Con rod nut stuck

[David Tinsley]

Trying to remove a chewed up castellated nut from a con rod big end. The other 3 went fine, but this last one was a bit chewed up and now it is really chewed up!
Anyone got any advice on the best way to remove it before I resort to hammer and chisel!

[limeyrob]

Which bits are you trying to save?  I would sacrifice the nut and bolt and save the conrod and crank.
I would put it all in a vice and with rags over everything centre punch the bolt end.  Then going up from a 1/8 drill drill out the bolt centre from the nut being careful to set the depth to about 1/16 less than the nut so there is no risk of damaging the con rod.  This is a slow way of doing it but doing it this way its very hard to damage the rod or crank. Take it slow.  At some point the nut will just break off.

[David Tinsley]

I just tried that for the last hour and my cheap as crap drill bits hardly make a mark! I have turned to a small cut off wheel and dremel to try and cut down without marking the conrod or crank. slow going though!

[limeyrob]

That sounds like a plan! So long as its slow going you have control and time to stop if its going wrong.

[Swarfcut]

  Dremel and cutting disc to weaken the nut, failing that Angle grinder and a steady hand to notch the most accessible side of the nut, then a few smacks with cold chisel to move it on one flat, then repeat. Be prepared to loose the bolt, but this is preferable to sacrificing the rod and cap.

 It's a perennial problem finding a thin walled oddball tube or socket that fits. Big journal bolts, being slightly longer, (3.5mm on a set to hand) plus a  custom spacer washer under the larger later nut are one solution, raising the nut, as long as the ensemble does not catch on the crankcase or pick up pipe. Machining a bigger chunk out of the cap to accommodate later hex nuts and thin wall socket takes more courage.

 Swarfy.

[limeyrob]

Try to get a replacement that is the same as the original, sounds obvious but I had real trouble.  Nuts that were claimed to be correct didn't fit, too long and hit the case.  Some bolt / nut sets seem to be different threads too.  The bolts for the small journal crank are shorter so check part numbers carefully.

[Swarfcut]

  BSA used CEI, BSF and UNF threads at various times. Nuts came as castle type with split pins, then a couple of self locking versions. Different torque settings also published, but defining what fastener combination you actually have to relate to a particular
 recommended torque setting is the difficult part.

  Swarfy.

[David Tinsley]

I just tried that for the last hour and my cheap as crap drill bits hardly make a mark! I have turned to a small cut off wheel and dremel to try and cut down without marking the conrod or crank. slow going though!

Well, I got the bugger off after a while of careful cutting with the dremel cut off wheel.

I have another question now. The drive side rod has a a number etched into it (could not see this when it was assembled to the crank) it is 20/3967, hand etched. Anyone got any idea what this means, if anything. The cast # is correct at 67-270

I did notice the oil hole in the rod that I did not think was there on a 55 GF and wondering if it could be that?

[trevinoz]

Oil hole should definitely be there.