Jet GHB-1340 (non-a) Oil Leak & Setting Spindle Bearing Pre-Load

[heli_av8tor]

I bought this lathe new. At the time it was sold under several brands including Grizzly model G9036.

It has developed an oil leak from the main head gearbox. I’m not sure yet but I think it’s coming from the outboard end of the spindle shaft (see Red Arrow). It’s not clear to me if the part labeled “202 Collar” forms an oil seal or if it’s part of part 203?

I need to make a couple parts before disassembly, but would like to get some insight beforehand.

Looks to me like the two spanner nuts (224) set the preload on the spindle bearings. How does one set this correctly?

Thanks, Tom

 

[heli_av8tor]

Just noticed that the Grizzly G9036 has a different quick change gearbox though the top end appears the same (?).

 

[Cadillac]

For setting preload it’s kind of a touchy thing. First I would put a tenth indicator on the working end of the spindle. See what the spindle reads. I would use a wood and a pry bar to check deflection and endplay on spindle. Run the machine to warm it up and check again.
Once you have base line numbers now you can tighten up the endplay if necessary. You would loosen the first spanner nut that’s a lock. Then tighten the inner spanner nut a touch. Shouldn’t need to much. With an indicator on the face of the spindle you can check your progress. I’ve noticed that tightening the locknut will load the nut Assy tighter. So you might want to have both nuts right to get accurate readings. Run the machine checking headstock bearings temp. Preferably with an infrared temp gun. They should get warm but not hot to the touch. Exact numbers idk. You want those indicator numbers to be as low as you can get a tenth or two.

 

[tailstock4]

The leak on the end cover is probably either the gasket or possibly one of the mounting bolts if they are drilled all the way through the headstock. It is also possible the labyrinth oil drain-back to the headstock is plugged or partially plugged. They will also sometimes leak if the headstock is overfilled with oil or too heavy a weight of oil is used. The oil can’t drain back quick enough and jumps over to the dry side of the labyrinth where it can migrate along the backside of the spindle.

 

[markba633csi]

I would get in there with a really bright light and look close. Clean off the area and then watch for the leak.
Tailstock4 made some good points, can't add much to that. That collar thing 202 might have an oil seal?

 

[heli_av8tor]

Ok, got a closer look today. The leak is from the shaft just below the spindle. It has a solid hard rubber seal (#279 in drawing above). About 1/4 of the seal has worked itself out of the housing. I suspect it is much harder now than when new.

I couldn’t find anything equivalent from regular vendors so I ordered the Jet part from ToolpartsPro online. I should be able to get by for now by pushing it back in.

I indicated the spindle and couldn’t detect any end play using a 0.0005/div indicator when cold or hot. Cold temps measured 74 F cold and 127 F after running 45 minutes @ 2000 rpm. I get quite a whine at that speed. In the absence of any end-play I wonder if I could (should) back off the preload a touch. I may play with it when I get the new seal.

I found my original receipt showing a purchase date of June 1998. Total price $3,607 with tax from J&L.

Thanks,
Tom

 

[tailstock4]

I assume this lathe has tapered roller bearings. You should get a little deflection both axially and radially. Make sure you are measuring directly on the spindle. If you are using a .0005 indicator, I would think you would want to see a half a division or even a little less.

127 degrees temperature seems a little high. Is it continually climbing, or does it begin to stabilize? Personally from what you said, I think you may be able to back off a little of the preload. Basically, you keep track of the deflection, the temperature and also the surface finish and chatter (say from a cut off tool - something that loads it up a bit.) Any negative effect seen on these means you have gone too far. Also, you need to open up the headstock and turn the spindle by hand making sure that every roller is turning and none are skipping or sliding as this would be another indication of being too loose. This is if you can see them - sometime you can see the intermediate or back taper bearing rollers.

If you loosen off on the spindle bearings, you’ll need to reseat them. Run it at a slow RPM so that the bearings are being oiled and the give both ends of the spindle a sharp whack with dead blow mallet or I use a lead hammer. You don’t want to get carried away, but sometimes they need a blow to actually move the back bearing on the spindle.

This is a little like headstock alignment – trial and error and keep track of what you do. Remember that when either tightening or loosing spindle bearings, a little goes a long way.