I want some of your old junk!

Hi Paul,
With all your experience with Cox engines, ever have a piston crack? What is the science to copper plating the top and insides of the piston?
Thanks
Agustin (coxaddict)

coxaddict wrote:Hi Paul,
With all your experience with Cox engines, ever have a piston crack? What is the science to copper plating the top and insides of the piston?
Thanks
Agustin (coxaddict)

It's my understanding that the copper plating prevents those areas from being hardened during the chemical hardening process. This ensures that the ball socket is soft enough to be swaged after the piston is hardened and ground.

Hi Augustin,

About the ONLY Cox pistons that I recall cracking were the 'lightweight' Venom pistons. On those the entire crown would crack & separate from the rest of the piston.
My 'cure' was to change to the heavier standard TeeDee piston & the problem vanished.
I really don't know about the copper plating. Sadly, most of the people that do have already passed away...

Cheers, Paul

coxaddict wrote:Hi Paul,
With all your experience with Cox engines, ever have a piston crack? What is the science to copper plating the top and insides of the piston?
Thanks
Agustin (coxaddict)

Thanks for the great info.    I understand that the Venom pistons were lightened in excess causing the piston failure. I wonder what the correct amount of lightening would have been.  Maybe I should do some crazy experimenting too,  although I don't have any badly worn cylinders. I've been saving single port No.2 stamped taper bore cylinders in the hope of one day getting enough skill and knowledge to cut a newfangled second port on the blank side.                                          
  

Hi Coxaddict,

You know, really I don't think the lightened (metal removal) from the piston is what caused the failure. What caused the failure was the incorrect tooling employed to do that particular operation.
Cox ended up using a sharp square cutter rather than a properly radiused tool.  The idea was right, but the production machining tooling was wrong.
The square cutter left a stress raiser & that was what set up the failure for later on.
I do believe that was the case because my original prototype Venom from Larry Renger continues to run strong even when running 70% nitromethane fuel,
which is the ultimate stress test. IF ONLY the production crew had followed Larry's directions on the drawing...their would be a lot more Venoms happily running out there today!

Cheers, Paul

coxaddict wrote:Thanks for the great info.    I understand that the Venom pistons were lightened in excess causing the piston failure. I wonder what the correct amount of lightening would have been.  Maybe I should do some crazy experimenting too,  although I don't have any badly worn cylinders. I've been saving single port No.2 stamped taper bore cylinders in the hope of one day getting enough skill and knowledge to cut a newfangled second port on the blank side.                                          
  

Thanks Paul, very informative and enlightening.

HI Augustine,

Yes, I have had pistons crack.
Most of the time its the complete top of the piston separates from the rest. This condition was predominately found on the original Venom pistons. I believe that was caused by bad / worn machine tooling leaving a stress raiser in that area. My original prototype Venom has never failed which is why I blame the incorrect tooling/process.

The other mode is when the con rod punches itself thru the top of the piston. Almost always this is caused by allowing the ball-socket joint to get too loose with continued high RPM running.

Sorry, I have no real knowledge about the copper plating.

Cheers, Paul

coxaddict wrote:Hi Paul,
With all your experience with Cox engines, ever have a piston crack? What is the science to copper plating the top and insides of the piston?
Thanks
Agustin (coxaddict)

.

Thanks Mudhen,
The hardening process was Nitride hardening?