Why no diesel motorcycles?

I have little firsthand experience with motorcycles or diesel vehicles but I was reading the other day about the newish motorcycle being issued to the Marines. It's a Kawasaki KLR650 converted by a company to run on diesel to meet NATO's requirements for all vehicles/equipment to run on diesel or aviation fuel.

This diesel version gets almost 100 miles to the gallon at 55mph. That's a lot of traveling for a gallon of fuel and would seem to be a good way to stretch limited fuel supplies during some emergency while still being able to get around off-road or on otherwise impassable streets. However, I notice that there really aren't any production diesel motorcycles on the market in the US. I was wondering what are the drawbacks or technical difficulties in making a diesel motorcycle which make them commercially unpopular?

I would imagine that one drawback for consumers would be acceleration, based on riding in non-turbocharged diesel cars. Sort of like gunning the throttle on a small boat--you have to wait for the boat to start moving and picking up speed. That's an annoyance in normal traffic, but much less so under emergency conditions. Are there other problems that keep them off the market?

Cost would go up

That wouldn't stop people from buying one if they wanted it though.

Bottom line is that performance is lacking.

1. Weight. Heavier castings to handle the much larger compression and combustion pressure.

2. Noise regulations. Diesel combustion is loud. Would require water jacketing to muffle noise. Maybe more than already designed it to most.

3. Lack of compression braking unless a version of the "jake brake" is fitted. Jake brake adds another noise suppression need and some additional complexity.

4. Lower RPM generally because of the heavy parts used. Also less RPM range which forces transmission differences.


The Germans produced some diesel engined bombers during WWII but they were underpowered.

It could be done but.... not enough benefit to bother.

I'll add that the limited distribution of diesel (relative to gasoline) has always made any diesel powered consumer transportation a tough sell in the US. Also, pollution regulations have kept many advanced designs for diesel cars out of the US recently. I don't know if these regs apply to motorcycles as well.

Did you ever listen to a Harley? Those things can be extremely obnoxious as far as noise. My back yard patio set is 250-yards from the main city street, and at times Harleys going by stops my brother and I from being able to hear each other while talking from across the table (5-feet apart). I can’t see a diesel bike being more intrusive or obnoxious then that.

Off subject but noise gets you noticed on a motorcycle, thats a good thing, except for the military.
IIRC the last price I heard on the KLR diesel was about 20k.
The gov't has Very Deep Pockets, oop's We have Very Deep Pockets!

I think it's hard to use the KLR 650 price as a comparison since these are all basically custom conversions for the Marines. From what little I've read, single-cylinder diesel motorcycles are common in China so it's not like they don't already exist in large numbers out there. Then again, until fairly recently, the vast majority of Chinese were perfectly happy with their bicycles, so obviously, tastes and needs vary across countries.

Actually, doing a bit more reading just now, I was rather surprised at how low the horsepower is on diesel motorcycle engines. Very broadly speaking, you're talking 400-500cc of displacement to get just 10 hp. That's not going to go very fast at all.

To comply with the NATO rules... lets see one designed for the other option.
Aviation Fuel should allow it to go Faasssttttt...

Aviation fuel (jet fuel) is kerosene, it’s just a cleaner version of diesel fuel. No big jump in horse power with it.

I was referring to DOT certification. Not illegal local muffler removal.

There have been plenty of diesel motorcycles produced over the years, unfortunately they have never been very popular stateside. The big issues being they're very underpowered and quite heavy for their size. Not really a good combination on a motorcycle. With forced induction (turbo/supercharger) the HP can be improved, but that just adds more complexity and weight.

The other thing too, is they are sometimes a PITA to start. Diesel engine have very high compression meaning you either need a compression release that you'll have to fiddle with to get it pull/kick started, or it needs a powerful electric start. Again, adding weight and complexity.

The another thing is cost. A small diesel will cost quite a bit more than a similar gas engine will, while still being vastly underpowered. With two stroke gas engines being so cheap, powerful, simple, and relatively reliable...diesels never really stood a chance.

With that said, if you really want one you could probably build one. Motorcycles are pretty simple in design, if you could find an engine that will fit and has enough power, you can probably get it to work somehow. There are plenty of guys who have built diesel mini-bikes, converted motorcycles to diesel, converted two strokes to run on diesel, ect. If you really want one it isn't impossible to get one. It just depends on how crafty you are and/or how much money you're willing to spend.


Personally, I would love to have one, just because I have huge tanks of diesel for the business, so it really wouldn't cost me much to keep it running and I could fuel it up right at my yard. Plus, if worst comes to worst, 5,000+ gallons of diesel could keep a diesel bike running for a long time. It's the same reason I have a diesel truck. In an emergency/disaster I wouldn't have to wait in gas/fuel lines. I can just fill up at my pump and go.

Let's not confuse matters with FACTS. Jets are fast, so jet fuel in a motorcycle should make the motorcycle fast. It's just common sense!

I sense the need for a new post--Why no jet motorcycles?

Oh! I take that back. Why no jet motorcycles except for Jay Leno's jet motorcycle?

Three wheeled diesel euro utility vehicle
Ape (pronounced ah-pay)

Lacks perhaps the bravura of a motorcycle. Cute though.

Interesting website re diesel motorbikes
http://www.dieselbike.net/

Though as others state above, there dont seem to be any mass produced readily available models

Wow, Jay Leno has two Jet Cycles? He certainly has a fine collection of rare and very interesting vehicles. I like his steam powered cars.

By the way, do you know, are the motorcycles actually pushed forward by the jet exhaust, or do the jet engines simply produce mechanical energy, like the jet-turbine engine in a helicopter? I suspect that it just turns the wheels but I don't know for sure.

SPAM

There are diesel motorcycles, but they are just not as common. HDT supplies them to the Marinees, and here is a write up on them. http://www.autobloggreen.com/2008/02/28/nyt-test-drives-the-marines-diesel-motorcycle/ They remind me of a turboed drag car, they take a second to get going, but then they go. As the report says, they are going ahead on a civilian version. Pretty sweet I think.

As to the illegal muffler thing. Every state/ county/ and most the time city, has its own rules. In SLCounty Utah, a motorcycle can be as loud as it wants. There are no rules for this, they must just pass basic safety. No IM or soundchecks. However if you have a altered muffler on any other type of motorvehicle in SLCity, then you run the risk of being pulled over for 12.28.100 that says if your exhaust "increases, amplfies, or alters the sound of the exhaust" you are in violation. I know speed bumps that can alter the sound of exhaust in the city.

Leno also has a car powered by the same helicopter turbine that powers his jet motorcycle. He brought it to a local weekly car show a few months ago while it was being built.

Fun to play with but don't stand behind him when he fires it up...


John E