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

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 .

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

Happydad

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

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.

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 .

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

sosam117

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.

 

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.

Ice

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.

M'y test subject is a .049 cylinder no3  Venom black widow? Not sur is a two bypas no boost port wit spi it has ben plated wit metal nickel piston fit Perfect wil test see if piston did god for crome plating as the crome piston To nickel métal is bad plating on cylinder Not Good for oem piston

davidll1984 wrote:Not sur is a two bypas no boost port wit spi

It is a standard Black Widow cylinder.

davidll1984 wrote:M'y test subject is a .049 cylinder no3  Venom black widow? Not sur is a two bypas no boost port wit spi  it has ben plated wit metal nickel piston fit Perfect wil test see if piston did god for crome plating as the crome piston To nickel métal is bad plating on cylinder Not Good for oem piston

It looks to be fitted with an OK Cub head, although the OK heads which fit a standard glow plug are the same as the early small diameter Cox heads, so shouldn't fit the cylincer that's shown. The OK glow head, as fitted to the later models OK Cubs can fit a standard later Cox cylinder, but your picture shows a larger thread Cox cylinder with a smaller thread OK head??? Unless of course it is a later OK glow head that has been drilled and tapped for a plug.

Glow is late model plug tink Not Perfect it run y dont no the year of have them from old man like 10 years from now it was parts wit couple complète engines 1 engine was runing exceptionnel rpm low compression so just want To bring back To work m'y old engine

Test was using standard glow plug runing on smal tank from m'y oem ez bee engine plastiques back plate try To run low rpm without runing To hi after run oil look light black color tink is normal for 1 run

Ok piston test on m'y plated cylinder y use ring To rc engine it help engine Not To rpm To hi during.brakin période use smal tank reduce runing time y did couple chort run wit rc ring play wit rpm range entire run let it cool during slow rpm change neadle litle To cool piston as mutch posible no change in compression after 3 run wit ring look Good tink cylinder now realy look like glass inside cylinder piston looks polished To no overheat line mark m'y first test without rc ring on engine first test after hi peak rpm drop over heat felt like piston sizing in cylinder from expansions of piston To fast y tink for best result wit aluminium piston use rc ring let engine time To heat litle befor max rpm raeched  litle fuel réserve low flight time wil help préserve engine piston cylinder tink engine redy for run

My humble opinion is - as others here already explained - that ringless aluminum piston in a steel cylinder is a suicidal combination because of the larger thermal expansion coefficient of aluminum than steel. For a reasonable compression a ringless piston needs a good fit in the cylinder even when cold. Heat may lead to the piston stuck or heavily rubbing the cylinder when hot, causing accelerated piston wear. I am not sure what material combinations e.g. the latest NV engines with ringless Revlite aluminum piston have? Maybe aluminum both? At least the nagnetic tip of my screwdriver does not attract the cylinder so it may well be aluminum.

My early NV 049 engine manual states the lifetime of the engine is not less than 6 hours....what???? My most used COX TD051 is past 300 hours on its clock and is alive and kicking...

Yes Balogh its true that for very hi rpm performance engine like Venom tee dee and Most hi performance engine using aluminium piston is Not Good for them unles if piston have ligned inside cylinder and becom useles than like y did wit m'y  plate nickel inside cylinder after Good hand laping of piston To new nickel métal cylinder piston react bether use of rc ring help retain heat on cylinder also help wit thermal exchange  wit cars cylinder is best for som reason Not sur how the cox .15 mark ||| aluminium piston cylinder is made of but tink is the Most powerful engine cox build in .15 size informations on its cylinder enyone ??is piston last long ??

Dave, as per the spectreflight engine test site the Conquest and Special Mark III 0.15 COX engines have cast iron piston, not aluminum.

http://www.sceptreflight.com/Model%20Engine%20Tests/Cox%20Conquest%2015.html

Yes sory y was tinking its piston was cast aluminium its me read To fast  just its look its confusion me
m'y bad sory

Wil continue expérience wit cars engine setup for try

When I ran into these pistons a while back, I believe they turned out to only be around 18%Si. To run in a steel bore you really need to be up around 60%Si. Could run them in a plated brass cylinder. A bit too soft to run in an AO bore like the revlites. When I did AAO Cox based hardware I had to go up to 30%Si to get any kind of life.

Which cylinder is plated brass y remember somewhere read Somting like cylinder color change after bath for clean up brass like color . m'y cylinder is plated wit nickel ??? Non sur if its heat expansions is ok compare To its piston somhow piston react Good wel bether than crome plated piston which over heat trade métal like balogh say it wil hapen after couple test on part just piston plated its ok in oem cylinder tink ice cold fuel help To cool piston litle engines run coold . weel Not very hot y can say plated nickel cylinder may have change Somting ?? How long was maximum life on aluminium piston in oem cylinder???

I never ran one on a steel bore. I made my own brass cylinders and plated them.....never again. Plated steel will not have the right COE and the 18% piston will run tight when hot, and be loose when cold. Not a good situation to be in. Best bang for the buck that I ran into, was to re lap the steel bore with a double taper, and fit a cast iron shell style piston with a threaded in aluminum pin carrier and an aluminum rod. Fitted with a killer bee crank, and mecoa diesel head, it makes a fine little sport diesel.