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Old 10-18-2017, 01:01 PM   #151
werowance
 
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Default think im getting closer

Morning all, last night I decided to give the little cicada another try after sitting in a box for almost a year with a broken rod.
so I made another rod and made a fake propeller out of a strip of wood that was a little bigger than the bough prop I was trying.

so I got to the point that I had some kick backs, a loud "ping" noise a few times like dropping a thin piece of steel on the concrete floor and some smoke / oil out the exhaust. lots of black/brown residue oil coating the case and some smoke out of the exhaust. but still would not fire up.

that ping scared me to death the first time then I realized it was just trying to fire.

I found that loosening the compression screw actually helped where I thought I didn't have enough compression at first I found that it would ping and smoke whith less compression.

I ended up after several hours and frustration breaking the rod again. totally my fault and stupidity.

but was wondering, those of you who have made this engine, how many screws out on the carburetor seems to work for you? example on a brigs and Stratton mower engine I usually screw all the way in and then back it out 2 and a half turns.

then on the compression screw lets say we screw it down just until you can feel the piston hit the contrapiston. then how many turns backward are you backing it off for starting?

Brian Runpow, I read that you made a venture sleeve or something on your carburetor? I never fully understood what you did there and was wondering if you had pictures.

I am using store bough tower hobbies diesel aero fuel. when I got close to it wanting to start I could smell the rich fuel smell sort of like trying to start an old diesel tractor in the middle of winter using lots of either. when that tractor starts it smells like either and rich diesel. so that was encouraging me to think I'm close.

and last but not least, if my next starting attempt fails, would any one volunteer to let me ship you my engine for a look over and tell me what all I did wrong on it? along with maybe a gift card for your favorite lunch restaurant


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Old 10-18-2017, 01:39 PM   #152
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Werowance--I have never built a compression type engine as you show here, but I have dicked around a lot with small carburetors. Sometimes, if a carburetor intake is too large for the engine the carburetor is on, the air flowing through the carb will not be fast enough to create sufficient venturi effect to lift fuel up from the gas tank. The answer to this is to build "sleeves" of varying diameters that are simply a "push fit" into the carburetor air intake. (This is not an exact science, so you have to try sleeves with different bores until you find one that works.) This makes the inrushing air to move at a higher velocity, creating more venturi effect to be able to suck fuel up from the tank.


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Old 10-18-2017, 03:17 PM   #153
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ok, that makes sense, and should be easy enough to try, ive got some teflon rod that should make that job easy to test with.

thanks
Bryan
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Old 10-19-2017, 12:17 PM   #154
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Hi werowance,
I came across some great videos a couple of days ago of the correct starting procedure for ci engines. I really wish I'd seen these before spending hours trying to start my Cicada.
Having now built a couple of these types of engines I have a better feel for them and there is a definite knack to it that you can't really convey in words.
Search "Brian Cox engines" on YouTube. Make sure to add "engines" to the end or you will be watching Videos of Brian Cox the Physicists until the sun fizzles out.
Good luck .
Steve.
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Old 10-25-2017, 03:06 AM   #155
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G'day Werowance
I found your story again.
Firstly, don't let someone else have the pleasure of starting your new engine for the first time, I would encourage you to persevere.
From the sound of things there could be a number of things going against you.
I would suspect that the fuel you are using isn't up to scratch if you are not even getting a pop out of your engine when flicking the prop.
The fuel mixture that I use is 20% caster Oil, 30% Ether, 50% Kerosene. Although the last time I bought kerosene from the local hardware it was poor quality and it was suggested to me that the suppliers had added something to it which retarded firing of the engine.
I would suggest that you try to find one of your local model flying clubs usually one of the other members can get Ether and they are usually happy to sell you some for a good cause like running a home built engine.
If you have made the venturi to the drawing sizes you do not need to restrict the air intake the engine will run fine as it is drawn.
As I remember it you said that you shaved off the top of the crankcase where the cylinder mounts to the crankcase have you made a packing piece to repair this because by doing this you will have changed the timing.
Also try and poor some fuel around the cylinder crankcase joint and then turn the prop over and see if there is any leakage around this joint. If there is you are loosing crankcase compression and the fuel air mixture won't be transferring to the cylinder properly even so you should still be getting a small bit of firing when you flick it over.
Try and put a very small squirt of fuel inside the exhaust port and then flick it over it should fire after the second or third flick if your contra piston is somewhere close to it's running position.
It could also be the fit of your piston, liner, contra piston. Invert the engine, and again put a small squirt of fuel into the exhaust and turn the prop to close off the port and continue to turn the prop gently, all the time looking in the exhaust port to see if there is any blow bye past the piston.
If all your fits are good there should be no leaks and provided the contra piston isn't backed off to far the propeller should come to a hydraulic lock, don't force it past this position. Also if it hasn't leaked so far remove the compression screw completely put your finger over the compression screw hole and flick the prop over. If you feel any pressure change from the hole then your contra piston is leaking.
When trying to start the engine, install an 8"X4"prop, set your tank up so that the centre line of the fuel feed pipe is in line with the centre line of your needle valve, make sure that your compression is backed off. Try to start with no fuel in the engine, open the needle valve about 3 to 4 turns. put your finger over the venturi and turn the prop over 2 times making sure that the fuel was already drawn up to the needle valve. At this point remove your finger from the venturi and give the prop a good flick. If it fires you are getting close to the running position. If not increase the compression by about an eighth of a turn and flick the prop again continuing until the engine fires, about every third try you will need to put your finger over the venturi and draw a little more fuel into the crankcase.
Once the engine fires increase the compression a little more and the engine should run.
at this point you will probably need to increase the compression slightly more and the engine should run steadily at this point you can wind the needle valve in and your engine should increase the rev's.
At this point don't run your engine to hard at first as everything will be bedding in and there will probably be a few tight spots, just let it run and settle down. Let it run for about 2 to 3 minutes at a time slowly increasing it's speed as well as slowing it down until it has had about 20 minutes running.
Remember if you force it and something breaks all spares will need to be remade by you.
I hope this helps please let me know how you go.
Rob Jenkins.
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Old 10-27-2017, 02:03 PM   #156
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Thank you Rob Ill give it another go. honestly I never got back to remaking the connecting rod from the other night. to much honey do work... and its my anniversary this weekend so probably wont get to this weekend. but the rod is a quick part to make and I think I still have stock the right thickness left over (fingers crossed)

on the fuel, its store bought aero Diesel fuel from tower hobbies specifically for diesel engines, I had also tried the homemade mix which is pretty much the same as your mixture some time way back. but since I am getting a few kicks now, I may try mixing my own again to see.

on the head and shaving it down etc, that was some time back and I had already gone back to the standard drawing dimensions (remade parts) so we are good there. I'm actually on about the 6th cylinder and pistons remake lol. but the contra piston has that slight taper and is good and tight no fuel blow by on that getting into the head.

on crank case leakage. that just might be one of the issues ill double check on that.

on 8x4 really don't know much about props dimension but the one I am using was a 2 blade 7 inches long prop. but on this last test I used a biger piece of wood that was about 9 inches long and thicker. but I assume 8x4 means 8 inches long and 4 blades? ill ebay for one if so while I'm remaking the rod
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Old 10-28-2017, 01:52 AM   #157
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8x4 is an 8 inch prop with a 4 inch pitch - it's still 2 bladed. The higher the pitch number the more force required to spin it, but the longer the prop the more 'flywheel effect' it has.
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Old 10-29-2017, 11:37 AM   #158
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G'day Werowance
from past experience, store bought diesel fuel is often low on the volatile component of the mix, so the home mix fuel is always a better bet, provided you can get the ether. Also only mix enough fuel for running on the day.
On the crankcase leakage also check around the front housing and the crankcase by pouring fuel around the joint and then turning the propeller over and checking for air bubbles.You might need to cut a paper gasket to suit.
As for the propeller size Cogsy is spot on. I only use the 8"x 4" prop to get the run settings and for initial running after the engine is starting consistently then swap to a 2 bladed 7"diameter 6" pitch prop.
I have been running a 7X6 on my Cicada to fly a control line Veron Viper for some time.
I'm currently working on a pair of Naylon Vipers but I haven't had a lot of time in my workshop lately.
Rob Jenkins.
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Old 11-20-2017, 11:33 PM   #159
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Hi there Werowance, just wondering how you goton with the littlediesel? any luck yet with starting it?
cheers
Dean
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Old 11-21-2017, 04:19 PM   #160
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havnt had a chance to do much yet. I started a major shop cleanup and strip cleanup on the lathe/mill combo. just finished that up this weekend and started cutting down a pice of 2024 aluminum to make the new rod.

if I'm lucky ill have a new rod by this weekend.



Last edited by werowance; 11-21-2017 at 04:23 PM. Reason: spelling
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