Seig SC4 Bearing Replacement / headstock rebuild

Be sure to file or stone the leading edge of the spndle bearing mounts as many I have seen are sharp and will cut the oil seal. I would micrometer (mike) the new and old bearing OD and ID before installation. How did it come apart? It may go in hard, so don't hammer it in. You may want to use a threaded rod to pull it in. It looks as if you have some skill and nice tools. Hope I'm not insulting your intelligence (lol) I also never use a hard punch to tighter the spanner nuts. I use a hook spanner, If you need a punch, use some leaded cold roll As far as the thrust setting. I would use and .0001" indicator and push the spindle laterally with the tails stock to push in and release to check the lost motion and then rig up a chaine and wood board to push it toward the Tail Stock, push and release - measure the lost motion and you leave it loose and tighten it so you haave no lost motion and then tighten the spanner nut one more notch on the spanner lock washer. The after you get it running do a wear in of the spindle bearings. Start out slow RPM for 10 minutes check for heat, then higher every 10 min, etc. . The temp should not be over 140 F and 120 F is good.
 
I’ve a bearing install kit with different cups and rods (from when I did my kit car) which I used to get the old bearings out of the casting, and the others where pressed off. Thanks for the advice - its nice to get it from such an esteemed member of the community. :beer:

I’m having a hard time finding Mobil 32 over here. 28 no probs. I’m assuming the only real difference between the two is the heat resistance / ant-melting properties of the 32?
 
# 28 is fine. I used it for years and 32 was a newer number for a similar formula. I buy 1 pound cans. Just don't overpack the n the bearing with grease. Less is better with grease. 30% unless your using Kluber. it's expensive and 25% is the number. a simple way to calculate it is to count the rollers and use 30% of that number. It appears the machine is made is Asia? If it is the bearing made in China is far inferior to SKF in my opinion..
 
So I’m still waiting on the grease. When it arrives, should I remove the rubber seals on the rear ball bearing, wash out whatever grease is there and replace with the #28? Or is what SKF put in there from the factory good enough?
 
Well, the deed is done. I've swapped out all the bearings as per the list on page 1 of the thread. I've also done some other modifications as I went along.

For anyone who's also looking to do this on their SC4, some advise on order of assembly, and some pearls of wisdom:

  1. Seat the tapered bearing race first. I had a bearing install / removal kit from when I built my kit car so I used this, which makes the job very easy.
  2. Seat the front input shaft bearing next, and then put its bearing retaining cap on.
  3. Install the rear input shaft bearing on the input shaft itself. I'm also lucky enough to have a press, so again this was no issue.
  4. Slide the input shaft in to the headstock and prior to fully inserting it, slide the cir-clips and lower gear with its key on. (This lower gear is supposed to slide back and forth on the shaft, when moved by a selector fork. The SC4 has an optional milling attachment, and this allows the spindle to be stopped but still power the lead screw in a stock machine. My SC4 is never going to have a milling attachment installed, and the lead screw is completely separate now due to my ELS - so I have modified the gear to install a grub screw to stop it from moving, and deleted the whole selector knob and fork.)
  5. Seat the input shaft and rear bearing into the headstock and install the rear bearing retaining plate.
  6. Pack the new tapered roller bearing with appropriate grease - I went with Richard's suggestion of Mobil #28. Then press the bearing on to the spindle - NOT FORGETTING THE FRONT 'OIL SEAL' / CAP which needs to be on there in front of the bearing. I was about to press mine on the second time (more on that in a mo) when I realised I was missing it...
  7. Tap in the rear 'Oil Seal' / Cap whilst you have access through the rear bearing seat. Don't bother getting replacement, real seals with lip seals and wipers etc. I did, and it was a waste of time. They will not fit properly due to be being too thick for the available space, and the front one will interfere with the proper location of the bearing. I tried but in the end I ended up stripping the spindle again to get rid of the new seal I'd Installed. Save yourself some grief and just clean up the old ones (which are actually turned steel components).
  8. Pull in / Seat the rear bearing - this is pretty easy.
  9. Pass the spindle into the headstock, and whilst the end is free inside, install the upper gear, cir-clips and the key. Be prepared to turn the air blue here as it's a pig trying to get them all on the spindle in the small amount of room you have - and the cir-clips in particular give a fight trying to get them in position.
  10. Pass the tail end of the spindle through the rear bearing. Add the rear bearing cover and the first of the spindle nuts. The bearing cover seats on the inner race of the rear bearing, and the spindle nuts press on it to provide the pre-load to the front bearing.
  11. Proceed to tighten the spindle nut, which will draw the spindle into the rear bearing. Keep going until the front bearing seats into the race, and then tighten it whilst checking for play and ensure it can still rotate.
  12. Tap the front bearing cover into place by using a long punch through the chuck mounting holes on the front spindle flange.

I then ran the lathe for 10 mins at the lowest speed as advised, and then slowly ramped the speed up. All seemed well and it didn't get hot. So I gave the spindle nut another 1/8th turn and did the same, and it still barely got warm - rinse and repeat until at max speed (2000rpm) it was warm to the touch, but not hot. Whilst doing this I kept monitoring the runout - and by the time I called it 'good enough, don't bugger about anymore' it was about as close to zero as matters on a lathe like this. I slight tick on a 0.01mm indicator. I installed the second spindle nut and snugged it up to lock the two in place.

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The other modifications I did was to delete that selector fork for good, but that left a hole in the head casting - so I printed a 'plug' for it to fit where the fork guide went through the front electrical box, to keep any crud from coming through:

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And as there was no knob to turn anymore, and also because the front panel on my lathe was so grotty, I designed and printed a new front panel - one that had physical buttons instead of the silly membrane switches it used to have. I had to remove the original switches from the circuit board - I replaced them with some header pins and crimped some matching connectors to the switches so I could remove everything if needed.

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Did the bearing swap cure my issues? You bet. I can put cuts on I never dreamed of now - no chatter, no drama from the lathe. It's like night & day, and well worth the hassle.
 
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I enjoyed the technical discussion and the final outcome.
You deserve a pat on the back for a job well done.
 
Thanks Jeff. I do hope my trials help someone else - there’s not a lot of info out there about doing this to an SC4. Plenty for the SC3, but really next to nothing for its bigger brother.

I really ought to do something about the paint job next. The flaky white paint is starting to bug me. ;)
 
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