I have a Super Cyke repro that I bought about 15 years ago that has been run a lot and has slowly lost compression. It was not bad cold with oil in it, but after it got warmed up it was hard starting.
  I was talking to Lew Wollard at Tulsa's contest, and he told me how to grow cast iron pistons mostly for McCoy Red Heads. So I decided to try that on my Cyke. I put a piece of 1/8" welding rod in my vice and put the piston on top. Then I took my propane torch and heated it to where it was just starting to turn red and dropped it in a can of motor oil. After it cooled I checked it with my mic, and it was about 1/2 to 3/4 thousandth bigger than when I started. I put it back in the engine and ran a couple of tanks of fuel through it, and it now has better compression than it ever did before.
 So if you have an old engine with a cast iron piston you might want to give this a try if it is down on compression. Being a cheap skate, I am always looking for ways to fix these old engines without spending a lot of money.

I usually try this dodge before making a new piston. Sometimes it works and sometimes not.

   If you are not careful, there's some non-zero chance of cracking the piston, too.

    Brett

I tried this on an old piston that was unusable first, before doing it on my good one. I know George Aldrich was doing this on some pistons, and he told me the same thing as you Andrew. I was going to have him do a piston out of my Madewell 49, and he said they had already been treated and would not grow. And yes, I think this would only be good if you had an engine that was no good any way, and you could try this to see if you could save it.

Quite a few people I know try this technique and some even hit the piston with an oxyacetylene torch! Even the most vicious heating treatment seems not to have produced a cracked piston!

    Well, I guess we are all stupid over here, because I have seen several cases of it. Like this one, the piston from a Phantom P30. This was gently heated with a propane torch and cracked long before any color appeared. Of course, it was already worn out to the point of needing replacement so no real loss, but it was (reportedly) the engine used for the last "B" Speed record set *below* 100 mph, it was broken the next day by the first flight over 100 mph.

   I believe this one is sintered iron, so presumably more likely to be brittle.

    Brett

Andrew; That is my prefered method on the McCoy Red Heads also. Just a little tap tap with the hammer and they are good to go for another couple of years. I put a half hour on the Cyke today, and the compression hot and cold is superb. I read over on RCU where a guy did the heat treating to a diesel and said it was the best running one of those he ever had. So I guess we do get lucky sometimes. The piston in the Cyke is a rather thick walled casting that is machined on the top and outside. I am hoping that it also hardened it a little to where it will last a little longer.

I may have to try the heat thing on one of my McCoy's next time it needs work. I have done the hammer trick on about 15 of them without problems though. Like the old drunken mechanic in my home town use to say, " don't force it, get a bigger hammer."

Hi Jim,

Just how do you do the "hammer tap"?   I have heat treated several McCoy Red Heads with mixed results.  Some came out very well, others not so.

Bill

Thanks for the info, Jim.  I suspect that any McCoys that I did this way would never be in threat of wearing out in my lifetime.   None will probably get to the 100 flight mark.........

Bill