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Machine Shop and Tool Talk

What Tolerance?


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  #1  
Old 07-18-2018, 02:55:08 AM
cobbadog cobbadog is offline
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Default What Tolerance?

I have a small Dumper truck rated at 1250kgs all up. I have excessive movement in the steering wheel and have traced it to 2 separate places. Mainly in the steering box but I found some movement on the rear steering axle where it pivots in the middle.
Today I removed the axle assembly and measured the pivot pin. It looks great with no signs of wear and the bushes that it goes through measure 1mm larger than the pin itself.

Is this 1mm too much clearance?

Thanks for any replies and help. After this is sorted the steering box is next to be attended to.
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Old 07-18-2018, 07:45:14 AM
Ray Freeman Ray Freeman is offline
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Default Re: What tolerance ?

To much I think. As a line borer I work with pin to bush clearances every day. 1mm is close to 40 thou.New fits on earthmoving gear is usually 8 to 12 if its a lubricated joint. Non lubricated and the pin fixed (non rotating could be a lot less than that)
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Old 07-18-2018, 06:53:15 PM
Andrew Mackey Andrew Mackey is offline
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Default Re: What Tolerance?

You want that bushing pretty snug, or movement will eat it up I would say no more than .005" (5 thousandths of an inch) Typically axle kingpins only have about 3 and if they get over 10 thousandths, they cause a lot of steering play. The pivot pin must be clean and straight. No wear or pitting. The bushing is driven in and reamed to clearance size. Not an easy job to do at home.
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Old 07-19-2018, 02:48:36 AM
cobbadog cobbadog is offline
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Default Re: What Tolerance?

Cheers guys for the information. I thought that it was a bit too much but today I found the biggest offender inside the steering box.
Yes this axle pin is a greaseable one but I put it back together for the moment as the amount of free play was way more than these oversized bushes and this is what I found.
The pin on the sector shaft shows a bit of wear. Why I hear you ask? Well some idiot filled the box with grease instead of fixing the leaky oil seal. This has caused the wear on the pin, the top and bottom bearings to almost disintegrate and a lot of tiny little bits of metal suspended in grease.
I will buy some new bearings and a new oil seal to replace the old felt style with a new model seal. I will experiment with different types of welding to see what is similar to the hardness of the pin so that the worm does not wear only the pin in future. The pin appears to be soft as I can file it to remove the burrs and as this is just a toy to take to the occasional Rally and not to work this type of repair should suffice.

I once again thank those for their advise and help in this matter. Cobba (John).
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Old 07-21-2018, 01:29:30 AM
cobbadog cobbadog is offline
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Default Re: What Tolerance?

I welded up the steering peg and roughly shaped it and assembled the box. It now has no free play in it or near it. Filled the box with 85/140 mineral oil which was like treacle today in the cool weather. now the only place with a bit of movement is on the rear axle pivot pin and I am not in a rush to do that as yet. Most of the problem has been resolved simply by doing the steering box.
Thanks to everyone who offered tips and help on this, I appreciate it.

"Now Humpty is together again"

I've been wanting to say that right from the beginning.
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Old 07-21-2018, 05:44:54 AM
tdmidget tdmidget is offline
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Default Re: What Tolerance?

Good work. Sound engineering is that the wearing parts should be the cheap or easily repaired ones. Many in your situation would have wanted to replace that with a hardened part which would have trashed the steering box in short order.

Last edited by tdmidget; 07-22-2018 at 08:10:30 AM.
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Old 07-21-2018, 11:49:35 PM
cobbadog cobbadog is offline
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Default Re: What Tolerance?

That is correct 'td' and was my first thought but good advise was received and taken from others and I went with that and I am happy with the result.
After a bit of more thought it was then I finally remembered about this very problem in replacing parts with something bigger and or harder. We used to be able to buy chromium rings for our old lawn mowers. The claim was that the rings would not wear and they did not, but they did wear the bore out so fast it wasn't funny. So standard black rings have only been used since.
If I ever do need to do this job again I will go to the next level and remove the old steering peg, make a new one from steel and fit it in place to get a more regular shape and so a better fit.
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