hello, i just got started building a few pop pop boat models and have hit a little snag.
i started with a simple coil boiler, and i got it to work but i wanted something that actually "pop pop-ed" so i made a boiler from a ring of steel and 2 brass sheets all soldered together. it worked a few times and then kept springing leaks. so i took that one apart and found a new boiler, an Altoids Strips can. its tin and just the right size. so, i drilled 2 holes for the pipes, and trimmed the lid to be soldered on. i got it all together today and it worked for about 15 seconds and sprung a leak!
i had read that as long as there is water in the boiler, the solder shouldnt melt so could i be using too low temperature of solder? what do you guys recommend?

i also made a small oil candle to go with the boat as i didnt like using wax candles

thanks for the advise guys

I would have to assume that the solder yer using simply isn't up to the job. I happen to be in the brewery right now so I a quick run back to the work shop reviels that we use 95/5 lead free solder, or staysilv 15 silver brazing rods for the really hardcore stuff.
the fun part about the brazing rod is that you need at least a MAPP torch to get it going.

make sure to really scruff and clean all your surfaces. those tins have a plastic food grade coating and could be fouling your braze, use flux as well.

looks good so far!

Wecome to the world of Pop-pop Derk. Made a few of these years ago and much prefer the coil design for its simplicity. I have a commercially made Pop-pop(made in India)which actually pop-pop with a small candle but can't be heard more than a few feets away. Coil design can be made more powerfull with sterno fuel and multiple tubes.
http://www.nmia.com/~vrbass/pop-pop/
http://www.rcgroups.com/forums/showthread.php?t=1240012
http://www.sciencetoymaker.org/boat/index.htm

another thing I'm thinking derk?
while the tin it's self looks perfect, you might want to replace the lid with some brass shim stock. I'm also thinking that the the tubes should be on the "deep" side of the "boiler"

this is just from my observations of the commercial models. I've only ever built the copper coil types. and not very well.. the little guy I made, i did in a couple of hours between tank cleanings and transfers in the beer mines, but... this thread is getting me thinking...

bgnome, in the side view pic it sort of shows how the part of the tin the tubes are in is level when its on the water. so it shouldn't have any back flow issues... also, do you think a soldering torch would be up to brazing? it gets hot enough to make the brass glow red

Boilers filled with water (conventional style) are protected against solder melt. But boilers that contain little liquid water (flash boilers & PopPop) may not be protected. Pop Pop boilers don't contain more than a few drops water during operation, and that eventually disapates with most boats. When the last drops leave, the boiler will overheat wrt soft solder.

like brooks said Derk. I think you would do better with a new tin, and the tubes put in the deep end. this is a flash boiler of sorts, and it basic function is to flash steam the water in the "boiler" where it explodes out, the drive tubes being cooler and the 'boiler" evacuated causes water to re=enter the system to repeat the process. the benefit of the diaphragm system you have here is the bi-metal diaphragm gives an extra push as it deflects, and draws the water back in as is reflexes..

that's a simple way of putting it and I'm sure someone more experienced will correct me.. but that's the gist of it.. this is also why I believe, and once again. folks, please feel free to correct me, that the flash tube is more efficient, because it does not require the mechanical push back of the diaphragm, the coil is simply flash boil , push condense, draw, repeat.

it just doesn't have the cool pop=pop sound that that diaphragm type boiler does

but as brooks pointed out.. this type of boiler pushes out the majority of its boiler water in its power cycle. so more often than not.. that thing is dry.. so .. yer working for a few power cycles before the heat catches up with you then BAM! critical failure.

so.. what I would do.. and someone else may come around and tell me I'm full of it.. I would get a new tin, because honestly? the body looks perfect. rotate the tin to the deep end for the tubes, replace the lid of the tin with brass, and giving that brass a bit of a up bend would not hurt.. then hot solder the whole thing with 95/5 plumbers solder, flux everything, and a propane torch should melt you in good.
bleed that solder in like you were doing a pipe fitting.. because, well.. you are..

once again.. its just how I would do it, and I'm still an idiot for most of this stuff, so someone might come back and correct me if I messed anything up, but that's what these forums are for..

looking at your pics of the original. to ME.. it looks like yer trying to do the job with rosin core electrical solder and a 40 to 100 watt pen iron..

once again.. not trying to offend, but if thats the case? then that's why its blowing out. 95/5 will melt and weep with a propane torch.. with metal thickness yer dealing with? keep the flame low and tight and try to heat up only the areas you need to. MAPP burns nice and hot, and can easily blow out that tin., you could probably even get away with using a butane micro torch, hell, even better would be a oxy acetylene with a micro tip.
but the temps and pressure involved? rosin core electrical solder is just not going to cut it, the melt temp is far too low, a sterno flame will melt that stuff, i have first hand experience on that.
good luck! and I intend to take my own advice

You could also try doing a rolled edge seal with silicone RTV around the seal and only hard soldering the tubes as they go into the boiler. The silicone RTV should be able to handle both the flexing and the heat of the boiler.