Cox aluminum piston?

Jason_WI Mon Feb 11, 2019 11:28 pm

Bought a babe bee with an advertised aluminum piston. Curiosity got the best of me and I pulled the BIN lever.

Is this something Cox experimented with? It looks professionally machined. Has a standard steel ball conrod and ballsocket in the piston.

1/2A Nut Tue Feb 12, 2019 7:39 am

How much does the piston and rod weigh? Was the ball socket fit good when received?

Jason_WI Tue Feb 12, 2019 9:12 am

The aluminum piston weighs 1.78 gram and the steel one is 3.05 gram. The ball socket fit is perfect.

Mudhen Tue Feb 12, 2019 10:20 am

Jason_WI Tue Feb 12, 2019 11:24 am

I don’t think it’s specific to any particular engine. It was from this eBay link. The aluminum piston is the only reason I bought it.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F292929953538

Mudhen Tue Feb 12, 2019 12:39 pm

EXModelEngines Tue Feb 12, 2019 12:50 pm

Forget exactly when they were experimented with but I believe it was in the late 70's and 80's. There were a couple versions, one like the one Jason had with the steel rod and aluminum piston and another with both aluminum rod and aluminum piston. The all aluminum version was not very durable from what I have heard, but the version with the steel rod worked well. I believe I have a small bag of all aluminum pistons somewhere.

Matt

balogh Tue Feb 12, 2019 2:35 pm

I wonder how the different thermal expansion of aluminum piston (higher) and steel cylinder (lower) will work out? I would expect that if the fit is as tight as with the stock COX piston/cylinder combo, the engine may tighten up when hot...if the fit is lose when cold, it may become well fit when hot, but then cold starting may become difficult. This metal combination in normal size engines is common but I believe the fit is lose and compression is maintained by compression rings rather than piston/cylinder fit dimensions.

Sorry for the theoretical approach, I know that real use in life will tell the truth more than theories.

Jason_WI Tue Feb 12, 2019 2:48 pm

The fit in the cylinder this engine came with was somewhat loose. I don’t have an accurate enough micrometer to measure the difference. Work has a laser mic but it’s kept in a locked temp controlled room.

KariFS Tue Feb 12, 2019 2:52 pm

That’s quite a weight reduction, I suppose much better than what was achieved with the lightened steel pistons. Probably good performance but short life... either because the expansion thing as Andras suggested, or the small end of the con rod getting loose quick.

It would be an interesting experience to see how fast would a Tee Dee or a Killer Bee run with a piston like that Eyebrows

1/2A Nut Tue Feb 12, 2019 5:29 pm

if used with the high performance crank the lower weight of the piston may balance out well enough
to provide a smooth running engine.

Matt if you have some and willing I would like to buy a few of the steel rod / aluminum piston versions.

Thank you! Small Cox Logo

Jason_WI Tue Feb 12, 2019 5:33 pm

Hard anodizing might help with engine life using these pistons but I’m not an expert in such things if that would be beneficial or ruin the piston fit.

EXModelEngines Tue Feb 12, 2019 6:02 pm

1/2A Nut wrote:if used with the high performance crank the lower weight of the piston may balance out well enough
to provide a smooth running engine.

Matt if you have some and willing I would like to buy a few of the steel rod / aluminum piston versions.

Thank you!

Only have a small handful of the aluminum pistons themselves, not assembled with the rod.

**Admin** Tue Feb 12, 2019 6:25 pm

It definitely looked like a Cox made piston when I first spotted it in the eBay listing. Had the same machining pattern in the top. After reading what Matt said, it sure seems to be legit.

Lower compression engines tend to start easier. So with an aluminum piston, it may start easier, and as it warms up, compression could increase to maybe the normal amount as with a steel piston. All in addition to the lighter weight.

Let me know if you plan to part with any of those pistons, even if un-assembled Matt.

**Cribbs74** Tue Feb 12, 2019 6:29 pm

I’d be down for a couple too... Eyebrows

1/2A Nut Thu Feb 14, 2019 7:49 pm

FYI guys I bought 3 from Matt will post results.

Matt said the steel rods are not connected to the aluminum ball socket, my plan is
to use a .09 socket reset tool to initiate the rod setting then finish out with the
.049 reset tool. If it works will post some results any helpful observations.
I will bench test with a Killer Bee clone engine I made up has all the lower end correct
parts but missing the piston and polished cylinder. I have a real KB can compare results
with my previous KB tests.

Oldenginerod Fri Feb 15, 2019 4:42 am

1/2A Nut wrote:
..... my plan is to use a .09 socket reset tool to initiate the rod setting then finish out with the
.049 reset tool.

It would take quite a bit of heavy swaging to fully enclose the socket, as opposed to just squeezing a couple of thousandths during a reset. My fear would be that the piston might distort with all that pounding.

coxaddict Fri Feb 15, 2019 6:06 am

Did some of the pistons with the circlip assembly have alloy rods?

Paulgibeault Sat Feb 16, 2019 3:33 pm

HI Jason,

I guess somebody must have put together a " one off " special for you. Alum. pistons were a failed experiment tried by Cox. (They wore out very quickly apparently).

I also obtained these alum. pistons off Ebay a long time ago. They polish up like a mirror so I made ear rings for my wife out of them!

Cheers,

Paul G.

[quote="Jason_WI"]Bought a babe bee with an advertised aluminum piston. Curiosity got the best of me and I pulled the BIN lever.
Is this something Cox experimented with? It looks professionally machined. Has a standard steel ball conrod and ballsocket in the piston.

1/2A Nut Thu Feb 21, 2019 4:00 am

Parts came in I went with a low compression head and thin walled cylinder
ground down cooling fins to reduce weight.

By doing so this .049 engine with prop spinner is the lowest weight
.049 I have ever owned, of course the aluminum piston assembly
has contributed to the effort. This engine is not much more weight
than a TD .020 or the Pee Wizzer. The engine can replace a .020
powered project that is lacking punch for just a bit more nose weight.

With my scale 1.9g vs 3.2g steel piston /rod.
All up engine weight is just 33.7g less spinner and prop.
Ready to run with a carbon 4x4.5 and TD spinner 38.7g!

When setting the steel piston rod to the aluminum ball socket use
the .049 reset tool and tap very light add oil to the socket first
light taps rotating the cupping tool every tap. Light taps like your
resetting a TD .010!

Compressing is good with a low compression plug which will help to put less stress
on the aluminum ball socket. Low mass prop such as a 5x3 will make a .020 plane
haul butt with possible unlimited vertical. Key is don't over load the over all setup,
avoid using with a heavy plane. Common sense can get some suitable lasting use with
the aluminum piston.

Oil the cupping tool end and piston footing to help avoid abrasion during the seating process.

EXModelEngines Thu Feb 21, 2019 2:18 pm

1/2A Nut wrote:Parts came in I went with a low compression head and thin walled cylinder
ground down cooling fins to reduce weight.

By doing so this .049 engine with prop spinner is the lowest weight
.049 I have ever owned, of course the aluminum piston assembly
has contributed to the effort. This engine is not much more weight
than a TD .020 or the Pee Wizzer. The engine can replace a .020
powered project that is lacking punch for just a bit more nose weight.

With my scale 1.9g vs 3.2g steel piston /rod.
All up engine weight is just 33.7g less spinner and prop.
Ready to run with a carbon 4x4.5 and TD spinner 38.7g!

When setting the steel piston rod to the aluminum ball socket use
the .049 reset tool and tap very light add oil to the socket first
light taps rotating the cupping tool every tap. Light taps like your
resetting a TD .010!

Compressing is good with a low compression plug which will help to put less stress
on the aluminum ball socket. Low mass prop such as a 5x3 will make a .020 plane
haul butt with possible unlimited vertical. Key is don't over load the over all setup,
avoid using with a heavy plane. Common sense can get some suitable lasting use with
the aluminum piston.

Oil the cupping tool end and piston footing to help avoid abrasion during the seating process.

Looks good! Let's see some tests and if they run well maybe something to experiment with in the future!

**Admin** Thu Feb 21, 2019 9:18 pm

1/2A Nut wrote:Parts came in I went with a low compression head and thin walled cylinder
ground down cooling fins to reduce weight.

By doing so this .049 engine with prop spinner is the lowest weight
.049 I have ever owned, of course the aluminum piston assembly
has contributed to the effort. This engine is not much more weight
than a TD .020 or the Pee Wizzer. The engine can replace a .020
powered project that is lacking punch for just a bit more nose weight.

With my scale 1.9g vs 3.2g steel piston /rod.
All up engine weight is just 33.7g less spinner and prop.
Ready to run with a carbon 4x4.5 and TD spinner 38.7g!

Really cool!

Replace the crankcase with a narrow neck case and cut the weight even more! Does the aftermarket "Killer Bee" cranks Matt n' Bernie offer weigh less than a stock crank? One of those might squeeze some more weight out of it too.

1/2A Nut Thu Feb 21, 2019 10:44 pm

Thank you gents Thumbs Up

yes true Jacob was wondering what the weight variance is.
Even after the least weight crank is selected I may need to remove some mass
off the flywheel side of the crank.

The crank weight is 4.5g:
Matt's site says:
Manufactured to Killer Bee Specs
Handles up to 30,000 RPM
Extra Hardened Steel Crank

This is good for all out power but in this case I need the least amount of weight.

Killer Bee

Stock

Jason_WI Thu Feb 21, 2019 11:15 pm

Those conrods that were sent have a thicker bottom than normal ones. They would be heavier and somewhat offset the lighter piston.

**Admin** Thu Feb 21, 2019 11:18 pm

What if one were to sacrifice an early 3-piece piston for it's aluminum conrod?

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