5HP Diesel Motorbike

[Tanshanomi]

I shared some of this information in another thread and @DaddyJohn suggested I start a new one.

Like my last project, The Bride, this will be built on a full-size motorbike frame—so technically not a "minibike." But with only 5HP and a centrifugal clutch, it is more in keeping with what folks here are into than your run-of-the-mill motorcycle enthusiast.

So, I got the bug to do a diesel-powered build. Before long, this nice little 173F [247cc, 5HP] Yanmar clone followed me home. $295 in total, w/tax & shipping.
https://www.amazon.com/dp/B0D95J65S9

I've had a 1979 KTM GS80 250 frame in storage for a while without a clear notion of exactly what to do with it, so I pulled that out and, sure enough, the 173F fits in the engine bay without too much effort.

Unfortunately, there isn't room to fit a typical 30-series torque converter: the crank PTO is waaay too far outboard, and there isn't fore-aft room for a CVT without significant mods to the frame. In order to avoid undue complexity, I am going with a simple centrifugal clutch, driving a jack shaft. That's not ideal, but with only about 5HP on tap, it’s going to be S-L-O-W no matter how I rig it up. I'll just gear it down low enough to practically facilitate take-offs, and then see what sort of top speed that gearing gives me.

As for wheels, I am going to stick with "real" motorcycle parts, but my gearing challenges mean the smaller the diameter, the better. I have chosen matching 16-inch Suzuki cast rims, circa 1983 (GS300L rear, GS550L front). Both are 2.15" (WM3) width and will take the same 90/80-16 tire size front and rear.

I have some additional chassis parts in the storage locker I can use to cobble together a rolling chassis. I've got some other bike projects on the front burner right now, but I'll post updates when I have something more to show you.

 

[cl350rr]

I like the plan, can't wait to see it come together

 

[sparkwizard]

Your projects are always very well done and I really like following along. This one will certainly be different.

 

[sparkwizard]

Can you mount a torque converter on a couple of jackshafts driven by a chain from the engine? That would give you a lot of options for your rear sprocket. I have one like that on the back burner, if you want too see my idea.

 

[Tanshanomi]

Can you mount a torque converter on a couple of jackshafts driven by a chain from the engine? That would give you a lot of options for your rear sprocket. I have one like that on the back burner, if you want too see my idea.

Interesting, but there would be some power transmission and packaging headaches with that. If I really wanted a CVT, I would just modify the frame. As it is, I'm going to go the quick-and-easy route initially. I can always make changes down the line if it's not satisfactory.

 

[Tanshanomi]

Since this project will entail hitting the easy button whenever possible, the jack shaft is a full-keyway 20 mm shaft supported by flange-mounted bearings in ridiculously heavy 3-bolt bracket housings.
A pair of 20mm sprocket hubs on their way.

 

[Skipp]

You should see the one @Mariah was riding at windber..

 

[RobertC]

You should see the one @Mariah was riding at windber..

It's a Bearkat frame, that @capguncowboy gave me.

I didn't have the wherewithal to work with it, so I gave it to @Mariah (she's done so much for me, that was the least I could do)

 

[Tanshanomi]

I bought a pair of Heidenau K66s, which I really like. (I used this same tire on The Bride). In this case, I'm going with identical tires front and rear, 90/80-16. They're on the small side for these rims (both 2.15" wide), but with only 5 horsepower and a single drive ratio, I was aiming for light weight and small diameter. Unfortunately, I cannot for the life of me get the front tire (which is a tubeless rim) to seat on the bead. I wrestled with it for about 90 minutes, and with a ratchet strap around it I could get it to inflate, but it just wouldn't pop into place. I went as high as 70+ PSI, bonked it with a rubber mallet, and even upped my game from soapy water to assembly lube. None of it would do the trick.
I haven't attempted the rear, which is a tube-type rim.

If anybody has any suggestions about what to try next, I'm all ears.

 

[DaddyJohn]

I hate to say it, I’d probably punt and get different tires. That said, I’ve had some luck in that situation by heating-up the tire with a heat gun, then doing the tire lube, etc. Worth a shot first anyway…

The Duro HF308 is a cool looking tire (think old-school flat tracker), or maybe a Pirelli MT15?

 

[Tanshanomi]

I hate to say it, I’d probably punt and get different tires. That said, I’ve had some luck in that situation by heating-up the tire with a heat gun, then doing the tire lube, etc. Worth a shot first anyway…

The Duro HF308 is a cool looking tire (think old-school flat tracker), or maybe a Pirelli MT15?

I think you may be right.
I've messed with this on and off for three days. Still no joy.

De-mounted and buffed rim.
Heat gun.
Ratchet strap.
Pam spray, then commercial Tire Mounting Lubricant.
Plenty of swings with a rubber mallet.

Then I swapped out the tire for the one I was going to use on the rear and tried it all over again.
I find myself at an impasse. I don't know whether to take it to a shop, or simply order another tire from another manufacturer.

 

[Triley41395]

I think you may be right.
I've messed with this on and off for three days. Still no joy.

De-mounted and buffed rim.
Heat gun.
Ratchet strap.
Pam spray, then commercial Tire Mounting Lubricant.
Plenty of swings with a rubber mallet.

Then I swapped out the tire for the one I was going to use on the rear and tried it all over again.
I find myself at an impasse. I don't know whether to take it to a shop, or simply order another tire from another manufacturer.

View attachment 324938

I had a mini bike tire do the same thing.
I put some o-ring lube on the rim, inflated the hell out of it and sat it outside in the sun. When I got home from work(about 10hrs later) it had popped on the bead. I figured the sun would heat the entire thing and allow it to stretch a little and it worked.

 

[Tanshanomi]

110 was the magic number.

I mounted the other tire on the tube type rear wheel; the bead popped at 85 psi. At that point, I had very little to lose so I cranked the air compressor up to 120 psi and gave it a go without the valve stem in. Great Success!

 

[Tanshanomi]

I aborted a couple of never-ending project bikes that I'd lost my enthusiasm for. That gave me the opportunity to think freely about what I wanted to pursue in the workshop. I decided to forgo the “high concept” projects, at least for now, and concentrate on “cheap and cheerful” — the stuff I can truly have fun with. The result is that the "Diesel Cruiser" won’t be so much of a cruiser after all. With three rolling chassis currently on hand, all in need motors, I have no business assembling yet another one. So the Diesel Cruiser’s original chassis layout won’t happen [probably ever, that KTM frame is toooo funky].

The plan now is to use my existing Benelli 2C chassis, which I originally mocked up to house a Honda first-gen air-cooled ATC250R engine. I yanked the incomplete hunk of Honda motor out and sloppily shoved the diesel into the engine bay to verify that this combination could work.

And, look! Everything fits with enough room behind the engine to run a jackshaft across the frame. Hot dog!



I still don't plan on running a CVT, just a centrifugal clutch. With plenty of diesel torque down low, a comparatively heavy chassis, and only 5 horsepower on tap, I think greater drivetrain efficiency when running WFO wins out over the more spritely acceleration a torque converter would provide. You guys, please tell me if I'm wrong.

The planned gearing works out to 30 MPH at 3600 RPM. I might be able to get more top speed out of this engine, but I think that will be a good starting point for initial testing. In the end, five horsepower is five horsepower; I'm going to want more on one side of the performance equation or the other.



What will the tank and seat be? Will it get lights? Get licensed for the street? Who knows. There’s a lot of fabrication ahead, but it all appears to be pretty cheap and rudimental stuff, in both concept and execution.

 

[Tanshanomi]

I've fabricated the diesel bike's rear motor mount.

Given these small, air-cooled diesels’ notorious reputation for excessive vibration, rubber engine mounts are practically a necessity. Fortunately, the Benelli frame has existing rubber foot peg mounting points that I can re-purpose for the rear engine mount. I discovered when I attempted to bolt up the adapter plate I had made that the engine mounting bolts fouled the bosses on the frame. As a result, I had to move the engine back within the frame about an inch.

Looking at the rear mount without the engine installed reveals the original holes toward the front, and the second set I had to add further from the other mounting bolts. It’s all well and good, actually, since I mis-drilled the original holes slightly.



From underneath, you can see the lack of clearance for the original holes, and the original Benelli damper rubbers. While they look somewhat dry-rotted on the exposed edges, the rubber material is still very solid overall.



As for the overly long bolts and mismatched nuts, my excuse is that my local Ace Hardware keeps a disappointingly limited stock of metric fasteners on hand.

With the engine bolted in place, you can see the extra space between the engine and the frame downtube. Thankfully, there is still enough room behind the engine for the jackshaft and drive sprocket — but just barely. I’m now thinking about clearances in terms of millimeters, rather than centimeters.



On the plus side, the flywheel shroud screws will all be removable with the engine in situ, and the oil filler cap in the front is less precariously positioned.

 

[Tanshanomi]

Motor mounts are complete.
In order to rubber-mount the front of the engine to match the rear, I purchased some vibration-isolating mounting pads, commonly used for electric motors, and air conditioner compressors. The integral M10 studs are the right diameter, but…OH NOES!



The studs are too short. Only a couple of threads are visible above the crankcase mounting boss. I thought about mounting them to an adapter plate in front of the engine, but that would be pretty ugly, and the mounting points would be cantilevered quite a distance from the closest mounting points on the frame.
Then I made a discovery.



There is a cavity under the front of the engine large and deep enough to accommodate an M10 nylon locknut. It was slightly off-center, but I could install the vibration damping foot in a tripod arrangement. That way, the adapter plate didn’t have to extend beyond the front of the frame or engine.

I still had the cantilever issue to deal with. There was nothing to prevent the front mount from rotating under the weight of the motor. So, I cut the upper stud off a second isolator block and ground it flat. I could install that on the plate behind the unmodified one. Even though it is not bolted directly to it, it bears the weight of the engine in line with the mounting axis, preventing any tendency to sag or rotate. I had to mount that one off-center to the left, but that’s where it fit. Asymmetry is fine here.



I used some angle iron to create the sides of the “tray” and bolted it all together. Here is the completed mounts without the engine:



And a couple views with the engine bolted in place:





It’s a bit kludgy, but it works. The engine is securely mounted but somewhat isolated from the rest of the chassis. I’m very happy with this.

 

[cl350rr]

Lemonade

 

[Tanshanomi]

I got the fuel tank mounted. I am going to use the fuel tank that came with the engine. It fits nicely under the seat, behind the engine, and it has the necessary fitting for the fuel return from the mechanical injector. The fuel spigot is located low enough on the engine that the tank can still gravity feed from this location. In fact, the engine is almost exactly the same hight in relation to the engine as when it was bolted directly onto it. There were convenient mounting points on the frame that I used to adapt the tank's original rubber mounting cushions and brackets. I used some M8x100 fully threaded bolts on the cast top mount so that I could adjust it to the proper height and then lock it into position.





Since I have no need for a fuel tank in the tradition position above the frame backbone, I grabbed a dummy tank shell I have from an early VX535 Virago. I'm not sure if I am truly happy with the way it looks on the bike, but I don't hate it. And it certainly would be the cheap/easy button. I'm thinking of installing total-loss lighting running off an 18V rechargeable tool battery through one of those PowerWheels adapter sockets. This tank shell would give me a convenient spot to hide the battery and dock.

 

[Tanshanomi]

The sun came out between thunderstorms, so I rolled the diesel Benelli out into the driveway for a couple of quick progress photos.



I bought a higher handlebar for $30 off Amazon, and the bend is exactly what I wanted. I do like the low clubman bars I previously purchased, but not for this bike. I like them so much that I want to use them for a project where they’ll be the perfect centerpiece, not just use them “because.” I am already much happier with these more conventional bars, visually and conceptually; I think riding the bike will be more comfortable, too.

Because of the damage to my right wrist, I want the throttle on the left handlebar. The Jet Ski trigger throttle I bought won’t work with this motor, so I am using an ATV thumb throttle, flipped around to become a fingertip throttle. I hooked up the throttle cable to the 173F’s throttle linkage and it functions perfectly. Since I have a drum front brake, I needed a front brake lever/perch with an integrated brake light switch. I picked up a used Suzuki GS300L lever and perch off Ebay.



After working out all the particulars of the jackshaft arrangement, I drew up a pair of mounting brackets for the pillow block bearings and ordered them from SendCutSend. The shapes might seem overly complicated, but that’s because I wanted to use existing frame mounting points. With the engine mounted where it is, there is precious little room behind it. So, I had to get fairly creative, especially because I wanted to build in primary chain tension adjustment. I will be a couple of weeks before I get the parts.

 

[cl350rr]

The engine looks like it belongs there