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somebody must have done chain drive right? (on a 2 engine machine of course) chain to run the prop on a twin just makes sense to me. I easily get 10-12,000 miles out of a chain on my motorcycles that drive dirt roads and trails as well as pavement. I have a sealed 520 "O" ring chain on my Versys & it makes almost 70hp to the rear wheel... 23 hp should be no problem. 520 chain pitch matches commercial #50 drive parts.
actually... it's 530 MC chain that matches #50 industrial chain, not 520 like I said above. 530 way overkill... thats what they run on the Hyabusa, which makes 180+ HP at the rear wheel on the dyno. it is a motorcycle that is limited by the factory to 180mph (300kph) unless you know how to bypass the blocker (people do... it goes over 200mph). so the chain is plenty strong. anyway... I'm going to give it a try. as for weight of the drive parts.... my old plans from 20ish years ago say for the twin engine install, the thrust engine uses a 2TB46 and a 2TB110. With bushings and belts the weight of those parts is 27.4 pounds. #50 'B' chain sprockets go straight on the 1" shafts with 1/4" keys and setscrews. this is the stuff that runs for years driving conveyor belts in gravel pits and such. anyway, a 50B15 and a 50B35 are close in ratio to what my plans call for. those 2 gears together weigh 6.8 pounds. the chain is about .7 pounds per foot, but its a short throw, so 7' of chain = about 5 pounds more. because of the smaller diameter parts involved.... the chain drive system is easily 15 pounds lighter than belt drive. I know... surprised me too. I left the tensioners out of the equation because I think it will be a wash. I may add a dynamic tensioner & thats maybe a couple pounds with a 13T idler. starting this modification I was thinking in terms of using MC chain because it lasts so long and needs almost no maintenance... thats how I ended up on #50. I believe #40 chain would be as much as any of these engines would ever need, and that is another 20-25% reduction in weight. food for thought
OK.... update. chain is not going to be that fun. it's way lighter, etc, but the power pulses make the chain whip in a very scary way. there may be some way to make it work with a bunch of idlers and tensioners, but thats not for me.. that energy simply transfers to some where else. when I first got on this idea I was watching a guy with an ultralight aircraft using the same engine. he has many successful hours of operation. I think the difference is that his prop is a much smaller diameter and the centers between the PTO and prop are pretty short. me using a standard Ivo makes the center to center distance 30 inches (because of where the PTO exits the crankcase). anyway.... it was a good idea but no. the good news is that experiment only cost 100 bucks in parts. the bad news is I had to buy more pulleys. and as an aside... the BK110H thats spec'ed in my old plans is not the same as a Bk110. the diameter is about 5/8" difference ad the bushings are different. the H is smaller