There have been a couple of threads in recent months on parallel motion links on beam engines, going into the geometry at some depth. The Google search halfway down the forum homepage should find them.

But I believe you are right in thinking the links need to be the same length.

Can you machine the outside of the bosses to make them concentric with the centres for the link pins. If you are doing this on a mill a suitable round nosed cutter in a boring head would tidy up the outside of the boss. JB weld to do a final blend and tidy up. Once it’s painted it will look the business.

regards Martin

I plotted the alterations to beam pivot onto the sketch I did the other week and if all 4 links are extended by the same amount (red)you get about 9 thou more lean of the piston rod from one extreme of it's travel to the other if entablature pivot is not altered

The drop links on that engine were the same 1.75!" will most likely get a different result with the shorter 1.125" Vulcan ones but shows it will not be the same. Also did not work out where the Vulcan entablature pivots will be as that again will affect geometry. Suggest OP does it in CAD either on the 'puter or Card and Drawing Pin method

Yes, I mean the main beam pivot. In reality I can't see the 0.013 dimension being critical. Send me your email via pm and I'll send you my drawing. Dxf or dwg?

I'd still do Martin's mod, blob some JBWeld around the boss where it will be short and machine using ball nose cutter, or even a round top tool in a boring head

This reply is probably a bit late. My father started a Vulcan but never finished it or got it working. I inherited his machines and tools and have recently retired so started to restore the Vulcan and get it running. I ran into the same issue with the links and entablature bosses. Initially I made the two links that fit to the entablature bosses slightly longer so that they would bolt centrally to the bosses, However this puts the parallel motion out and the connecting rod had about 0.010" lateral movement over its stroke. Solution was to re-make the links to standard size and hence all 4 links are now exactly the same size and as per the drawing. I machined the old bosses flush to the channel on the entablatures then drilled a hole through them at the correct centre position and silver soldered in a set of new bosses and now the links are bolted centrally. The connecting rod now runs perfectly true and the repair turned out very neat. I can send some pictures if you are interested.

I have had the Vulcan running on air and it runs well. I am currently building the governor valve and regulator as described by Edgar T Westbury in later editions of Model Engineer. I will have to make my own castings for the bridge and control arm bracket which will be interesting as I have never done this before. Hopefully it will look like the model on the cover of September 1967 Issue of ME when finished.

I have all the original ME build article which was very helpful in restoring the Vulcan.

Good luck with your build.

Regards Peter

Thanks for the advice. I will try the casting first as an experiment and new experience. If this does not work out I will go the fabrication route.