Can I fix it? Brass B&O P7 Pacific by Key

[wm3798]

Yes, the entire valve gear assembly on the engineer's side is closer to the wheels than the other side.  That does seem to be where the bind is occurring.
But I can't see any obvious reason for this to be so.
The hangers attached to the frame seem symmetrical,  and the axles float freely in their bearings, until they don't.

I should be able to work through a few more experiments tonight.

Will keep you posted.

Lee

[wm3798]

Okay, two questions...
When it locks up, are you sure it's a mechanical jam and not a short circuit?   If another engine is on the track when this engine locks up, does the other engine stop dead?

No, there is no short circuit.  I was having issues with pick up from the tender via the drawbar, the stiff wire was loosely attached to the drawbar so contact was intermittent.  I re-soldered the wire at its mount, which helped with that issues.  But no short at all.

Did you try the wiggle test when it is locked?  See if the non-geared drivers and all the rods can move just a little back and forth?
See if you can tell exactly which little rod or linkage is jammed tight and won't move at all.

It's definitely in the eccentric linkage on the engineer's side.  There's a noticeable bow in the eccentric arm itself, and the expansion link appears to be bent to try to compensate, but that impedes its movement, which I believe contributes to the bind.

If you do confirm that it isn't a short, when you get it in its locked state, can you take some super-close, sharp photos of each side and from underneath again?

From the underside photo you just posted, it looks like the right-side front-driver crank bolt can easily be catching on the valve gear up front.

I'll see if I can more clearly identify the hitch.  I think I'm getting close, and the information provided thus far has been helpful.
Stay tuned.

Lee

[wm3798]

After a few adjustments, I got the drive train running very smoothly when disengaged from the motor.

When I put Humpty Dumpty back together, though, nothing good happened.  Close inspection revealed no problems in the valve gear, so the last thing to check was the main gear between the drive worm and the driver axle.

This is what I found...


The spur gear is badly worn on one side.
The gear is skew cut, which I find a bit odd since the driver gear is not, but in either case, it's not engaging for a full revolution.

I was able to nudge the engine ahead a bit, but then the drive shaft would just spin.  I'm assuming the stall occurs when the gear failed to engage the worm, since the axles felt locked against the "good" side of the gear.  With gentle pressure, it would move again, then repeat the stall/spin cycle at regular intervals.
Sow now the question is, how does one obtain a replacement brass gear for a 35 year old brass locomotive?

Lee

[wm3798]

A quick dive into the parts bin found a delrin gear of approximately the same diameter, although the tooth count is lower.



Would anything bad happen if I crossed the streams?

Ray?  Egon?
Lee

[garethashenden]

Model manufacturers are really bad at gear design, basically everyone gets it wrong. The worm wheel should be skew cut, because the worm is and they need to mesh. If further reduction is needed, straight cut gears can be used, but they can't mesh with the worm wheel. There should be a second gear on the same shaft as the worm wheel. This can be straight cut and meshed with other gears.

Lee, Ideally you would want to replace both the destroyed worm wheel and the driver gear with skew cut gears if they're going to mesh with each other.

[Chris333]

Well that's your problem. 

[wm3798]

That's pretty clear.
Looks like I have a nice shelf queen until I can get the right parts.
I tried adding the delrin gear I have, but it's a tiny bit off, and therefore won't work.

Oh well.  On to more productive pursuits.

Lee

[peteski]

While using the same gear as a worm wheel and an idler is a bad idea (unless the gear on the driver axle also had angled teeth), the main cause of the excessive wear is usually that both, the worm and work wheel are both brass, where the worm and worm wheel should be made from different metals.



Similar example, although not as severe as Lee's example.  But all those brass shavings (occurring even when lubricated) tell the story.

[wm3798]

That's exactly the set up I have, @peteski .

right down to the brass shavings.

I have put the engine back together sans the worm wheel.  I even reinstalled the original universal joint, which apparently wasn't the problem at all. 
I had fun pushing the engine around the layout with a switcher, then packed it back into the box with the damaged gear, the hex head wrench, and the non traction tire driver set, and put it back on the shelf.

I'll need to see if I can source a replacement gear, because:
A) I really like the looks of it, and would love to run it.
B) I'm really not in the market for a $400 paperweight.

Oh well, back to the priority list.  I have to redesign the second floor of a house in Oxford today.

Lee

[u18b]

After a few adjustments, I got the drive train running very smoothly when disengaged from the motor.

When I put Humpty Dumpty back together, though, nothing good happened.  Close inspection revealed no problems in the valve gear, so the last thing to check was the main gear between the drive worm and the driver axle.

This is what I found...


The spur gear is badly worn on one side.
The gear is skew cut, which I find a bit odd since the driver gear is not, but in either case, it's not engaging for a full revolution.

I was able to nudge the engine ahead a bit, but then the drive shaft would just spin.  I'm assuming the stall occurs when the gear failed to engage the worm, since the axles felt locked against the "good" side of the gear.  With gentle pressure, it would move again, then repeat the stall/spin cycle at regular intervals.
Sow now the question is, how does one obtain a replacement brass gear for a 35 year old brass locomotive?

Lee

Ouch.   That's worse than I have seen before.

[u18b]

If anyone else as an adventurous person who has a P7d could open up theirs and pull that gear..
and take good photos, that would help Lee.

Could clearly count teeth.
And then if you have a caliper, you could measure diameter.

[Roger Holmes]

Lee--Thinking WAAAAY outside the box, would this shell fit on another chassis like BLI or Model Power?  If it did, you would have a classic body on a modern mechanism. 

[garethashenden]

What's the diameter of the shafts for the worm wheel and axle?

[peteski]

I counted 22 well-worn teeth.    Which is the same number of teeth in the gearbox in my photo. Might be a same gear. Unfortunately since I was working on that model for someone else, I do not have it anymore.

Didn't someone here ( @u18b maybe) know a source for spare vintage brass model parts?  What condition is the worm? Also worn down?


If it was me, I wouldn't want to put that beautiful shell on some commercially made plastic model frame.  The brass models have very finely made running gear. Delicate see-through spoked drivers, and very fine etched valve gear.  Most non-brass loco's running gear looks very clunky in comparison.

[Mike C]

  Hey Lee how about a printed gear ? That would also solve the wear problem . I'm pretty sure I read a post about printing them somewhere here .   Mike