Knocking Headstock - P&W Model C

Happily working away on my 1952 Pratt & Whitney 12x30 Model C, and noticed the machine was getting louder. Played around a bit and came to the conclusion that it's relative to the drive motor RPM. Checked belts (they are old, but not visibly cracked), and took a good look at the motor output shaft runout, and belts on there while turning. Looked good. Turned speed down on the VFD and the sound is certainly coming from the headstock, high up, rather than from the motor.

Pretty discouraging. I don't get a lot of garage time these days (hobbyist) and it took the wind out of my sails a bit. The next steps are somewhat obvious, remove the headstock cover, run the machine at low motor speeds and see what I can do to isolate the noise.

Why am I posting? Just want to share my pain and am hopeful that a seasoned pro might tell me "normally it's XX"... wishful thinking I know! One idea that pops to mind is that the belts are hard and due to the machine sitting (as it has off and on for long periods of time) they aren't pliable. Can't see it looking good at the motor end in that scenario though.

Any words of encouragement are welcome.

Big angular contact ball bearings support input pulley - see how they feel rotating pulley with belts off

Note also oil pump right end of input shaft. If this ran dry for any length of time pump would likely self destruct. It has to raise oil from way down. Oil sight for reservoir is down low on back

Yeah good call on the pulley, will try that next.

Oil pump, another good suggestion. I have some suspicions it ran dry briefly. However, for this machining session the oil is new this past month and at an appropriate level, and the system was primed with the headstock cover off so I could see oil flowing while turning everything by hand before it was under power.

Assuming the oil pump is labelled #29 on your diagram?

Assuming the oil pump is labelled #29 on your diagram?

Click to expand...

Yes, that's it. If you need manual scans (Op and Parts) private message me your EMAIL address

Turns out I have both manuals but didn't realize the parts manual was there. Thank you for that. Will post up more once I have more info from my investigation.

A bit of an update:

Removed belts. Overall ok shape, but two of them have a slight cut in them. Will see if I can source replacements.

Motor under power: Quiet and smooth
Lathe drive pulley: Rotates smoothly. Will freewheel. No side to side play, no drag, no noise...?
Headstock oil level: At fill lines, clean.
Turning chuck by hand: I can replicate the noise. I guess we keep digging deeper.

Maybe try a mechanics stethoscope . see if you can isolate exactly where the noise is coming from. Just be careful if under power.

Thought I found it. Took me a while because everything looked good and it also took a while to get the sound to replicate. Had to try a bunch of different spindle speeds before I could spin the chuck by hand and get enough speed in the geartrain to make it happen.

Picture of the issue here:
IMAG142.jpg - Google Drive

So it's part of the clutch mechanism that looks like it's slapping against the clutch plates. Every revolution there is a slight bit of contact, and I imagine as we have more heat in the system we have slightly more contact. Here's the funny part, it's spring loaded and appears to be operating as designed...?

A bit hard to tell from the photo, so there is also a video here:
VIDEO6.mp4 - Google Drive

And I thought this was the source of the noise, but I was wrong, as when I put it all back together...

P&W loved LOOSE needle bearings - even used them in rear spindle bearing up to the replacement ball bearing shown in the supplement section

How does spindle feel turning by hand in neutral? Any catching or momentary hang up could be the needles in your rear spindle bearing

OK, productive day in the shop. I'm getting more information as I go.

First order of business is that I had to get the machine away from the wall a bit at the headstock end. A couple 1" round stock bars made great impromptu rollers (which worked much better once I swept the floor in front of them). I really should build a pair of skates sometime. Anyway, I can finally get at the backside of the headstock as intended. Win!

Pulled off the belt cover assembly so I could get a little closer.




With the headstock cover and belt cover removed, I managed to replicate the sound (a metallic "clunk") turning things by hand, which I can feel through the input pulley quite clearly. I was able to isolate this sound to the bearings between the input pulley and the clutch - so in the area of the main thrust bearings John mentioned earlier. The odd part to me is that only at certain gearbox settings and belt tension could I seem to make this happen.

So I pulled it apart until I had the bearings in hand. (or mostly in hand)




And everything felt good. No play, no drag, nothing but smooth bearing movement. However, between the 2 bearings are a couple spacers, an inner one on the shaft, and an outer one clearly visible in the photo above. The right bearing in the photo slides axially on the shaft depending on clutch position. And what I'm realizing, is that the outer spacer is just rattling around between the 2 bearings. Is it possible that cold oil damped the sound this creates moving, but once my oil was hot and thinner, it moved around more?

I'm 99% sure the noise is coming from this assembly. Only a stubborn woodruff key has kept me from dissembling further. In the mean time, I'm going to price (not order) new bearings, just to re-motivate myself to prove it's the bearings.

Look in parts book at previously posted page. Is #11 slinger there?

Spaces that bearing away from pulley

Yes, it is there, and was installed the right way around.

Got the bearings off over the woodruff key with some fiddling. Not sure what to think of the bearing condition. They had some crud in them (rust coloured, lack of oil?) which isn't great for bearings obviously. However, once cleaned up they looked and felt pretty good. You'd think that if I was getting an audible clunk, I'd be able to feel something click, drag, grind or something when rotating the bearings in my hand...

A couple videos of the issue prior to dissassembly.

Pratt & Whitney Lathe Input Shaft Noise 1 - YouTube

and

Pratt & Whitney Lathe Input Shaft Noise 2 - YouTube

Well back together and the noise went away for a while. But today it's back. So much for the "disassemble and reassemble" school of repair. Take a look and let me know if you have any thoughts!

Pratt & Whitney Model C Input Shaft Noise - YouTube

Zengeneer,

I also own a P&W Model C, a 16x54 with a War Production Board tag circa 1943. I had a similar problem when bringing mine up to operational condition. It turned out to be the drive pulley on the headstock. It didn't feel loose when I felt of it, but when I tightened the locking nut, the knock went away. I do hope you find an equally simple fix. The machine is a beast and more than I needed for the type work I do. I needed a bed length to handle some shafts I regularly see and pick this machine up cheap. In spite of decades of abuse that scarred the ways left serious dents and dings it still holds close tolerances.

Yeah that's a good comment. I was surprised at how tight the drive pulley fit on it's shaft, and even when it seemed "tight" there was still more room to move.

I've decided that since the noise comes and goes, and I can't completely nail it down, I'll keep an ear on it and see if it get's worse so I can isolate easier. I've got some peace of mind given where the noise is coming from.

Have used it steadily the past 2 days, all good.