Recommendation for smokebox fasteners?

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gwerhart0800
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Recommendation for smokebox fasteners?

Post by gwerhart0800 »

I am rehabbing a 2 1/2" scale Mich-Cal Shay. The previous owner decided to make some changes to the engine when he bought it, but passed away before finishing. In the process of removing the headlight stand and smokebox braces, he broke off five 6-32 fasteners that held things in place on the smokebox. I only have one more to remove at this point, but I wanted to ask what material I should be looking at for the replacement fasteners ... stainless or standard steel? These fasteners are threaded into the smokebox shell and the previous ones rusted in place. Given the tiny size, there is not much strength if things get rusty.

Secondly, should they protrude into the smokebox or not. The last broken off fastener clearly protruded, but is worn down to a point. The engine is fired with propane, but it reminds me of the erosion that burning coal does. I am assuming that to keep the smokebox tight, I should keep them threaded into the shell and not clearance drill and use a nut? (Sealing the inside with a flat nut on a curved surface seems to me that it would not necessarily seal air tight.

Please let me know your thoughts.

George
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ALCOSTEAM
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Re: Recommendation for smokebox fasteners?

Post by ALCOSTEAM »

I would drill and nut. If it appears you have a sealing issue pick up some copper washers and use on the inside. The copper has a bit of smoosh to it and should conform to the shell.
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Re: Recommendation for smokebox fasteners?

Post by Glenn Brooks »

Also you probably could use thick shim stock. It’s brass and very malleable. Drill a bunch of holes, cut to size... smoke box temperatures might be as high as 600-1000* at the top. So perhaps you could also use high temp engine gasket sealer.

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Kimball McGinley
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Re: Recommendation for smokebox fasteners?

Post by Kimball McGinley »

Just a comment; years ago, a machinist at work mentioned that 6-32 screws and taps are the weakest. You have the threads of an 8 or 10 wrapped around a narrow center section. Of course, by that time, I had them all over my loco...
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makinsmoke
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Re: Recommendation for smokebox fasteners?

Post by makinsmoke »

If you ever have to cut off or drill out any of those puppies I would think you’d want to do that with carbon steel, not stainless.

Just my two cents.
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Bill Shields
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Re: Recommendation for smokebox fasteners?

Post by Bill Shields »

If you use internal nuts then no need to drill. At worst case drift pin.
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Greg_Lewis
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Re: Recommendation for smokebox fasteners?

Post by Greg_Lewis »

I vote for nuts, stainless or brass. As to sealing, if you have only five fasteners, I wouldn't think you'd get any significant leakage. OTOH the Permatex Ultra Copper should have no problem with the heat of a normally aspirated smokebox.
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SteveM
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Re: Recommendation for smokebox fasteners?

Post by SteveM »

From what I understand, the minor diameter of a 6-32 is actually smaller than that of a 4-40.

If you've ever tapped with 6-32, you've probably broken a lot of taps and that would be why.

As to using fasteners in the smokebox - whatever you use, use an antisieze compound, which will make it easier when you need to remove them again.

Steve
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Re: Recommendation for smokebox fasteners?

Post by Glenn Brooks »

Iam with Makinsmoke to use mild steel screws, so,they can be easily drilled out latter on. Just spent the afternoon trying to drill two hardened bolt shanks that snapped right off in the holes - impossible to drill or remove. Had to drill and tap new different holes and leave the existing ones in place.... stainless would be impossible to deal with...

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Dick_Morris
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Re: Recommendation for smokebox fasteners?

Post by Dick_Morris »

Could you use 8-32 as a replacement for more strength? Possibly with the same head size as 6-32. If there are only six of them, maybe make replacements from bronze?
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gwerhart0800
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Re: Recommendation for smokebox fasteners?

Post by gwerhart0800 »

There are 3 bolts for each of the 2 smokebox braces and 4 for the headlight stand. (So 10 total.) The smokestack uses four 10-24 bolts and the petticoat is held to the bottom of the stack with three 10-24 cone point set screws. Based on the mangled metal, I suspect that the previous owner had issues with removing most of those fasteners. In my case, there were five of the 6-32 bolts broken off below the surface of the smokebox shell.

Based on the feedback on this forum and a posting to a Facebook group. There seems to be unanimous agreement that a through hole and using a nut is the preferred method as you can cut off the bold head and use a punch to pop them out.

In terms of materials, I was thinking that stainless would not corrode, but as has been pointed out, it would be a pain if I needed to drill the out for a reason. (I am wondering if the two that cause me so much trouble were stainless.) The idea of annual PM to remove/replace the fasteners might be a good idea. The other thing is that I think all the fasteners that were used previously were button head. I am thinking that I would prefer hex heads, as they would be less likely to strip out when trying to remove them.

Thanks for all the feedback. I miss not going out to the club and talking these issues through with other steamers.
George Erhart
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Greg_Lewis
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Re: Recommendation for smokebox fasteners?

Post by Greg_Lewis »

And lots of anti-seize compound.
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