Anyone thought about a diesel bike?

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LongboardMalinois

LongboardMalinois

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Jul 5, 2015
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I too have a 10hp Yanmar clone engine sitting in a box in my garage. I would love to put it in a bike, but i don't have a welder to make it happen, and i'm too cheap to buy one just to use it to build a frame!
 
cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
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Colonial Coast USA.
I just recently bought a 6hp clone for a fishing boat I am building. I considered a 10hp but it weighed 100+ lbs. The 6hp weighs 82 in electric start. That's a heavy engine for a bicycle based build. Fine for a M/C conversion. There are smaller ones out there.

But the greater issue is the inherent vibration associated with the diesel. The Yanmar clones do have a balance shaft and seem smoother than the old Hatz 6-8hp I have from the 70s. This engine sat on 4 isolators that were basically the same mounts used in the earlier Volvo cars(they used only 3).

That's a nice looking bike in the pic. The engine looks like a 6hp, but cant really tell. 6 would be PLENTY with the torque it makes. It would be wise to get a seriously honest answer as to how well the vibes are dampened by a frame sized for bicycle components before spending a lot of time on a build.
A 66cc CG can buzz hands and feet numb on certain frames, and its a crap shoot on harmonics with a one off frame. You wont know til its built.

I would love to have a small MB/MC diesel powered build and I'm not trying to discourage any one thinking about it. I just wouldn't want to spend a bunch of time on a build only to have it rideable for a short duration. A diesel would need to be a good long distance traveler.
 
Ludwig II

Ludwig II

Well-Known Member
Jul 17, 2012
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V twin in a motorcycle frame seems the most logical way. You could also go Isolastic, and have the engine/trans/back wheel in a subframe and isolate the seat/front tubes/forks with bushes if you use a single.
 
jolfstn

jolfstn

Member
Oct 30, 2011
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Seattle, WA
on youtube.com typed "2 stroke on diesel" & found weed-whackers & leaf blowers and a lawn mower that start using usual mix fuel, then after warmed up switched to diesel, and generally it seemed they ran a little slower, but had more torque.
Here's what Im thinking, have 2 fuel tanks on a switch, start with 2 stroke mix fuel, then after warm up switch over to diesel. Obviously it'll smoke, but based on what I've seen it appears it might work. Perhaps towards the end of the ride I would switch back to reg gas for easier starting next time. I'm thinking of rigging up a proof of concept and I'll let y'all know what the results are.

Only the last few weeks have I been able to ride at all, I was hit by a car in November and 5 broken ribs as well as other injuries do not make bike riding fun. I was Jones-ing for a while but am back on my bike!
 
Z

ZekeNoScooter

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Jun 18, 2019
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Agreen said:
Diesel carburetors...

Glow plug ignition...

I don't like being a nay-sayer, but it's not going to work. Converting a china girl to diesel is not impossible, but extremely impractical. It's like converting a cat to a dog.

But let me explain a couple things first. (I'm really not trying to be a jerk here, I genuinely want to help!)

Diesel engines don't have a carburetor. They can't. Diesel engines control the speed of the engine by fuel flow, not air flow. As a matter of fact, diesels don't even have a throttle plate! That's why cars and trucks with diesel engines have to use power steering assist brakes. Gasoline engines create vacuum when the throttle isn't fully open, so the brake booster uses vacuum to assist the brake force. Diesels don't have a throttle, so at any speed the manifold pressure is always zero.

So how do you control speed with fuel flow? Diesel engines use a very special high pressure fuel pump called an injection pump. It pressurized the fuel to somewhere between 3000 to 15,000 psi (depending on the engine or manufacturers) and a port gets uncovered at the right time to deliver the high pressure fuel to a poppet valve, known as an injector. The injector is positioned directly in the combustion chamber. Fuel flow is throttled through a valve, and engine speed is directly related to fuel.

At idle, there is very little fuel flow. There's a lot of air, and not a lot of fuel. That's why they're so loud at idle. That clackety clackety noise is detonation! But don't worry, the engine is designed to handle it! They have BEEFY components. Cast iron cylinder blocks, huge cooling channels, cast iron heads, mega-beef conrod, etc. They're beasts. That's why they last forever! Plus, the fuel is an awesome lubricant, so it gets lubricated from both sides of the piston as well.

As far as ignition is concerned, it's as easy as it gets. The compression ratio is in the neighborhood of 25:1. So when the air is drawn in, it fills the chamber with ONLY fresh air. No fuel. The piston starts heading up and compresses the bejeezus out of the air, which superheats the air. So hot. The injection pump sends fuel to the poppet, and a blast of atomized diesel comes rushing in to the hot air. Boom. And the rest of the cycle is the same for gas 4 strokes.

Glow plugs are used to preheat the air coming in so it makes the engine easier to start cold. It does not sit in the combustion chamber. It's in the intake.

Now, you may ask "but aren't there 2 stroke diesels?"

Of course there are. But they utilize a "scavenging air blower", which is effectively a supercharger. It blows exhaust gasses out the exhaust ports so that the piston only has to compress fresh air.

So there. MAJOR differences, and not too practical to try and figure out on a bicycle.

I hope this has been educational for everyone reading.

I like your way of thinking, though, longboard. If you can find a small diesel (they're out there) then you may be on to something...
Click to expand...
Thanks Agreen! Best explanation of how a diesel operates I've ever heard. I always assumed they operated on the same principal as automatic transmissions, which as everyone knows, run on FM...... (here's a hint: the M stands for Magic. The F is for.... well, that's NSFW or this forum. ) Anyway, super heated air meets atomized fuel and BOOM! Got it!
 
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