My first Engine - ML Midge
- Thread starter froudeg490
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Rodrigo Castellanos
Well-Known Member
Looooks amazing!!! please share a video!!
Beautiful job! Hope she runs well
Here is a short video of the break-in. I'm using a 8 X 4 prop.
No issues so far. It's a very quiet engine.
No issues so far. It's a very quiet engine.
jack620
Well-Known Member
Well done! I built a pair a few years ago. One ran beautifully, the other was a bit rough.
Froudeg. An lovely bit of work. We do love shiny metal things that make exciting noises! CONGRATULATIONS ON A FIRST!
Next you'll be making bigger engines, 4-strokes and maybe even radials?
Just something someone with expertise can advise... It sounded to me like it was mis-firing a bit - but the exhaust looked clean? Is it a bit lean perhaps? Had there been a hint of smoke or oil I would have suggested it was rich, but it seemed better when the compression was wound-up a bit? When the compression screw was slackened off I thought it was trying to mis-fire more, and stall, which suggests to me it is lean. But I finished a friend's model diesel and never got it to run. Converted to Glow plug with a different head and it ran for a minute or so but has lost compression so needs a new piston. I was wondering about mixture as I had a divvle of a problem and spent hours before getting anywhere. I suspect my needle was far to coarse to give sensible control.
But Froudeg, you have started really well. I am impressed.
K2
Next you'll be making bigger engines, 4-strokes and maybe even radials?
Just something someone with expertise can advise... It sounded to me like it was mis-firing a bit - but the exhaust looked clean? Is it a bit lean perhaps? Had there been a hint of smoke or oil I would have suggested it was rich, but it seemed better when the compression was wound-up a bit? When the compression screw was slackened off I thought it was trying to mis-fire more, and stall, which suggests to me it is lean. But I finished a friend's model diesel and never got it to run. Converted to Glow plug with a different head and it ran for a minute or so but has lost compression so needs a new piston. I was wondering about mixture as I had a divvle of a problem and spent hours before getting anywhere. I suspect my needle was far to coarse to give sensible control.
But Froudeg, you have started really well. I am impressed.
K2
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jack620
Well-Known Member
It could be that. My rough-running Midge sounds exactly like that and will only run with the fuel tank elevated above the carburettor. I suspect a problem with the spray bar/needle assembly, but have never bothered to rectify it.
Nice Job!
Thank you for the compliments and words of encouragement. Expert advice also greatly appreciated!
After a lot of running on the 8 X 4 prop. the engine is still a little tight, but I went ahead and changed to a 6 X 4 to try out my new optical tach.
With the 8 X4 prop the engine runs at about 4500 to 5000 rpm and is very docile. I'm getting about 8500 to 9000 rpm with the 6 X 4 prop and discovered that a glove in now mandatory!
The Midge turned out to be a fun first project and ideal for the Taig II lathe. I added a leadscrew to the lathe so that I could cut the 32 TPI thread on the fuel bowl and cap.
I had to make two pistons because I lapped the cylinder bore taper the wrong way...I fixed the cylinder and the second piston fit came out about right. By holding the prop driver by hand it was not possible to turn the engine over TDC, but with a prop. installed, I was able to ease the piston up the bore and over TDC. I used the David Owen method to make the contra piston and it worked like magic. When I back off the compression lever and give a couple of flicks of the prop, I can feel and hear the contra piston snap up the bore.
Lapping was a fun process. Started with some 8 micron diamond compound off Amazon, that worked well and was about $12. I used Brasso after I fixed the cylinder taper. I was surprised how well it worked.
After a lot of running on the 8 X 4 prop. the engine is still a little tight, but I went ahead and changed to a 6 X 4 to try out my new optical tach.
With the 8 X4 prop the engine runs at about 4500 to 5000 rpm and is very docile. I'm getting about 8500 to 9000 rpm with the 6 X 4 prop and discovered that a glove in now mandatory!
The Midge turned out to be a fun first project and ideal for the Taig II lathe. I added a leadscrew to the lathe so that I could cut the 32 TPI thread on the fuel bowl and cap.
I had to make two pistons because I lapped the cylinder bore taper the wrong way...I fixed the cylinder and the second piston fit came out about right. By holding the prop driver by hand it was not possible to turn the engine over TDC, but with a prop. installed, I was able to ease the piston up the bore and over TDC. I used the David Owen method to make the contra piston and it worked like magic. When I back off the compression lever and give a couple of flicks of the prop, I can feel and hear the contra piston snap up the bore.
Lapping was a fun process. Started with some 8 micron diamond compound off Amazon, that worked well and was about $12. I used Brasso after I fixed the cylinder taper. I was surprised how well it worked.
Rodrigo Castellanos
Well-Known Member
hi Froudeg!
i finished mine last week, i really love the way those little engines work, is a very easy to build engine, so quiet, and runs good. mine needs to be primed by two drops of fuel in the exhaust to start... it does at 2-3 flips..... i think a left my piston a little bit looser than yours, but still holds compression. after maybe 20 runs, i can get 5600 with a 7x4 prop.
now i´m finishing my Boll Cicada... not as easy to build as the Midge, but is going nice.
i finished mine last week, i really love the way those little engines work, is a very easy to build engine, so quiet, and runs good. mine needs to be primed by two drops of fuel in the exhaust to start... it does at 2-3 flips..... i think a left my piston a little bit looser than yours, but still holds compression. after maybe 20 runs, i can get 5600 with a 7x4 prop.
now i´m finishing my Boll Cicada... not as easy to build as the Midge, but is going nice.
Very nice! I'm working on a Boll Aero 18 at the moment. The Cicada is next on my list.
Duke Doner
New Member
I built a Boll Aero about a year ago but never tried too get it running . The fuel issue had me by the biscuits so i just put it on the shelf with the rest of the engines that don't run. I know Sadness! I am hoping you could help me out with your process and how you deal with the ether. Thank You Duke
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