Pivot pins

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Grumpy21
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Pivot pins

Post by Grumpy21 »

So I have a question/thought.

I’m just about to replace a slightly leaky front damper. I need to swap over the pivot pin from the old damper, being a taper fit it’ll be a sod to get off especially as there looks like little chance of getting a puller on.

So why would people go to the trouble of removing such an awkward part when there’s no apparent market for used pins anyway. New ones aren’t available.

Why not just leave the seized pin in the shock arm?
philthehill
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Re: Pivot pins

Post by philthehill »

New pins are available from ESM.
https://www.morrisminorspares.com/front ... es-p830516

Here are a pair of NOS on 'e' bay.
https://www.ebay.co.uk/itm/313172971840 ... SwBm9fKrBH

Yes they are hard to remove but that is down to the shallow taper of the stub which fits into the damper arm. Even using my hydraulic press they are hard to get out.
I would recommend fitting the the later after market pins with the one piece bush retaining washer and UNF thread. They have a much better finish.

grumpy2
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Re: Pivot pins

Post by grumpy2 »

Yep I agree. So why do people bother removing them before selling them on eBay. Surely more bother than it’s worth?

I’ve got one I could remove but shan’t bother, too much hassle by far.
philthehill
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Re: Pivot pins

Post by philthehill »

I would suggest that the 'e' bay vender thinks they will make a few more quid by splitting the two and at price of new pin assys who can blame them.

Grumpy21
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Re: Pivot pins

Post by Grumpy21 »

All sorted.

As a point of interest old pins removed quite easily. Worked on three. No fancy press involved.

Wedge the big washer off, two legged puller on the conical end of the pin and a gentle heat from a plumbers blow torch. Very easy.

Cheers

Anyone need some pivot pins?
philthehill
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Re: Pivot pins

Post by philthehill »

The only problem with removing the large washer from the pin is that the knurling that retains the large washer can be damaged leading to insecurity of the large washer allowing it to move/rotate so loosening the top trunnion and bushes.
My advice is - remove the large washer if that is the way you decide to remove the pin but do not use the pin/washer again.

Grumpy21
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Re: Pivot pins

Post by Grumpy21 »

I bow to your wisdom Phil, but I can’t see how removing the thrust washer that’s not in contact with the shock arm on one side and only in contact with a poly bush on the other side could cause the trunnion to work loose. Ultimately the trunnion is fixed to the shock arm with a locked nut at either end of the pivot pin. I’d struggle to see how anything could work loose unless either or both lock nuts came loose.

Happy to be corrected though

Ps the intact knurling makes a very good guide to pulling the washer back into place.
philthehill
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Re: Pivot pins

Post by philthehill »

The knurling is what keeps the large washer from rotating. If the knurling is damaged and allows the washer to rotates the shoulder of the pin and the face of the washer in contact with the pin shoulder will wear allowing the bushes to loosen and the trunnion becoming slack on the bushes. The large washers at both ends of the pin are restrained from rotating by the knurling and the flats on the pin. There is considerable rotational forces acting on the washers through the bushes when the suspension moves up and down.

Grumpy21
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Re: Pivot pins

Post by Grumpy21 »

I see your argument there and again bow to your experience - have you ever seen evidence of this happening?

My thinking, and thats all it is based on minimal evidence, is as follows.

Rotational forces applied to the face of the washer would be oscillatory in nature and of a limited angular extension. ie, as the swivel pin assembly moves up and down the arc of rotation between the top trunnion and suspension arm would be small - maybe 30 degrees max?? (estimate). The poly bushes are red greased to provide smooth operation including the contact surface between the poly bush and the large washers at both ends. The coefficient of friction between the poly bush and washer would therefore be relatively low in comparison to the coefficient of friction between the knurled washer and knurled pin. Exactly as manufactured with three exceptions, the friction between the bush and washer has been reduced by the use of poly bush and red grease and the fixing friction of the knurled washer has also been reduced by its removal and refitting.

Relatively new to Minors but have lots of experience with MGs and the lower suspension on MGBs has some similarities. On those the wishbone pivot has a machined face on one side of the bush and a freely rotation large washer on the other side of the bush. Having rebuilt perhaps 7 or 8 MGB front suspensions I've never experienced one where rotation of the large washer has caused failure.

Ultimately everything will fail but I cant imagine that pivot pin washer causing a problem in the foreseeable future given its operational and maintenance parameters.

However, as I said earlier, I've limited experience with Minors so will make checking this part of my maintenance schedule, its easy enough to check for wear and rotational movement.

Cheers
philthehill
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Re: Pivot pins

Post by philthehill »

Poly bushes and grease will reduce the friction between bush and washer but not everyone fits poly bushes and I suspect that not everyone removes the large washer to remove the pin.
The MG bottom inner pivot/bush arrangement is similar to but different to the Minor top trunnion arrangement in that the inner large washer is well fixed to the pivot shaft and in my experience precludes the possibility of moving.
https://www.moss-europe.co.uk/pivot-wis ... soc=112094
The outer washer retaining castellated nut should be done up tight enough to hold the large outer washer hard against the shoulder of the pivot pin.
Whether the Minor washer retaining knurls gets damaged/worn or not - it is bad engineering practice to remove a fixture off a retaining knurl, refit it and expect the knurl to have the same holding power as before.

Grumpy21
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Re: Pivot pins

Post by Grumpy21 »

Like I said above I don’t expect it to have the same resistance to rotation but I don’t expect the forces on it to be as high either.

I guess time will tell

Ps the MGB bottom pivot is a single cast/machined part, the inner ‘washer’ is a machined face, the outer washer is tightened against the other face of the bush and has no way of preventing it from rotating. I’ve never seen any evidence of wear due to friction or rotation on the unfixed outer washer
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