Seeking plans for twin cylinder inline i.c. engine

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Brian Rupnow

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2023 has not been a great year for me. I have built 3 model engines of my own design, and they don't run at all or not as well as I had hoped. Now I'm looking for a complete set of plans for a two cylinder, inline, four cycle, air-cooled gas engine. Not a diesel, not glow-plug. Plans must be complete, and I want to see a completed running engine made from these plans. I have done a web search, and while there are lots of 4, and 6 cylinder inline engine plans for sale, I haven't found any twin inline plans. This engine will not power an airplane, will just be a desktop model.--Thank you.--Happy New year.----Brian
 

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This engine looks close to what I want, but the low end rpm is about 1500 rpm. I would like something slower than that with an idle speed of 900-1000 rpm.
 
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The Jung plans are all methanol glow plug engines which Brian said he didn't want. But spark plugs can be had with same 1/4-32 threads, they are just a bit longer body. Or smaller plugs yet as mentioned in another post. So long you can figure out the rest of the spark ignition system & gasoline specific issues vs. methanol (C.R., carburation, minor lubrication & heat differences).

I'm working modifying Jung's opposed 2-cyl boxer for spark ignition as we speak. So far the plan is RCEXL twin firing CDI box.
 
This engine looks close to what I want, but the low end rpm is about 1500 rpm. I would like something slower than that with an idle speed of 900-1000 rpm.
If this RPM came from Jung specs, he is probably being realistically accurate & reflects typical 4S glow ignition performance. Lower RPM on glow can be had (within reason) but typically comes by adjusting specific things: fuel composition, timing, carb, onboard glow... & may come at the expense of even mid level RPM levels or transition.

But this might be a good example of 'glow type' engine converted to gasoline/spark from idling & transition perspective. There are many on this particular website as he is a seller & service outlet. Part of what the CDI is providing is built-in (RPM sensing) advance / retard curve which also helps with idle & hand starting. I haven't graduated to understanding coil ignition & manual advance/retard distributers like many fine examples on this forum.

 
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The Jung plans are all methanol glow plug engines which Brian said he didn't want. But spark plugs can be had with same 1/4-32 threads, they are just a bit longer body. Or smaller plugs yet as mentioned in another post. So long you can figure out the rest of the spark ignition system & gasoline specific issues vs. methanol (C.R., carburation, minor lubrication & heat differences).
petertha,
I changed mine(Jung V Twin) over to Spark, used the RCEXL LV spark box, required two magnets at 90deg apart, first south, second north facing.
Done the same with the same engine(Magumn) 20 years ago, still run on glow fuel, spark for better idle and transition.
Cheers
Andrew
 

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Charles--that Seagull engine looks very nice. I wonder if anybody has ever built that engine from bar stock, not using castings.---Brian
 
Brian, you have commented (about 2 years ago, over on the MEM forum) on the video of my Seagull running, and my website which you have probably seen: Seagull Engine Construction Diary goes in to a lot of detail about building the standard water-cooled one from castings.

Building one from bar stock would be perfectly feasible, but quite a lot of work to make it actually look like an engine. I think about the only castings Graham ended up using on his engine were the crankcase and sump. But look at his timing case. That involves some quite intricate milling. There is also a lot of work in his built-up brass manifold. On the other hand, I put in a lot of cosmetic hand work to make my castings look as good as they do. I ended up making the exhaust manifold (sandwiched between the inlet manifold and cylinders) from solid, and there was a lot of hand work to make that look like a casting too. The photo near the top of my home page shows the engine nearly complete.
 
Okay--I see that I'm not getting a lot of action on this page, and that, along with my own web searches more or less confirm what I thought. There simply haven't been that many 2 cylinder inline engines built. In general, I have more luck with 1" bore engines than with smaller sizes, and that size bore leaves me enough room in the cylinder head to use two valves and a 10mm thread diameter sparkplug. I'm setting here looking at my Tee head engine from two years ago and thinking, Hmmm----I wonder---
 
Strictly IC magazine had a huge selection of different engine build articles and plans over the many years it was published. I don't know if back issues are available anywhere or not. I have every issue ever printed, really lucked out and got them from a local fellow for $40 !!!
 
Thanks Ghosty. I have sent them off an email requesting price for a set of plans in Canadian dollars.--Brian
Not sure if you got your reply already but but when I dealt with him, I added to cart, populate address/Canada (so it calculates shipping cost). I can't recall if I paid Paypal or Visa but it completes FX conversion. At 29.80 euros shown, works out to 43.52 KanuckaRubles sans shipping. The plans are 2D dimensioned (metric) from 3D model, BOM tables etc. I note that the upright twin has plugs are on the opposite side of rocker box which is not the case for the opposed boxer twin I'm working on, but I'm planning several mods anyways. Its a big engine so looks like lots of room for typical ignition boots & same 1/4-32 plugs if you go that route.

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Assuming this is what you were looking at.

https://www.cad-modelltechnik-jung.de/construction-plans-model-engines.html
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Brian, why not build the Bobcat, most of your engines that have run are based on that design anyway so you have the drawings and know it works.

Scale it up to 1" bore if you want or use readily available 1/4" spark plugs and stick with the original sizes

Bob Shores Hercules would be a good candidate for a slow runner, could make a boxy aircooled barstock one easy enough rather than use the castings.
 
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