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:
- 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.
- Seat the front input shaft bearing next, and then put its bearing retaining cap on.
- 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.
- 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.)
- Seat the input shaft and rear bearing into the headstock and install the rear bearing retaining plate.
- 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...
- 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).
- Pull in / Seat the rear bearing - this is pretty easy.
- 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.
- 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.
- 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.
- 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.
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:
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.
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.