Drive Rod Repair

[Mark W]

At our last set-up back at the Rocky Mountain Train Show, I thought "I haven't run British Railways "Tornado" in a while.  So, I got it out, set everything on the track and dialed it up.  After about two inches, it jerked to a stop and someone pointed at the drive rods dangling in the ballast!

The issue was quite simple on first inspection, there's a linkage that has a little zig-zag and rides along a railing to guide the main rod and piston rod, this had come out of it's guide.  Unfortunately, trying to put it back in place, I noticed that little zig-zag itself dangling, and then break free.  Disaster!


https://i.imgur.com/vlnn0AI.jpg

I contacted Bachmann.uk for a replacement and received both good and bad news.  Good news, they have spares!  Bad news,  £38!  That's roughly $47 USD 
(To be fair, that is for the entire drive rod/motion assembly (less drivers), but still!)

https://i.imgur.com/MTzKMRG.jpg


So, taking inspiration from some to the amazing talent here on the Railwire ( @mmagliaro for one ), I decided to try my hand at fabricating the replacement. 


https://i.imgur.com/dmPUOAN.jpg

I cut a small brass strip and soldered it to the top of the linkage.  Unfortunately, the linkage is made out one of those metals that doesn't like solder.  I roughed up the face as best I could give it more surface area and used a generous amount of flux so the solder would flow into every little groove and hopefully grab on.  It took about 7 or 8 tries, but I finally had one that seemed to have a decent amount of hold.


https://i.imgur.com/oelphvE.jpg

And Tornado runs again!


https://i.imgur.com/Anw5bzY.jpg

I quite like the little brass 'accent' the new part provides.  Will be a nice little DYI reminder. 

I'm still worried about the solder joint though.  I wonder if it will be fine, or if there's a better method I might use to attach the 'zig-zag' piece.   

[ns737]

what if you made the brass piece  u shape?

[MK]

Remove it with your soldering iron and clean as much of the old solder off.  Or just make another piece.  Then re-solder it with silver solder.  Much stronger.

[mmagliaro]

First, congratulations on taking the time to make a metal piece, use flux, and hang in there to get a solder joint.
I do not think even a good 2-part epoxy would last in this application.  And in fact, looking at the super-close-up
photo of the broken part, it sure looks to me like the top bit that broke off was actually attached with some sort
of ACC or epoxy.  I'm looking at that clear glue-like material in the photo.

I am not sure about using brass, however.  It is soft, deforms easily, especially in a rapidly moving part like this,
and after some bending around, is prone to breakage.  I'd try to use a strip of nickel or phosphor bronze.  These are not quite as readily available, but you can buy it from Eileen's Emporium in the U.K., or maybe you can harvest some phosphor bronze off the pickup wipers from an old engine in your junk box.   

The same thing is true of a conventional solder joint (assuming you just used regular electronic rosin-core solder).
I second the idea of silver solder.  True "silver solder" requires a torch.  I don't think you need to go that far.  But if you just use some silver bearing solder, the joint will still be a lot stronger.  It commonly comes in 2% or 4% silver content.

But overall, I think you did a fine job.  Soldering a piece of metal on there is definitely the way to go if you want this to last.

[peteski]

Like Mark mentioned, the alloy the original was made from is likely white metal and not easily soldered.  I would be surprised if he can get a good solder joint (silver solder or not).  It will likely be just mechanical joint (depending on the roughness of the surface rather than solder wetting the metal. I never had luck soldering white metal.

I don't think brass will be a problem.  After all, most metal gears in our models are made of brass!  If brass was weak, those gears will be wearing out like crazy!    There really is not much pressure or friction on the crosshead, and brass has good wear characteristics.  Plus, most brass N scale steam engines have that part made from brass (lost-wax castings) and they are quite robust.  The brass is usually plated with nickel. Or they might be cast from nickel silver (which is just another brass alloy).

That is a tough one Mark - especially since it is such a small piece.  Maybe fabricate the entire piece (crosshead, and the piston rod) from brass?  You're pretty good at miniature modeling.  Or just spend that $47 . . .

EDIT: attrocious atrocious  spelling.

[Mark W]

Thanks for the feedback guys!  I did use silver bearing solder.

I'll keep an eye out for some better metals. With reassurance that solder is likely the best option, I think I'll keep this fix in place and upgrade the metal if I have to repair it again.  In the mean time, I'll be sure to keep the rods lubricated. 

The original part was one solid metal piece.  That residue in the close up is actually Bondic from the first failed attempt at gluing the original part back together. 

[MK]

Thinking WAY out of the box and I'm no metallurgist, not even close, but I was wondering if you can further heat treat brass or using some other methods to make it stronger, like "Super Brass"?

[randgust]

That's vaguely reminiscent of the crosshead and guide repair I had to do on my Jamco 4-6-2.   I do like anybody that just 'goes ahead and fixes it' before 20 other ways surface that are more difficult and you have it running already.

I used just plain old brass to refabricate the worn crosshead guides and other that regularly lubricating it, haven't done a thing different.  It's working fine.

Remember on most real steam locomotives, sustainability is achieved by using materials that can be replaced at critical points,not armoring them so they don't wear and are a beast to remove and repair.  Then lubricate the bejeesus out of everything that moves, particularly metal on metal.  As much as I thought I 'did it for the ages' I still drilled and tapped and put the entire replacement assembly on with screws.   Peteski, my own version of overkill.

[Cajonpassfan]

Yea, running steam is not for the weak of hart😬 Nice work and hope it lasts.
What a fine looking model though, I particularly like the wheels, spokes and relatively narrow threads. I don’t follow it closely, but it would seem European models have come a long way...
Otto K.

[peteski]

Yea, running steam is not for the weak of hart😬 Nice work and hope it lasts.
What a fine looking model though, I particularly like the wheels, spokes and relatively narrow threads. I don’t follow it closely, but it would seem European models have come a long way...
Otto K.

You are right on target, and it is not a new development as shown by this comparison.  Even some models of U.S. prototypes had decent looking spoked drivers, but they had some no so good ones too, where most European steam has good looking see-through spoke drivers.

[mmagliaro]

I guess if this solder joint doesn't hold, I would start trying to cobble something together behind it where it won't show... maybe a little plate, with tiny #80 holes and inserted pins to reenforce it with epoxy or ACC on them. 

I still wonder about how this part broke in the first place.  The close-up of the broken part sure looks like a broken glue joint.

Mark, did you buy this engine new?  Or is it possible that somebody owned it before you, and the part broke, and they repaired it with glue that broke again?

[peteski]

I still wonder about how this part broke in the first place.  The close-up of the broken part sure looks like a broken glue joint.

To me it looks like a weak white-metal casting that broke at the thinnest point, or had a fracture since it was manufactured, and it simply broke.

[Mark W]

I guess if this solder joint doesn't hold, I would start trying to cobble something together behind it where it won't show... maybe a little plate, with tiny #80 holes and inserted pins to reenforce it with epoxy or ACC on them. 

I still wonder about how this part broke in the first place.  The close-up of the broken part sure looks like a broken glue joint.

Mark, did you buy this engine new?  Or is it possible that somebody owned it before you, and the part broke, and they repaired it with glue that broke again?

I purchased it new, but from a UK Ebay seller.  It did arrive pristine.  I'm confident it was more of a manufacturing defect that just manifested itself after some time.  I better photo would show the jagged metal edge of a break.  However, on closer examination, it appears the plating itself is thicker than the metal where it broke.  That might explain how it operated a fair amount to start with. 


You may have something on reinforcing the fix via the back of the crosshead.  Unfortunately, the rear is where the drive rod connects, however there is quite a bit of extra space on pin.  I could drill a hole in the replacement strip for that pin, and would then have the whole backside for extra support.  Then shape the fix up and over the top.  That should still leave enough room for the drive rod to slip back on.

[narrowminded]

Want it just remade in brass?  I suspect I could do this.  

Might start with some material soldered up to make a blank with which to finish machine.  But glue is more fun!

[peteski]

Want it just remade in brass?  I suspect I could do this.  

Might start with some material soldered up to make a blank with which to finish machine.  But glue is more fun!

I envisioned making the crosshead piece out of brass, then soldering the piston rod into a hole drilled in the crosshead. What might be bit difficult is riveting the main rod and linkages to the crosshead.