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Cox Engine of The Month
September-2020
sosam117's

"Traded an electric charger for this "Complete" (original) Cox Thimble Drome Olympic .15 engine. Right corner is photo as received."



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I want some of your old junk!

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Wanted I want some of your old junk!

Post  TexasWade on Thu Mar 29, 2018 11:12 am

Looking for maybe 3 or 4 extra loose .049 cylinder/piston sets to mess around with.  I want to do some experiments to see if I can tighten up the fit by either stretching the piston or shrinking the cylinder.  Hoping to do about $20 shipped to North Texas (76205)
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Wanted Loose Cox cylinders

Post  Paulgibeault on Wed Jul 04, 2018 6:24 pm

Hello there,

If you're still looking I have several excellent condition but too loose .049 Tee Dee & Black Widow cylinders.

Cheers, Paul G.
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Post  coxaddict on Thu Jul 05, 2018 4:54 pm

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)
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Post  Oldenginerod on Thu Jul 05, 2018 5:05 pm

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.
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Wanted Re: I want some of your old junk!

Post  1/2A Nut on Thu Jul 05, 2018 5:58 pm

Hey Wade whatever happened to the Hammer 010 project started on RCG did you ever get some vid of it flying?

https://www.rcgroups.com/forums/showthread.php?3058623-Hammer-010&highlight=hammer


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Wanted Cox Piston cracking

Post  Paulgibeault on Thu Jul 05, 2018 10:28 pm

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)
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Wanted Re: I want some of your old junk!

Post  coxaddict on Fri Jul 06, 2018 6:59 am

Thanks for the great info.  I Love This Forum!  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.                                          
  lol!
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Post  Paulgibeault on Fri Jul 06, 2018 11:58 am

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 Love This Forum!  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.                                          
  lol!
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Wanted Re: I want some of your old junk!

Post  coxaddict on Sat Jul 07, 2018 4:07 am

Thanks Paul, very informative and enlightening.
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Wanted Piston failure modes

Post  Paulgibeault on Sat Sep 29, 2018 12:52 pm

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)
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Wanted Re: I want some of your old junk!

Post  Mudhen on Sat Sep 29, 2018 4:43 pm

Cox needed both to case-harden the piston as well as being able to turn the socket around the ball on the connecting rod.
Any area that had copper plating would not accept the hardening process.
The copper left the socket malleable enough to spin it around the connecting rod.
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Wanted Re: I want some of your old junk!

Post  coxaddict on Sat Sep 29, 2018 5:05 pm

Thanks Mudhen,
The hardening process was Nitride hardening?
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