King Pins, what steel?

Off the top of my head and I am willing to be corrected by anyone who knows better, you want a case-hardening steel which En8 and 16 aren't. 32 is, but not very strong (around 32 ton strangely enough) though 32b is better than

32a, but not much. Things get stronger further up the 30's, but not linearly IYSWIM. 35, 36 or 38 would be fairly safe bets I would have thought, but get a second opinion before you commit yourself, especially as you don't say what the car is.

Have you considered having the old ones hard chromed?

Ron Robinson

I'm puzzled by the 598 Rock. AFAIR the Rock 'C' scale doesn't go above double figures. 65 the highest IIRC.. You sure it's not Vickers or Brinell?

I've no idea what steel was commonly used for kingpins, but obviously it needed to be tough, with good wear characteristics, rather than just hard.

About the toughest case hardening steel, would be EN36. A nickel chromium case hardening steel. Gives a hard surface with a strong, and high degree of toughness, but I'm not sure that would be the best steel to use.

For surface hardened pins, I'd suggest a better steel might be EN40B. A 3% chromium molybdenum nitriding steel. Gives a good core strength, with a hard nitrided surface.

Presumably the car won't be doing thousands of miles annually, so I wouldn't think a surface hardened pin has any particular advantage over just a tough steel pin. Apart from that, there's the hassle after turning, of having them c/hardened or nitrided, and then cylindrically ground to take into account.

EN24T. This is what I think I would go for. A nickel chromium molybdenum high tensile steel. In it's natural state it has good wear and shock resistance, and it's tensile strength is around a 100 tons. Probably stronger than the original ones. And as they wouldn't require heat treatment, they could be made completely on a lathe. Allowing enough on the turning for a final polish to the finished dia. It's tough steel to machine, but can be done with ordinary HSS toolbits. Mike.

Wheatley and Morgan in their Totality of Human Knowledge (Vintage Restoration) book recommend KE169, which I believe is equivalent to EN36, case hardening it "in accordance with Kayser and Ellison's instructions".

There may, of course, be more up-to-date views on the subject - mine is the 1967 edition, after all, but W & M have such good, solid "this is the (only) right way" advice they're still my first port of call. And I want their "ideal motor house" - for the restoration of one car at a time, it's 30ft x 24ft (with roof storage) plus a 30ft x 12ft workshop.

Although EN36 might be an ideal steel to use, it's use does involve hardening and cylindrical grinding operations.. Unless these can be done 'in house' which I very much doubt, at least as far as the hardening is concerned, it just creates unnecessary expense IMO.

My advice for using EN24T was given on the assumption that mileages would be comparitively low, therefore adequate strength would be more important than longevity or originality.

And I

Wouldn't we all. I have three cars. 2 of which are kept in local lockup garages. Neither of them have any power, or are large enough to work in. Mike.

The problem with things like king pins and suspension joints lubricated by a mixture of oil and road muck is that the harder of the two metals in the joint always wears first, as the grit gets embedded in the softer one. It is surprising how quickly it can grind the pin away if it isn't suitably hardened. My original suggestion mentioned hard chroming the old pins, but you would have to grind them. You might avoid grinding if you turn yourself up something out of En24 or 25 (certainly tough enough for the job I would have thought) and hard chrome that.

Ron Robinson

Not that quickly. Used as an everyday car, I would agree that doing the job properly with hardened and ground pins might be the right choice, but I'm assuming the OP doesn't intend to use it that way. We are presumably talking about a 'show' car, or at least one that will not be expected to do high annual mileages, and bearing that in mind, unless one is a stickler for originality, or do in fact intend to do annual mileages in the thousands, rather than hundreds, I can see no practical objection to using EN24T in it's natural state. Maybe you are forgetting the way plain king pins and bushes are designed. As far as the ingress of road grit is concerned, providing the grease gun is used regularly to purge the old grease, and replace it with new, there is no reason why EN24T pins should not last as long as c/hardened ones. Crankshafts are not hard, neither are the trunnion bushes and stub axle forgings on a Morris Minor front wheel strut etc. Unlubricated they do fail, which is why failure of them was/is common, but given regular correct greasing they last for years, even on cars doing comparitively high annual mileages.

My original suggestion mentioned hard chroming the old pins, but

Yes. Twice. Once to reduce the diameter to allow for the hard chrome thickness, and to give a suitably clean surface, and again to finish the pin to the correct size.

You might avoid grinding if you turn yourself

Hard chroming is not a cheap process. Whereas hardened toolsteel and c/hardened steel can be ground with a general purpose wheel, hard chrome needs a different type of wheel, and is a slower grinding operation, as you can only take light cuts on hard chrome plated surfaces. Too heavier a cut can cause the hard chrome to flake, due to local heating, even though the actual cutting point could be flooded with coolant. I speak from experience, having cylindrically ground many hard chromed shafts, over a number of years. Anyway, the final decision is up to the OP. Only he can decide which is best for him from the various choices available. Mike.