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MG Midget and Sprite Technical - Kingpin tolerances

Hi

Over the last year I've progressively stripped more and more from the front end of my midget, repaired, replaced, reassembled, improved, road tested and then started over again.

Finally, Ive ended up with Barry King wishbones, uprated springs, pan spacers,recon fully built up stub axle / king pin assemblies, a stiffer ARB, 4 pot callipers and mintex pads.

However, im not entirely satisfied with the fit of the lower trunnion into the kingpin. Even though both items are "new" there is still too much slop (rocking of the king pin in line with the car) for my likeing.

Installing the cotter pin does stop it but is it right that the pin should be doing all the work. The main purpose of the cotter is to stop the trunnion rotating out of the wishbone, not to compensate for any play between the trunnion and kingpin.

The play is definitely in the king pin / trunnion interface - the trunnion is rock solid in the wishbone, as you would expect with one of Barry's premier items.

Is it worth trawling through a selection of recon kingpin / stub axles assemblies to find one with a closer fit, or should I just live with it and check / change the cotter on a regular basis

I know this subject has been covered many times and I've read all I can around the subject. I just need to know, should I live with some play between the trunnion and kingpin and rely on the cotter, or should I be aiming higher?

Thanks
S G Macfarlane

It's been a few years since I replaced my Midget's kingpins, but I have two new sets of kingpin kits on the shelf (they date from approx 1975). I've just checked their 'kingpin-to-fulcrum pin' clearance.

One kingpin wouldn't accept any of the fulcrum pins without some serious 'persuasion'. The other kingpins took the fulcrum pins without too much effort, one had a bit of 'play', another was tight. On a 'used' but serviceable kingpin, the fulcrum pin had a clean fit, very slight 'slop'.

When you say you have 'too much slop', does the excessive clearance make a knock when you handle them? If so, I'd say that your kingpins haven't been machined accurately enough to accommodate the fulcrum pins. My guess is that they are 'new' kingpins and maybe come from the far east (where questions are being raised as to the quality of repro car parts).

As you imply, I suspect that your fulcrum pins are ok because of their origin (Barry).





Andy Hock

I was told around 1991 that the OE spec king pins, Unipart IIRC, were going out of production in the near future. I made a lower wishbone outer trunnion replacement and that relied on the OE spec kingpins being faced on the sides of the boss which the trunnion passes through. Not had to replace any kingpins since but the pattern kingpins were left as forged and what the tolerances would be is anyones guess.
David Billington

Don't they usually rust solid in a years time anyway?
Trevor Jessie

Thanks for the replies - its actually worse than I thought, with 2mm to 3mm of movement at the top of the kingpin when you rock it (without the cotter fitted).

I'm going back to the supplier on Saturday armed with my fulcrum pin to hopefully find a king pin thats a better fit.

Regards



S G Macfarlane

I recently fit a new wishbone. It came w/ a fulcrum pin that was a little on the loose side. I had an older, unused pin that fit quite snugly.

There was quite a little difference in diameter, so I used the older new pin.

Phil 'I realy need to learn to read my micrometer'
Phil Burke

This thread was discussed between 02/02/2011 and 03/02/2011

MG Midget and Sprite Technical index

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