Re-setting a piston?

How does it work? Is that only for the 3 piece pistons?

It's only for the 1-piece pistons as used in all Cox .049 engines. Instructions are included with the tool.

I've seen the subject debated. The only time during the rotation when there isn't force keeping the rod and the piston tight against each other(by compression and friction during the upstroke through TDC, and by expanding fuel gasses and friction during the downstroke) is at the transition at BDC. If the socket spreads, it seems like this might be where it happens. When it opens up, there is then more room for lateral movement of the ball in the socket. In extreme cases, that lateral movement can wear through the crown and punch a hole in the piston top. That lateral motion is also wasted energy that would otherwise be used to move the piston.

Well there you go, answers came in while I was writing that up.

Holy crap! I just accidentally clicked on the minus sign on the right hand margin of Rusty's reply! I humbly apologize sir!

lousyflyer wrote:Holy crap! I just accidentally clicked on the minus sign on the right hand margin of Rusty's reply! I humbly apologize sir!

I just chipped in my vote to help "green him back up"!

WingingIt74 wrote:Why would you need to?

Several things affect the ball socket. First is high RPM by using a small prop and high nitro, and second is high temperatures from combustion. The top of the piston is probably the hottest spot on a running engine.

If you get a lean run, heat increases and lubrication in the ball socket can break down, especially if you use synthetic lube found in many fuels. If the lube reaches flash temperature, lubrication fails and you get excessive wear.

To lessen this, have some castor lube in your fuel (gums up instead of burning) and try to not run over lean.

The harder you run the engine, the more you need to reset.

George

Kim wrote: [I just chipped in my vote to help "green him back up"!

Me too.

George

lousyflyer wrote:Holy crap! I just accidentally clicked on the minus sign on the right hand margin of Rusty's reply! I humbly apologize sir!

Why you lousy... Just kidding. Not a problem. Thanks for the green, Kim.

gcb wrote:

Kim wrote: [I just chipped in my vote to help "green him back up"!

Me too.

George

Me too.

Bob

Yeah...uh...don't try to reset the rod on a three piece cox piston. The results are disastrous. Don't ask how I know this. (Poor little piston never stood a chance)

In my own defense, I had no idea that it was a three piece piston when I destroyed it. I had never seen a three piece piston before.

What really was tragic is that it was the first time I ever tried to reset a cox piston, and I was so proud of the new tool that I just had to try it out.

lousyflyer wrote:Holy crap! I just accidentally clicked on the minus sign on the right hand margin of Rusty's reply! I humbly apologize sir!

I gave ya a few for owning up..........

Also to piggy back on Rusty's comment. If the ball is not reset periodically you get a flat spot on top of the ball. This isn't a huge deal until you go and reset it and then........Egads! I no longer have SPI

cribbs74 wrote:Also to piggy back on Rusty's comment. If the ball is not reset periodically you get a flat spot on top of the ball. This isn't a huge deal until you go and reset it and then........Egads! I no longer have SPI

Yeah, I forgot about that. Either a flat spot on the rod or else you domed your piston. Check your SPI gap before and after. If it happens, I wrap the piston in tape, chuck it in the drill press and shorten it slightly as it spins with a small file.

I think there is another lenghty thread where we had some good posts on resetting pistons,,dang if i can find it tho'.

lousyflyer wrote:Yeah...uh...don't try to reset the rod on a three piece cox piston. The results are disastrous. Don't ask how I know this. (Poor little piston never stood a chance)

Again, me too!

Not only a 3-piece piston, I had used my .09 reset tool. DOUBLE DUMB!

George

gcb wrote:

lousyflyer wrote:Yeah...uh...don't try to reset the rod on a three piece cox piston. The results are disastrous. Don't ask how I know this. (Poor little piston never stood a chance)

Again, me too!

Not only a 3-piece piston, I had used my .09 reset tool. DOUBLE DUMB!

George

Ouch! Talk about a hard lesson.

cribbs74 wrote:

gcb wrote:

lousyflyer wrote:Yeah...uh...don't try to reset the rod on a three piece cox piston. The results are disastrous. Don't ask how I know this. (Poor little piston never stood a chance)

Again, me too!

Not only a 3-piece piston, I had used my .09 reset tool. DOUBLE DUMB!

George

Ouch! Talk about a hard lesson.

But a GREAT Christmas Tree Ornament !!!!!!

Kim wrote:
But a GREAT Christmas Tree Ornament !!!!!!

Tell folks it is a tiny bell that you cracked while ringing in the New Year.

andrew wrote:

Kim wrote:
But a GREAT Christmas Tree Ornament !!!!!!

Tell folks it is a tiny bell that you cracked while ringing in the New Year.

"Every time a Piston cracks, an Angel gets their wings"!

Kim wrote:"Every time a Piston cracks, an Angel gets their wings"!

Two thumbs up on that one!

George