Pennsylvania A3 Switcher (Kozo)

[crueby]

Nice motion Kim!

My first thought on the shim would be to make it from steel and bond it place with some JB clamped up tight. Make it a little oversized so it could be dressed back down to the original surfaces.
Silver solder would be ok but there is always some risk involved with something going wrong on your finished part. 

Dave

That was my first thought too. Or a little steel-colored paint on the brass edge... Not that I have ever done that. Today, anyway!

[Don1966]

You’ll make the right decision Kim. Just think it out but like Dave said silver soldering something could go wrong. Myself I feel comfort enough to give it a try and silver solder, if it failed start over it’s the risk I would take. Just my two cents.


Regards Don

[Kim]

Thanks for the input Dave, Chris, and Don,

I like the JB Weld idea... Yes, making the added part a bit larger would be a good idea, Dave, thanks.

My one concern would be how the JB Weld would hold up during powder coating.  The spec says standard JB Weld is good to 500F so it ought to be OK.  The max you need for powder coating is 450.

Does anyone have experience with powder coating and JB Weld?

Kim

[Steamer5]

Hi Kim,
 Nice work & great progress! Keep up the good work!

On the shim leave it as it is! The orginal full-size drawings I have for my project has brass shims on the plans! So you are spot on to full size!

Cheers Kerrin

[cnr6400]

Loved the motion in the latest rolling video Kim! The crossheads and rods look really great! 

+1 on using a shim or two being just fine. On most full size steam locomotives and traction engines (and cars too, for that matter, ie body shims etc.) shims were widely used to adjust running and assembly tolerances. As a steam locomotive saw hard use out on the road, wear was a reality and it is a lot cheaper faster and easier to add a shim than make a new crosshead bar or valve guide part, so that's what was done. On one traction engine I was involved with years ago, I found .140" worth of shims under a crosshead slipper, in .002", .005, .010 and many other denominations - including bits of coffee cans! Don't feel bad about using a shim or two. The old mechanics were masters at taking up wear and adjusting things to work. If they'd had JB Weld they likely would have used it. 

[Kim]

Thanks for the encouragement Kerin and CNR!

I'm thinking I'll be epoxying a shim in place today.  Then trim it down to size tomorrow.  The thought of having it look more prototypical with a shim is encouraging though!   My frustration is mostly with me not trying the more obvious fixes first.  I should have started from the basics like I did eventually. Unfortunately, I put it all together and tried to figure out what was wrong.

But what eventually got me there was to take everything apart (the thing I tried to avoid), and take it one step at a time:

• With the crossheads removed, I checked to make sure the guide bars slid easily in the crosshead grooves.  They didn't.  That's when I removed the slippers and did a touch of file work on the grooves - just taking the burr off the edges.
  
  
• Once the guide bars slide through the crossheads easily, then I put the bars in place (between the yoke and the cylinder) with the crossheads between them, but NOT connected to the piston rod.
  
  
• When the crossheads moved back and forth freely between the guides on their own, I checked to make sure the piston rod lined up with the crosshead.  Which it did.  So I reattached the piston rod to the crosshead and saw that they all moved well together.
  
  
• The final step was to re-attach the main rod and make sure that all was still moving freely.
  If I'd started with this I could have saved myself time and heartache.  But such is the way of learning, eh?
  
  

Thanks for all the help and encouragement!
Kim

[Admiral_dk]

I understand some of your frustrations .... and we have all been there in one form or another 
But I certainly enjoyed to see it all move as it should 

[Kim]

Thank you Per!
Kim

[petertha]

I'm not up to speed on powdercoating baking temps but you might be pushing the heat limit of epoxy. It may not fail but if it softens & resets, that's not good either. I've also read where JB (any epoxy really) can 'out gas' at elevated temp & cause paint adhesion grief, bubble defects etc. If it wasn't for the temperature aspect, I think any of the proposed fixes would be fine. The added material would be hard to spot unless you were looking for it. There are lots of super tough finishing systems out there, but a) usually involve part B catalyst containing isocyanates in the good stuff b) not typically sold in thimble quantities.

[Dave Otto]

Yes, when I suggested the JB approach I had forgot the Kim was going to powder coat these parts. Might be a good idea to do a sample part/assembly.

Dave

[Kim]

Thanks Pertha and Dave,

JB Weld is supposed to work even at high sustained temperatures (500-550F), so it ought to be OK.  I did a little more Googling and found some references to where people have used JB Weld as filler in their powder coated parts and they have had good luck with it.  Someone found that it outgassed if you didn't let it cure 24 hours before powder coating.  But I'll certainly be beyond that.  I'm going to give it a shot.  If it falls off during the coating process then it will probably be a shim. (or I can super glue it on after coating ).

Thanks for thinking this through with me,
Kim

[petertha]

Yes some references I saw regarding powder coat bake temps were ~< 400F if that is considered typical. So on that basis hopefully all will be OK.

Terry on the other forum has been using GunKote (POR-15) which has a lower bake temp, 275-325F +/- duration according to the specs if that's helpful. But presumably you are getting a batch of powder coat parts done & not wanting to mix & match coating systems.
https://www.homemodelenginemachinist.com/threads/ford-300-inline-six.33115/page-9#post-365314

[kvom]

I would leave the shim alone.  Also powder coat the yokes and tie as onr piece if possible to avoid changing dimensions among the parts. Don't coat the tie bars.  Don't coat anything until you have the valve gear made and all assembled.  There is a bracket still to be attached to the yokes and the clearance in the slots to be verified.

I spent a lot more than one day getting things to move smoothly, so you did very well.

[PJPickard]

Why not soft solder a shim on? Make it over size and file it to match after. I use and love TIX solder. JB weld might work...but well, its JB weld. Really good stuff and very easy to use. I often use a small butane torch with it. Be sure to get the flux with it.

https://www.amazon.com/Tix-Solder-Boat-Train-Parts/dp/B000RB5BQU

[Kim]

I would leave the shim alone.  Also powder coat the yokes and tie as onr piece if possible to avoid changing dimensions among the parts. Don't coat the tie bars.  Don't coat anything until you have the valve gear made and all assembled.  There is a bracket still to be attached to the yokes and the clearance in the slots to be verified.

Good idea about powder coating the whole yoke together, Kvom.  And yes, I'll be waiting to coat it for a while yet.

I spent a lot more than one day getting things to move smoothly, so you did very well.

Well, I've spent the last two days continuing to refine things.  If you notice, I didn't have the O-ring retainers in the cylinders around the piston rod yet (what would normally be called the packing glands?).  It took some work to get those in and smoothly, plus a lot of other little work.  I think I'm almost ready to move on to the valve gear!


It's nice to have someone who's done this before giving me tips along the way!  Thank you!
Kim