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Has anyone tried those "Cox .049 Piston (Aluminum)"? Babe_b10
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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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Has anyone tried those "Cox .049 Piston (Aluminum)"? Empty

Has anyone tried those "Cox .049 Piston (Aluminum)"?

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Has anyone tried those "Cox .049 Piston (Aluminum)"? Empty Has anyone tried those "Cox .049 Piston (Aluminum)"?

Post  sosam117 on Wed Aug 05, 2020 12:43 pm

I was wondering "if" someone has tried those  cox .049 aluminum pistons?
How do the work. Or how well do the work out?

I received two of them from EX Model Engines in my last order.
Just want to know if someone has tried them in a engine and how well do they work?

If someone had a good experience with them, I might try them in a Cox Jr. Texaco engine?

Thanks,
sosam117

Photo borrowed from EX Model Engines' website.
Has anyone tried those "Cox .049 Piston (Aluminum)"? Cox_0411

More photos of the Aluminum piston (mine)
Steel connecting rod
Has anyone tried those "Cox .049 Piston (Aluminum)"? _049_a10

Under side of piston -- ball and socket connection to steel con rod.
Has anyone tried those "Cox .049 Piston (Aluminum)"? Cox_0412


Last edited by sosam117 on Wed Aug 05, 2020 2:21 pm; edited 1 time in total
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Post  balogh on Wed Aug 05, 2020 12:57 pm

I think Brad aka 1/2ANut has tried it but I am not sure with what result. From a pure physical standpoint IMHO  a ringless piston is better made of the same material as the cylinder because of the different thermal expansion properties of metals. Aluminum expands more when hot than steel, so in order not to freeze an aluminum piston in a steel cylinder the latter shoud have slightly larger diameter so that at hot running conditions the piston and cylinder fit should be just right.
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Post  getback on Wed Aug 05, 2020 1:05 pm

sosam , did you get one and did it come with the rod detached ? It was Brad that did the test and i think he had a fair experience with it >Nothing Great < He is into performance and speed so , i got a couple myself but haven't did anything with them Yet LOL He will probably see this and bee on i can't recall the thread or where aboust it was in it . Small Cox Logo
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Post  happydad on Wed Aug 05, 2020 1:23 pm

getback wrote:sosam , did you get one and did it come with the rod detached ? It was Brad that did the test and i think he had a fair experience with it >Nothing Great < He is into performance and speed so , i got a couple myself but haven't did anything with them Yet LOL He will probably see this and bee on i can't recall the thread or where aboust it was in it . Small Cox Logo

getback: weren’t the original Cox pistons made from a hardened aluminum with a beryllium coating on the piston top?

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Post  Admin on Wed Aug 05, 2020 1:38 pm

Up until about 1956 (I'd have to check my notes), the connecting rods were aluminum.

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Post  balogh on Wed Aug 05, 2020 1:44 pm

COX pistons have always been made of steel except the early light alloy  rods. The inside and top of the piston were copper coated to prevent carbon infusion (causing carburizing hardness:https://blog.metlabheattreat.com/posts/nitriding-and-carburizing/ ) into the copper  clad parts as it was only the outside wall of the piston,left unclad, that was hardened then ground and polished.
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Post  sosam117 on Wed Aug 05, 2020 2:23 pm

getback wrote:sosam , did you get one and did it come with the rod detached ? It was Brad that did the test and i think he had a fair experience with it >Nothing Great < He is into performance and speed so , i got a couple myself but haven't did anything with them Yet LOL He will probably see this and bee on i can't recall the thread or where aboust it was in it . Small Cox Logo

getback,
It came with a steel connecting rod attached.
Ex Models Engines are selling these.

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Post  1/2A Nut on Wed Aug 05, 2020 4:41 pm

Matt only had so many aluminum rods on hand when I bought mine.

You have to run low rpm good and rich first for 1oz of fuel.
2nd run up the rpm some another rich oz thru the engine.
3rd run up you can peak the NV then back off 1/2 turn.
4th can be near peak if you have a good castor mix in the fuel.

Reset the piston rod before running it any further at which point
you can go fly the engine. Do not use a 6x3 prop the ball socket
can't really last long if you put that much load on it.
Recommend if Cox props: 5x3 / 4.5x4



Cox Aluminum Piston and Rod Bench Test Break In .049
3 short runs prior to this one aluminum surface was
dusting off small particles as it seated into it's thermal
harden surface state.

If leaned up too much it expands to the next level
of heated state subject to binding enough to shut down as
demonstrated during this bench run.
Will require patience with some rich runs till fully broken in.
Grish 5x4 used 25% nitro / 20% castor.

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Post  Iceberg on Wed Aug 05, 2020 7:41 pm

I don't know about EX models Aluminum pistons. Mat is awesome seller so no doubt they are good.

However a few years back I did get one aluminum piston in a lot sale I purchased on FleaBay. I tried it and it didn't really have much higher RPM. I feel that it wore out much quicker too than the normal piston. Worked good for about 5-10 runs then seemed to lose compression. However I would not personally comment on any new ones being sold as they might be much better. I seem to remember posting a similar question on the Forum when I did the testing a few years back.

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Post  GallopingGhostler on Wed Aug 05, 2020 10:52 pm

Hijacked FYI, there may be a scientific reason why the Cox aluminum piston, although a novel idea at the time would probably not work for longevity.

See https://www.engineeringtoolbox.com/thermal-expansion-metals-d_859.html

Materials shown are not necessarily the exact ones used but close enough for illustration purposes):

Thermal expansion units are in 10-6 in/(in DegF). This is millionths of an inch change per inch of material per Degree F.

Piston:
Ductile Iron, A536 (120-90-02):  5.9 - 6.2
Aluminum: 13.1

Cylinder:
Mild steel:  5.9
Yellow Brass: 11.3

Iron is closely matched to steel, why most older model engines were iron piston in a steel sleeve.

Aluminum is closely matched to brass, why newer model engines were ABC (Aluminum piston running in a Brass sleeve that is Chrome (or nickel) plated.

Unless the piston is ringed (where piston/cylinder fit can be loose), given the differences in expansion between steel and aluminum, it would not be hard to imagine encountering the loss of compression by aluminum forced erosion against the steel sleeve due to expansion when running very hot.
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