B.J. Cicada build

[werowance]

Super nice work on the gas tank. Be proud!!!

Thanks Brian, the tank was a fun diversion.

got started on the carb body last night and things were going very well and quick to. got the whole body cut out and was threading the back of it and was to the point that I only needed about 1 and a half turns left when snap it rung in to. CRAP!:fan:. the D bit cut the inside taper very very well and the whole thing was going really great. a few things I think will help the next time.

1. use 2024 instead of the scrap unknown alloy I had
2. make the area that will be threaded a little smaller diameter. I used my cheap plastic thread gauge that also has bolt hole size's in it to but I could have gone down a little bit more and still had full threads.
3. possibly thread it first before I drill the full bore of the carburetor thus I am not threading a tube.

oh well, just glad this doesn't seem to be such a difficult piece to make. however this time im just going to source some 3/8 square stock so I don't have to cut it down to size just to get started.

also finished up the fuel tank by adding a cap. also wanted to experiment a little and come up with a paper gasket like you would fine in an older briggs and Stratton lawn mower engine gas cap. the metal syle gas caps. they are sort of yellowish/redish/brownish and are flakey brittle. yeah I know that's a lot of colors for a description and yes I am green brown color blind.
anyway for my testing I started with some card stock I get free from work. its a tad thicker than a Tide soap box and is plain card board with no printing on either side. I found some indian head gasket shellac at the car parts store and rubbed a little on it. when it dried it looked and felt almost exactly like the old brigs gas cap gaskets. will test it with a little gas to see if it will hold up.

anyway here are some pictures of the failed carb body and gas tank with cap.

 

[werowance]

Almost ready to attempt a start. Gotta go get some fuel and have company coming over in a few. Man I hope I can start this thing tonightView attachment ImageUploadedByModel Engines1422204069.416489.jpgView attachment ImageUploadedByModel Engines1422204097.456545.jpg

 

[werowance]

A few kick backs with a pop and some smoke coming from around a leak between head and cylinder and also have a leak around block and prop snout flange.

Well gotta stop and clean up for family

Hope to try again tonight

 

[werowance]

View attachment ImageUploadedByModel Engines1422212175.180336.jpgView attachment ImageUploadedByModel Engines1422212228.760867.jpg

 

[werowance]

Well, no luck getting it fired last night. got the leaks sealed up with some gasket shellac on the head and prop snout but still no fire. so last night I started shaving the head down a little as well as deck the cylinder top a tad bit to increase compression. didn't get finished with that though.

a friend also came over last night, he thinks I am using to much oil in my fuel mix. here is my recipe, what do you all think? is their any fuel that ignites at a lower compression ratio?

3 tablespoons of catrol 2 stroke racing oil
3 tablespoons of ether obtained by poking a hole in a mason jar lid and spraying the contents of a can of starting fluid through the hole with a wd-40 straw and allowed to sit for a while
4 tablespoons of kerosein.


also a note on the ether, after I emptied the can of starting fluid in the mason jar, about 5 mins later it started bubling like a can of soda after shaking it or like water boiling. it was about 40degrees in my shop at the time. was that the propane propellent separating from the either?

I left the lid on loose so it could vent that out some.

 

[goldstar31]

Me? I'd make a flywheel with a groove for a pull cord instead of a propellor. Not quite the question asked but a damned sight easier than flicking a prop.

Mind you, I doubt whether your so called ether was 100% ether.

Just a thought or three?

Norman

 

[werowance]

started using a battery drill to spin the prop last night just to see if I could even get any pops or smoke. im slinging fuel out the exhaust but no ignition.

yeah im positive its not 100% either. but its pretty much impossible to source either in the USA for home use. im sure if I was a commercial account or a doctor or something I could get the real stuff but all the meth/crack heads ruinded getting etiher for everyone.

but I may whip up a fly wheel to test with.

just found this on tower hobbies, pre mixed model diesel fuel, im going to buy a can of that to try as well.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXANCP&P=0

 

[goldstar31]

Meantime, has squirting a bit of 'neat' ether in the exhaust port been tried? Sounds obvious but well?

Norman

 

[werowance]

Neat ether? do you mean just starting fluid? yes I did try that.

 

[goldstar31]

Yes, I did mean that. You've got to watch that you don't 'bog' the engine with too much liquid but lubrication is not a concern because if it does fire , your next cycle should be what is in the carb.

From a long distance away, I suspect fuel first, then wrong metering on the needle valve. Here, I can be wrong as it is a long, long time since I had my knuckles wrapped on a prop.

Just knocked a chunk out of my ancient fingers removing chipped cutter blades on a wood branch shredder. I DO sympathise- been there.

Norman

 

[werowance]

still no luck last night trying to start it after shaving the head and decking the cylinder a little. I do have more compression but I don't think enough.

a few thoughts / questions
1. the piston going up - the bottom just clears the intake hole to allow fuel to be taken in from the bottom of the piston - is this correct?
2. the piston going down - it almost completely clears the exhaust hole just a little bit of the top of the piston can be seen - is this correct or close enough?
im worried I have intake and exhaust positions reversed.

3 as a test if I fill the compression screw hole with fuel, It will lock the piston and takes a good while to leak by. not sure how else to do a compression test.
4. tried pure ether sprayed in the carb with fuel turned off. no fire
5. the carb seems to work well, can adjust to just barely any fuel to fuel running out like crazy. from experience with other store bought airplane engines this is doing just like it should.

so if the intake and exhaust ports are correct then im probably left with just not enough compression right? thinking of putting some jb weld in the top of the contra piston where its counter sunk so that if there is blow by on the contra piston it will not have as much volume for air to compress hopefully increasing compression. what do you think?

I cant even get any more pops or kick back like I did on the first attempt. although I was pre-heating the cylinder with a plumbers torch. but don't want to do that with all the ether being sprayed around it and possibly not evaporated off yet when I re-heat it over and over during attempts. good way to burn down the garage and all. (already had a small fire yesterday is how I know. a towel put it out quickly didn't have to use extinquisher)

I am using a cordless drill for attempting to start, I should at least get smoke or pops using that shouldn't I?

 

[Jasonb]

Obvious questing do you have the drill in reverse as these engines run anticlockwise when looking at the prop end.

You should be able to adjust the compression enough by screwing down the contra piston screw

 

[canadianhorsepower]

1. the piston going up - the bottom just clears the intake hole to allow fuel to be taken in from the bottom of the piston - is this correct?
2. the piston going down - it almost completely clears the exhaust hole just a little bit of the top of the piston can be seen - is this correct or close enough?
im worried I have intake and exhaust positions reversed.

QUOTE]

this sound totaly wrong
when the piston is completely up the complete intake port must be open
and when the piston is down the complete port should be open also:hDe:

good luck

 

[werowance]

this sound totaly wrong
when the piston is completely up the complete intake port must be open
and when the piston is down the complete port should be open also:hDe:

good luck

CanadianHorsepower, thanks for the quick reply. looking at sheet 4 of these plans http://modelenginenews.org/plans/BJ_Cicada.pdf there is a .250 semi circle milled up the side inside the cylinder. it reaches almost center line to the exhaust hole. or at least what I call the exhaust hole. I thought that was for when the piston was on the down stroke it pulled gas in the intake and pushed it into the crank case, then on the upstroke it was pushed up that .250 semi circle to make to to the top of the piston then once past the exhaust hole it started compressing it.

so looking at the drawings the .125 hole is intake and the .157 hole is the exhaust right?

 

[Jasonb]

.125 intake. .157 exhaust.

As the piston rises it creates a vacuum in the crankcase so as it continues to rise past in the intake hole the vacuum will draw fuel/air into the crankcase.

As the piston drops it will compress the fuel air in the crancase until the piston is below the transfer groove so the fuel/air mix gets pushed into the cylinder at the same time as the spent fuel exits the exhaust.

As it goes up it compresses the mix in the cylinder while drawing in the next lot of fuel. Fires and goes down allowing that mix into cylinder and exhausting spent fuel and so on.

 

[werowance]

.125 intake. .157 exhaust.

As the piston rises it creates a vacuum in the crankcase so as it continues to rise past in the intake hole the vacuum will draw fuel/air into the crankcase.

As the piston drops it will compress the fuel air in the crancase until the piston is below the transfer groove so the fuel/air mix gets pushed into the cylinder at the same time as the spent fuel exits the exhaust.

As it goes up it compresses the mix in the cylinder while drawing in the next lot of fuel. Fires and goes down allowing that mix into cylinder and exhausting spent fuel and so on.

Thank you Jasonb, that means I have that correct so pretty much leaves compression right? I should fire on just raw starting fluid at worse case for at least a pop or 2 right if compression was good enough?

 

[canadianhorsepower]

Thank you Jasonb, that means I have that correct so pretty much leaves compression right? I should fire on just raw starting fluid at worse case for at least a pop or 2 right if compression was good enough?

just try spaying wd 40 in the intake track

 

[werowance]

had a little time to work in the shop this weekend and I am sad to say that the cylinder is tapered at both ends is why I believe I cannot get it started.

so I will likely make another cylinder. im going to try and see if I cant just get the taper out of this one but not going to waste a whole lot of time trying before I just make a new one. the next one im just going to ream it and then polish it

 

[canadianhorsepower]

I am sad to say that the cylinder is tapered at both ends is why I believe I cannot get it started.

thats sad,
I personaly don't like the fack that you are soldering that port:fan:
If you would to build another cylinder maybe considering a billet pieace
instead of soldering.

you can also try reaming it and make a piston to fit the new bore

good luck

 

[werowance]

on soldering that port, that's what the plans call for but I wonder if I shouldn't do the soldering before I bore it. wish the plans had procedures along with it. sort of like the kits from Hemmingway, they are great with full drawings and setup procedures that I learn so much from. oh well guess I need to learn to set things up on my own some time or other.

anyway, did a little lapping and the new piston I had cut that I found out my cylinder was tapered and smaller in the center of the cylinder now goes all the way through and has much more compression with my thumb over the top now.

sealed all the mating surfaces and left for the sealant to cure over night. will hopefully give it another shot at starting tonight.

if it doesn't start then im going to do anther cylinder. but after my new DRO kit comes in. could only afford 2 pieces right now, mill and cross slide dro. should be helpful cutting the fuel passage inside the cylinder though.