Spent yesterday running the two piston and liners in on the Midge. No.2 would not run consistently but No.1 after 5 minutes was the equal of the Midge.
Put No.2 back in this morning and still the same (funny that)
things really don't heal on the shelf - so as all the components were within a thou externally, decided to use the Midge internals as No.2
Assembly took some time - as rods have to be assembled then pistons and gudgeons on the rods after. It felt a little scratchy to start with with not a lot of compression feel to it - not unusual on first assembly however.
I noted the contra piston depths as I disassembled off the Midge to give myself the best chance of a start.
First few flicks and nothing, after about 5 minutes decided to try flooding it a bit down the venturi, cylinder prime no good as the exhausts are angled down and it runs away too quickly. Succeeded in getting a few revolutions then a few seconds - but nothing like a run - and obviously just the No.1 cylinder, not a peep from N0.2
Much flicking and trying different settings then lunch.
After lunch more of the same - but the second or so became a couple of seconds - then a bit of a run, but only No.1 cylinder.
Then I remembered I had a electric starter so made a spinner to fit the nylon boss and tried that, sure spun it up but again no consistency. So I put it aside and didn't use it again.
Then I thought ok it seems starving for fuel, how about I try it inverted. Straight away it ran maybe 10 seconds. It was then a matter of trial and error and then I had it running 20 plus seconds, and an occasional pop from No.2
So I thought, ok if you want to do this how about we go in reverse so No2 becomes No1 - and again it ran this time on No2 as the first cylinder and a bit more popping from No1
I stopped it purposely and started it normal way and this time it ran well, I started to up the comp on both cylinders ever so slightly and No2 then cut in with a increase in power, but not as much as I had thought - obviously it is being starved big time as many of you have said.
In the end it ran beautifully for 15 minutes and only stopped when the tank ran dry and both cylinders were hot, indicating that they were sharing the load.
So it does work, power is very poor, 4800rpm on an 8x4 wood Turnigy prop - but the sound is terrific, and it runs ever so slowly when on 1 cylinder, in fact you could almost count the piston strokes through the exhaust window.
A success - well it does run, but I think it is more a curiosity than a practical design. 4800 rpm on an 8x4 for a 1.6cc engine is very low power - but it is very light - will post the weight later.
It is obvious that it only wants to run inverted where the fuel droplets have gravity help them find their way down the transfer ports.
I guess total build time would be a bit over 100 hours to get to here. And it sits on the test bed with about 20 minutes running now.
Will have to work out how to use U-tube so I can post a photo of it running.
OK enough reporting ..... back for one more start !
Ed
