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MG TD TF 1500 - Loose kingpin

I dismantled my TF 1500 28 years ago when I could not get it registered and now it's time to put it back together. 28 years ago I prepared the chassis and suspension ready for assembly, but now 28 years later I have a problem.

The problem is the Kingpins rotate slightly when installed in the stub axle with the steering arms bolted tight. Ray Lee suggested trying the steering arm without the woodruff but this did not stop the rotation. [in case I have my terminology wrong the kingpin is the swivel pin that is threaded both end for the Links or trunnion joints screw onto)

The stub axle has the 8640 stamped on the back of the LH axle and as far I can tell its definitely TD,TF or A, and the kingpins orginal on the car have the same problem. This is on both LHS and RHS. So I'm at a loss.

The photo in this post is of the axle and shows the tapered hole for the kingpin with the steering arm protruding fully into the cutoff to lock the kingpin in place

This rotation (which is about 1-2degrees) cannot be normal and would only get worse overtime.

Any suggestions on could be the problem or what else I can try?


Chris Cullin

This photo is looking into the steering arm hole of the stub axle and shows how the kingpin groove is not perfectly aligned with the stub axle hole.

It is on the right side of the photo but not in the left.

You can see how the kingpin can rotate 1-2 degrees when the Steering Arm is installed (as shown the previous post).

Any thoughts?


Chris Cullin

Hi Chris,
I had always presumed that the kingpin was positively
locked in by the steering arm. Attached is a photo of a stub axle that is factory, never been tampered with. I bought it over 40 years ago and know it's history
As you can see there is clearance between the steering arm taper and the kingpin.
I suggest you lightly knurl the affected area or get a bike shop to hard chrome that section if it worries you.
Ray TF 2884

Ray Lee

Chris, the king pin should be a press fit in the stub axle. The ones I have taken apart needed a 10 ton press and sometimes a little heat. I do not think the steering arm should come into it except for a safety. It's hard to to see how the steering arm would actually lock the the kingpin in position since the steering arm has a taper which fits into the taper on the stub axle. Therefore the steering arm would need to fit at a very precise distance into the taper to simultaneously be tight in the tapered hole and press against the king pin flat.
Cheers, Hugh
H.D. Pite

Hi Hugh,
I agree, when I fitted new ones some years ago I had to press them in.
I think hard chroming would do as I have used this method on worn M/C fork stanchions.
Ray
Ray Lee

Thanks Guys

My swivel pins are definetly not press fit and I can easily install and remove by hand. I will look into hard chroming. I will also see if I can find another set if pins to try.

I will let you know what I find. .

Chris.
Chris Cullin

Chris, The swivel pin is definitely a press fit in the steering knuckle. I just measured one from an original TD where it fits in the steering knuckle(stub Axel) and it measures .8750" to .8755". It took a hydraulic press to get this one(bent)out.
I suspect someone may have mistakenly honed the bores in yours where the pin fits.
Richard Cameron

After discussions with two local mg workshops the cause of the issue is not any clearer. My swivel pins are definitely not a press-fit, but I don't think a press-fit is sufficient to stop the ping rotation.

As a fix I am thinking of rotating the swivel pins by 180 and machining a new cotter pin groove that aligns tightly with the steering arm. I will then install the swivel pin with some loctite.

This means the flat surface on the swivel pin will face inward towards the engine rather than outwards towards the wheel, but I cannot see an issue with that.

Does anyone see any problem with this approach?

Chris.

Chris Cullin

As I think this through and I'm wondering if the 1-2 degree rotation is really an issue, or an issue that needs to be fixed.

Given the steering arm has a tight and stable connection to the stub axle there will be no wheel wobble. So while not ideal there is no performance impact caused by the swivel pin rotation, and it's most likely only vibration that would cause it to move. Wear appears to be the only risk.

So now I'm thinking the use of loctite will be sufficient and this will stop the rotation and wear.

Chris.
Chris Cullin


Chris, I'm not an engineer, but I did notice some wear and chafing on the pin I just removed from the stub axel I measured. It was only in a couple of places on the inner and outer faces but was enough to notice and feel with a finger nail. I have no idea of the mileage on these old parts. Some have said that these parts are possible failure points, but mostly in racing applications. One of the threads on this forum talked about special material ones being manufactured for racing years ago.
I am convinced that the primary design feature of these pin stub axel fitting together is the significant press fit of the two parts. The steering arm just locks it all together. This said, it might be wise to have your parts checked for cracks especially due to your parts un explained loose fit.
Therefore, I would recommend cleaning the mating surfaces with thinner, and using JB Weld to fill the loose fit and keep them from turning.
I suspect this would be a permanent fix, and you probably would never get them apart again, so it would be important to confirm your using good serviceable parts with clean threads and remember that the left parts and right parts are entirely different. If you experience damage in the future for some unusual reason, your only option would probably be replacement of the whole assemblies, but I see them for sale on EBAY quite often. This option would give you time to look for a bargain pair as spares if you desired to do so.
Richard Cameron

I've had great success with these products when the fit up is not what it should be. I think it's better than epoxy products with the added feature that heating with a torch will allow you to disassemble again. I'm not disparaging JB weld, I just don't think this is the place for it. I've got a John Deere tractor that's been sporting a JB repair on a casting for 15 years!


http://www.henkelna.com/industrial/retaining-compounds-loctite-anaerobics-14963.htm
JE Carroll

Chris, definitely use Loktite of which I am a big fan. The high strength red would be the way to go since this product is designed for sliding fits. Once the kingpin-stub axle is assembled with Loktite it is never going anywhere until a big press is used and some heat applied. I think JB Weld is much to viscous for this application.
Cheers, Hugh
H.D. Pite

This thread was discussed between 04/05/2014 and 07/05/2014

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