Pee Wee .020 - What years?

Hi Ron -
I uz mistook - no "Made in USA" on either older engine ("Thimble Drome" tanks), just the newest one, along with "Cox" on the backplate.
Screen may just be missing from one of the older two.

Here's a linc to Martin's web pages on Pee Wees

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

Linc does not take you directly to page I was on. Click on "BEEs" on left hand menu, then select "pee Wees" on upper portion of screen.

Marleysky wrote:Here's a linc to Martin's web pages on Pee Wees

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

Linc does not take you directly to page I was on.  Click on "BEEs" on left hand menu, then select "pee Wees" on upper portion of screen.

Thanks - good info!
I found this thread, with Mark B. explaining all things Pee wee ( ):
https://www.coxengineforum.com/t9250-how-many-kind-of-pee-wee-cylinders-were-produced

Hi Terry, Good to know that you're having some fun running your engines! How'd they "start" for you? I see that the one with the needle-extension has a starter-spring. What are you running in them for fuel? Prop-size?

Any thoughts on models for any of them? You'd only need a 50' circle for a nice little C/L profile airplane.. (hint hint..) maybe a little sheet-wing Ringmaster for the upcoming fly-a-thon....

Something like "this".. only scaled-down a bit to around 18" span.. like the Carl Goldberg "Swordsman".

roddie wrote:Hi Terry, Good to know that you're having some fun running your engines! How'd they "start" for you? I see that the one with the needle-extension has a starter-spring. What are you running in them for fuel? Prop-size?

Any thoughts on models for any of them? You'd only need a 50' circle for a nice little C/L profile airplane.. (hint hint..) maybe a little sheet-wing Ringmaster for the upcoming fly-a-thon....

Hi roddie -

I was very surprised that they hand-started fairly easily, 'though slapping the prop rather than flipping.
Cox 4.5x2 on my 23.5 N/22 O homebrew, the 2 older (well-used) turned ~16k, other ~17.5K.
Need to get a tool to reset the piston on that last one.
Biggest problem is loose, sloppy needles, but tank capacity doesn't allow for much fiddling.
While they do well for F/F, I had in mind to post separately about whether it was worth the trouble to try 'em on C/L, model suggestions, etc.

Terry, regarding the engines with loose/sloppy needles... try omitting the spring and "sleeving" the exposed needle-threads with small-size silicone fuel-line.. with a flat-washer above. You'll need to find a flat-washer that's the right size.. and you have to cut the fuel-line sleeve to a length that seals within the range of operation. This can take a couple of tries.. but you'll know when it's right.

Paul Gibeault shows this adaptation to the center-backplate in this photo.

Yes, I've done that to my .049s.
Had so much fun just running 'em I didn't have time this evening to do the Pee Wees.
Tomorrow I'll do that and rebuild kits.

Another inherent thing (some may call it an issue) with the pee wee engines is the conrod length, or deck height of the piston. This really varies a lot, I wrote about that in another thread somewhere...

These differences in deck height means that one cannot simply use the same fuel and number of head shims, and expect a similar performance. Instead each engine has to be set-up for the length of the conrod it has been given. If the SPI is too large one can shim under the liner, while of the piston sits too low, one can remove a bit of material from the head in order to have a proper compression ratio.

Below are two pictures of two different pistons in the same engine:





Here is also one head where I have removed about one head-shims worth of material from the sealing surface (and some from the lowest cooling fin to avoid it hitting the cylinder top). This also helps on lower nitro fuels, I'm currently playing around with 10% nitro and it seems quite okey actually.

Not sure I want to attempt adjusting SPI/deck height, Kris, but the newest one turns the Cox 4.5x2 (23.5 nitro/22 oil) @ 17.5K and I discovered it has no head gasket, so I tried the 2 older ones without and they both now turn 16.5K.
Good enough for now.

Those are good numbers.

Do you see any difference in the amount of SPI between the different engines?
That is perhaps the easiest way to spot any deck-height differences...

I measure .012", .014" and.018" SPI, Kris, but also have loose rods in the two larger.
It may mean nothing but greater SPI corresponds to higher rpm in these bench runs.

With greater SPI you have a higher compression ratio, unless it is a measuring error from a sloppy balljoint, as the length of the very piston is identical. So I'm guessing the older engines have a worn piston balljoint, and these could then benefit from a smaller head volume. If you have access to a lathe it is really only a 5 minute job.

Another way to do it would be to grind on the crankcase top in order to lower the whole cylinder, but I think it is better to rework the head. If you overdo it on the head you simply add head shims to get back, while the crankcase mod is irreversible.

When I checked a few of my brand new spare piston I also saw a great variation, so it is no only wear but possibly a fabrication problem. It seems they where not very accurate when they made the assembly. This could be a machining problem, it is not that easy to make two matching spherical surfaces in a lathe.

Since there is looseness in the rod sockets, I need to tighten those before considering any surgery.
Maybe the dole elf can bring a reset tool soon.

wha-tah-hey wrote:Since there is looseness in the rod sockets, I need to tighten those before considering any surgery.
Maybe the dole elf can bring a reset tool soon.

Maybe someone here has a .020 socket reset-tool that they'd be willing to lend-out. Cox International does stock the tool if you don't have one.. and want to source it to always have on-hand. Where you have these three recent engine-acquisitions; I would..

https://coxengines.ca/cox-.020-piston-reset-tool.html




I have the .049 reset-tool. It's a good tool to have on hand.

I have the .049 tool also, roddie.
I bought these Pee Wees about 30 years ago when I was working.
I'll get an .020 tool but "available hobby bucks" don't always immediately coincide with the need/desire for a new goody.