LNER V3 Leaking Superheater Flange

[1234567Participant @1234567]

<p style=”text-align: right;”>hi,</p>
The superheater fixings are 3/16 x 40 model engineering threads. These aren’t holding and was a failure point when I purchased the loco. I can’t see how it is possible to get this tight with such a thin blind hole.

Should I drill and tap through into the boiler and screw stainless cap heads from the inside with thread sealant, using these as studs ?

 

Any suggestions?

 

It’s 3 1/2″ LNER V3 Green Arrow, HP Jackson. Baught as a running restoration.

 

Thanks

[Nigel Graham 2Participant @nigelgraham2]

How would you reach the far side of the plate to insert the screws?

Using a screw from the opposite side as a stud is prone to fail because as you tighten the nut it may simply loosen the “stud”.

The proper way to secure a flanged joint in situations like this is by studs, preferably in blind holes, from the same side as their nuts. Proper studs that is, not bits of studding, so they enter only to the ends of their holding threads.

This seems a fundamentally weak detail-design, and the original builder may have had problems making the threads. Or had dis-assembled and re-assembled the superheater several times, damaging the threads in the purpose.

How thick is the flange and how well has it been silver-soldered to the tube-plate? If the structure is sufficiently sound it may be possible to drill right through and re-tap with a slightly larger and coarser thread. You need do some very careful measuring and thread-chart studying to establish the best.

Then use proper studs inserted with sealing-compound, using a stud-box to fit them. I would suggest stainless-steel studs with bronze nuts (or a different grade of stainless) with a touch of anti-seize compound to avoid galling.

The obvious snag is that the appropriate nuts won’t fit alongside that banjo-fitting – a spanner certainly won’t – so would need extended nuts and studs.

[1234567Participant @1234567]

The plate is only approx 3.7mm thick, so no opportunity to blind tap this. I can easily fit the cap heads through the regulator hole using an extension bar, this bit seems straight forward. Obviously these unwinding is an issue when tightening the nut. I may be able to hold them again through the regulator hole working around the shaft now in place.

Either way would you feel it ok to drill through into the boiler? M5 çoarse pitch would be a good size to just clean out the 3/16 and still just pass through the superheater flange plate without enlarging.

 

 

 

[Nigel Graham 2Participant @nigelgraham2]

No – I do not mean tapping only the boiler plate! That is definitely wrong.

I assumed the thread is in a flange silver-soldered to the tubeplate so the new thread, which would need be larger diameter, would be through the fixed flange as well as plate.

Otherwise, your original suggestion is probably about the only one that could work, although not ideal.

 

[1234567Participant @1234567]

Yes, that’s what I meant, tapping through both.

Thank you for your help. I will double check I have clearances to access the tool bits and for accessing the nut before I do anything.

 

Thank you

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