Stiff king pin rotation

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jonclancy
Posts: 942
Joined: Tue Nov 01, 2011 9:30 pm

Re: Stiff king pin rotation

Post by jonclancy »

Any joy with this, Morris?
Morris
Posts: 109
Joined: Wed Aug 08, 2018 12:05 pm

Re: Stiff king pin rotation

Post by Morris »

Well hooray(!) I've finally come to a satisfactory conclusion for this.

I took it all apart and re-assembled just to make sure again that everything had gone together correctly (which it had), but I still had the stiffness issue. I even thought that it may have been the king pin assembly itself, but given that they are new (from Moss) and essentially are a king pin passing through some bushes with a nut on top, provided they have been reamed correctly will not cause an issue.

I spoke with the factory again but no joy, with the advice being to assemble the car, run it for a few hundred miles and if still stiff take it to them for assessment. They did say though that a few mm tolerance is acceptable and yes, the wishbone I returned to them was not quite right... the engineer in me though says out of design stiffness leads to wear and likely premature failure.

The solution suddenly hit me, and that was to shift the lower wishbone backwards along the chassis by 5 mm (2 off 2.5 mm washers). Hey presto the stub axle flops around the king pin nicely now with very low friction. I still have a couple of tweaks to do to ensure that the front lower wishbone bush carrier does not fowl the chassis (I've removed 5 mm from the tube so it is very close), and I most likely need to reduce the diameter of one of the spacer washers to ensure it only contacts the inner bush tube.

Sorry website will not allow me to update photos again...!
Simon Marks
Posts: 66
Joined: Sun Mar 29, 2015 2:05 pm

Re: Stiff king pin rotation

Post by Simon Marks »

Hi, Morris,

I'm glad to read that you have found a solution. Are the lugs, welded on to the chassis, to receive the wishbones symmetrical on the chassis?

Simon
Morris
Posts: 109
Joined: Wed Aug 08, 2018 12:05 pm

Re: Stiff king pin rotation

Post by Morris »

Yes, I couldn't see anything wrong with the placement of the lugs themselves into the chassis. I'm convinced it is only related to the wishbone itself.
Westfield 129
Posts: 867
Joined: Sat Jun 04, 2011 4:20 am

Re: Stiff king pin rotation

Post by Westfield 129 »

Don't forget to check the caster when you align the chassis. You want equal caster left and right sides, or you will get a pull in the steering.
What bushings are you using? The mentalistic, or the poly with the center tube and thrust washers?
Morris
Posts: 109
Joined: Wed Aug 08, 2018 12:05 pm

Re: Stiff king pin rotation

Post by Morris »

Metalastic bushes on all the wishbone to chassis mounts (standard as supplied with Kit). Yes I'll check the caster once finally assembled.
Westfield 129
Posts: 867
Joined: Sat Jun 04, 2011 4:20 am

Re: Stiff king pin rotation

Post by Westfield 129 »

Don't torque the bushings tight. Around 5 lb.ft is enough. That way, the suspension will move freely, and the bushings will last much longer.

If you use tighter torque, the suspension will not move freely, and in short order, the bushing's rubber element will shear.

Grease the suspension bolts with a high quality chassis grease prior to installation.
Morris
Posts: 109
Joined: Wed Aug 08, 2018 12:05 pm

Re: Stiff king pin rotation

Post by Morris »

Thank you W192. Good advice. I feel like the project is thankfully moving again now.
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