ML Midge homebuilt diesel

[Mark Lubbock]

Hi all,

A number of folks have been in touch with me regarding building the ML Midge .5/.8cc diesel engine which I designed a few years ago.

I just thought a thread like this would be useful for prospective bulders to share their experiences & get answers to any questions they may have.

Any thoughts all?

[Allan Jordan]

 Hi Mark. What a good Idea. I built a small diesel years ago. At the moment I'm trying to finish an engine which was given me in a part machined state. It should be spark ign. but I think it is going to end up as a glow motor.I'll have to see if I can get some photo's organized.

[Phill L]

Greetings Mark,

 

So far, so good.  This is my first engine, but work is progressing fairly smoothly. 

 

The only gotcha that i've come across so far is with the screw placement for the cylinerhead / crankcase interface.   Luckily I discoverd my error in TurboCad and not the workshop!

 

These screws are placed on an _8mm_ radius.  (the magazine is transcribed incorrectly, mark's original plans are fine)  and _not_ at  90o.

 

The rest of the build is progressing nicely, although I have borrowed some of the idea's from Ron Chernich's fantastic step-by-step on modelenginenews.org  Building the ML Midge Diesel

 

Modifications include, splitting the crankshaft at the journal and using a threaded shaft to carry the prop driver and spinner and a hollow, thin-walled contrapiston (also described on ron's site)

 

I am considering milling the crankshaft webbing to counterbalance the rotating mass, but I'm not sure if the increase in crankcase volume will offset any gains in stability... any thoughts?

 

Phill L

 

 

[Mark Lubbock]

Hi Phil-I did get some questions about the head bolts when it was first published!

 

Ron's site is a great help-have you noticed he built his the 'wrong' way round? It's cos Aussies are upside down!

 

The mods you describe are all ones I have done myself, the contra piston was a real breakthrough I worked out myself after looking at an Indian Mills & wondering why the inside was threaded.

 

I normally turn the crankpiin as on the drawings & the take another 1mm off to around half the diameter, not critical, leaving a small bearing surface for the big end-have a look at a Cox shaft, you can do this without taking the shaft from the jig, so it doesn't take long. I have not noticed  any difference in running either! The originals did not vibrate much, partly due, I think, to the heavy, rigid construction.

 

Good luck with the rest of your build.

[Steve biplane]

Hi Mark,

Another (very slow) builder here. At the moment I'm trying to figure out how to machine the cylinder cavity, in the crankcase, at right angles to the crankshaft bearing using my tiny, table-top lathe.  I think I will have to make a small angle bracket for the face-plate (but it will be a bit of a squeeze! - not much space)  Good fun figuring out these problems though.   I liked the look of your rear induction version on the modelenginenews site.  Presumably that lets you put in some extra transfer ports to get a bit more power.  But before I set off down that path, I'll make one to the drawings - just getting something to run will be a milestone. 

Regards,

Steve

[Mark Lubbock]

hi Steve,

 

Doesn't matter how long it takes as long as you get there in the end!

 

I either use a jig, similar to the angle bracket, or a 4 jaw chuck. Either way, I do all of the boring & thread tapping while the crankcase is still a rectangular blank. It is easier to grip this way, & the most likely way of ruining the job is to break a tap (don't ask me how I know!!!) I do the shaft bearing last, so the front of the case can be machined at the same setting.

 

The rear disc version has two exhaust ports & four transfers & is fairly powerful, but a lot noiser.

 

Hope this helps

Mark

[Steve biplane]

Hi Mark,  words of wisdom. I can see now that the job would have been a lot easier if I'd done like you said and machined the inner cavities while the outside was a simple rectangular block. After all, a lot of the outside just needs to be something about the right size - not too critical at all.  And it would help prevent the outside machined surfaces getting  marked by being held during later machining.   I will know better next time.  

The other thing i'm finding takes a lot of time is making the tooling so I can do the job I want to do.  A simple indexing tool,  boring bars etc.  But they will make future jobs quicker now I have them in the toolkit.

 

Steve

[Frederick Burman]

Hi Mark

I am going to have a go at your engine-the 0.5 cc one I think.

Do you think a mild steel bolt would be Ok for the crankshaft, as I only have a small Sherline lathe and don't know whether it can handle high tensile steel.

Also,what do you think of drilling and threading the crankshaft and using a stud to hold the prop, so there is less chance of it getting bent in a crash?

Fred

[Frederick Burman]

Mark

The drawings I have are not very well done or readable.Would it be possible for you to email me your original drawings?.My address is [email protected]

Fred

[Mark Lubbock]

Hi Fred, drawings on the way. Again, I have tried the stud method & it works well & saves some machining.

[Frederick Burman]

Mark

Thanks for the drawings , they are much clearer. 

[Frank Marshall]

Hi there,

 

At the age of 65 I'm, finally, getting some machining equipement together (thank heaven for the Chinese!!) and have been looking at the delightful and, apparently, very successful Midge design. 

 

The Aeromodeller article, apart from being a damn entertaining and informative read, points to the engine having good power (perhaps due, in part, to the clever Schneurle like porting concealed behind the vintage look!) good longevity due to good material selection and being reasonably easy to make.

 

Looking through the drawings, though, I was surprised to see that no effort has been made to  counterbalance the crankshaft against the conrod and piston weights, as far as I can see.  Usuallly you see scalloped crank webs or similar to satisfy this 'requirement'.

 

Soooo, I'm intrigued to know what effect this has.  Does it vibrate like a good 'un or is the need for  mass balancing over stated....especially in small engines.

 

Has anyone got a comparison with something like a Mills 0.75 for example (scalloped crank web if I remember correctly.)

 

Thanks if you can help.  I would also appreciate a set of original drawings if they are available.  Please advise source and cost to [email protected]

 

Cheers

 

Frank

 

 

 

 

[Frank Marshall]

I just noticed that the Boll Aero 1.8 hasn't got crank balancing features either.....Hmmmm, I must be out of date!

 

 

Edited By Frank Marshall on 28/03/2010 17:54:08

[Mark Lubbock]

Hi Frank, Many thanks for your kind words, glad you are having a go. Have a look at posting no 4 on this thread, this covrs the balance question.

I will send you the drawings, anyone else want some? It saves broadband usage if I  can bundle a few together.

[steve 1]

Hi Mark, i would like to take you up on your offer for the drawings (if not to late) with a view of maybe having a go as you say, although not that experienced at machining i do enjoy making things on me lathe it might be a bit much for me but you never now until you try.

Thanks.  

[Frank Marshall]

Hey Mark,

 

That's a very kind offer....and I would like to take your arm off!!   Thank you!

 

Apologies for not reading the posts properly....sometimes it's like snow or 'fact' blindness....I think I'm suffering from 'reading-it-but-not-taking-it-in-itis'.....or similar!

 

I did wonder if the robust construction played a part.  It's sometimes worhtwhile to just try things which are against the perceived wisdom....to see what the affect is.  It's very interesting to me that both your Midge and the Boll Aero get away with it without the extra work.  It's also very useful to read that you've done it both ways and can't spot the difference...useful results!

 

So I won't bother with the Lanchester balancing shaft mod just yet then!

 

Best regards

PS I wonder if Alex Whittaker's Firefly uses a balance....it's a quite a lot bigger engine.  I think his video presenting the C1 micro-lathe and his engine run video at his flying field are inspiring.  Perhaps better off with a 7x14 Amadeal if within reach.

Frank

[Mark Lubbock]

Hi Steve, let me know your email address or just send a  message to [email protected] & I will send you & Frank the drawings.

 

Frank, I suspect you can only get away with not balancing on the smaller sizes although many commercial diesels, DC, AM & Frog etc. used plain cranks, probably sacrificing balance for strength & getting away with it at the lower revs diesels tend to operate at. Anyway, no point in complicating a job, particularly a first attempt?

[Frank Marshall]

Posted by Mark Lubbock on 29/03/2010 23:13:09:

Frank, I suspect you can only get away with not balancing on the smaller sizes although many commercial diesels, DC, AM & Frog etc. used plain cranks, probably sacrificing balance for strength & getting away with it at the lower revs diesels tend to operate at. Anyway, no point in complicating a job, particularly a first attempt?

 

 You've done your homework better than me Mark....I'd assumed, foolishly, that all the engines I had seen, with counterbalanced crankshafts, were just examples of state of the art technology and that every other manufacturer were following suit....or 'on trend' as the smart money is saying these days....!

 

'Anyway, no point in complicating a job, particularly a first attempt?'

 

Ain't that the truth!!

 

Best regards

 

Frank

[Frederick Burman]

This article may help on that subject.

[Klippy]

Thanks, Frederick, that article makes interesting reading, and, for me, 'just hit the spot'.

[Frank Marshall]

It's a funny old world....it really is! 

Frederick, thank you very much indeed for taking the time to dig out that article from your files and to scan and share.  Very generous.  As Tony says it hits the spot in many ways. 

Now the funny thing is this.  When I was 15/16 my Auntie in Vancouver was kind enough to send me a McCoy35 Redhead, after much nagging. I’d spotted how affordable it was in one of the US model mags which I treated myself to very occasionally. It was a very cheap engine relative to similar size engines of those days; especially here.....which were generally quite out of reach for the likes of me.  Yes, it was rip-off Britain even then! .  A '35' was a BIG engine then. But I was desperate to build the, Ray Brown designed, Coy Lady.  It turned out that I ended up only affording/making the rib set which just ate 1/16 balsa....ending up selling them to a school friend!  

The McCoy was a beautiful sight with its polished aluminium crankcase, black fins and red painted head all set off in a purpose moulded blue case with a clear hinged plastic lid. These days engines are often chucked into a cardboard box with foam in a bag!! Testors knew about presentation and marketing. Some would say that the box was better made than the engine...by all accounts....but we’ll see.  Some say it was a race to get it run in before it wore out!

Having retired, a year ago, I was in the grip of nostalgia and I found myself eBaying for engines which I had as a boy and also those I had  lusted for in those days. Some of those engines were the, very expensive, Mills .75...I had to make do with an ED Pep at the time which was very affordable and mine was a super little engine...maybe I was lucky?  Also the wonderful Oliver Tiger....my substitute for this missing experience was to purchase a Rustler copy. 

So, I was looking for a McCoy 35 last year on the UK and US eBay....and I was very lucky to spot a McCoy Redhead R/C on the US one....yes R/C!!!  I didn't even know this model existed, as I’m no collector, but I suspect it’s pretty rare.  Being R/C was a practical bonus (although I have again dabbled in CL over the last few years.  I was lucky enough to win it and the only disappointment was that the flexible needle valve drive broke off on installation into the carb.....a weakness in the design....it had  been hanging on to one of the four wound wires!

I finally found a replacement last week; having wasted money previously with Mecoa as I hadn't noticed that their McCoy 35 needles were for the later '21 series' which I didn't even know about! I even bought two just as a backup....anyone want to buy one??

 Anyway, FINALLY, getting to the point, I ended up having an enjoyable email exchange with the seller who was.....yes, you guessed it, Joe Wagner.   Look who wrote the article which Frederick shared!!  Joe had several careers and one of them was as the 'engine man' in Model Airplane News for a number of years.  Indeed, the name had been vaguely familiar to me because, as I said, I did buy a copy of MAN, perhaps once a year, when funds permitted....and would have seen his name there....and how cheap the McCoy was! 

Joe is a bit of a Polymath whereas, by contrast, I’m a bit of a Polymug and he is quite a remarkable man overcoming poor eyesight etc to accomplish a hell of a lot in a lifetime. If you Google his name you will see his tribute on the AMA site. The Americans are much more into this than us aren’t they? 

It's a funny old world....apologies for the lengthy digression....ModelFlying will just have to buy a new hard disk! 

Frank

 

Edited By Frank Marshall on 30/03/2010 11:15:48

[Frank Marshall]

Oh, and another thing....

 

I just remembered that I have a 1960's OS15. 

 

Now... that engine has a cunningly, slightly larger diameter than normal, aluminium prop driver which is hollowed out eccentrially at the back to provide an out of balance force.  This scheme can, theoretically, balance out the primary couple perfectly. 

 

Some, finely balanced, souls attempt to achieve the same result by cutting off one propeller tip.

 

Significantly, I would say, the great OS company saw fit to never bother with this feature again....so there's another example of Practice triumphing over Feery.  I could post a photo of the driver if anyone's interested....or even if they're not interested...

 

Frank

Edited By Frank Marshall on 30/03/2010 12:50:34

[Mark Lubbock]

Drawings are on the way to you Frank & Steve. You're getting anothe set by accident Fred-sorry! Hope they are of use.

[Frank Marshall]

Thanks a lot Mark I got them Ok....very generous of you and much appreciated . 

 

BTW I got in touch with Joe Wagner to say that his 1987 article came up!!  He's still well and going strong!!

 

Cheers

 

Frank

[Frederick Burman]

Frank

Thanks for the interesting remininiscence of your coincidental contact with Joe Wagner.

I am the same age as you and find I am getting more nostalgic for the models , engines etc. of my youth and like to read about anything to do with them.

I get Flying Models magazine which is quite good in that respect and seems to cater to "Old Farts" in its articles.I enjoy reading old Aeromodellers as well, when I can find them.

I will be interested to hear how other people get on with making the Midge, and as a beginner I can probably learn from them and the methods they have used to make it.

My equipment is fairly rudimentary, but I have made one engine, a 1cc Weaver diesel, which runs quite well, after a bit of modification.I really like the look of Mark's little Midge and the way he has designed it to be easy to build.