The DIY Open Crank Engine Moped

opencrankbike

Anyone can strap a two-stroke engine on a bicycle to create a moped. But [robinhooodvsyou] has created something infinitely more awesome. He’s built an inverted open crank engine on a 10 speed bicycle. (YouTube link)  As the name implies, the engine has no crankcase. The crankshaft, camshaft, and just about everything not in the combustion chamber hangs out in the open where it can be seen and appreciated.

[robinhooodvsyou] started with an air-cooled Volkswagen cylinder. He filled the jug with a piston from a diesel car. Camshaft, flywheel, valves, and magneto are courtesy of an old Briggs and Stratton engine. The cylinder head, crankshaft, pushrods, and the engine frame itself are all homemade.

Being an open crank engine, lubrication is an issue. The crankshaft’s ball bearing is lubricated by some thick oil in a gravity fed cup. Even though the engine is a four-stroke,[robinhooodvsyou] adds some oil to the gas to keep the rings happy. The camshaft and connecting rod use Babbit bearings. While they don’t have an automatic oiling system, they do look pretty well lubricated in the video.

Starting the engine is a breeze. [robinhooodvsyou] created a lever which holds the exhaust valve open. This acts as a compression release. He also has a lever which lifts the entire engine and friction drive off the rear wheel. All one has to do is pedal up to cruising speed, engage the friction drive, then disengage the compression release.

We seriously love this hack. Sure, it’s not a practical vehicle, but it works – and from the looks of the video, it works rather well. The unmuffled pops of that low 4:1 compression engine reminds us of old stationary engines. The only thing we can think to add to [robinhooodvsyou's] creation is a good set of brakes!

[Read more...]

Home brew motorized bicycle is a super grocery getter

[Thor] sent in an awesome motorized bike build he found coming from the fruitful workshop of [Jim Gallant]. It’s an incredible piece of work built nearly entirely from scratch.

[Jim] welded the frame together on a home-built jig that keeps all the chrome-moly tubes in alignment before they’re pieced together. With the jig, the frame was kept extremely straight making a bike that turns very well and can be ridden no-handed.

All of [Jim]‘s previous motorized bikes used small Honda engines, but after hearing Robin Subaru engines are more reliable he decided to give one a go. The motor is attached to the derailleur gears with a continuously variable transmission usually found in scooters. [Jim]‘s earlier motorized bikes didn’t have indexed shifting and disc brakes like modern motorized bikes, but he decided to throw them in anyway. Everyone who rides his new super grocery getter comments on how smooth the ride is with these additions.

While [Jim] doesn’t have an official speed or MPG rating, he’s guessing this bike can carry three bags of groceries at 30 mph at 170 miles per gallon. A very efficient mode of transportation that is much safer than the other motorized bikes we’ve seen before.

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