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MG Midget and Sprite Technical - Don't forget to check the cotter pins...

Evening all

Just a quick note to say that I've just discovered that the bottom end of my front suspension can happily move backwards and forwards by about 1/4 of an inch.

This is caused by the cotter pin nuts coming undone slightly and allowing the cotter pin to pop up a bit and the kingpin to slide on the trunnion pin.

Interestingly, the only reason I noticed this is because the brakes were stuck on slightly while I was checking for tyre clearance while carrying out my bimonthly suspension checks, and the act of moving the tyre round with the brake stuck on meant the bottom movement was very obvious.

I don't know if you can 'find' this play in other situations, there were no clonks and the car felt fine and stable when driving. It has just passed an MOT, but there's no way you'd see that play without trying to turn the wheel with the brakes on.

So when you're greasing or oiling the front suspension, just give those little nuts a tweak, just to check. As it were..
Rob Armstrong

I second the above.

When I got my Sprite last year it had a slight front suspension rattle. It didn't disappear with the new shock absorbers and I assumed it must be the lower fulcrum pin. It was only when I was half way through the strip down that I found the cotter pin was loose and tightening it would have cured the rattle.

Re-building the suspension at least gave me peace of mind. I now know that all the wearing parts have been replaced and everthing else checked, cleaned, and painted.
Colin Mee

a good reminder Rob

a knowledgeable friend told me that one of the checks for the front had to be done with someone pushing the brake pedal

and that those cotter pins have been know to break or come apart and that the design to rest with them was very poor

as you probably put more stress on the front of your car than a standard car it makes sense that you need to check more

my friend was very concerned about those cotter pins and glad to hear I'd had new cotter pins on mine. I wonder if he thought about poor quality modern parts :)
Nigel Atkins

Have you considard upgrading to nylocs ??

Prop
Prop and the Blackhole Midget

I haven't seen nylocs that small Prop. Do they exist?

Often because the thread on the cotter is so small, it gets over tightened and strips, or partially strips, and comes undone later. Loads of experience of that on push bikes in my youth.
Lawrence Slater

I've not seen a nyloc that small...

They're double nutted now with a star washer as well.

The whole bottom joint with cotter and threaded bearing is daft IMO, but I've not got round to making a better joint yet. Got some ideas (mostly from David B) on this BBS, but no time yet...
Rob Armstrong

Rob, before I do the cotter up, I beat it into place as far as it can go, to expose as much thread as possible, and get the head almost flush with the King pin base. Only then do I tighten the nut. I've also found that they often aren't ground flat enough, and won't go in far enough without a bit more grinding.
Lawrence Slater

you can get not only small but tiny nyloc nuts

(not by me obviously but) my car was supposed to have advanced David Billington's front suspension conversion by using Sierra components and the brakes but it never happened as life got in the way
Nigel Atkins

I've often had trouble getting the cotter pins out...probably after they've been fitted by someone like Lawrence! ;o)
Dave O'Neill2

Yup. To remove one of my cotter pins, I cut the threaded end flush with the king pin, and centre punch it out. They certainly don't come out on their own, that's for sure. :).
Lawrence Slater

I never thought about the significance of those cotters becoming loose. On one side a po just hammered in a length of silver steel and burred it over (so subtle!) so one time when I had thought about removing it, I discovered there was no way I was going to get it out without destroying something.
I'll check it all on my next bi-monthly "lets see what's falling off" round.
GraemeW (Kent!)

I'm with you Lawrence as thats the way I was taught to fit them and thought the nut was only there as a safety device. I have also never seen one come loose on anything and as you say removal is usually more of a problem than them coming loose.

Trev
T Mason

The nyloc nut you need is GHF206, readily available at the usual suspects.
Paul Walbran

Paul,
just out of interest what spanner size is that (i.e. thicker or standard size wall)
Nigel Atkins

5/16", standard size for the thread
Paul Walbran

thanks
Nigel Atkins

That's not shown as a nyloc nut though Paul. Well not at lacey and a few others anyway.

http://www.leacyclassics.com/ghf206.html

Or maybe coz it's so small, it's hard to see the nylon. I've never seen one that's for sure and the QH King pin sets I've got only have plain nuts too.
Lawrence Slater

This looks like the nyloc version of that nut?

http://www.leacyclassics.com/ghf220.html

Jim
J Smith

Yup, that does, but is that larger? It's listed with Moss here.
http://www.moss-europe.co.uk/Shop/SearchResults.aspx?SearchText=GHF220&WebCatalogID=0

But not as a cotter pin nut.
Lawrence Slater

GHF206 is a plain nut, GHF220 is a nyloc as per the list on Paul Hunt's web site - http://www.mgb-stuff.org.uk/partnos.htm#

T*ss have GHF206 as also 2BA - page 6 - http://www.moss-europe.co.uk/Shop/SearchResults.aspx?SearchText=ghf206&WebCatalogID=0
Nigel Atkins

T*ss also have in their catalogue -

Nyloc Self Locking Nuts
YN2905 - 3/16" UNF

but then you can't find this part number with their web site search - and yes it is so like T*ss to make cataloguing mistakes
Nigel Atkins

If the nyloc version in the same size is available, I wonder why it isn't supplied on the cotters? I'd have used it if it was. Used with a spring washer, and if the cotter is driven in far enough before tightening the nut, I'm happy with the plain nut. But I agree a nyloc would be good here.
Lawrence Slater

perhaps 3/16" fittings are just too small for some of you macho engineers to deal with

myself being of a delicate nature and stature have these items in my small shed (but not macho engineering machinery, oh the shame of it)

Nigel Atkins

I have come across the issue where the pin extends too far down after battering meaning spacing washers are needed to be able to tighten the nut up.

Moore fuel - my pins are metric thread, 8mm nut.
Rob Armstrong

That's on cotters that are ground too flat Rob, and hence go in too far, I've had some of those too. I've got some from Sussex that are hardly ground at all, and I had to grind them myself to make them fit in enough to even see the thread. The cotters included in the QH kits are "exactly" the right size.
Lawrence Slater

I have had that too. Not all of the fulcrum pins are identical either. In the case mentioned the flat on the F-pin was considerably deeper ground than normal.

Its important when fitting the cotter, to turn the F-pin too and fro so that the flat face of the cotter lies snug and true against the ground section of the F-pin. If not, it can appear tight and then the F-pin rotates a fraction and the cotter frees up and comes loose. Most times it will self-align, but just once in a while it won't!
Guy W

Rob,
no doubt you can get 8mm nylocs too - I can look in my small shed if you like
Nigel Atkins

I don't batter the pins in but do give them several gentle taps. I've never had one come undone.

I have had to grind more off the flat as it won't go in far enough.
Jeremy Cogman

Guy, that's more of a concern if the fulcrum groove is ground too deep. It must weaken the fulcrum pin. Hopefully there's plenty of strength to spare.
Lawrence Slater

Ha! I see I had brain fade on that part number (blush).
GHF220 it certainly is, don't know how I managed that one.
Paul Walbran

Paul,
if you notice I missed the number too as my thoughts were on confirming wall thickness
Nigel Atkins

This thread was discussed between 30/10/2013 and 05/11/2013

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