James Coombes Drawing Error (or mine?)

[Steve WithnellParticipant @stevewithnell34426]

I finally got round to putting the James Coombe back on the bench.  It’s mainly all done now, but the fitting shows this, which I think is a problem.   Pretty sure that’s going to clash “in service”.  I can’t find an error in my parts, despite lots of measuring,  anyone else built one of these?

If there is an error, how do I correct it?

[Martin ConnellyParticipant @martinconnelly55370]

This is the Stuart version, similar small clearance.

Martin C

[DiogenesParticipant @diogenes]

Even a small chamfer or radius on those meeting edges would likely give enough clearance?

[JasonBModerator @jasonb]

With the “hump” left on the bearing there is really no clearance as it is about 7/16″ radius. Correction may be to flatten the top as martin’s picture shows. Alternative is to make the short lower bigend section a bit longer and shorten the piston rod but do check movement of the cross head guides. If not its a whole new conrod with longer bottom and shorter top bits

I modified mine quite a bit so have the hump, boss for an oiler and a short oilcup, this is at it’s lowest point.

[Steve WithnellParticipant @stevewithnell34426]

Thanks.   I’ll complete the trial fit and see if enough clearance can be teased out without looking bodged.  If not sounds like re-making the short conrod a bit longer.   I could then add square plates to the bottom of the columns as in Jason’s drawing, to compensate. The strap for the eccentric isn’t cut yet, so that sounds like a decent plan B.

Thanks all.   I didn’t spot the similar issue with the bearing height on the Victoria either!   Next time, I’ll take more care over checking the drawings…

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