New undersized kingpins!?

[howardjs]

My special was given a MOT advisory for kingpin play last year so its off the road now having a general overhaul. On disassembling the offending kingpin (a very tight fit) I noticed the upper part of the pin where it revolves in the bush was slightly worn (and no doubt the bush also). I purchased a set of new kingpins and bushes. However the new kingpins are smaller in diameter than the old (see pictures). It can be pushed easily through the knuckle by hand, so obviously no good.
This is the second time I have had this experience. Has anyone else? Does anyone know of a way to shrink the diameter of the knuckle?
As an engineer of 50 years I would say impossible, however I am sure I have read that someone put a band of weld around the knuckle to achieve this...true or not? I would have expected this to have expanded the knuckle rather the contracted it.
Otherwise I will have to clean the old pin and ream the bushes to fit this. (Fortunately I have an expanding reamer)...
Any ideas would be most welcome.
Does anyone know what the correct diameter of the pin should be? As you can see in the photo the old one is 17.035mm dia and the new one is 17.005mm, enough to make the difference between a VERY tight interference fit and what we call in engineering terms a p**s fit.
Thanks
Howard

[Geoff Ryall-Harvey]

Ken Hannah is the expert on this but I recall it needs a heavy weld bead vertically on the "knuckle". He says it works in most cases.

[Ken Hanna]

Ken Hanna is the expert on this but I recall it needs a heavy weld bead vertically on the "knuckle". He says it works in most cases.

Geoff,
guilty as charged, I guess...

Howard,
shrinkage on cooling of a run of weld on the exterior of a kingpin 'eye' exerts a compressive ( or 'hoop'?) stress on the bore.
It's unlikely to be uniform, but since the interference fit is perhaps a couple of thou, any lack of circularity of the bore which may result doesn't seem to cause any problems.
In my experience, the 17.005 pin is nearer to the mark than the one that's larger. Whenever I've dropped the digital calipers onto pins to check them, 17.00 has proven to be acceptable. The variation in internal bore of some bush sets is another matter, however.

Kingpin bore 'shrinking' prep. by slcchassis, on Flickr

Kingpin bore 'shrinking', testing fit by slcchassis, on Flickr

[howardjs]

Hi Ken, thanks very much for the info.
Re the first prep photo.
Is that a shallow groove ground into the arm or is the weld just done onto the surface?

Thanks
Howard

[Geoff Ryall-Harvey]

Howard - if you don't have a welder just bring the arm over and I will do it for you.

[Geoff Ryall-Harvey]

Ken - I'm glad I don't work with parts that filthy anymore I'd end up spending all my time with a paraffin gun and a wire brush.

[Ken Hanna]

Ken - I'm glad I don't work with parts that filthy anymore I'd end up spending all my time with a paraffin gun and a wire brush.

Geoff,
this is a working car, not a museum piece, so there's not much point in my spending time cleaning things down when it would be back onto muddy farm tracks just as soon as I've got it through its MOT test.
Oddly enough, it's reminded me that there was another, fairly pressing, reason for not bothering with cosmetic aspects on that particular day, 19th December 2010.
I've never had heating in the workshop and the ambient temperature for most of that month of December was less than balmy...

[Ken Hanna]

Hi Howard,
yes, there is a shallow groove and in addition, the surface to both sides has been flattened off slghtly with the grinder.
There's no special reason for cutting the groove, it's mostly to provide a guide for running the weld.
( I've had cataract operations in both eyes a couple of years back, so the setting on the auto-darkening mask is kept high.)
Ken
( Don't forget about letting the kingpin eye cool before trial fitting the pin, as it's possible to overdo this shrinking dodge. )

Hi Ken, thanks very much for the info.
Re the first prep photo.
Is that a shallow groove ground into the arm or is the weld just done onto the surface?

Thanks
Howard

[howardjs]

Thanks all, Kingpins now done! After a search through my "never throw it away" stock I managed to find an old but unworn pin which is a good fit. The new bushes went in nicely and required only a very slight ream with the expander to achieve a nice play free fit. So no welding this time...we will see!
Was a bit reluctant to weld actually coz the arms going back on have had their castor angle reduced and already been powder coated. So hoping that next years diving will be free of slow speed shoulder wrenching...
Rgds
Howard