5HP Diesel Motorbike
- Thread starter Tanshanomi
- Start date
I was able to get back into the workshop long enough to button up the jackshaft assembly. I shortened the keyed shaft, then faced it and cut a channel for the circlip in the lathe.
I made the last remaining spacer needed and assembled it all. I was a little bit generous on the shaft length, because I wanted to ensure I could align the sprockets correctly.
I installed the primary chain, and my adjusters worked perfectly (though they’re a real bear to get in and adjust). Here’s the chain at the most slack setting:
And here the jackshaft has been moved to the third position, out of four. You can see there’s about a 1/4” extra shaft sticking out on primary side, but everything spun smoothly and easily.
I made the last remaining spacer needed and assembled it all. I was a little bit generous on the shaft length, because I wanted to ensure I could align the sprockets correctly.
I installed the primary chain, and my adjusters worked perfectly (though they’re a real bear to get in and adjust). Here’s the chain at the most slack setting:
And here the jackshaft has been moved to the third position, out of four. You can see there’s about a 1/4” extra shaft sticking out on primary side, but everything spun smoothly and easily.
With the primary chain sorted, it was time to start up the Chinese Yanmar clone motor for the first time. I decided to attempt a static “pad test,” the primary chain fitted, but no final chain to the rear wheel. This would allow me to make sure the jackshaft and centrifugal clutch were functioning smoothly, and just generally observe the engine running, with the bike still strapped into its shop stand.
I filled the crankcase with oil, checked the fuel lines and engine mounting bolts, opened the fuel cock, and gave the starter rope a tug. Nothing. Well, I expected that it would take a couple of attempts to get the injector lines primed. I verified the fuel was on, and tried again. And again. And again.
And again. Several hundred times. I tried pulling the engine through multiple times with the compression lever off and the fuel on. Then with the fuel off. Half throttle. Full throttle. Full throttle followed by no throttle. Every possible variation I could think of. My utter lack of knowledge or experience with diesel engines didn’t help. The pull-starter is not horrible to use, but it’s not pleasant or easy, either. Of course, I painfully discovered that forgetting to flip the decompression lever was like yanking on a rope tied to a brick wall.
After 90 minutes, with dusk approaching, I gave up without so much as a glimmer of life from the engine.
I also learned another crucial tidbit from online research that I should have learned in the planning stages of this project: small diesel engines like these will usually only start at full throttle. WOT, and nothing less. If a centrifugal clutch is the only thing de-coupling the crank from the rear wheel, this is a fundamental problem I had not considered. Either the bike lurches forward immediately, or the drag on the clutch kills the engine just as it’s catching fire.
On top of that, I was already aware that (without any electrical system) the only way to kill a diesel is to shut the throttle completely. That means that either you adjust the throttle so low it won’t idle and you must keep with running with your hand on the throttle, or you need to invent some other linkage set-up to close the throttle further when you want to kill the engine.
My wife and I have a saying: “Not every clever idea needs to happen.” This is a perfect example of a project that sounded promising, and went really well at the start, but became more unworkable the deeper I got into it. All of this is sucky — the difficult starting, the incompatibility with a centrifugal clutch, my cluelessness about diesel maintenance, the lack of an effective kill switch. I have determined this engine was a very ill-advised choice. I’m going through all of this to end up with something that will be no more than a novelty at best. Uh, NOPE. It’s not worth any more effort. I’ve pulled the plug.
I pulled the engine and fuel tank out of the chassis, reassembled them as they came, and put the engine back in its crate. The chassis is still worth completing, so I am going to carefully consider another engine to slot in this frame. I’ll probably keep the jackshaft and run just a centrifugal clutch, rather than a CVT, just to minimize the cost and effort needed to complete the project. But it’s going to run on gasoline, whatever it is.
And I am going to make sure the damned thing runs before I install it!
I filled the crankcase with oil, checked the fuel lines and engine mounting bolts, opened the fuel cock, and gave the starter rope a tug. Nothing. Well, I expected that it would take a couple of attempts to get the injector lines primed. I verified the fuel was on, and tried again. And again. And again.
And again. Several hundred times. I tried pulling the engine through multiple times with the compression lever off and the fuel on. Then with the fuel off. Half throttle. Full throttle. Full throttle followed by no throttle. Every possible variation I could think of. My utter lack of knowledge or experience with diesel engines didn’t help. The pull-starter is not horrible to use, but it’s not pleasant or easy, either. Of course, I painfully discovered that forgetting to flip the decompression lever was like yanking on a rope tied to a brick wall.
After 90 minutes, with dusk approaching, I gave up without so much as a glimmer of life from the engine.
[The seat is temporary. I just needed something I could flip up to access the fuel filler.]
The next day, I tried troubleshooting. After watching a few YouTube tutorials, I disassembled the fuel pump and verified the throttle linkage was properly connected. I verified that the petcock flowed properly and the fuel pipe was primed with fuel. The only new result was that with the air cleaner removed, I could get a puff of smoke out of the air intake once in a while. My only guess is that the fuel pump is not shimmed properly, so the injector timing is off. Either that or this is truly a defective engine. It cost me $300 total with shipping, shipped directly from Guangzhou, so that’s not an unreasonable explaination.
I also learned another crucial tidbit from online research that I should have learned in the planning stages of this project: small diesel engines like these will usually only start at full throttle. WOT, and nothing less. If a centrifugal clutch is the only thing de-coupling the crank from the rear wheel, this is a fundamental problem I had not considered. Either the bike lurches forward immediately, or the drag on the clutch kills the engine just as it’s catching fire.
On top of that, I was already aware that (without any electrical system) the only way to kill a diesel is to shut the throttle completely. That means that either you adjust the throttle so low it won’t idle and you must keep with running with your hand on the throttle, or you need to invent some other linkage set-up to close the throttle further when you want to kill the engine.
My wife and I have a saying: “Not every clever idea needs to happen.” This is a perfect example of a project that sounded promising, and went really well at the start, but became more unworkable the deeper I got into it. All of this is sucky — the difficult starting, the incompatibility with a centrifugal clutch, my cluelessness about diesel maintenance, the lack of an effective kill switch. I have determined this engine was a very ill-advised choice. I’m going through all of this to end up with something that will be no more than a novelty at best. Uh, NOPE. It’s not worth any more effort. I’ve pulled the plug.
I pulled the engine and fuel tank out of the chassis, reassembled them as they came, and put the engine back in its crate. The chassis is still worth completing, so I am going to carefully consider another engine to slot in this frame. I’ll probably keep the jackshaft and run just a centrifugal clutch, rather than a CVT, just to minimize the cost and effort needed to complete the project. But it’s going to run on gasoline, whatever it is.
And I am going to make sure the damned thing runs before I install it!
First the centrifugal clutch and wide open throttle can be solved with a center stand lifting the rear wheel off the ground. Second, set up a means of turning the crankshaft with a LARGE electric drill. Lastly are you sure you have no air in the fuel system, any large diesel i ever messed with had to have the fuel system properly primed prior to start.
A change of engine?
After pulling the diesel engine out of the bike, I tried positioning a couple of other NOS engines in the frame to see how they might work. First was a Tecumseh OH195SA. It would fit great except that the carb is situated a fair distance away from the rear of the engine, and I’d have to raise the engine up about 2 inches or so for the float bowl to clear the jackshaft. That meant that I had to remove the muffler. Regardless of how it might fit, it is not a very attractive engine. This one was ultimately a “no.”
Next up, I tried my new Honda GS190 engine, which I recently purchased without a firmly defined use in mind. I just knew that the vertical cylinder would make it easier to swap into an existing motorcycle frame, and look better, too.
I removed the rear-mounted fuel tank and airbox, then set it in place so the crankshaft was the same distance from the jackshaft sprocket as the diesel had been. Not gonna lie, I don’t dislike this. It doesn’t have the seemingly “made to fit” aesthetic that made the 173F look so cool in this frame, but this combination will probably be a much more practical and useful end result.
I have not made any firm decision at this point. I’ll sleep on it for a few nights before I decide how I want to move forward. Several people have expressed deep disappointment I’m not sticking with the diesel, and I feel as though I’m letting down everyone who has expressed enthusiasm for this build. I suppose I will need to mess with the diesel engine again at some point, even if just to sell it off to another tinkerer.
After pulling the diesel engine out of the bike, I tried positioning a couple of other NOS engines in the frame to see how they might work. First was a Tecumseh OH195SA. It would fit great except that the carb is situated a fair distance away from the rear of the engine, and I’d have to raise the engine up about 2 inches or so for the float bowl to clear the jackshaft. That meant that I had to remove the muffler. Regardless of how it might fit, it is not a very attractive engine. This one was ultimately a “no.”
Next up, I tried my new Honda GS190 engine, which I recently purchased without a firmly defined use in mind. I just knew that the vertical cylinder would make it easier to swap into an existing motorcycle frame, and look better, too.
I removed the rear-mounted fuel tank and airbox, then set it in place so the crankshaft was the same distance from the jackshaft sprocket as the diesel had been. Not gonna lie, I don’t dislike this. It doesn’t have the seemingly “made to fit” aesthetic that made the 173F look so cool in this frame, but this combination will probably be a much more practical and useful end result.
I have not made any firm decision at this point. I’ll sleep on it for a few nights before I decide how I want to move forward. Several people have expressed deep disappointment I’m not sticking with the diesel, and I feel as though I’m letting down everyone who has expressed enthusiasm for this build. I suppose I will need to mess with the diesel engine again at some point, even if just to sell it off to another tinkerer.