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jim:
i'm paying a lot of attention to this now i've decided i'm building one of these.

i so look forward to your "its a runner" post :thumbup:

NickG:
Unfortunately not Rob! Distinct lack of shop time - I chose to do something different tonight - played badminton and caught up with a mate at the pub. I do think about this engine about 80% of the time at the moment though which is quite annoying! I might make a start tomorrow and Fri night and hopefully on Saturday morning I should get a good chunk of time to myself as the wife and kids are off to see grandad and grandma without me! :ddb:

So fingers crossed by the end of the weekend, the engine should be 'finished' and I should know what action I need to take to get it running!

Nick

bogstandard:
Be very careful Jim with these types of engines, as Nick is finding out, they can be a soul destroyer, and with only a slight push, could put you off making model engines for life.

This one that Nick has made deviates a lot from the normal practice for this type of engine, so if you really wanted to make a flame licker as a starter project, I personally would start with one of the more common designs, with the sucky in bit on the end of the cylinder head.

I have been having a bit of a discussion with Nick, and have come to the conclusion that the way to go with these engines is a change of fuel. I actually knocked up a basic gas burner for mine, and the engine ran lovely with it, unfortunately my burner design wasn't 'clean' enough, and the engine got choked with unburned deposits and needed to be cleaned out between runs.

Then I found these,

http://www.jerry-howell.com/Propane.html

Having purchased the plans, they look fairly easy to make, a couple of D-bits to make the venturi and the rest seems to be very straight forwards

To make the jets for the above, even though Jerry sells them in an American Imperial size, I want to make them in metric or English Imperial, then I have still to construct a very high speed drill. I have all the bits to make it, and is a very similar design to Jerry's

http://www.jerry-howell.com/Micro-DP.html

Only mine will be air powered, as that seems to be the best way for me to reach the speeds required for 'stable' drilling. Over 60K rpm should give enough centrifugal speed to the drill bit to enable fairly rough handling and feed of the drill without breakage. Just to see the sizes of drills that are needed, look at the pic below. The big one is about 1mm diameter, the one at the opposite end is the size required to drill the jet, 0.15mm.

This isn't meant to detract from Nicks post, just as an add on to give an insight into what can be done if you want to pursue it.

John

NickG:
I would concur with John on this one Jim. It looks a simple design, that's what attracted me to it but with hindsight, I think the simplicity gives it less control and means things need to be more tightly controlled. Last night i was actually looking at the poppin versions with a sliding valve operated by a cam. Although this initially seems a little more comlpex, I think it is a much more proven design.

John,

Those burner's sound excellent but I think are beyond my capabilities. As you pointed out, you need the specialist drill too.

Nick

NickG:
Hi all,

I know this has gone a bit quiet but I haven’t given up on it! If I’m honest, I am a bit disappointed that it didn’t run and I couldn’t even detect it trying to run. It passes I think the tests on Jan Ridders problem solving page. If anything I’ve done is a bit marginal, I think it was the cylinder and piston tolerances.

I haven’t done nothing on it, I spent a few nights messing around trying to get it to run but nothing. Then I thought, just finish the thing off and then try to troubleshoot. So I started by finishing the aluminium base off.

I sanded it with the bosch mouse sander then got a stick with some wet & dry and rubbed it back and forth a bit. Then I did the same with some white spirit which gives a sort of matt sheen to it. I could really go to town polishing it but it takes ages to get the machining marks out completely so this’ll do for me. I haven’t put polish anywhere near it, just a quick rub with some wet & dry and oil seems to give a nice finish in my opinion. I decided not to put an edge around it as I’d probably spoil it if I didn’t take care in clocking it square on the milling table.

After this, I could then make the base from some brown stuff. This needed little counter bores for the screws underneath the alloy base. I was wondering which way to go to fasten it down. At first I thought, could make some nice hex bolts and bolt from top. Then I thought I could keep them hidden like the rest of the engine, but then I found some 0 BA screws with nuts so decided to drill through the lot and leave the nuts on top as a sort of feature. This meant giving my nuts a bit of a polish so to speak!

Again, this was sanded with the mouse and oiled with teak oil. I did put an edge around this with a countersink in the milling machine. It worked ok but it was a mess on getting it clocked straight.

Then I decided to re-do the crank pin. As discussed before with Bogs, it’s better to retain the big end with a set clearance to stop it wondering. So I made this from stainless:

Along with a little bronze spacer. This is the first time I’ve ever knurled anything since uni. The set of knurls I have are sort of sprung and you turn a screw which makes them closer together (need a pic!). I didn’t really know how much to tighten it so I went easy, but then of course you can’t go back and do it again incase it goes in a different place and mashes it up so the knurl isn’t very deep! I should have pointed out that it's a 2p coin in the photo! Not sure why I put it that way around!

I then assembled the engine together. Here are some pics, looking much better on its real base!

Hope it doesn’t stay in here for the rest of it’s life! :

The base was needed as it was wobbling about when trying to flick the flywheel over. Now it’s very stable so it will give me a better chance when I try to get it to run in anger!

Almost forgot to mention that I re-lapped the bore and made a better fitting piston and valve. How much better remains to be seen though! I also took the opportunity to extend the spigot on the piston slightly as I noticed my port wasn’t opening quite fully – not sure why, I must have calculated something wrong.

All I need to do now is the burner, then I am hoping my little tweaks and improvements are enough to get some life out of the thing. If not, I’m a touch puzzled. The only real thing I can think of is that I may have to revisit the cylinder and pistons again. I have a sneaky feeling that when I lapped it, it may have taken a bit of parallelism & circularity out of the bore. I think I have some adjustable reamers which may correct that, then make new piston and valve again.
There are another couple of suggestions with regards to the mass of my piston and valve as they aren’t hollowed out and the only other things that are different are the flywheel and con rod length. If anything the conrod length should improve things though and the flywheel should be ok, it should be better and don’t think it’s any heavier. If things such as the mass of the piston affect it’s running, it is, as I thought a marginal design.

Here is a little video flicking it over by hand, sorry about the lighting!

So, hopefully will get started on the burner tomorrow, and by the weekend, fingers crossed I’ll have some good news. But I’m not holding my breath, could be back to the drawing board I think!

Nick

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