Finding gearhead noise cause

One of my 1440 lathes has developed a rattling noise in the headstock, more at some speeds than others but high RPM seems to make it worst. We took the cover off and inspected the teeth but they all look good, these are induction hardened and ground gears throughout As the RPM increases with no load the rattle comes in about 400 RPM (In high gear) and goes away as it gets nearer top speed of 1800 RPM, which makes me think it's an angular contact brg that's lost it's preload.

At any rate my assumption is that it is a bearing going out. Every bearing we could see from above looks good, no broken rollers or balls, but the big end bearing is hidden.

We tried to find where it was coming from using a stethoscope but with the cover off we have to pull it over by hand, lest it shower the shop for some distance with oil.

So, my question is this, is the only way to go forward to tear it apart or are there other methods so we can isolate the problem and not tear anything apart that doesn't need it?
Thanks,
parts

Have you put the HI/LO lever between ranges and run the lathe. This would at least narrow it down to something not spindle related. I would also do the same with the gear speed/feed lever..get the gearbox into a neutral state and see if the noise goes away. Someone didn't leave a sleeve or something in the spindle bore and that's what's rattling around..it's been known to happen.

Stuart

Next time you take off the cover take a mag base/ indicator and put it on shafts, gears and take a pry bar and see if you get backlash. Don't pry hard to bend anything. Pry and let go and see if you get at lost motion. You could drain the oil and run it a bit and be super careful listening around moving gears and parts. Have you checked the motor pulley and motor. Check the motor mounts. Did someone crash the lathe?

When prying see if the gears are loose on the shafts, maybe a key is worn...hmm hard to find issues sometime. Another thing if you can isolate a sound to a gear set, then spay some contact cleaner on the gears and then spray with dykem spray ink and turn the shafts and look at how the dye on the gear teeth rubs off. Just tossing out idea's.

Let us know what you find when you find it please. Rich

Stuart makes a good point as long as it can't slip into gear while running.

My Hendey did that one time . I finally found a piece of bar stock that I had used to knock the center out of the taper two days earlier.

Thanks for the advice guys. First Thing I guess is set a DTI on the chuck and see if there is deflection under a side load with a bar. I like the final drive in neutral idea too,hadn't tried that.

Start at the beginning The motor
Remove the V-belts and feel if the pulleys and bearings have no play
You must remove ore slacken the V-belts to detect this

Peter

Possibly a shift collar may not be retracting far enough, allowing the teeth on the collar to rattle against the end of a spline. Sometimes this can just be due to a worn detente which allows the shift lever to drift out of position, if in fact, it ever was in its ideal position. Wear on shifter fork fingers can also result in the same issue.

A very remote possibility but easy to do..pull the chuck and see if it makes a difference when you run it.

Stuart

We used a 3' 1 1/8" bar in the chuck and pushed up and down, only under 1/2 thousandth movement which seemed like bending to me. With the hi-lo in neutral the noise is gone but there is a weird clicking noise at a much slower frequency, totally baffling as we didn't hear that before, or it blended into that rattling sound.
C&M Spindle's Bill told me over the phone it could be gear slap, and try some power punch. If it goes away I guess that's that.

That makes sense to me because at 1800 RPM the rattling comes in at about 3-400 RPM and goes away at top RPM. I tried taking a heavy cut and the rattle got quieter but not totally gone.
Going downtown for power punch-

Update;

I pulled the input shaft out, because my maintenance guru said sometimes the first ball bearing in from the pulley is the culprit. The bearing felt and sounded fine, as did the one on the other end.
My brother came over today and we looked it over, ran the motor without the belts and it sounded fine, and finally I decided to put it back together because my other small lathe was having a problem with the DRO and it won't do to have both small lathes down.
So we reinstalled the input shaft and put the belts back on.

The amazing thing, when we were done I started the lathe and the noise is gone. I tried several speeds and nothing will make that knocking noise return. I'm very thankful, though I do wish I knew what we did, if we did it somehow.

In my almost 40 year career of working with machinery I have come to a fairly basic realization, and that is if you didn't find the cause of the problem when you took the thing apart, but it's gone when you put it back together, then it probably really isn't fixed and the problem will be back.

Stuart

I wonder if the belts hadn't taken a set? We put them back on in no particular order.

I went up to Portland a while ago and looked at a Tos lathe for sale, and the belt was so loose that the thing screeched like a banshee starting or stopping with it's electromagnetic brake. I wonder if he hadn't had trouble with input shaft bearings in the past. Serpintine type belt.