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The 5cc found!

but what model can it go in?

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Simon Chaddock08/05/2008 13:19:00
5488 forum posts
2887 photos


I now have the 5cc petrol 4 stroke that my dad made, see previous post "4 stroke lubrication". It is complete and undamaged. Despite having been made nearly 40 years ago (it was one of the first small powerful 4 strokes) and not having been run for well over 25 years, it still has excellent compression.

My intention is to first get it running again, probably with a modern solid state ignition system (Just Engines?), and then to get it into the air.

It weighs 8.5 onzs (300 gms) dry, but including the 10x6 prop, which I believe it turns at about 12,000 rpm with the current performance carburettor. Unfortunately the engine cannot be inverted with this carburettor as the float chamber fouls the rear rocker cover when mounted the other way up although with the first carburettor design it could. Note the extra large finning on the head ot ensure adequate cooling when running at full power for long periods.

For the endurance attempt the engine would have to have been inverted so it could be gravity fed from the "wet" wing that was to carry the fuel.

Given the uniqueness of this engine I would appreciate any suggestions for a suitably docile design!




Brian Parker08/05/2008 13:38:00
538 forum posts
David Ashby - Moderator08/05/2008 14:24:00
10922 forum posts
1680 photos
610 articles

What a lovely thing Simon.

I'm not really the one to ask but I guess a vintage type so the engine can sit up and be seen?

Allan Jordan09/05/2008 18:18:00
495 forum posts

 Hi Simon, That engine is a little beauty, are you sure you want to commit aviation with it ?

  By the way, your surname rings a bell ! Are you related to the late Prof. Dennis Chaddock perchance ?

Simon Chaddock10/05/2008 01:32:00
5488 forum posts
2887 photos

Hi Allan

Yes he was my dad!

He always intended this engine to be used, hence the development of the second performance carburettor and was a bit dismissive of engineering models for show.

I remember spending a evening with him experimenting with the fuel flow and ignition timing of John Lowden's 1/4 scale Gnome Monosuopape to get it to run properly on all of its 9 cylinders. 

I understand when the first of the scale Merlins was demonstrated to him he was impressed but felt that it was not working nearly hard enough!

He never quite finished his V8 BRM (with its 4 cam shafts and 3 oil pumps) but calculated that it would produce peak power at well over 20,000 rpm and intended to find out if it did!

I trust that with a good airframe (e.g. a Ben Buckle Super 60) and modern radio gear the 5cc will not actually be at that much risk. 

Steve Hargreaves - Moderator13/05/2008 16:06:00
6728 forum posts
191 photos

Wow, wow & wow again.......what a great little engine & a fantastic story. I for one would love to see that motor in use powering a vintage model but pleeeease don't crash it.

Simon could you bench run it & post up a video? That really would be a worthwhile addition to the MF site

Simon Chaddock30/05/2008 22:52:00
5488 forum posts
2887 photos

The 5cc runs!

The follows pics show the engine mounted in its original (40 year old) test stand firmly srewed to the bench.

Note the full size 12V coil (I just wanted to make sure that sparks were not going to be a problem) and the oil tank.

It took a an evening of prop flicking to get it to run as I had no idea of any of the settings or even a starting routine but eventually it started "popping" and then burst into life. Only a couple of short low power runs so far - its 10pm and no silencer!

It will post a video of it running (with sound) when I get my new camera.



Brian Parker31/05/2008 20:27:00
538 forum posts

Fascinating, It truly is a little gem!

Adam Chambers 201/06/2008 06:47:00
38 forum posts

A nice vintage is the order of the day!!

 5cc is only a 30 size four stroke, and given its age we must allow a bit for that.

Go for a nice junior 60 from Ben Buckle.. ahh summer days......

 you may want to speak to Just engines for a smaller cdi ignition unit (!! )that is designed for this type of engine. About £45 and runs off a 6v pack.

Simon Chaddock01/06/2008 20:50:00
5488 forum posts
2887 photos


I did contact Just Engines about their CDI unit but unfortunately it is triggered by a magnet and Hall effect switch and the 5cc uses a miniature contact breaker. I could replace it and install the hall effect switch but I would prefer to keep everything as original as possible. It is possible to run a CDI unit using the contact breaker, my Dolomite Sprint had one (how old am I!) but JE don't think theirs could.

I have run the engine a few more times now and with the right routine starting is not a problem BUT it appears that the full speed range cannot be achieved with a fixed ignition timing. Anything like full power requires a lot of advance (25 degrees or more) but with that timing it stops dead much below half throttle (and I mean it stops dead!). I recall my Dad did encounter this problem but as most of his testing was to determine its maximum output (actually not much less than a 2 stroke of the period) full "throttleability" was not addressed. I suspect the answer will be to move the timing with the throttle linkage.

Nobody said it was going to be easy!

Brian Parker01/06/2008 23:35:00
538 forum posts

A CDI unit only needs its input signal  to go 'high' to allow 'primary 'current flow.

 I would have thought the Just Engines unit was usable if you used its 'signal' wire to your contact breaker terminal  and take its black wire to ground. Red wire not needed. A better (safer) way would be to use  a transistor as a buffer/shaper  between the CB and the CDI signal wire.

 CDI units usually provide auto ignition advance.

Your engine CB dwell angle will need to be checked against the CDIs requirements.

If it works you would be able to dump that massive coil! 

 Just some random thoughts.

Good luck with the project.

Simon Chaddock13/06/2008 19:33:00
5488 forum posts
2887 photos

The 5cc now has an ignition advance. Simple - it just advances with the throttle but it allows a good full power setting and a smooth slow idle.

The first pic is throttle closed/retarded, second, full throttle/advanced.



video to follow.

Incidentally the oil system works well, probably too well, as there is quite a bit of blue smoke when you open the throttle after idling for a bit but at least I know there is plenty of oil getting to the main, big and little ends!

Next is a CDI (thanks for the info Brian) then a suitable "flight" oil tank and then something to put it in!

Brian Parker14/06/2008 10:45:00
538 forum posts

A little excess oil in the upper cylinder will be an advantage as the exhaust valve was expecting a flow of solid lead particles from vintage 96 octane petrol.

Take care with your ignition control setup, the ignition advance will follow the throttle setting rather than the engine RPM and could lead to detonation if you 'blip' the control to quickly with the engine under load.   Although with its hemispherical head, domed piston and the angle of its spak plug, detonation will be minimised.

Ideally the ignition should momentary retard slightly as the throttle opens then advance should resume in line with increased RPM. Optimise maximum ignition advance to maximum RPM then retard slightly until the RPM just begins to drop.

(Forgive me if I'm teaching you to suck eggs).

Looking  forward to the video.

Simon Chaddock14/06/2008 20:29:00
5488 forum posts
2887 photos

I now have video of it running. I was the only person who would stand near so its me holding the camera as well as running the engine , note the oily hand! The sound is not that faithful i expect the camera mic was abit overloaded so close to the open exhaust!

Yes the advance is proportional to throttle position rather than speed but I judged that driving a propellor the engine is never asked to labour at full throttle at low revs.
Simon Chaddock14/06/2008 20:32:00
5488 forum posts
2887 photos
Lets try again!
Mark Lubbock17/06/2008 09:47:00
313 forum posts
13 photos

What a smashing engine!! As someone who makes a few small diesels, I can really appreciate the skill involved to produce such a thing. I applaud greatly the intention to use it as intended-much better than a complicated paperweight!

Regarding the ignition, have a word with Jim Shelly of Minimag fame-he does a combined coil/condenser unit that runs of 2-3 pencell nicads, I think it costs around £35.

Don't worry about the weight in a vintage model-An ideal subject for this engine IMHO, they normally have to carry a substantial amount of noseweight when using modern gear-just replace the lead with a coil, battery & heavy engine!

Eric Bray17/06/2008 12:21:00
6600 forum posts
2 photos

Health and safety! Standing at the side of a spinning prop is a bit naughty! Interesting to watch the prop flexing as it span, though!

It certainly sounds nice, not the familiar yowl of a screaming 2-stroker! 

John Van Buuren17/06/2008 12:45:00
20 forum posts
Magic! And yes, a Junior 60 would suit very well.
Simon Chaddock18/06/2008 00:57:00
5488 forum posts
2887 photos

I agree it looks bad standing beside a spinning prop but I wanted the sun behind me! I have actually had a prop break and the blade flies off forward, so the REALLY dangerous place is standing in front.

As you can see in the video there is a lot of blue smoke at idle but the exhaust virtually clears at full power so I have been trying to work out what is happening.

In this engine the crankcase is effectively being used as an air pump. When the piston rises it is below atmospheric & oil is sucked in, with the piston descends it is pressurised & the excess oil is blown back into the oil tank. At idle the below atmopheric periods are relatively far apart giving time for the oil to coat the cylinder wall.  At full power these pulses are much shorter such that the inertia of the oil in the inlet pipe means only a little gets in before the crank case is pressurised again. In other words I fear the oil flow is rather the opposite of what is desirable!

Over the years the engine has been run for quite a few hours so I am sure enough oil is getting in when it matters, it just there is rather too much at low speed. More thought needed to come up with a neat solution!

Brian Parker19/06/2008 18:58:00
538 forum posts


I would leave well alone. As they say...if it isn't broke don't fix it!

However, out of interest have you monitored the crankcase pressure/depression against RPM (a mercury gauge would be useful if you can find one). A diaphragm air bleed valve might be possible but on the whole, a lot of work for little perceived benefit and if incorrectly set ...a disaster.

Best left!!

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