Any thoughts:

Use a transaxle with sprockets on each cv, with a locked diff to drive a single wheel. you'd have to work out a sprotor of some sort.

This way you could use a car engine/trans with reverse etc if you wanted to .

WHY?: There are no (available) diesel bikes

any comments?

Thinking about building a diesel motorcycle? I have, and I have ran into some problems you will most likely encounter as well. Using a transaxle with one output welded was one of the first thoughts I had, too.

The problem is two-fold; first off, you will end up with an immensely long drivetrain. There are plenty of pictures available here of Audi transaxles. Those things are not small by any measure. Most other transaxles are of similar size. More important however, is that shifting is going to be a major pain in the @ss. Not only do you have to work a relatively heavy clutch (when compared to a bike-clutch), but also you'd have to manage a manual H-pattern shifter. 'Conventional' suicide shifters are hard enough to work with (and aptly named, too!) Just imagine having to find and select the proper gear in a very long, and very heavy motorcycle with only one hand on the handlebars to help in balancing it. Not much fun!

I figured that if you'd want to use a transaxle, you'd be best off using an automatic transmission. But there are problems with this, too. Again, the size problem remains. Furthermore, there are not all that many automatic transaxles about, and the few that are available are likely to be pricy. What ultimately killed the idea for me though, is that it would be very difficult to match engine and transmission characteristics. The torque converter would have to be adapted, among many other things, to change from a high-revving, low torque (relatively) engine, to a low revving, high-torque application. Finding suitable parts would be a nightmare.

I figured it would just not be worth the hassle. Next idea was using a transverse engine layout, and transplant it from a car onto a bike. since there are no cheap and plentiful FWD diesels with automatics, it would be likely that a manual transmission would have to be used. The shifting problem would remain, yet the whole set-up would be much more compact, and you wouldn't have to mix-and-match parts...

Then I shifted focus. There are tons of diesel engines available, but every time, it seemed the transmission was the problem. So I started collecting some more ideas.

One of the most promising (and indeed already used) ideas was to utilize a BMW motorcycle transmission. It is, in essence a transaxle with only a single-side output. These transmissions, albeit a bit expensive, would do the job just fine for a medium-powered diesel application. I compared the torque of the BMW engine to that of some diesel engines, and I found that the transmission ought to be able to handle the power and torque of a VW 1.9 non-turbo engine with ease, if an adapter plate could be made. This was easily my favorite set-up as it would use parts that are reasonably priced, extremely reliable, and would just plain work for the application I had in mind.

When I moved to Thailand, I had to rethink my ideas yet again. My plans had become seriously delayed, but nevertheless I looked around to see what could be done using local materials. In terms of diesel engines, the options I have here aren't the greatest. Diesel saloons never have been very popular, and the omnipresent pickup trucks all come with engines far too large/heavy/powerful to be of much use in a bike (a 3 liter dieselbike is only good for bragging rights. It would be rubbish to ride!)

Then I got inspired by the most unlikely thing; tractors. Over here, farmers use tiny little Kubota tractors to work the fields. The engines are moderately sized, with a displacement of only 1 to 1.2 liters, no turbo, no nonsense. They rev up to 3000RPM max. I got enchantd by them because of their typical plop-plop-plop tractor sound, as well as a gargantuan flywheel on the side... the flywheel reminded me of those antique steam-powered behemoth tractors.

Anyway, having a side output would mean finding a suitable transmission all over again. Luckily, the Discovery Channel offered a solution in the form of American Chopper. Mind you, I despise the show, and hate the sissy bikes they build, but I slapped myself for completely overlooking the Harley Davidson external transmission. A four or five-speed HD transmission would do the job perfectly. The diesel engine only got about 20Hp, and the trannies can take quite a bit of torque from their stock application. Furthermore, these tranmisions are not too large, and can easily be sourced, ordered and shipped through e-bay. If I were to stay here and ever start this project, this would probably be the way I'd go. It would be a slow and sluggish, easy going and burbling machine. But I know it would be fun to ride!

In your situation though, I'd recommend looking at the BMW transmissions and finding an engine to match. The N/A Volkswagen diesels are great. Perfect reliability, plentiful and dirt-cheap. However, they are also quite large and heavy. If your budget would allow it, also have a look at the newer 3-cylinder diesels from VW, or SEAT and of course Smart. Daihatsu also has 3-cylinder diesels I believe, as do a number of other Japanese makes. Newer engines will be more expensive, and may be harder to work on due to all the electronics, but they will also be a lot more compact, lightweight and perhaps also more fuel-efficient.

FWD transaxles are quite compact.
I've thought of industrial engines,torque averters HD external trans etc.
I would like to stick with a car engine, just looking for thoughts on the output/ sprocket question.

Unless you find a cheap and compact automatic transaxle that is compatible with your diesel engine of choice, you're still going to be stuck with a manual gearshift that is far, far from ideal. Especially if you plan to do a reasonable amount of city-driving, I think it's fair to say that a manual transaxle is no real option.

That is, unless you want to bother with solenoid-actuated shifting or something like that. No idea how you'd pull that off though.

But to answer your original question; yes, it is entirely possible to weld up one side and attach a sprocket on the other side.

Here's an idea though; why bother with gears at all? Unless you wanna go fast, or attempt to set a fuel-economy record or so, do you really need more than one gear?

Sounds crazy, but the Tomahawk concept bike only has two gears.. it relies solely on massive torque.

Now assuming you'd use a slightly more sane engine than the Tomahawk did, you might get away with using a torquey diesel, mate it to a clutch of choice which in turn is mated directly to a differential. (Freelander diff?). Then, do the same trick as above. Weld up one side, fit sprocket to the other side. Figure out the gearing so you have a 140 km/h top speed at 'redline', and you should end up with a reasonably simple design that could work.

If you need more torque, pick a turbodiesel engine. Since the turbo won't do you much good at take-off, just scrap it, and replace it with a small supercharger that delivers pressure from idle and up...

Hope that helps..

I just did a quick calc... If you want a top speed of 140kph, a single-speed bike would need an overall reduction of approximately 4:1.

I wouldn't really know how realistic that is in terms of driveability. I guess you'd have to go for a heavy duty clutch though..

Actually, thinking about it.. I think it should be doable.. assuming an all-up weight of 340kg including the driver, and a 60Hp diesel engine, you'd have about 175Hp / ton. And you'd have plenty of torque low-down where you need it.

Hmm, I did a quick calculation on that ratio;

code:
 

RPM    MPH   	 

0  	  0.0   		  	  

100  	2.0   	  	  

200  	4.0   	  	  

300  	6.1   	 	  	  

400  	8.1   		  	  

500  	10.1   	  	  

600  	12.1   	  	  	  

700  	14.2   	  	  

800  	16.2   	  

900  	18.2   	 

1000  	20.2   		  	  

1100  	22.3   	 	  	  

1200  	24.3   	 	  	  

1300  	26.3   	  	  

1400  	28.3   		  	  

1500  	30.4   	   	  	  

1600  	32.4   	  	  	  

1700  	34.4   	  	  	  

1800  	36.4   	  	  	  

1900  	38.5   	  	  	  

2000  	40.5   	  	  	  

2100  	42.5   	  	  	  

2200  	44.5   	 	  

2300  	46.6   	   	  	  

2400  	48.6   	  	  	  

2500  	50.6   	  	  	  

2600  	52.6   	  	  

2700  	54.7   	 	  	  

2800  	56.7   	   	  	  

2900  	58.7   	  	  

3000  	60.7   	   	  	  

3100  	62.8   	  	  	  

3200  	64.8   	  	  	  

3300  	66.8   	  	  	  

3400  	68.8   	 	  	  

3500  	70.9   	  	  	  

3600  	72.9   	 	  	  

3700  	74.9   	  	  	  

3800  	76.9    	  	  

3900  	79.0   	   	  	  

4000	81.0   	 

If you were going for a single speed, I'd do a torque-a verter or centrifugal clutch with a single cyl engine in a lightweight package.

most fwd trans.are cable shift, so I don't see that as a major obstacle.

quote:

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Originally posted by tigris
most fwd trans.are cable shift, so I don't see that as a major obstacle.

---

I am intending a 3 wheeled vehicle, not a 2 wheel.

In my original post I should have specified, but the fact is that there are no diesel bikes I could use as a donor.

Well a trike definitely makes things a lot easier

Would you put two wheels in the front and one in the back, or the more traditional two in the back and one in the front?

If you put two wheels up in the back, you may not have to deal with fitting a custom trans at all. Just find a diesel donor car that has a transversely mounted engine, such as most diesel cars, I guess.. VW would be good.

If you'd put two wheels on the front, you could do the same trick, and just drive the front wheels. If you want to drive the rear wheel, you could stick to your original plan and weld a sprocket on the transmission.

This is how I thought it might work:

Why not use a shaft drive bike swingarm and just extend the shaft? It would save reinventing the wheel.