1913 douglas big end

[Adam55]

Would anyone be willing to help with some technical details that a friend needs in order to machine me new bronze big ends for my 1913 douglas?

I think he just requires the outer dimensions.

Any help would be greatly appreciated.

Regards,

Adam

[Jonathan Hewitt]

Hello Adam, the outer dimension will be entirely dependent on the size of the conrod after cleaning up ( if it needs it )
Eddie did suggest in one of his posts that soldering the shells to the conrod before final finishing was a good way to keep it all tight.
Regards Jonathan

[Adam55]

Thank you jonathan, much appreciated.

[eddie]

I have refrained from giving any further instructions on refurbishing big ends on 2¾'s because there are likely to be too many deviations from standard on machines that are 110 years old! Each engine is likely to be different in crankpin diameter and bigend eye diameter, so shell sizes will need adjusting to suit. Also, recently there seems to have been a spate of big end bolt failures, without a common cause being identified - I suspect (and this is only my personal opinion) that it may be down to modern production methods on the repro bolts (I have reservations regarding certain CNC produced components). Bearing in mind that anything in these old bikes could be seriously worn, I prefer to open out the big end bolt threads from 17/64" x 25 tpi to M7 x 1mm, then replace the original bolts with good quality M7 x 1mm socket cap screws (GKN or Unbrako - don't mess about with cheap Chinese bolts!) - then retain the locknuts with Loctite. Another item which will vary in thickness is the big end keep plates (which also need to be in good condition in order to keep the individual shells pinched up into their respective halves of the con-rod). A lot of these details may seem trivial, but if a rod does let go - it does a lot of damage, so these jobs should only be entrusted to a reliable engineer - it's not something that can be easily taught via e-mail. Now a final piece of advice - these engines are old, and rely on splash feed lubrication - dont try to build them to modern tolerances - the big ends need to be slack enough to allow the oil to get into the bearings - if a rod wont fall under it's own weight, the big end is too tight!

  Regards,
                Eddie.

[Adam55]

Thanks Eddie,

The assembled big ends are all done and look great, thanks again for all your help.

Just need to crack on and get it all back together now!

Regards, Adam 

[Jonathan Hewitt]

Well done !  Could we see some pictures perhaps ?