The International Cessna^® 170 Association

Walker wrote:Perhaps George Horn should do his research a little more carefully when talking about hydrogen embrittlement. The baking is to be done before the plating process. The plating on the '52 that I am dealing with is actually cadnium. To an untrained eye, I guess it would be easy to mistake clear cadnium from chrome.

The above statement is incorrect. I did a bit of research and found the following from a technicial website:

After plating, parts which are susceptible to embrittlement are often subjected to a heat treatment (baking) procedure, called "hydrogen embrittlement relief". Often, a temperature of 375 deg. F for 3 or more hours is used. Sometimes, specifications require that the embrittlement relief bake be performed within a certain number of hours after plating. The process serves to remove or redistribute the hydrogen, but may further reduce the fatigue limit of high strength steels. This phenomenon was described by R.A.F. Hammond and C. Williams ("Metallurgical Reviews", 5, 165, 1960) and again by J.K. Dennis and T.E. Such ("Nickel and Chromium Plating - Second Edition", 1986, p.72).

To reduce the adverse effects of hydrogen embrittlement, you can consider whether or not the following concepts are pertinent or applicable to your situation:

- Avoid or reduce pretreatment steps which can introduce hydrogen.
- Ensure the post-plate hydrogen embrittlement relief is effective.

There are some instances where parts need to be heat treated before plating processes are conducted, but for hydrogen embrittlement it should be done very soon after the plating process is complete.

Thanks n1410d.

My plane had some later style C-172 plastic yokes when I bought it. They were attached to the shaft with longer rivets than the original C-170 yoke had. I was able to machine these rivets and reuse them when attaching original 170 yokes. I ran across a post on the 120-140 website that offers a couple of alternatives to the expensive original rivets when reattaching control yokes. Using Hilok rivets looks like a good solution. http://www.cessna120-140.org/forum/viewtopic.php?t=5605

Walker,

It's spelled C R O W and is best not eaten. Leaves a lingering, bitter aftertaste.