Resetting Cox 049 piston/rod ball joints

In getting ready for "Kids' Combat", which spec's reed valve 1/2A engines, I found one of my Black Widows had a piston/rod joint that was pretty loose. Now last August I had ordered a reset tool from Cox, but it showed up with a note that it was the wrong size, that they had none for 049's but that it would work. The socket part of the tool looks like it would fit an 09 piston, maybe a 15, however the reset tool itself fit around the rod just fine.

The result...the joint tightened up nicely...but what I feared might happen did. The piston head mushroomed. It will go up the cylinder until it hits the top of the exhaust port, and HIT it does.

A Cox tech advised me to throw the tool away, and said, "Of course, it would mushroom the piston. It's the wrong size socket." Unfortunately, they still have none of the 049 size, and they may never make them again. I have no probem with the way Cox has handled my problem. They are making up for the damage and my screwing around with it all, so I'm pleased, except that I wish they could supply the proper tool.

Question...does anyone have one of these animals he'd like get rid of? Does anyone have a suggestion on how to reset the joints without the right tool and without damaging the piston?

Kustom Kraftsmanship ought to have them. Davis Products used to make one, also. Both advertise in Model Aviation and Flying Models. I have an extra 09 tool but no extra 049 tool. The ball joints do need resetting from time to time, else the rod will come out through the top of the piston.

I have two, one with and one without the recepticle for the piston. If you set the piston on a piece of wood and don't hit the thing too hard, it may be OK without the rest of the gadget.

Now, true confessions. I used the "without" tool and reset a piston on an old, nearly worn out, Black Widow. Taking the philosophy to heart that "if a little is good, a little more is better" I set the rod, then hit it one more time after it was set, all the time with the piston sitting on a metal plate. The result was, it grew.

Undaunted, I lapped the now larger piston to the sleeve and the result was one of the best running .049 engines we have. I found out you can actually "fix" an old worn out piston/sleeve assembly this way. However, I would recommend it only for a worn out set that was going to be discarded, because if you mess up in the lapping process you could be worse off than before.

However, with your present set-up, it could be worth a try. Just remember, use fine lapping compound and lap the piston backwards up the sleeve.

Leonard, is the lapping motion up and down, or what?

You need to rotate it, while working it up and down. Use a very fine compound and only enough to get the piston to fit. Any more and you might have to "reset" it again. By working it up backwards, you end up with the tighter fit at the top. All you need is enough so the piston can go up and down under pressure. A little running will "break it in" again.

Denny,
I got one of those Cox resetting tools as an apparent "freeby". It was in the box with a Cox engine I bought new. This was about the time Cox moved.
My feeling is that since the instructions said it was for an .02, .049/.051, and .09, it should have come with three reset tools with the base, and possibly a couple of base inserts of the proper size. Since I never saw these advertised, I'm not sure. I do know that the reset tool says .09 on the side and there is no way you could use it on an .02.
It appears that the .09 reset tool hits the side instead of the center when used on a .049 piston. You are lucky you did not split the piston (ask me how I know).
I have a good reset tool I got from Davis years ago. I don't know if they still make them.
George

Thanks for all the help...everyone. I'm going to check with Kustom Kraftsmanship and Davis Products, and I may give Leonard's lapping a try, as well.

I hate to sound stupid, but will someone tell me how to lap the cox ball socket piston into the sleeve from the bottom??? Especially by rotating the piston? How do you hold the piston to get it to rotate? The rod will spin in the piston before the piston will rotate in the sleeve. Am I missing something???
Bigiron