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MG Midget and Sprite Technical - Kingpin shims typical number

What is the typical number of shims needed at top of kingpin? I'm on the first side and, even with 4 shims (total supplied with kingpin kit) the stub axle is still extremely tight when swivelled with top nut tightened. Oil-lite washers are new and trunnions original.
Bill Bretherton

Normally only one or two, in my experience.

How thick are the thrust washers?
Dave O'Neill 2

Dave, 0.155"(5/32") or 4mm.
Bill Bretherton


Bill, have you replaced the swivel hub bushes and if so, did they push fully into place? The lower bush should stand proud at the top by around 3mm to create a seating for the square section rubber seal you were asking about earlier.

If the bush isn't fully pressed into place it might explain why the king pin is binding?
GuyW

Guy, yes the bushes were replaced but by a local MG workshop who also reamed them for my supplied kingpins. The mechanic who did it is very familiar with Spridgets so I assume he did it correctly. I've just looked at one of the stb axles and it looks right with a recess created for the square seal. I assume it is the distance from the bottom of the lower bush to the top of the upper bush that matters.
Bill Bretherton

originally the shims were available in 3 sizes 0.003,0.008 and 0.012. how thick are yours?
Bob Beaumont

Bob, Shims are .004". That could explain it then i.e. I need one or two more. It's clearly quite a critical fit.
Bill Bretherton

Yes I recall having the thicker shim in the rebuild kit I had. It was a genuine BMC one with the castellated nut. Did you keep any of the original ones? The top trunnions clearly vary in size when they are machined!
Bob Beaumont

When I stripped the orginal hubs I probably didn't notice or think about shims so doubt I have them. I'll have a trawl though my bits and pieces just in case though! Otherwise I'm awaiting more from Moss if they're still operating.....
Bill Bretherton

Bill

If you’re stuck, I can probably find you some in the garage. I’ve got plenty of time to look, now.

I think I even have some spare trunnions, and the shims often stay in them when removed.
Dave O'Neill 2

Dave, that's very good of you. When/If the Moss parts arrive I'll see if that solves it, otherwise will contact you.
Bill Bretherton

Dave, could you contact me please at:

brethertonwilliam(AT)yahoo(dot)co(dot)uk
Bill Bretherton

There is still a problem with the stub axle going tight even with 0.048" of shims. If I just place the copper washer in the trunnion (removed fron kingpin), the trunnion is deeper than the (new) washer by a noticable amount (maybe 1.5mm, I don't have a depth gauge to hand) - is that correct? Surely the washer should be about level with lower edge of trunnion so that, when shims are in place, the washer is just bearing on top of the upper kingpin bush? Have I understood it correctly? In which case, could I have very worn trunnions? They are the original Frogeye front hub ones but the stub axles are off a later disc brake car. Kingpins and bushes are new. Lower bush is flush with axle housing at its base and upper bush is flush with housing at the top.
Bill Bretherton

Bill is the phospher bronze ( if that is what it is made of) bearing seating properly into the trunion? No foreign objects or dirt behind it? I noticed on the photo that you posted on a different thread, that the bearing was very visible whereas it would normally be almost fully recessed within the lip of the trunion.
GuyW

The trunnions are the same for all the cars right up to the 1500 midget. Guy is correct the bronze thrust washer usually sits inside the trunnion. The shims regulate the 'gap' between the top of the swivel axle and the trunnion. This is filled by the bush. The ideal is that when the top nut is tightened there is just a slight resistance of the swivel axle on the king pin. I have tended to reuse the original bushes as unless there have been starved of lubrication they don't wear too much. I have not come across worn trunnions.

The king pin should flop up and down if there is no bush as the top of the king pin where the shim sits registers on the inside of the trunnion. If the bush is oversize then more shims will be needed. I have seen some of the replacement bushes, Supplied by a well known stockist, made of copper and not bronze



Bob Beaumont

Guy, In my picture, the nut is loose so the washer/bush is showing more than it should.

Bob, but shouldn't it be the washer/bush that is bearing on top of the stub axle? What I mean is that if the washer does not protrude below the trunnion a few thou, then the trunnion itself will end up binding on the stub axle? In which case, the shims need to slightly exceed the gap I'm seeing between the washer and the base of the trunnion. Have I understood this correctly?
Bill Bretherton

Yes Bill, I realised that is why it was quite so prominent in the photo, but wondered if, when you do tighten it down,the bronze bush was entering its recess in the trunion fully, or maybe catching or sticking with something behind it and remaining slightly proud. That would account for needing excessive number of shims to regain the necessary clearance.

Maybe it's an aftermarket bush, poorly dimensioned?
GuyW

Guy, I still don't understand properly! As I put it to Bob above, should the bronze bush (let's call it that from now) not protrude slightly BELOW the trunnion, with nut fully tightened i.e. so it is bearing on the stub axle? Otherwise the base of the trunnion itself will surely bind on the stub axle? In which case I seem to need more shims.

I should add that the shims currently installed are crushing with nut tightened.
Bill Bretherton

Bill The washer is not visible when assembled inside the trunnion. The trunnion extends below the washer and should clear the top of the stub axle. The shims fitted to the top of the king pin just control the gap as you say between the top of the axle and the inside top of the trunnion. It rather sounds like the washer may be too thick. Have you got the original ones??
Bob Beaumont

Bill,

Just checked mine in the garage to verify my memory and the trunnion recess for the thrust washer fits over the top of the stub axle with a 0.5mm or bit more play and the thrust washer is recessed into the trunnion by about 1.6mm in my case, this affords the thrust washer a degree of protection from the elements. My thrust washer should be the correct phosphor bronze sintered bearing as it came from an OEM kit.
David Billington

Bob, My bronze bush/ washer does go inside the trunnion, I thought that was the problem! Sorry if I'm being slow, I'm trying to understand what keeps the trunnion away from the stub axle. I think that's the problem - when tightened the trunnion seems to be binding on the axle housing indicating that the kingpin isn't high enough perhaps, in relation to the axle. Where does the axle actually sit on the kingpin? Looking at it I can't really tell. I assume that location has to be precise?
Bill Bretherton

David, thanks, the 1.6mm is similar to what I've got. Ah, so the trunnion should slighly clear the stub axle - I need to check that.
Bill Bretherton

hi Bill

the bottom of the king pin should sit snugly against the bottom of the stub axle. At the top, the position of the trunnion is controlled by the shims. Sorry if I am being too simple but these should fit over the top of the king pin and stop where the pin is wider. They then register on the inner bore of the trunnion effectively regulating the gap between the top of the axle and trunnion. This gap is filled by the bush. The 'step' on the king pin does not allow the king pin to go fully through the trunnion, only the smaller top section. The shims rest on the 'step' They then regulate the gap between the top of the axle and the inner top edge of the trunnion. This may be hard to explain in text. I'm off for my bit of excercise now but give me a call on 07734785245 and we can chat on the phone.

bob
Bob Beaumont

Bill, it may help to think about it the other way round.
When in use, the wheel and therefore the stub axle sits firmly on the ground and the weight of the car is transmitted through the spring, via the bottom wishbone which pulls the kingpin and trunion downwards, and then taken by the bronze bush pressing down onto the stub axle. The bush should be thick enough to prevent the lip of the trunion from contacting the stub axle as the steering turns. The bush acts as a steering bearing and as a spacer.

The small shims go on top of the kingpin but adjust the clearance at the BOTTOM, preventing the kingpin from being pulled up too tightly against the stub axle at which point it would begin to bind. Adding shims increases the king pin length to give the clearance. But too much and the stub axle will have too much vertical free play on the kingpin, giving the characteristic knocks and bangs as you go over rougher roads and speed bumps.

Since all of the weight of the car is taken through the bronze bush at the top, there isn't a need for any proper bearing arrangement at the bottom of the stub axle. It's pretty primitive and just relies on the edge of the lower stub axle/ kingpin bush to limit vertical play. That's partly why I asked earlier if that kingpin bush was fully inserted properly.

PS I see Bob has also explained it and although slightly differently, the end result is the same!

PPS Are you doing this with the TRE, or alternatively the steering arm, disconnected?
GuyW

Guy,

In my case the trunnion fits around the top of the stub axle with clearance and with the thrust washer removed it'll go down about 1/8" until it hits the point where the stub axle widens.
David Billington

Bob/Guy/David

Thanks, that helps a lot. I understand how it works now! I've had a quick look at it and the trunnion does clear the stub axle, but I cleaned up inside of trunnion and top of axle in case of burrs. At the base of the kingpin there is a slight gap where the kingpin curves out a little but I assume that is ok. The rounded rubber seal in the bottom of the lower bush protrudes slightly but I assume that is also ok.

No TRE yet Guy so the axle is free to rotate.

Tea and cake is nearly ready so I'll look at it properly tomorrow and report back. Thanks for your patience gentlemen, I haven't fitted kingpins since about 1973! Thanks for the number Bob, will ring if I can't solve it.
Bill Bretherton

I should also thank Dave (O'Neill) for supplying extra thicker shims. The Moss kingpin kit (I bought some time back) only included four 0.004" shims.
Bill Bretherton

Bill the base of the king pin is rounded and the rubber o ring does protrude slightly. This ensures the pin is fairly weatherproof and lubricant stays in!
Bob Beaumont

A couple of thoughts.

Either the lower bush is fouling on the radius at the bottom of the kingpin, or the kingpin has been incorrectly machined, so it is effectively too short - between the lower face and the step where the shims sit. Assuming that the bushes have been fully inserted.
Dave O'Neill 2

It might help if you could establish what is binding at the bottom. Is it the stub axle itself, binding on the kingpin base, or the bush binding on the radius of the pin?

I will see if I can measure the radius at the bottom of a kingpin.

As mentioned in the previous post, the dimension marked in red on this image is fairly crucial, although difficult to measure.

I've just realised, I was probably within the new 15 minute window to either delete or edit the previous post, but have since run out of time!



Dave O'Neill 2

Thanks Dave, I'll spend some time on it tomorrow and report back.
Bill Bretherton

I’ve just checked the radius at the base of a kingpin and an 8mm drill bit seemed a snug fit, so it would appear to be about 4mm.
Dave O'Neill 2

Here are two pictures showing bottom and top of kingpin with bronze washer for reference. The washers are (both) 0.155" and I've filed them slightly to ensure flatness. I've tried both trunnions with several shims. Without the washer the hub rotates. With it the hub goes tight when I fully tighten the (nyloc) nut. Is it therefore likely the hub is sitting slightly too high on the kingpin? I suppose I could file the washers a little but is that wise?





Bill Bretherton

There appears to be a gap between the stub axle and thrust washer.

Is the top bush in the stub axle flush with the top of the stub axle?
Dave O'Neill 2

I would still question whether the replacement bushes in the stub axle are correctly and fully inserted.I was previously thinking of the lower one but maybe the top one is a little proud still as well.
Did you check that the lube hole in the bushes aligns with the grease nipple as well? It's easy to check at this stage. Harder later!
GuyW

The lube holes are aligned. The top bush was slightly rounded Dave so I've filed it flat - still going tight with 0.048" of shims. The shims are tending to crush and bend a little and I'm only going just tight with the ratchet.
Bill Bretherton

Bill

Is the king pin fully inserted in the second image. The O ring is normally not visible.

Bob Beaumont

Problem finally solved! Following a conversation with Bob and bearing in mind everyone else's comments, it seems my kingpins are dimensionally incorrect. Referring to the picture of an old kingpin, the distance between the steps indicated by my fingers is about 1mm less on the new kingpins so about 40 thou. So I removed about 40 thou from the bronze washer and the axle stayed loose, admittedly with still quite a few shims inserted. But I now know what to do. This has cost me several hours but I guess that's how it goes sometimes.

This is another example of poorly made parts as has so often been discussed on the forum. Thanks everyone for your help.



Bill Bretherton

Well done for tracking that down Bill. Not an easy measurement to be that accurate with either. Good to get it sorted though.
GuyW

This thread was discussed between 23/03/2020 and 30/03/2020

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