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MG MGB Technical - binding kingpin

I posted earlier about whether kingpins were matched to stub axles as I had one assembly that was stiffer than the other, having disassembled and painted them. I have examined the stiff kingpin and have come to the conclusion that the top bush in the stub axle is not in line with the bottom bush. There is a more shiney patch on the top inside of the kingpin and the bottom outside of the kingpin on the part of the kingpin that fits in the bush. This implies that the top bush is inclined outwards at the top very slightly, just enough to cause some stiffness. The kingpin does rotate but there is some stiction there. Is it likely that this will free up over time as the kingpin beds into the bush? If I insert the kingpin upside down in the stub axle the kingpin does not bind in the top bush so the kingpin diameter at the top bush is not oversized.
Steve Church

I'm sure that when the axles are re-conditioned the bushes are pressed in slightly under sized, then reamed to open and line them up. Sounds like bad product again.
Allan Reeling

The stub axle assembly was the one I took off the car. I suspect that they are replacement units as there is no hole at the top of the kingpin for the castle nut locking pin. Also the nut was a nyloc. Would running a reamer through it do any good? I'm going to MGOC tomorrow so may ask there.
Steve Church

Steve. It would depend on how the bushings were reamed. As Allan notes, when properly done, using the factory style of reamer, the bushings have to be cut in line with each other. When reamed separately, it is quite possible for there to be a minor misalignment present--it all depends on how well the machine shop is able to get on the exact centerline of the workpiece.

Have you measured the lower section of the kingpin, first one direction, then 90 degrees from that, to ensure that the lower section of that kingpin is perfectly circular? The way they seem to be made, it would be almost impossible for it to be not round. But, only almost.

Les
Les Bengtson

Steve. You were posting while I was. No, running a reamer through there, if they were reamed properly in the first place, would not help. It would only open up the hole larger. While that might correct the problem, it would induce some slop that should not be present. I have reamed a number of sets of stub axles, using the factory style of reamer, without seeing the problem you have. Either the holes were reamed slightly off of centerline, or the kingpin is slightly bent, or the lower section of the kingpin is not perfectly round.

Les
Les Bengtson

Les, I measured the lower section of the kingpin and it appeared circular, at least to within a few thou.

My concern is that if the top bush has had a knock which has caused this misalignment then the surface which bears against the top trunnion shims will not be at 90 degrees to the kingpin which may be a problem. Maybe I should get an exchange unit just to be sure? although that has not come into my budget considerations!
Steve Church

If the best match between the two pairs results in one being stiff then relieving the bushes *fractionally* in that would ease it up, maybe fine wire wool on the shiny patches if you are sure they relate to that king-pin, but like Les I think reaming is likely to introduce too much play. It depends on the width of the patches but if they are narrow then with the visible wear on one side of the top and the other side of the bottom of the top bush that implies that it is the bush that isn't true. If the king-pin were bent the wear would be wider than the normal rotation of the king-pin in the bush. If you can turn it by hand then I don't think it is that much to worry about. I can't really imagine the casting being bent, and again I can't imagine the thrust washer and shims being fractionally out of square is going to make that much difference, they aren't clamped between the trunnion and swivel axle but have free play. It all depends how particular you want to be, if very, or if in doubt, then you have answered your own question.
PaulH Solihull

I stopped by MGOC and showed the offending items to Roger Parker. His opinion was to remove a small amount of bush surface where the tightness was indicated by the kingpin. He advised that I check the stubaxle for straightness with two flat edges on the top and bottom first. This I did and all is well. I wrapped a piece of slightly undersized dowel with emery paper and carefully abraded the relevant areas of the bush. I have left it with a little stiffness as I expect the surfaces to bed in. It has certainly recovered the situation and I can continue with the suspension rebuild.

Thanks everyone for their comments.
Steve Church

This thread was discussed between 23/02/2011 and 24/02/2011

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