Bride of Frankenstein - a cure for leftover parts cluttering the workshop.

Mini Bike & Go-Kart Parts

#1
Hi, I'm new to the forum and though I've been building motorcycles for many years, I've never had a CVT-equipped bike. Well, that's finally changing. Since my knowledge of industrial engines and torque converters is less than diddly, I've recently spent a bunch of hours online, educating myself on mini-bike/go-kart tuning and fabrication. More often then not, the most useful search results led me to this forum, so I figured I should register and jump head-first into the very deep rabbit hole of Predator/GX performance. There are lot of very knowledgeable people here, building some very cool little machines!

I have a fairly well-equipped shop, but its quite compact, and I recently found my parts shelves running out of space. So, I decided to take a pile of very random cast-off parts from various motorcycle projects and see how cheaply and easily I could build a bike out of them. For my framework, I bought a salvage frame from a '74 SST/Panther 175 Black Shadow for under $100 off Ebay. I started hanging parts off it with a vauge idea of building a street-legal gravel runner for exploring the flat, unpaved farm roads of rural Kansas.

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Originally, I was thinking that a Yamaha Blaster 200 motor would go nicely in this frame, but that turned out to be a more expensive proposition than I had expected. Meanwhile, a friend of mine recently helped build a KX/Predator 212 swap, which got me excited about that option.

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So... I picked up an LCT 208 clone off Ebay for $99, along with a generic TAV 30 series knockoff. I'm just getting started, but the components are coming together.

For most Predator-style conversions, builders are forced cut the downtubes off the donor frame in order to fabricate some sort of homebrew engine mount. I really hoped to avoid that, and it turns out I will barely be able to make it work. Rotating the position of the torque converter backing plate down to the lowest set of bolt holes shortens the overall length enough to allow the assembly to fit within the existing frame cradle. This leaves the engine pretty high in the engine bay, which looks weird, but in this case that's a good thing, since the engine is just high enough to clear the cross tubes at the front and middle of the frame. Other than chopping off a few extraneous tabs, I can leave the frame unmodified.

From the right side, the engine's sky-high placement looks pretty odd, but I am thinking I can utilize the space under the engine by integrating an electrical box into the engine mount and putting the battery under there. (My engine has an electric starter and I'm going to add a 60 watt alternator and lights eventually.) I grabbed an old Rebel 250 battery cover and slid it in just to get an idea how that might look.



The whole thing has to sit a bit further forward than I'd like, but if I moved it back, the frame would block both the intake and exhaust. As it is now, there is juuuust enough clearance on each side.



The downside is that the output sprocket is pretty far away from the swingarm pivot, which may play havoc with the chain clearance and tension. I don't know if it's necessary, but one idea to resolve this would be to run a narrow jackshaft with twin sprockets directly on swingarm pivot bolt, so that the chain geometry wouldn't change as the rear suspension moved. This arrangement would have the fringe benefit of allowing me some flexibility in the positioning the engine/CVT side-to-side in relation to the chain run to the rear wheel.

There's no way around it; this is going to be a weird bike, on multiple levels. Overall, however, I would say that all my random pieces continue to go together much more conveniently that I had any right to expect they would.




I said, I am a complete novice with this type of engine and lot of the specific details are pure voodoo to me — governors, splash lubrication, CVT tuning, parts interchangability, etc. — so I would welcome any help and assistance folks here can provide.
 
#2
I like it. It is an interesting mix of stuff. But I would think that the angle of the engine will lead to oil starvation as well as a lot of oil soaking the cylinder to the point that the rings wont be able to control it. I dont think the rod will last long enough for the rings/cylinder to be much of a concern though. Just my thoughts.
 
#3
I like it. It is an interesting mix of stuff. But I would think that the angle of the engine will lead to oil starvation as well as a lot of oil soaking the cylinder to the point that the rings wont be able to control it. I dont think the rod will last long enough for the rings/cylinder to be much of a concern though. Just my thoughts.
I’m not sure I understand. The engine is only a few degrees from level.
 

mustangfrank

Well-Known Member
#4
I’m not sure I understand. The engine is only a few degrees from level.
I agree, it looks like too much angle for the engine. What about ditching the TAV mounting plate, mounting the secondary clutch on a jackshaft, giving more room to move the engine back? Jackshaft could even double as swingarm mount point?
 
#5
@Tanshanomi love the project. While it's not the traditional mini, it's super cool! I personally don;t think the engine is far enough off level to affect the oiling. Kart racers run more engine mount angle than that. However, if it should be a concern, research the motorized bicycle conversions. Some of those guys have them mounted 90 degrees off level. I'm not sure what they are using, but there are plenty of them out there with success. Keep up the great work!
 

mustangfrank

Well-Known Member
#6
@Tanshanomi love the project. While it's not the traditional mini, it's super cool! I personally don;t think the engine is far enough off level to affect the oiling. Kart racers run more engine mount angle than that. However, if it should be a concern, research the motorized bicycle conversions. Some of those guys have them mounted 90 degrees off level. I'm not sure what they are using, but there are plenty of them out there with success. Keep up the great work!
Static angle is fine but in acceleration and picking up the front tire the oil will be pooling right at the piston skirt was my thought. I'd go for level flat mounted or preferably tilted forward if possible.
 
#7
That makes total sense. I put an angle cube on the engine as it sits, and it's angled rearward 7 degrees. I'd read that anything under 15 degrees was okay, so assumed I was good. I didn't even consider the difference between tipping the cylinder downward versus up. See? That's the sort of thing I'm here to learn.

I took a quick look this morning and I think I can just cut out the frame cross-tube at the front and rotate the motor level.
 

DaddyJohn

Well-Known Member
#8
You may be able to add additional holes to the TAV plate to alter it's angle yet further. That might allow for rotating the ports away from the frame (thus leveling the engine), and getting the sprocket closer to the SA pivot. Makes the whole assembly a little taller, but looks like you have room.

I noticed a Can-Am tank and Honda VTR250 wheels?
 
#9
You may be able to add additional holes to the TAV plate to alter it's angle yet further. That might allow for rotating the ports away from the frame (thus leveling the engine), and getting the sprocket closer to the SA pivot. Makes the whole assembly a little taller, but looks like you have room.

I noticed a Can-Am tank and Honda VTR250 wheels?
Good alternative, but it’s the engine itself that is limiting me. I think there are compelling reasons to modify the frame, so I’m going to explore that direction.

And, yes, you are correct on both counts. The tank is from a Can-Am Qualifier enduro bike, and the VTR250 wheel had been squirreled behind my work bench for 15 years!
 
#12
Had some time before work this morning to start modding the sprocket carrier.

In order to gain a bit more leeway in wheel/swingarm alignment, I decided to reduce the overall width of the sprocket carrier housing. By switching out the unsealed OE bearing for one with integral rubber seals (6205NSE to be specific), I can eliminate the separate grease seal outboard of the bearing.

First, I needed to extract the sprocket studs. After 30 minutes in the oven at 250°, I was able to break them loose with hand tools and the proper grunting sounds. It cooled down enough by the time I got to the last two that I had to break out the propylene torch, but they all came out.



I first chucked it in the lathe by the outboard bearing face and slowly, carefully, turned the insides of the rough-cast cush-drive bosses so they'd be nicely parallel and concentric. After talking this picture, I did a very light facing skim.



I could then flip it around use three of my freshly machined surfaces to center it in my 3-jaw chuck.



Crank up a bit of WHRRR and I easily cut down the casting with a series of facing cuts. I love how easily cast aluminum machines. The black sharpie line you can see in the photo was was my rough target.



A bit of chamfering, and it looks factory! Not having had much technical training in life, I so enjoy owning a lathe. Even though I'm doing super-basic stuff here, I still can't help but feel a sense of wonder that I can form and shape metal parts. Not only can I do it by myself, I can do it pretty damn accurately.

 
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#13
I'm working on a jackshaft setup. I picked up a double simplex #40 sprocket in decent condition for $30. This morning before work, I enlarged the center bore to take a couple of 6203 sealed bearings. I still need to make the spacer that will go in-between the two bearings, plus a 17mm to 12mm sleeve to adapt the bearings' ID to the swingarm pivot.

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