Will The Second Engine Start Automatically?

5-7HEAVEN

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Hello. I'm throwing this out into the universe, hoping someone has had a similar problem and solved it. I'm installing two Tanaka 47R engines on my 7-speed bike. Each has its own identical chain drive, sprockets and 5:1 reduction gearboxes. Gearboxes bolt onto each engine and have 11-tooth sprockets. They each chain to separate 72-tooth driven sprockets at the bike's bottom bracket. All three sprockets at the bottom bracket spin on a freewheel, and a single 24-tooth chainring sprocket drives the 14t-28t rear cassette.

The bike hasn't run yet. Being that each gearbox has a clutch, I figured that would keep both engines to run separately, with their individual throttles.

Twin engines CAN run independently of each other. I know this, because I built a cruiser with an engine on each tire(friction drive.)Their throttles need not be synchronized.
It's like two football players pushing a small car. One guy's using all his might, and the other player's faking it and just has his hands on the car.

It was a given that both engines' drivetrain would be spinning, even if I chose to fire up just one engine. I figured since they both have clutches which engage about 1500rpm, the dead engine wouldn't be spinning its own clutch.

Knowing that both engines' drive trains would be turning, an engine speed of 3000rpm will have the rpms reduced by the time it gets to bottom bracket. The engine spins at 3000rpm. Its gearbox reduces it to 600 rpm. The 72t/11t further drops the revs to 92rpm.

Then something odd happens. The 92rpm from the bottom bracket now spins the non-running engine's gears. From 92rpm, it rises to 600rpm at the gearbox's shaft.....then spins that clutch and compounds(not reduces) the revolutions to 3000rpm at the dead engine's clutch!

Talk about the tail wagging the dog! LOL!

So the dead engine's clutch spins to 3000rpm, engages the engine and fires it up, if the ignition switch is on!

My question is.....do you think this will happen? I can't install 5000rpm clutch springs on the dormant engine. Then I wouldn't be able to run both engines at low speed.

Eventually, I'll find out, when the bike's done and running. I'd like to know now, if possible.

Thoughts?
 
I still have to fab the motor mounts. I have room in the frame to mount the engines in a "V-Twin" position. Depending on clearances between the rear engine's air filter and the front engine's exhaust, it might end up in a 90-degree angle.

I can post mock-up pics, as soon as I find out where I hid my second engine.:)
 
Doesn't the force from a running engine spins the clutch to engage it? If you put a chain around a clutch gear and run that with another engine, nothing will happen, you're just spinning the bell and not the ramps inside.
 
it shouldn't. as the clutch only spins the bell and not the actual clutch.
im assuming its going to be a side by side twin.
heres how id do it:

i would have one attached to a gear reducer and then extend the chain from that one to the other one, and make the clutch tooth count higher on the second one, so it gives you the most torque for a broader range. as the first one spins out the second one comes in its power band and gives you that extra top end.
as well as being a overall simpler system and would be more efficient as well.

just my opinion
 
Thanks for the quick responses, guys. I believe you all are correct that only the bell would be spinning on the dead engine. Thanks.

mark20, your plan would work for me. Right now, both engines are geared at 38.18:1 in low gear and 19.09 in 7th gear.

Hmmm. If I change the second engine's sprocket to 14-tooth, its low gear would be 30:1, with final drive at 15:1. If the first engine's buzzing too high, I can turn it off and run the second engine alone in high gear!

One of my previous twin-engine bikes had two different sized friction rollers. If I throttled the one with the smaller-diameter rollers, then slacked the gas and throttled the engine with the large-diameter roller, it was almost like I shifted into another gear! That was FUN!

That might work out VERY well! One of my engines has been ported. If I can use the Tanaka-specific tuned pipe I had on my previous bike, it can be my primary, higher spinning engine. The second engine will have a stock muffler or generic pipe that can fit my bike. Two different sounds and power levels, but hey.

However, I'm not keen on running a single chain for two engines. For one, the extra engine is the "back up". If one fails, the second engine brings me home. This worked well on my first twin-engine bike. When one engine failed(usually running outa gas), I "limped home" on the second engine.

Also, the engines' "V-Twin" centerline won't be directly above the bottom bracket, but positioned a few inches forward. I guess I'd need a chain tensioner.

I like two chain drives, independent of each other. I use T8F/pocket bike chains and sprockets; I've never any of them fail, except for one circlip. It machined down to a perfect "fish hook", due to the misaligned T8Fchain rubbing against it.

This isn't as simple as my first twin-engine bike was. I finished that one in a day. That was fun; I always ran with both engines on.:)
 
Thanks for the quick responses, guys. I believe you all are correct that only the bell would be spinning on the dead engine. Thanks.

mark20, your plan would work for me. Right now, both engines are geared at 38.18:1 in low gear and 19.09 in 7th gear.

Hmmm. If I change the second engine's sprocket to 14-tooth, its low gear would be 30:1, with final drive at 15:1. If the first engine's buzzing too high, I can turn it off and run the second engine alone in high gear!

One of my previous twin-engine bikes had two different sized friction rollers. If I throttled the one with the smaller-diameter rollers, then slacked the gas and throttled the engine with the large-diameter roller, it was almost like I shifted into another gear! That was FUN!

That might work out VERY well! One of my engines has been ported. If I can use the Tanaka-specific tuned pipe I had on my previous bike, it can be my primary, higher spinning engine. The second engine will have a stock muffler or generic pipe that can fit my bike. Two different sounds and power levels, but hey.

However, I'm not keen on running a single chain for two engines. For one, the extra engine is the "back up". If one engine or its chain or sprockets fails, the second engine will bring me home. This worked well on my first twin-engine bike. When one engine failed(usually running outa gas), I "limped home" on the second engine.

Also, the engines' "V-Twin" centerline won't be directly above the bottom bracket, but positioned a few inches forward. I guess I'd need a chain tensioner.

I like two chain drives, running independent of each other. I use T8F/pocket bike chains and sprockets; I've never any of them fail, except for one circlip. It machined down to a perfect "fish hook", due to the misaligned T8Fchain rubbing against it.

This isn't as simple as my first twin-engine bike was. I finished that one in a day. That was fun; I always ran with both engines on.:)
well, good luck to you!

post up some pictures of the build, im very interested on how this will play out.
 
I would just have them both at the same RPM and gearing, the torque from the double engine should be enough to get fast. I think you shouldn't have a gearing that makes you faster than 70kmh, or like 45mph, because, to be honest bikes are not that safe, and you will feel the road at that speed. I have only went 62khm or like 40mph, and that was scary enough.
 
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