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Completed Twin Inline IC Engine

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Steve G01/01/2019 20:56:45
19 forum posts
8 photos

Twin Inline Engine.jpgtwin parts.jpgHi All,

I have machined, completed an IC twin Inline Engine that might be of interest to those something doing similar.

I have run the engine but not too impressed with the glow plug ignition system, I think spark ignition would be better.

Engine running here



Edited By Steve G on 01/01/2019 21:01:52

Edited By JasonB on 02/01/2019 07:05:49

Ian Skeldon 201/01/2019 21:26:15
421 forum posts
29 photos

That's lovely mate, nice one.

AJW01/01/2019 21:49:09
278 forum posts
117 photos
Great, makes it all worthwhile!

Hopper01/01/2019 23:39:04
3991 forum posts
85 photos

A beautiful piece of work. Lovely to behold.

Thor02/01/2019 05:04:30
1159 forum posts
33 photos

That's a very nice engine, impressive.


JasonB02/01/2019 07:06:21
17097 forum posts
1841 photos
1 articles

Very nice.

John Penfold02/01/2019 08:07:50
23 forum posts
3 photos



LADmachining02/01/2019 14:41:15
101 forum posts
10 photos

Very impressive work - thanks for sharing!


Niels Abildgaard02/01/2019 18:45:55
260 forum posts
89 photos

Lovely engine

Can you describe how crankshaft is made?

I have tried to make normal ,pressed up two stroke cranks and failed miserably.

More than once

Mogens Kilde02/01/2019 18:54:29
60 forum posts
25 photos

Hi Steve

Absolutely great piece of work

Thank you for sharing this


Neil Wyatt02/01/2019 20:01:52
17109 forum posts
690 photos
76 articles

Great stuff, must be satisfying to achieve that range of speed control on your first run.


JasonB02/01/2019 20:32:24
17097 forum posts
1841 photos
1 articles

Looks like a schillings style crank shaft to me.

Craig Booth 102/01/2019 21:15:55
79 forum posts
143 photos

That's beautiful Steve, lovely work.

I have the plans for both that one and the 4 cylinder boxer which is next on my list.

Is yours going in a plane?

Would love to know more about it if you don't mind?

Did you stick to the materials, specifically the piston liner and ring combo? I was planning on changing to steel liner and CI ring.

What do you think the issue with the glow is? I was also thinking of changing it to petrol, but was nervous about losing power. Mines destined for a plane if successful.



Jeff Dayman02/01/2019 22:29:29
1723 forum posts
45 photos

That's a fine engine Steve, runs really well! Great job.

John Olsen03/01/2019 06:03:39
1002 forum posts
86 photos
1 articles

It's quite often a bit tricky to get multicylinder engines to idle nicely on glow, the plug naturally cools down at slower speeds, and if you use a hotter plug to compensate it may be too hot at high speeds. One solution is a glow driver. These can turn the glow plugs on at low power settings, usually by connecting to the servo wiring. Of course for ground testing one doesn't always have a servo connected, but you can always just have a switch and turn on the glow plug at lower speeds.

Craig, I have messed around a bit with spark ignition on a commercial engine (Saito) and I don't think there is any loss in power worth worrying about. Perhaps just a little since it is usual to drop the compression ratio a little to run on petrol. The biggest problem is getting the mixture right if you also use petrol instead of methanol, but they will run fine on spark with methanol and give a lovely slow idle. You do have the weight of the extra battery for flying, you don't want to use the ignition battery for the RC gear!


Craig Booth 103/01/2019 12:26:48
79 forum posts
143 photos

John, not wanting to hijack Steves thread, but what compression ratio do you think would be required to convert to spark ignition?


Buffer03/01/2019 12:33:44
132 forum posts
35 photos

That is lovely. What other engines are on the shelf then?


Steve G03/01/2019 14:24:45
19 forum posts
8 photos

Hi All,

I am stunned at the interest for this engine and very humbled by it - I work alone from time to time in my garage and no-one here, at home that is, seems in the slightest interest!

I will try and answer some questions;

Niels; The crankshaft is made up in sections as illustrated and a press fit of the crankpins (with some bearing loctite) was used. The mail problem was, on first assembly, is ending up with a lot of run-out (a banana). The remedy is to try and maintain concentricity during the removal and replacement of the same component during machining operations. It took a while getting that right and I fear is the main downfall of many of these types of engine cranks. I used 12L14 for the main crank parts with two ground silver steel rods for the crank pins.

Craig: Contact me any time, glad to support you - I have cheated in some areas and more than happy to share. I am also building the 4 cylinder boxer engine and happy to report that the crank is turning with no binding (with some tweaking) - no small feat with built up cranks. I used the same cast iron Meehanite for both liners and rings, seems to work fine. I see no reason for using steel liners, they should work fine and be less messy around the lathe although take longer to hone. I put a You tube video out on my 'Heath Robertson' cam grinder, it is a real hotch potch but works which is the main thing. Finally the heads require some thought working out what the drawings say.

John: The engine has a lot of compression, and is difficult to start due to this, but I believe that spark ignition is the way to go. I think I left too much material in the head, for fear of drilling through too much, leaving long glow plug holes - thereby leaving the business end of the glow plug a bit far up the hole. I think spark plugs would work better as this is a large engine - and finding 1.2 volts at 5 Amps is a pain, read 10 Amps for the 4 cylinder!

My cam grinder, for those interested is here -



Edited By Steve G on 03/01/2019 14:25:19

John Olsen04/01/2019 04:20:04
1002 forum posts
86 photos
1 articles

Steve, you might find it easier to start if you splash out for an electric starter unit. Saves a bit of wear and tear on the hands too. You do have to make sure you don't flood the engine and then force it over with the starter, that will bend things.

I can't remember how thick the shim is under the Saito cylinder, maybe 15 or 20 thou or so. There was some info in RCM&E a few years back, not sure if I can find those issues now. The cdi unit I used is the RCEXL unit. They are available from places like Hobby King or on Ebay. (No connection, just a satisfied user.) There is a twin cylinder unit, but I think that is meant for twins that fire 360 degrees apart, eg a waste spark will occur on the exhaust stroke. I don't know if Steves engine above is 180 or 260 degrees. If it is 180 you would want two single cylinder cdi units and two sensors. You can also get an optically isolated switch to let the RC side of things turn the ignition off, a handy feature.

Or you could try the Minimag people...I don't think they have any kits in stock currently but I am hoping they will put one together for me shortly, and maybe if a few other people show interest they would make some more.


Mick B104/01/2019 09:22:04
1366 forum posts
75 photos

Outstanding piece of work.

I'm familiar with 4-stroke parallel twins from motorbikes a long time ago, and this has a similar configuration, but what about ongoing lubrication? The parallel twins I remember had oil pumps, internal oilways to crank- and camshafts, dry sump systems and separate tanks.

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