Enlarging a Pistion

This is more of an Isky type question and I do remember a thread about this subject but not the details. I have a few old tired engines that would benefit from a slightly larger piston. As I recall it involved heating the piston but that is all. So, how do you do it and has anyone actually done it with success?

I did try the pipe cutter deal on an old McCoy piston that took a beating when the rod blew - no success for me there.

Cary (Of all the things I've lost I miss my mind the most)

I heard of two cases where the cylinder was chrome plated, thus decreasing the bore slightly and allowing the original piston to be used. I never heard how well it worked or didn't work. Just a thought. What type of engine is it and what vintage??

I think someone said you could bash the crown with a nail to cause a slight flaring out of the top of the piston. However, they also said that the effect was very short lived and would result quickly in an even more worn out piston.

Cary,
I remember the thread. I think it was also the one that had the pipe cutter tip.
If memory serves, the gest of the thread said that in most cases the iron piston had already stabilized and would not grow further.
GMA mentioned many times over the years how he fixed engine fits. First problem is that the piston and cylinder are usually worn out-of-round. He would grind/hone the piston and cylinder round, then chrome plate the cylinder enough to make a good fit. I'm sure other engine reworkers do something similar.
You might find someone who would do a "quick and dirty" plating to make a better fit but it would never be as good as a complete job.
My suggestion would be to either "go for a complete job" if the engines are worth it (or have enough sentimental value to warrant it), or make a good stand and display them on a shelf if not.
Of course this is merely the opinion of a "non-expert", individual results may vary.
Good luck with the engines either way.
George

John McCollum, Bob Oge and Tim Gillott are the only engine tuners I know of that chrome, but only John McCollum has a hone, AFAIK. You can contact him through EDOM's Website (Bill Lee). GMA charged $60 for a chrome/refit, and that was a bargain. Steve

I wonder where GMA's famous "SUN" hone ended up? I understand he got it from Fox when they upgraded.
Bob Hunt (Robin's View Productions) made a tape a few years ago titled "George Aldrich, The Father of Modern Stunt". It is a very interesting tape. In part, it shows George using that SUN hone.

Thanks for the info. None of these engines are worth spending much money on. Old OS .29 and the Veco .29 They both run but have low compression and the leaking between the piston and sleeve. Just have a memeory from that old thread at Isky's that heating the piston would make it "grow" just a bit. Perhaps I'll just give it a shot and see what happens.

>Thanks for the info. None of
>these engines are worth spending
>much money on. Old OS
>.29 and the Veco .29
>They both run but have
>low compression and the leaking
>between the piston and sleeve.
>Just have a memeory from
>that old thread at Isky's
>that heating the piston would
>make it "grow" just a
>bit. Perhaps I'll just give
>it a shot and see
>what happens.

There is another technique that was outlined as well. I believe the piston was heated with a torch (temp unknown), then dipped in an oil of some sort. Both GMA and our host, Leonard, used this technique in the past. Apparently, after the piston was heated it had slightly expanded. The oil quench helped keep the piston at its now very slightly larger diameter.

I may be wrong on some of this. Perhaps Leonard can further elaborate.

Personally, I would hate to see a fine old OS 29 and Veco 29 get wrecked. This are good engines - and they aren't making them any more. I would consider getting them chromed.

Another thought (if you are in the mood to experiment) would be to nickel plate the pistons. While it might not last as long as chrome, it might also do the trick.

I think the thread ran at Isky's, but could have been on the Engine shop at RCO when George still was the moderator. The gist of the thread was heating the piston to about 400 degrees, which would cause the iron piston to "grow" somewhat, then quenching it in dirty motor oil to fill the pores and preserve the oversize. George EMPHASIZED that he would heat the piston by setting it atop a 4" square piece of 1/4" thick steel plate and then heating the plate with a torch. No direct application of torch to piston. He also emphasized that the effect would improve things by a SMALL increment and would have a relatively short life. Sort of a last gasp for that favorite engine if no other options exist.

Cary,
If you haven't already tried it, run the engines with a fuel that has a high castor content ~29% and NO synthetic. Sometimes the castor varnish will supply some additional compression. This used to be one of the selling points of Fox Superfuel.

While GMA did in fact grow some pistons a (very little) bit bigger, it doesn't sound as if this is something a person should be experimenting with. For one thing, heating a chunk of steel with a torch is interesting, but how does one control the heat?, know when the temp is just right?, know for how long to keep the piston at a certain temperature?, etc. I did once ask GMA about the heating process and he told me my oven wouldn't get hot enough, "Forget it, send me stuff and I'll fix it."

I don't know about this pipe-cutter deal, sounds really crude. But a very old trick to, in effect, making pistons bigger is to knurl them. I have a long-time Combat friend who (I believe) did this trick back when flying Fox motors. Please don't ask who, how, why, did it work, and so on.

I just know that knurling was a technique used in rebuilding worn industrial engines, even some automobile engines. Before my time, okay...

Only works on ringed pistons to eliminate piston slap. Old Flat Head Ford saturday mechanic talkin here...

So stick the piston in a lathe, cut a ring grove, make a ring and go fly.. Humm wonder if that might actually work....