I’m having concerns about building up a crank using new big ends that I have. The big end pin when pushed into the flywheel has a gap of around 20 thou between the shoulder on the pin and the face of the flywheel. There is no way that the shoulder of the pin will sit against the flywheel when the pin is pulled into the taper. Offering up old (knackered) pins gives a gap of around half this, which is what I believe is correct. It’s not the flywheels as I have a box full of the things and the new pins consistently give this larger gap compared to old pins. The tapers appear good with no ridges or whatever to stop the pin seating in the flywheel and a bit of engineers blue seems to confirm this.

Is this a problem? Do the shoulders have to contact the flywheels (or is the taper the critical part) and would the additional sideplay of the conrod be a problem? Also what about the position of the timing side oil pump drive and centering of the conrod in the cases (probably the least of the problems)?

If conrod side play is excessive can the rings riveted to the flywheels be replaced and what are they made of? (hardened? Can I knock up thicker rings from mild steel on the lathe?).

I did have a crank built up by a workshop using such a pin a few years ago and it all ran OK with the increased side play etc., until some crud got in and buggered the bearing – that’s the one I want to rebuild myself now and, with the parts in my inexperienced hands, I’m getting jittery.:fearful:

Cheers
Pete

email (option): petercomley@web.de

The pin should be on the taper and the shoulder when pulled up tight...The specified gap before tightening produces more or less the correct fit when the pin is pulled in...

A problem I have come across is when the radius in front of the shoulder (at the 'top' of the taper) is too large compared to an original pin..That stops the pin going in far enough initially...I opened up the chamfer in the flywheel a little to remove the 'pinch point'.....Worth a look!....Ian

email (option): ian@wright52.plus.com

Thanks Ian,

I did notice that the new pin has a larger radius than the old ones,it doesn't seem to be stopping the taper going in but I'll have another look tomorrow to double check.

Pete

email (option): petercomley@web.de

Radius match between wheels and new pins seems a common problem. Fought this when truing a Panther crankshaft until it became clear what the issue was.

(Yes, and there’s some excessive wear on the cheeks, but that’s another story)

email (option): teladelujo@msn.com