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Brian Rupnow

Design Engineer
Project of the Month Winner
May 23, 2008
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Barrie, Ontario, Canada
I have been so impressed by RReid's build of a v-twin engine on "Model Engine Maker" forum, that I've just had to start modeling my own version. I will use the same cylinder, piston, and cylinder heads (although one of the heads has to be machined "opposite hand") as my 7/8" bore horizontal engine. It is not terribly difficult to design a V-twin engine. However, I'm thinkin' Lincoln,--what if? What if two V twin "stand alone" engines were completely finished then mounted on a common baseplate. Then, with the correct rotational aspect between the two engine crankshafts (using a Lovejoy coupling), wouldn't that make a reasonable v4 engine? I think the second engine would have to be a complete 180 degrees out of phase with the first engine to make this work right, but I'm not totally sure yet. I'm not going to build any engines this summer, but I do love to design.---Brian
Okay---That's enough silliness for today. The timing gears are just hanging in space for now, not really positioned accurately.
Pardon my ignorance on this subject, but back in the late 60s my dad bought a new Ford Transit minibus. It had a V4 1750cc engine, with two crankshafts. The second crankshaft was a balance shaft. Do all V4s need one?
As a side note, we did 150,000 miles in that Transit in 3 years, same clutch and the heads were never taken off.
Hell, yes!!!--We can do this. All four valves have lifters. I have one idler gear on backwards but that will be changed. Tomorrow I will figure out how to support the idler gears and work on ignition.
Lee Webster--I can't answer your question, because I really don't know. I've never built a v-style engine before.---Brian
Why not put the cam between the cylinders, I know yours would be different, but less machining. Twin I built, 35cc


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With all the gears turned to have the hubs facing in the correct direction, I went ahead and designed a gear guard. I'm not sure of the final shape---It currently looks a bit too much like Mickey Mouse ears. I'll worry about that one tomorrow. The endplates for the crankcase are 1/2" thick, so that lets me use two 3/8" diameter shoulder bolts to support the idler gears.
You may want to look at some Harley engine pictures , their engineers fit a lot of parts in the lower ends of their engines .
As your cylinder/head layout can be traced back to Malcom Stride's Bobcat engine he was also ahead of you in other option s for these common parts. This was the beginnings of the NE45 -V6, I would think he was going to run the single cam down the middle at the top of the block, only needs one set of gears and a lot less friction. It has a Schillings type crankshaft


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Are you thinking about just basically connecting the crankshafts up to each other?? Am I reading that correct. I ask because I am pretty sure this will not work do to the slight difference between engines such as RPM and getting the firing order on the cranks just right. If you look at pulling tractors or anything else with multi. Engines they all are connected through gear boxes and such.
My thought was to couple the crankshafts together end to end. This would give the same result as one long crankshaft. The crankshafts would have to be "timed" with each other rotationally in order to have the firing order work correctly.
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With two cylinders, each of which must be timed more or less independently of each other, the simplest way for me to do this is with two sets of ignition points. That doesn't really trouble me, and I've found that by mounting the ignition cams to the camshafts, I can bolt a 1/4" thick flatbar across the back of the crankcase endplate to support them. My original thoughts on this engine was that I would run it with an open crankcase similar to what RReid done on his engine, but I see now that I can run it with a closed crankshaft with splash lubrication for the con rods.
I've never had a lot of luck putting tight bends into small tubing without kinking it. So---I'm going to make the intake manifold out of a piece of 1/2" aluminum plate. The carb is my old tried and true Traxxas 4033, same as I've used on my other engines.
After giving this design some thought. I think you may want to think about connecting your camshafts together. I think that this may be a easier way to get your ignition timing to work. I just don’t think you are going to be able to just connect the cranks together. I believe if you do it that way one engine will always try driving the other engine. And that will happen back and fourth. But if you also connect the cams together then I think your design has a very good chance becoming a great design. There is one other component that may allow you to use both engines independently of each other and that is by using a viscous coupling that would allow the engines to have normal variance’s between the two and maybe prevent a dominant engine. I truly look forward to see this engine development
There is no problem with coupling two engines together as Brian is proposing.
A V4, V6, V8 etc. Is no different to a row of V twins.
I have been working on a land speed record bike which had two parallel twin engines (supercharged and running on methanol and nitromethane) coupled together with gears.
They need to be timed to one another to minimise stress on the gears at maximum power.
Model engines which are to be run under no load will be fine the way Brian wants to do it.
That’s kind of what I was saying that it had to go through a gear box first. Brian was originally talking about just using a love joy coupler to couple the engines together. If anything I would not use a lovejoy. I would use a omega coupling at the very least.
It's not a gearbox, just a row of three gears of the same size, adjusted for minimum backlash. The gears are from Aerial Square fours (which are effectively two parallel twins in one case).
Brian's idea with effectively two independent engines and no load will be fine with the Lovejoy coupling.
Either that or rigidly fixed cranks, which would give the option of a single set of timing gears.

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