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

[Sdynamo]

I had some luck earlier this year getting a replacement gear from Gene Maddox for a Hallmark N M-190.  While your unit is a Key, it looks like it has a Samhongsa gearbox, similar to the Hallmark engines.

You can reach Gene at dmaddox AT tx.rr.com.  I've attached the chart that covers the gears he (hopefully) has.  The chart has a few lines labeled for Key, but they are listed as gear for a diesel.  You'll need more info about your gear, but this might get you started.

NWSL also has replacmeent gears for some N scale brass, but it's a bit more hit and miss to try and get the right one.

JW

[wm3798]

That should be a useful resource, thanks.

I did not open the case to the point where I could inspect the worm.  Now that I've seen @peteski 's photo, I know how it's pressed together, so I can be a little more fearless next time I'm under the hood.

As for fitting it over a modern mechanism, odds are it would require quite a bit of surgery.  As you can see, the OEM drive is very slight, and the shell is open just enough to slip over it.  I'm sure that some judicious Dremel work could do the job, likely as much on the new drive as on the old shell.  I'd worry mostly about friction and heat screwing up the factory paint work, which is beautiful.

Also, I think I can probably buy 100 replacement gears in hopes of getting one that works for the price of a BLI mechanism.

As for printed replacement gears, I just don't think they'll hold up.  Since the grain of the print will always have striations, to me they are potential weak points.  I've tried replacing cracked Bachmann gears with printed ones, and they failed pretty quickly.

If anything, I'd like to try a properly sized and toothed Delrin gear (cast slippery plastic) as I believe that would be the most durable.  This isn't the sort of surgery I want to do twice.

It is a Samhongsa drive, so my guess is the part should be fairly common.  It looks like Peteski was working on a PRR Consolidation, so it's possible that the design is used across several platforms.

Lee

[Chris333]

Spookshow gives the loco a A http://www.spookshow.net/loco/keyp7d.html

I'd first try to fix it before swapping the chassis.

Also there are 2 on ebay right now for $999.99 and $799.99 so if it is original you may be able to sell it one day. I should add that both of them have been listed at least since I sold mine. So they are not selling that high, but you can dream 

[u18b]

Remember from my Shay thread...

Max made me a believer in Polish produced gears.  I had great success with mine.

https://shop.kkpmo.com/product_info.php?info=p21680_spur-gear---customized-gearwheel.html&XTCsid=829ilsbgpu7sfbt2ugmnmpv8j5

You have to input the desired parameters.   And the teeth are not skewed at an angle.... but that did not matter in  the end with my Shays.

It's true that the unskewed gear may wear prematurely, but it's really easy to replace it with new ones.

When I bought my Shay gears, I just ordered 6. 

[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.

To better illustrate this point, I found an image. Two locomotives I have under construction. The one on the right is single reduction, with the worm wheel mounted on the axle. The total reduction is just the number of teeth on the wheel, in this case 38. So the reduction is 38:1 meaning the motor turns 38 times for every time the drivers turn. The locomotive on the left is double reduction. It has a worm and worm wheel, and then a pair of spur gears. The worm wheel has 30 teeth and the spur gears have 14 and 18, if I'm remembering correctly. Which gives a total reduction of 38.5:1. So the total reduction is the same, but the worm can be further from the axle. The gears are all brass and will last for ages in a quiet mechanism, because they're properly engineered, not just slapped together the way Samhongsa did it.

[u18b]

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.

I've only spoken about the main gear in Kumata locos.   KMT uses the same main gear in almost all of their locos.

But this one is 18 teeth.  And not skewed.

[peteski]

It is a Samhongsa drive, so my guess is the part should be fairly common.  It looks like Peteski was working on a PRR Consolidation, so it's possible that the design is used across several platforms.

Lee

Yes, the brass model manufacturers used the same gearbox in most of their models.  In my example it is a Samhongsa model imported by Key Imports. For more photos, you can see the entire writeup at https://www.therailwire.net/forum/index.php?topic=36396.0

Here is another photo from that writeup.

[mmagliaro]

Getting the gear custom made in Delrin is the way to go.  Not only will it last, it will be quieter.  No, these gearboxes don't have the correct angled mesh, but you can get away with a lot when you run a brass worm onto a Delrin worm wheel.  You need the number of teeth, outside diameter, size of the center hole, and the thickness of the gear in order to get a custom one from that link in Poland that Ron posted.  I replaced some of the brass idlers in Rivarossi steam that way, and the engine runs much better.
The friction from brass-on-brass is pretty high, even with oil in there.

[wm3798]

Excellent.  The Railwire Hive Mind has delivered.

I'll do the necessary information gathering and see where it goes from there.
Thanks to everyone.
Lee

[wm3798]

For those of you playing along at home...


Looks to be a 6mm diameter 22 tooth gear with a 1.5mm bore.

The diameter is a guess based on the wear pattern.
Thickness appears to be 1.5mm ( also a guess because I can't put my hands on my calipers. )
Lee

[nickelplate759]

That would be a module 0.25 gear.

[u18b]

Hey Lee,

If you order some gears from Poland, order a few extra.
Peteski may eventually need one.   

(shipping is high of course, but the hears themselves are not that much when I bought mine).

[peteski]

That would be a module 2.5 gear.

That seems too fine for a typical brass model.

[wm3798]

The delrin gear I have turned out to be about 7mm, so it won't work.

I got all excited because last night while I was rooting through the last boxes of stuff from the storage unit, I came across a bag full of brass engine bits... looks to be frames and parts from two USRA Mikes, I think.  Sadly, there were no gears.  I believe these came to me from the DKS collection, and I think he had scavenged them to use in a scrap yard scene.  There's not enough there to complete a working model, and the drive train bits there are not the same as the bits I need.  Oh well, back in the bag until the right diorama or module comes along.

Lee

[Dave V]

This is the stuff of nightmares for me.

I've been able to do repairs on my Blackstone running gear and I've torn N scale Bachmann and MDC engines down to rebuild like this, but brass... You're a braver man than I, Lee.

There are two things I'll outsource before I'll do myself... Handlaying turnouts and disassembling/reassembling brass engines. You are definitely a better model railroader than I! I'm following this thread with rapt attention in the event I have a similar event with one of the three brass locomotives now plying the 3-foot rails of the Rio Grande Southern First District.