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MG MGA - Swivel pin failure (crack testing)

It has been recommended that I crack test the swivel (king) pins on my 1600 A whilst I am renewing the lower suspension arm bushes and the swivel link seals because these pins supposedly regularly fail with disaterous consequences.

Is this the case and has anyone had such a failure?

I couldn't find this mentioned on Barney's web pages but rather that the swivel pins are strong items and it is not worth upgrading to B suspension components if you already have disc brakes. (My swivel pins only have about 20,000 miles on them mostly on sealed roads, obeying all the road rules - plus an odd hillclimb, sprint and motorkana here and there).
Thanks for any comment.

Mike
Mike Ellsmore

From what I have heard and read over the years I believe it is an issue for racing, but not for normal driving.
John H

Hi Mike. I have heard of at least one non racing swivel pin failure, but I believe the swivel pin in question was extremely old. I am aware that these swivel pins also bend quite easily under collision impact. In the scheme of things, your swivel pin is a "youngster" and I dont believe it requires crack testing unless it has been subjected to some traumatic event during it's short use, or unless you are planning on competition use. Swivel pin threads are subject to rapid wear and galling if not regularly lubricated. I recommend frequent greasings, using high quality lubricant, preferably synthetic grease. Cheers, Glenn
Glenn

I'm not sure if they will last forever. Mine only have 357,000 miles on them, including wearing out several sets of sticky race tires while autocrossing. They will bend just below the knuckle if you hit a curb hard. It hasn't happened to me, but I have straightened a couple for friends who did.
Barney Gaylord

Thanks guys - I can sleep easy.
Mike
Mike Ellsmore

A chap sent me this alternate view that I post for comment.
http://www.geocities.com/practicalmg/fsp2.htm
Regards
Mike
Mike Ellsmore

Certainly. Racing is hard work. Also Magnaflux all wheels, studs, all other suspension bits. Put in a full cage, fuel cell, fire suppression system. Bellhousing/gearbox scattershield. Wear a firesuit and helmet. Repeat after each race, er, drive.
Or: Stay home and drink beer, get fat, have heart attack, fall off couch, die.
Pick your level of difficulty - as long as you enjoy it!
FRM
FR Millmore

I have one comment about the linked article. They mention using either grade 8 bolts or "AN" aircraft bolts as substitutes for the originals. An article in the current issue of MGA! magazine also suggests this. Nothing against either type of fastener, but this implies that the two are interchangeable when in fact they are not.

AN bolts are actually closer to an SAE Grade 5 bolt in terms of strength and failure mode characteristics. Both Grade 5 and AN fasteners will tend to deform prior to ultimate failure, whereas a Grade 8 bolt will generally just break without giving any prior indication when it is stressed to its point of ultimate failure (which, of course, is much higher than that of either AN or Grade 5).

If you want to substitute aircraft hardware in place of original, you can get the strength equivalent of Grade 8 by using certain "MS" (military standard) hardware. If you are ordering from a supplier like Genuine Aircraft Hardware or Aircraft Spruce, they will generally list the material specifications for each piece of hardware that they carry, which can then be compared to the specs for Grade 8, or whatever strength level you are after.

FWIW, the reason that AN bolts are used in most locations on general aviation type aircraft, is that they are inspected regularly (or, are at least supposed to be), and a bolt that gives a little before it breaks will hopefully allow potential problems to be identified during inspection before they become catastrophic. Where a higher ultimate strength is required, MS bolts will be specified.

Del Rawlins
A&P Mechanic
Del Rawlins

Further to Del's excellent comments, AN or MS don't tell you how strong the bolt is, only that it "meets" some requirement - and you don't know what that means until you read the spec number detail. It doesn't say anything about whether the bolt "exceeds" a particular requirement, or if it is suitable for "other" use. If you know how to do and understand all that, then you don't need any of us or any "expert" to tell you.
When an "expert" describes forged parts as having "flaws in the original casting" I leave, but I do still catalog every rumor as something to be thought about later - sometimes rumor and fantasy prove worthwhile if investigated.
FRM
FR Millmore

As noted above, bending of the kingpin is very common--we see this fairly frequently on street and race cars that have been curbed at some point.

We have seen cracks and breaks, mainly on race cars, but at least once on a street car. We magnaflux them when we rebuild them.

While I agree with Barney that they last a long time, I can say that MGB ones don't bend. We have seen MGB ones break too, mainly when wheel bearing failures snap the axle off.

--Carl
Carl Heideman

This thread was discussed between 26/04/2007 and 29/04/2007

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