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MG Midget and Sprite Technical - King Pins again

MOT failure. Buggerit.
Only 4 years old and have been a problem every MOT since I fitted them. They were reconditioned and matched with stub axles so all I can assume is that they were off spec from day 1.

Grrr

Another Saturday gone....
Steve 59 Frog

too bad you didnt make it to the midget front suspension rebuild in illinois
S.A. Jones

Are you and the MOT man sure it is play in the kingpin and not for example in the wheel bearing?
Robert (Bob) Midget Turbo

Thanks for suggestion Bob. Its movement of the sub axle relative to the kingpin (up and down). Not the bearing.
S
Steve 59 Frog

well if I understand you correctly that is just a matter of correct shims between the top of the kingpin and the trunnion.
David Smith

Unless the movement is the lower fulcrum pin moving in its housing.
(they had me on that one last year :-(

Mark
Mark Whitmore

It can be hard to get that vertical endfloat right first time, so that could well be it. Test it with the wheel removed to see if that's where it is.
Paul Walbran

Its vertical movement of the stub axle on the kingpin. The tester showed me under the car by levering it up and down.

My understanding is:

King pin is a taper - so if you tighten down the stub axle too much it will be too tight.

Hence there is a step at the top of the king pin that the top trunnion bolts tight against. The design intent is that the spacing between the bottom face of the top trunion and the face on the bottom of the king pin are EXACTLY the right distance for teh stub axle to be "just tight" on the kingpin.


The shims are there to get this distance just right.

So if (as is my case) all shims are removed ie teh "space" for the stub axle is as small as possible, but the bl00dy thing still moves up and down, then replacement is needed.


Is my logic clear/correct?

Any new thoughts appreciated before I strip it all down again.

s

Steve '59 1275 Frogeye

The shims are meant to take up float when the top trunnion is in place. Shim it correctly and you will have no excess movement (and an MOT ! )
na munn

As there are no shims left to take out I have run out of adjustment....

hence new KP required.

:-(
Steve '59 1275 Frogeye

firstly the kingpin is not tapered where it matters, the bushes are parallel. Secondly if you are still not tight with zero small shims you need to vary the thickness of the big PB shim/washer but I can't remember if in your case it needs to be thicker i.e. try a new one, or thinner i.e.get the fine file out.
David Smith

Further to David Smith's advice . . . .

If there are no shims sitting inside the top trunnion and there is still excessive vertical play of the stub axle then, in theory, a thicker phosphor bronze washer is required. I have only ever seen these available in one thickness, so trying a new one will be the first thing to do (because maybe the existing washer has worn thin giving rise to the excessive vertical play of the stub axle).
A Hock

Agree with the above but I must say that I have never found a set up where the shims have all had to be removed. Have you something else missing in the setup?
Robert (Bob) Midget Turbo

If a new bronze washer doesn't do it then a look at a oilite thrust washer list may indicate whether a thicker standard item is available. IIRC the thrust washer is an oilite bearing not solid PB and about 1/8" thick but with measurements you can see if it is a standard OD ID bearing. Worse case is it could be machined out of oilite bar stock to suit.
David Billington

I'll be willing to bet that the shims are there.... just they are often difficult to spot. They will be stuck up in the top trunion and can be picked out with the bent end of a marking out scriber (remember the ones from your metalwork lessons at school..?).

Like Bob, I have never come across a King Pin set up with NO shims.

Mark.
M T Boldry

Further to David Billington's comment, I've just measured the thickness of the OE phosphor bronze(?) 'thrust washer'. I make it 4mm (not a convenient imperial figure).

But, yes, I agree with the consensus - have a good pick around the inside of the upper trunion with a small hardened spike. The good money says there's sure to one or two shims compacted in there . . .
A Hock

Actually - you might need 'no shims' if the scintered washer was very worn...

A
Anthony Cutler

Thanks for all the advice. Really helpful.
I have never had KPs with no shims before either. Usual failure is worn bushes or the lower fulcrum pin I recall.

I have dug into the top trunions and there are no shims there! I took them all out last year when I had the same problem.

My new parts have arrived so I tried putting the new bronze washer in on the old set up but it seems to make no difference. Have looked a number of times at the assembly and I dont believe I have anything missing.
Not impossible though of course:-)

I have to conclude I have just been unlucky with the ones I have (came from Moss I recall. Even the year I fitted them - due to KP MOT failure - the MOT re-tester could see they were new but was surprised there was still some play....

Lets hope those cotters and bottom pivots come out OK. EEk.
Steve '59 1275 Frogeye

Remind me - will I need to disconnect brake pipes to do this or will slave cylinder assembly just bolt on/bolt off without opening the fluid lines up.
Steve '59 1275 Frogeye

Just a thought - and I don't mean to throw more confusion onto Steve59Frog's problems . . . but I notice that Moss show different part numbers for early and late Sprite/Midget stub axles and king pins(presumably the change in part numbers occurs for drum or disc brakes).

I personally don't have knowledge of the front drum brake configuration but understand that the physical difference between the (drum/disc)steering parts is subtle.

Is it possible that Steve has got incorrect kingpin or stub axles for his application which is giving rise to his vertical play problem?
A Hock

excellent point, 'drums' had escaped my notice thus far, does anyone actually have experience of both types to know the detail differences?
David Smith

I just got off the phone to Paul at PBW, he suggests taking the hidden shims out too

:-)

I told him Steve'd already gone that route, whereupon he next suggested that Steve should shim behind the phosphor bronze bush to push it down behind the trunnion.

He's only had one "bad" kingpin (crap machining) in the last four years he says and is sure that normally 'tis only lost shims up in he void.

I dont know whether it's both or only one side. Which is it Steve?
Bill sdgpm

I've heard of one person that assembled a disc stubaxle with drum brake kingpins and didn't get very far before they realised there was a problem, the drum brake kingpins being smaller in diameter than the disc brake ones.
David Billington

On the basis that we've got a good kingpin, good thrust washer, good top trunnion and no shims . . . then the only other possibility that would explain excessive vertical movement is that a previous owner has had the stub axle machined or 'skimmed' at either the top or bottom face (or both!).

A Hock

Progress. This evening, remarkably, both sides were dismantled without any problems. Hopefully tomorrow evening it all goes back together...




Steve 59 Frog

... and the other side


Steve 59 Frog

hmmm the plot thickens, you have a goodly mix of non-standard parts there, I didn't know you had antiroll bar, disc brakes, teles and a replacement top arm kit. Does the latter still use the standard top trunnion?
(also is it an illusion or are your a/r bar bushes a sloppy fit?)
David Smith

Steve,

On the 14th May you reported " . . . as is my case all shims are removed".

But your photos today show the upper trunnions and bolts still connected to the suspension arms (presumably of Frontline manufacture?).

I don't wish to doubt what you are saying, but how did you inspect the trunions inner recess for the presence (or absence) of shims when the trunnions are still attached to the suspension arms?

You are aware that the shims are approx 16mm in diameter and, relative to the phosphor bronze thrust washer, they sit deep inside the trunnions?





A Hock

David,
Top trunions are not specials. Unsure if there is a difference between disc and drum but set up is for disc.

You are right the roll bar rubber bush is not as tight as it was. Looks worse in pic because it has some spring pressure on it.

A Hock.
Yes shims are removed. Top trunions hinge up almost vertically with the suspension arms so its possible to see into the inner recess. Also poked about vigorously with a scriber. No spacers left honest...

S


Steve '59 1275 Frogeye

Did not get back until 7pm so not quite finished, but only hubs and brakes to fit so should not take long tomorrow morning.

All went together fine. Packed as much grease in as I could when assembling and then pumped it full again with the gun.

Nearside was a (I think!) a perfect fir with both shims. The nearside bolted up with the stub axle too tight on the kingpin with two shims so I fitted two extra and then there was just a tad of vertical movement. Removed one and now seems fine.

I tried to find some vertical movement with a crow bar on both sides and could not spot any. Lets hope the MOT man says the same.




Steve 59 Frog

and the other


Steve 59 Frog

I meant...

Nearside was a (I think!) a perfect fir with both shims. The offside bolted up with the stub axle too tight on the kingpin with two shims so I fitted two extra and then there was just a tad of vertical movement. Removed one and now seems fine.
Steve 59 Frog

This thread was discussed between 13/05/2009 and 22/05/2009

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