Twin engines anyone?

Anyone try two engines on one bike?

I have a Raleigh women's cruiser bike on steroids that I call "Girlie". She's had a 72-volt electric motor but now runs a Mitsubishi 2.2hp engine with tuned pipe, friction drive and 1.5" roller. I had a 1.125" spindle on it, but the engine redlined at 20-something mph. Acceleration was good, but the engine overrevved if I tried to keep up with traffic. I wanted more speed, so I installed a larger-diameter spindle.

Since I installed the bigger roller, I can live with the soft low end because I now ride safely with the flow of traffic. I also like the top end, but I need more acceleration. Also, hillclimbing needs improvement because of the 1.5" spindle. I COULD reduce to a 1.375" roller, but the thought of running engines front and rear fascinates me!

Here's my idea: One solution would be to install a second engine, like a Staton front-mounted friction kit designed for trikes. To simplify matters, I'd use another 2.2hp Mitsubishi engine and a 1.125" roller. This would give enough low and midrange power to scream to 25mph. At that speed, I release its throttle back to idle and floor the rear engine, which had been idling all along. With the 1.5" spindle, the rear engine takes over for high end duties while the front engine idles. If the engines are identical, it'd almost be like shifting gears.

Do you think it'd work?

Hey Norman, you think like me!

I still have the front hub kit. The LiIon batteries cost more than the engine kit, and then there's that awful ritual of R&R batteries. If LiIon cells become more reasonable, I MIGHT reinstall the electric motor. The bike was a sleeper with electric power.

I still want to try the twin-engine setup.

Both of your drawings seem plausible and should work. Good luck in your creations.

For myself, I ordered the friction drive front mount 2.2 hp Mitsubishi engine kit from David Staton. It is scheduled to arrive tomorrow and be installed over the weekend. That's what I like about friction drive kits. They bolt on in short time. If I had the workspace, I'd love to scratchbuild a motorized engine system.

Well, the kit arrived and I pre-checked for fitment. Dang, the front mounting bracket won't bolt onto the suspension fork without fabbing a horshoe-shaped plate to distribute the stress.

Sooo, I drove to the bike shop and bought a new Raleigh Retroglide 7 that I'd been wanting to buy for the past three years. It has multi-speed derailleur, dual v-brakes, cruiser-type frame and a solid fork. Once I solve the Rockshox mounting problems, I can install that suspension fork on my new bike. Then I'll donate my old girlie bike to charity.

Installing the front engine friction drive kit took 45 minutes, after carefully removing both fenders. Transferring the rear engine took another 45 minutes. I need longer bolts so finishing will take a few days.

I figured I'd swap over my front HD rim and HP tire before the maiden run. Of course, when I did that the v-brake arms hit the mounts because of the wider rim. The rear v-brake also hit the mounting bracket, so I clearanced that too.

When I rolled the bike onto the sidewalk, I thought both brakes were locked! Then I remembered friction drag and when I raised both engines, the bike rolled well enough, considering the extra weight. There is massive amount of friction drag to take into consideration now, and the front engine assembly drags more than the rear drive. The new bike takes getting used to, since men's bike frames are at least an inch taller, and because of the extra 16 lbs off to the left front.

So I walked my bike to the nearby park and picked a remote location. The rear engine started with two pulls. The front engine started in three pulls and both idled well. I sat down for a 5-minute water break and let the new engine start the break-in. It sounded much crisper than the rear engine. Maybe because it was tight, and the mass of the lighter spindle allowed it to rev quicker.

In a couple minutes, I was driving down a medium-size hill using both engines. The rear engine felt weak. It took a few minutes of driving to warm up, and there's that extra resistance with the front engine idling.. When the new engine kicked in, I was SOOOO glad I chose the 1.25" roller instead of another 1.5" spindle. Acceleration is UNBELIEVABLE! The engine needed break-in, so I kept the revs reasonable. There is a definite major power boost at low and medium end with dual engines. It could be a number of factors that made the front engine more responsive, such as smaller-diameter spindle, HD rim and slick tire.

All was going well for three miles, when I floored the new engine and it immediately died. And it's still dead and unwilling to start. I yanked that pull start numerous times but it still won't start. Driving with the rear engine only was sluggish until I remembered the front engine resistance. When I raised the new engine, it was much easier for the rear engine to drive home. When the new bike charged up the medium-sized hill, it was much easier than previously, because the 7-speed option helped me pedal when the engine needed it.

Everything went well until the new engine quit. I felt the power of the dual engines, and it was awesome. If you start off with the front engine then kick in the rear engine, you can feel the little extra help. When you're at low speed with rear engine only, you can SERIOUSLY feel the extra help from the new engine and smaller-diameter roller. I only have three miles on the dual-engined setup, so I can't comment much on it. There's no smoke in the face from the front engine, and the extra noise at idle and speeds below 15 mph was very little. When the new engine breaks in, there will be serious power and acceleration available!

Man, I miss my front suspension fork. It definitely smoothed out the bumps, especially the slow-speed ones. I either need to fab a special mounting bracket for the engine, or find one of those early single post suspension forks.
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Someone on the other forum mentioned that it might be that the gas cap was too tight. After letting the engine sit for two days, I checked the cap. Sure enough, it was VERY tightly screwed on, so I loosened it up and retightened it. After three pulls, the new engine started up!!

So I rode itr to work, which is five miles away. It rained enroute, and I was pleasantly surprised that the bike's rear tire slipped just once during the ride. With single engine, I'd have to feather the throttle all the way for miles. Traction with twin engines is excellent. Since the roads were wet, I wasn't able to full throttle both engines, and the new engine is still breaking in. Power and acceleration with the extra engine with 1.25" roller is excellent. I just need to keep both clutches engaged. If not the idling engine's spindle drag causes substantial resistance which the working engine has to overcome.

No problems whatsoever so far, except fore that one incident with vacuum lock in the fuel passage. Today, I'll take the long way home and challenge the hills.