TOPIC:

OK, I got it off.

I had to grind very deep to get the bottom weld off, so by the time I could see the pin distinguished from the yoke, much of the yoke was gone. So I cut sideways and in the end I could cut a piece out, force the yoke open and press the pin out.

From the pictures you can see it is a simple press fit (steel on steel) and welded at the bottom with a thick weld. The bearing race seat is part of the yoke, with top bit unpainted.

My advice: if you ever need anything done with this, buy a new/secondhand one. Unless like me you need just the pin, its not worth the trouble.

But at least everyone now knows how this part fits together!

Paul

Success. You got your yoke shaft out and that's all that counts. It's a difficult spot to have to cut a weld out. A dermel tool and a hand full of small cutting discs or you could have machined it out on a lathe if you had access to one with a big enough swing. All that counts is the end result. Kudos.

Thanks.

As the hole in the new yoke is bigger than the pin diameter I need to create a sleeve to go between the new yoke and the old pin. And although it is not that important as the new yoke has a spring clip retaining design and the top nut will clamp it in, AND the steering bars will attached to the forks rather than the top yoke, I will still want to make this press fit as well as weld, so this is where your calculations DO come in handy.

The sleeve will be made out of steel, so to press fit the pin into the sleeve I intend to freeze the pin and heat the sleeve before inserting. Then I will again freeze the pin/sleeve combination and put the (aluminium) yoke in the oven, then fit the spring clip and insert the pin/sleeve into the yoke from the bottom.

.... like building a Spitfire aeroplane!

But first I have to take a few measurements in terms of pin length and where the swing clip groove needs to go, etc. Then apply your maths to see what 'room' that gives me for a press fit and therefore the tolerances I have to make up the sleeve.

However, according to my Vernier readings the yoke ID is 35.17mm and pin OD is 30.02mm... So, if an 0.002 difference is a good interference fit, the sleeve would need have a total OD of 35.172-ish, and and inner dia of 30mm exactly. Correct?

Possibly a stupid question, but does the expansion coefficient work the other way as well, ie with shrinking? And maybe no heating will be necessary as freezing the steel will shrink it enough to get them fitted,

Wish me luck!

Possibly a stupid question, but does the expansion coefficient work the other way as well, ie with shrinking? And maybe no heating will be necessary as freezing the steel will shrink it enough to get them fitted,
Yes it does. It's all about "delta T" So the change in temp multiplied by the co-efficient is the "change" in length or in this case diameter and in this case you would subtract the change from the original diameter.

Ok, so may I please run my maths by you Kawboy?

Yoke (aluminium) inner dia is 35mm. Pin (steel) outer dia is 30mm. Sleeve (steel) ID is 29.08mm and OD is 35.02mm to achieve press fits on both inner and outer walls. Correct?

Remember, there will be a retaining ring keeping the whole thing from popping out, so exact press fit is not that important for the sleeve/yoke fit. It however IS for the sleeve/pin fit. The latter will be the weakest link.

Yoke: 0.000025 x (180C-20C) x 35mm = 0.14mm (wider)
Pin: 0.000012 x (-20C-20C) x 30mm = 0.0144mm (narrower)
Sleeve (steel - heated): 0.000012 x (180C-20C) x 29.08mm = 0.0558mm (wider)
Sleeve (steel - frozen): 0.000012 x (-20C-20C) x 35.02mm = 0.0168mm (narrower).

So:

When inserting the (frozen) pin into the (heated) sleeve I will have 0.0558 + 0.0144 = 0.0702mm 'space' to press-fit
Then when inserting the (frozen) pin/sleeve combi into the (heated) yoke I will have 0.14 + 0.0168 = 0.1568mm 'space'.

Will that work? Are the dimensions for the ID of the sleeve and the OD of the pin sufficient to hold the pin in under stress of riding?

Paul

Maybe I’m talking rubbish, but rather than relying on interference fit between the stem and sleeve, would welding, brazing, or otherwise bonding the two be an option?