track dust back into the bearing. Bearings fail because the grease drys out and stops lubrication the bearing, ie lack of maintenance, or the grease in the bearing becomes contaminated with dust etc. A bearing that is FULL of the correct clean grease will not fail. The older motors I used to work with had a grease zerk (we call them nipples) at the top, and a screwed plug at the bottom, we used to remove the plug every six months, and pump in grease till all the old grease exited the plug, and the new grease appeared. I have stripped motors from a local factory that had had this done to them since their installation in 1934, and were running on their original bearings when the factory closed down in 1967. they were stripped, cleaned, bearings repacked, and went on to other homes in other factories. Properly maintained, unsealed bearing will outlast a sealed bearing by many years. which is good for the owner, but not for the manufacturer. Like mihit above , I too have been shocked by how little grease the manufacturers put in their "sealed for (short) life bearings"
    Last edited by hermetic; 02-10-2019 at 02:18 PM.

  8. #8
    Join Date
    Jan 2003
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    On the Oil Coast,USA
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    The original seals were probably leather(the Rawhide in Chicago Rawhide) here is the SKF seal catalog including application and dimensional data,odds are you can find something that will fit the hole.

    https://www.skf.com/binary/21-129139...10919_2-EN.pdf

    You can also if you have access to another lathe turn up your own shields from plastic such as Nylon,Delrin or even UHMW.

    But it is also perfectly acceptable to simply replace your original bearings with quality sealed ones and get back to running your lathe.NSK,NTN,Nachi,Koyo,Timken,INA,SKF all make good bearings.
    I just need one more tool,just one!

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