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…

[Diogenes]

On Diogenes Said:

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

Exactly,

I would make the bearing look a little more like a Victorian casting and remove all the sharp edges. I like Martins fillets as well.

[JasonBModerator @jasonb]

I’m not sure the fillets are right. Victorians would have had a horizontal split line and separate bearings, the straighter edge of the round spigot either sid eis meantto represent the separate bearing. If it were larger you might be able to add a decorative fillet but there is really only enough metal to have them match the diameters that run up against them.

Once I have test run an engine then I will go back and knock the corners off and add fillets around bosses etc to get more of a cast look. Then paint them as it’s unlikely the victorians made the whole thing from GM.

Decorative fillets to the corners of the bearing brasses if you like

[Steve WithnellParticipant @stevewithnell34426]

It looks like you have removed most of the ‘bump’ at the top of the casting and run a ball end cutter to produce that nice fillet.  Looks a good way of teasing out that extra clearance.

I’m surprised that Stuart Models haven’t bothered to deal with that after all the years the engine has been on sale.  Like Jason noted,  there is no room for oil cups and the fit really doesn’t make much sense.

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