Cox Piston/Rod Ball Socket Resetting

microflitedude wrote:
I don't have a reset tool, yet run my engines on a normal basis. What's going to happen?

Worst case scenario, the rod punches a hole thru the top of the piston. I've never had it happen, but have seen failed pistons. I think Kim has brought up an excellent subject for discussion since the ball/socket joint can be a point of failure or a contributing factor.

Let's back up and look at the some of the stresses the ball and socket are placed under. The top center portion of the piston is the hottest part of the engine. The only way heat can be removed is thru conduction to the edges of the piston or by heat loss on the bottom side from being bathed in a fuel/oil mix. Heat in the piston walls passes into the cylinder walls and the cylinder dumps heat by radiation and dissipation via the fins. While running, the piston rotates and the walls are also cooled by the fuel/air mix passing thru the bypass ports. But, the bottom line is that the ball joint functions in the highest heat zone. Lean runs raise the heat signature and further aggrevate the problem due to lower available lubricant.

In addition to heat stress, the joint is placed under some of the highest mechanical stresses in the engine. Unless the rod ball perfectly matches the piston socket, then pressure points exist where only a portion of the ball touches -- these areas eventually get peened away. I think the argument for high castor content fuels comes from the high film strength of castor oil, the high flash point and the ability of castor oil to maintain its lubricating properties in high heat environments. Film strength is a measure of how well a lubricant can keep two moving surfaces separated. The flash point is the temperature where lubricant vapor will ignite in an appropriate air mix. As castor oil heats up, it forms long chain molecules that actually improve the lubricating quality. Film strength and the ability to polymerize make castor an ideal lube in the ball joint area. Synthetics generally have a lower film strength, lower flash point and break down under high heat.

As an example of what happens when the ball loosens in the socket, make a fist with your right hand and cup your left hand. Take your right hand and push hard against the left, feeling how much pressure your left hand experiences. As the socket opens up, the rod ball is able to move away from the top of the socket. Rather than having your right hand (ball) against the left (socket), pull back about 4" and hit your left, again feeling the pressure imparted. Imagine this occuring 16000 times a minute and you can see that once the socket opens up, it doesn't take a long time for the rod ball to beat itself out of the piston. Castor oil, with its high film strength, can keep the rod ball and socket separated, but if the socket gets too loose, it can be pounded out.

Resetting the socket keeps the parts in close contact and lowers the chance of punching a hole in the top of the piston or of the rod pulling out of the piston.

There's lots of knowledge here -- some others may want to add how to check for a loose socket and how to effectively reset it.

Excellent examples/explanation! There's considerable debate over whether or not this is a concern for competition flyers who REALLY crank out the RPM's verses the sport flyer (like me) who just wants the maximum life from their engine. Most engines (one suggestion) flown by sport flyers might never need to be reset as the RPM's are not pushed and there is "Work-Hardening" that occurs at the joint to stabilize the things, or, at most just need to be reset one time after some break-in running. I've run Babe Bees for a decade or so with no resetting, and they seem totally happy, but they have a pretty easy life, also.

In recent years, I've reset pistons that had a VERY noticeable "Click!" when I held the rod and pulled or pushed on the piston. I can't honestly say that the reset improved performance, because I was also cleaning, changing gaskets, pick-up tubes, and the reed while I was in there poking around. To nail down a change's effect, you really need to isolate it by making only one change at a time and checking the results.

Still, I figure that it's GOT to better for two surfaces to be tightly fit rather than hammering themselves at 12,000+ RPM's...

I too ran Cox engines for many years without a reset tool, but then it was strictly sport flying, usually with a 6x3 prop.
I have read that for sport flying you should reset the ball socket after an hour or so of running. That should last a LONG time for sport flying.

If that is your situation, you might want to get someone who already has a reset tool to help you with your engines instead of purchasing your own tool. The reason is not frugality, it's because you may ruin a piston or two learning how to reset, especially if you are a bit ham-handed.

I got my .049 reset tool from DDD about twenty years or so ago and it has served me well. One VERY important thing about using a reset tool is to put the base on a hard surface like metal or brick that will withstand the hammer blows. Do NOt use the reset tool on something like a board because the board will absorb the force and the socket will not reset. This will cause you to use heavier blows, and you may damage the piston (don't ask). I think Cox International now sells reset tools. I don't know all the current sources.

George

Thanks George!

One of the posts on the .049 Collectors Group rightly recommends "lots of light taps" working around the socket, rather than a few hard taps. I forgot to mention the importance of having the reset tool on a hard surface. I use the anvil flat on my big bench vise.

Considering the age of some of mine, it would seem that a sport flyer's engines could probably last their entire career without resetting, but it DOES give me something else to do to make me feel like I'm taking care of business !

The also discussed the raised "bump" on the top of some pistons. I've noticed it on at least two on engines I own, and thought that they indicated impending disaster. Turns out that there are possibly lots of pistons manufactured that way, so at least one of my old war horses will be pulled out of it's box and put back in action!

I have both the davis diesel resetter that I bought years ago and one of Bernie's tools. I have used both and the CI tool is by far better. My davis tool wasn't machined that geat, I could see inconsistency's. Absolutely Light taps when resetting, you can overpinch that socket VERY easy and then you have a bound rod. I punch a hole in a piece of nylon strapping tape and strap the piston to the arbor so it cannot move. Everything is hospital clean before I start, all oil and residues are washed out from under the rod and socket area.

Once I reset one, I treat the motor like a NIB motor during break-in. A slightly rich tank (1 oz or so) of fuel, then back on the needle setting it had before.

A good, professional procedure !

I've used my reset tool from coxengines.ca on an anvil with a tack hammer. After about 75 light taps with no sign of tightening, I increased the force and finally got the rod to a minute click. Then it wouldn't go back into the cylinder. I did that to two of them, including my 1995 BW.

I was rebuilding a BW for my new Li'l Satan tonight and wanted to check the play, bit the rod wouldn't come off of the crank pin. It would come part way off, but I didn't want to scar anything up, so I quit and put it together, figuring it was probably okay anyway. Anyone ever had one stuck on like that?

[hijack]Off topic, but While I was building it, I wondered if a Dragonfly clunk tank would be good for this plane. I hate running out of fuel just as I'm getting good and wild. I always run out at the top of a loop or something and have no glide speed and crash nose first and brake the fuse. Maybe with more fuel I could finish the pattern. But that long tank may cause it to be too nose heavy. Opinions?[/hijack]

The play from the ball not being set properly will also effect the engine tiiming or that is what I have been told. Shouldn't matter for sport

George

[hijack]Off topic, but While I was building it, I wondered if a Dragonfly clunk tank would be good for this plane. I hate running out of fuel just as I'm getting good and wild. I always run out at the top of a loop or something and have no glide speed and crash nose first and brake the fuse. Maybe with more fuel I could finish the pattern. But that long tank may cause it to be too nose heavy. Opinions?[/hijack]

When I get home, I could put one on a scale and see how much weight it would add...and there's the option of using a plastic backplate and external tank. Think I've got a dragonfly tank if you need one.

RknRusty wrote:I've used my reset tool from coxengines.ca on an anvil with a tack hammer. After about 75 light taps with no sign of tightening, I increased the force and finally got the rod to a minute click. Then it wouldn't go back into the cylinder. I did that to two of them, including my 1995 BW.

Opinions?[/hijack]

RknRusty,

What you describe is often a result of not having a substantial HARD surface under the piston. When this happens, the force from the hammer is transmitted through the tool, through the piston, through the base, and is then absorbed by the softer surface. This causes you to need harder hammer blows which can cause the piston to "mushroom". I did that once to a Texaco piston. Fortunately, I was able to lap it back into the cylinder.

This may not be your case, but something to watch for.

George

Kim wrote:
[hijack]Off topic, but While I was building it, I wondered if a Dragonfly clunk tank would be good for this plane. I hate running out of fuel just as I'm getting good and wild. I always run out at the top of a loop or something and have no glide speed and crash nose first and brake the fuse. Maybe with more fuel I could finish the pattern. But that long tank may cause it to be too nose heavy. Opinions?[/hijack]

When I get home, I could put one on a scale and see how much weight it would add...and there's the option of using a plastic backplate and external tank. Think I've got a dragonfly tank if you need one.

Just drill out the venturi to BW specs.

kaplang wrote:The play from the ball not being set properly will also effect the engine tiiming or that is what I have been told. Shouldn't matter for sport

George

Definitely affects the timing and also you don't get the normal load of fuel pushed up thru the ports if that piston is stopping higher in the cylinder than it normally does.

A quick way I check is to nail a brad nail, or picture hanging nail to a wood board, then slip the rod over the nail,,pull the slack out and measure with digital slide calipers,,then push back twoards the nail and take that measurement to see where you are at. Not completely accurate, but it is a quick check.

You can take a new piston and rod assy and measure/check that as well using the same method.

gcb wrote:

What you describe is often a result of not having a substantial HARD surface under the piston. When this happens, the force from the hammer is transmitted through the tool, through the piston, through the base, and is then absorbed by the softer surface. This causes you to need harder hammer blows which can cause the piston to "mushroom". I did that once to a Texaco piston. Fortunately, I was able to lap it back into the cylinder.

Agreed. The potential for mushrooming a piston increases if you use a base that can absorb some of the hammer energy. I have an old railroad switch shoe that weighs about 30 pounds that serves as my base.

When the Sure Starts were being sold off for $6.99, I bought several lots -- the common opinion was that these engines were being cobbled together from any parts available. Most of the engines that I got needed cleaning and most had loose rod/piston joints. However, one batch had pistons "seemed" to be softer than any in the other batches. After resetting a number of joints, you can get a general feel for how much force is needed to set the socket. These did not appear to need as much force -- I had no way to measure the softness of the piston other than by feel (I might have had a senior moment).

However, of all the COX engines I've run across, more of the Sure Starts were in need of initial resetting than any other model.

andrew

andrew wrote:

gcb wrote:

What you describe is often a result of not having a substantial HARD surface under the piston. When this happens, the force from the hammer is transmitted through the tool, through the piston, through the base, and is then absorbed by the softer surface. This causes you to need harder hammer blows which can cause the piston to "mushroom". I did that once to a Texaco piston. Fortunately, I was able to lap it back into the cylinder.

Agreed. The potential for mushrooming a piston increases if you use a base that can absorb some of the hammer energy. I have an old railroad switch shoe that weighs about 30 pounds that serves as my base.

andrew

I have a old 75lb blacksmith anvil I use, no give or jump whatsoever. I use a gunsmith hammer with a machined hammer face that is perfectly flat. a claw hammer usually has a round face to the head, and can cause a glancing blow to the reset tool, and you can side pinch the socket to much,,which makes it garbage then.

Something else to watch out for is to make sure that what ever you set your anvil, vise, etc. on can not bounce or move. I have tried several different set ups that rested on the top of my tool box. Since the top of my tool box had some play I might as well been resetting the ball joint directly on the tool box. It took a few destroyed pistons for me to figure this out.

i have destroyed many pistons while resetting. I first got my piston reset too from cox many years ago. I remember when i took it with me to the field and while a couple other guys were flying, i thought i would reset my black widows piston since it would make a clicking sound every time i would turn it over. i took the engine apart and took out the piston. i put the piston in the holder and started to lightly tap it while turning it. the piston was loose when i started out but after about 5 minutes of tapping i noticed it tightening up. after another 5 minutes it had no play at all in it. I put it on the crankshaft and began to screw on the cylinder, the piston had a very tight fit in the cylinder. it was so tight i could barely turn the engine over. i figured i must have done something wrong so i took the engine apart and forcefully pulled the piston out of the cylinder to notice it had a slight domed and flared out top. after getting laughed at by all my buds, one of my friends said he had a brand new piston and cylinder for a Babe bee in his flight box so i bought the off him for something like 5 dollars. now that i think of it, i must have been moving around on the table and also it was a old wood picnic table.

Many of the other pistons were ruined the same way, sometimes i wish i would have left the dang things alone and replaced them when they failed, not cutting their life short with a damn tool

Carl wrote:...now that i think of it, i must have been moving around on the table and also it was a old wood picnic table... l

Carl,
That's the type of surface we were talking about that absorbs the hammer force and causes mushrooming. I'm guessing that many of us ruined pistons before we knew about using a hard surface.

I now use the flat surface on my big, old, ancient shop vise to hold the base of my resetting tool.

George