MTFCA Forum

I am needing to press a new bushing into one of my triple gears. The engine appears to have maybe 1-2 thousand miles on it after new aluminum pistons and a ground crank done by an owner 30+ years ago. 2 gears and bushings are fine but one was loose making a rattle and the cotton low band deteriorated from age, necessitating the tear down. I found the bushing spun in the gear and tight on the shaft. I am contemplating either pressing in a new bushing or freezing the new bushing undersize in liquid nitrogen (minus 320 F) before I drop it in place and let it thaw, then having the center machined to fit. I have easy access to liquid nitrogen. I know that rifle barrels are often cryo treated to improve accuracy, and that it alters the crystalline matrix of steel, but does it alter, improve, degrade, or have no effect on bronze? Perhaps I'm overthinking this.
Noel

You will most likely find the bushing will be loose in the gear without the freezing. After they spin in the gear they seem to be loose in the gear.
Look in to ball sizing or ball burnishing. If you want more info email me. Dan

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The standard linear expansion coefficient for brass is about 19x10-6 per degree C. To go from room temperature, 20oC to the temperature of liquid nitrogen, -196C you would get an shrinkage factor of about 0.4 percent.

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I was wondering if dry ice -110°F (-78.5C) would be enough - for those that don't have access to liquid Nitrogen

freezing or even cooling is unnecessary. press alone is all you need. i do use a bearing locktite product to help secure bushing.
i suppose if one had no press & were using a hammer, freezing would be useful. Give the bushing .0035-.004 clearence. boring to center hole way better than reaming.

The Ford specification for interference between the bush and the gear was 0.0045" - 0.0065". That's a pretty tight interference and I'm not sure how much shrink you good get out of liquid nitrogen. (Yellow metal generally behaves exactly the opposite of Ferrous metal when heated and cooled on a crystalline structure.). Also, for that level of interference, an insert tool should be used on a bush, and I believe that part of the historical problems is folks didn't back then on rebuilds and the bronze just smushed out of the way without providing an actually 'seat' into the gear. Just my .02...

As to the ball reaming comment...I convinced myself years ago that at some point in the process life that Ford itself resorted ball reaming the bushes in place. I had bought the technical library of Humber Motor UK, relating to Ford T and in it was a memo about trial and error experiment to determine 'spring back' due to ball deformation as it passed through. Whether Humber had a working relationship with Ford or not I have never determined. Who authored the 'spring-back' concept is unknown. What size ball they finalized on is unknown. So, I've never really pushed the idea forward.

We do know for a fact that Ford was using surface crush finish as early as 1915 with cylinder bores...ball reaming of yellow metal would not have been a stretch. For the heck of it, just to see and for kicks...years ago I designed an automated process using only technology available pre world war 1 for constant cycling of 'balls' including the ram to 'ball ream' in place. Ironically if any of you get the laser cut wood kinematic kit adverts, the pinball lift and drop kit is very similar...

Go to Northern Tool, Harbor Freight, or your local Farm & Home type store and buy the cheapest hydraulic press they sell. It should be able to do most any pressing required on a T with the exception of the axle shaft gears if the press isn’t tall enough. They are usually made of a metal frame and a bottle jack. A press is sort of an “essential tool” for working on T’s.

Thanks for the suggestions. I have a 12 ton press that will work well and am thinking of acquiring the tools to do a ball sizing after having an insightful discussion with Dan earlier today. A chronic problem that I have is that a machine shop that can do other work is a problem as they are 3 hours away unless I can find a local hobbiest with time, tools, and talent.
Noel

I've been freezing bushings with liquid nitrogen for over 30 years. Works great. I have done it in a work setting, never yet on Model T parts. Consider a few things...

- The smaller the bushing, the less it will shrink. So you get diminishing returns in smaller bushings.
- Place the bushing in the nitrogen bath. When the boiling stops, the bushing will be fully cooled. (Interesting phenomena, in the moment just before equilibrium, the nitrogen boils the hardest, then stops.)
- You must work FAST. If it doesn't immediately slip in, go back to the nitrogen bath and try again later.
- The length will shrink, as well as the diameter. So, in the case of a flanged bushing, when it reaches room temp, the length will have grown, which will push the flange away from the triple gear. Therefore, you'll still need a final "push" to reseat the flange against the gear face.
- Proper protection of hands, eyes, etc. is essential, as well as working in a well ventilated space as the nitrogen gas will displace oxygen, (which you probably knew already, but it's worth stating).

Bottom line, no harm in trying it, as long as it's done safely.