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.