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

Mini Bike & Go-Kart Parts

Tanshanomi

Active Member
#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.

IMG_2036-web.jpg

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.

9E0B4388-FE02-479F-A750-1CE6A281142A.jpeg

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.
 

Tanshanomi

Active Member
#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.
 
#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.
 

Tanshanomi

Active Member
#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?
 

Tanshanomi

Active Member
#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.

 
Last edited:

Tanshanomi

Active Member
#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.

IMG_2257.jpg
 
#15
The jackshaft idea turns out to be a no-go. There's just not enough room available to shift either the engine sprocket or the rear sprocket inboard far enough to make the idea work. I will have to just run the chain over a single idler sprocket mounted on the swingarm pivot.

I re-drilled the CRF150R rear sprocket to match the EX500 bolt pattern. I used the sprocket carrier as a jig and used a transfer punch to mark where to drill. The new sprocket fit perfectly snug against centering faces on the interior diameter, and the two existing bolt holes I'm using in the sprocket are tapered, and thus self-centering. So I am fairly confident that my sprocket will be concentric, or at least within normal mass-produced tolerances. That being said, one of my new bolt holes was perceptibly off, and I had to remove a bit off one side with my die grinder. On the other three I could screw the bolt in, but there was some drag and no wiggle as I caught the threads. Afterwards, I checked and could see faint witness marks from the threads on the side of my drilled holes, so they all got a light touch with the Dremel as well. Overall, it went pretty smoothly.

IMG_2327.jpg

I failed to take a photo of the sprocket side when I was done, but there's not much to see. It looks like...a sprocket.
A bit of checking with a straightedge confirmed that I am a going to have to machine the face of the sprocket carrier to move the sprocket inboard at least 5-10mm. As it is, the chain would foul the frame tubes.

After years of dealing with worn, barely serviceable salvage parts, on this bike I am going with new components where economically feasible. I picked up an alloy handlebar in a nice gray anodized finish ("titanium") and a matched pair of generic master cylinders for the front and rear brakes (this bike will have scooter-style brakes and no foot controls...just because the torque converter makes it an option). The 1/2" (12.7 mm) bore is spot-on for the Honda Inboard caliper on the front.

IMG_2330.jpg

For the rear brake, I'll just have to make something work. I bought a Volar replacement EX500 rear disc off Ebay for $35. Since this project is all about using up spare parts, what calipers are on my shelf? Well, there's a three-piston Grimeca off an Aprilia Atlantic 500 Sprint, and a two-piston from a Yamaha XV250 V-star — nope, both are left-side mount with asymmetric pistons, so they can't be swapped over to the right. The only thing I have on-hand that might work is an unused rear caliper from a Suzuki Vinson 500 four-wheeler. It would be a very straightforward install, but it only has a single 34mm piston: a mismatch for the 12.7mm master cylinder up front. I could potentially end up with a spastic, lockup-happy rear brake.
Hmmm...what to do. Think, think, think...

IMG_2329.jpg
 
#16
I did some work on the Bride's idler sprocket this morning. Since it was made for #40 industrial chain instead of 420 drive chain, I first had to take 0.8mm (0.31") off each side of the sprocket — visible as the shiny silver ring on either side of the sprocket teeth. I then turned two spacers of the same width, with a small enough OD to fit within the outer shoulder and butt up against the inner bearing race properly. As you can see, the sprocket has a shorter shoulder on one side, but I wanted to leave plenty of room for the width of the chain itself to clear everything around it.

The frame is still in the jig, so I can accurately measure the chain offset from the centerline. My next steps will be to:
  • modify the rear sprocket carrier to match the chain offset,
  • shorten the drive side of the swingarm pivot to make room for the idler and install the swingarm,
  • make up the proper width rear axle spacers to center the rear wheel in the frame (important to calculate in the jig because the swingarm will remain offset slightly),
  • mount the engine so that the drive sprocket on the torque converter lines up with the other two sprockets.
At that point, I can unbolt it from the jig and make a rolling chassis out of it. My wife will be very happy about this, since it will stop taking up prime real estate in the middle of the basement.

IMG_2341.jpg
IMG_2338.jpg
 
#18
After measuring a bunch of times, I conjured up the gumption to cut into the swingarm. I went slow, with a hack saw, and actually managed to make a perpendicular cut. I assembled it and it fits! The part I cut off the left still needs to be welded to the right side, so I can use the stock width bearing bushing. In this photo, I just slipped a shiny washer in between the two pieces to replace the width of the hacksaw blade.

IMG_2383.JPG

I've ordered a larger diameter piece of DOM tubing to use as a reinforcing sleeve over this joint. I only have a 125 Amp Titanium flux-core welder, so I might take it to my local welding shop. I haven't decided yet.

Once I had the swingarm positively located, I made up spacers to center the rear wheel. You can see from these photos why I had to do the lathe work on the sprocket carrier. Even with my mods, there is no room to spare!

IMG_2391.jpg
IMG_2387.jpg

The spacer on the other side is a temporary "dummy." Eventually I will need to fabricate a rear caliper hanger that will occupy the extra space on this side of the axle.

IMG_2389.jpg

There's still a lot to do, including all those little things you don't think about, such as pins for the snail adjusters. However it feels really good to have the swingarm in position and rear wheel centered. Looking at the bike with the rear tire on, I have to say I'm pleased with how it looks. It makes me eager for more progress.

IMG_2390.jpg
 
Last edited:

Tanshanomi

Active Member
#19
Front end got wheel spacers and new tire. Mocked it up for a preliminary geometry assessment and then rolled it outside. The front end measures out at right about 5 inches of trail. I actually got on and did some s-turns down our sloping driveway as fast as I dared with Flintstone braking. Seemed to handle easily and predictably at walking speeds.

C2E68AF1-A9A6-40FC-9759-CFF16AFE017D.jpeg 5AB722AB-47E0-4A39-82F1-183D9D7F8E98.jpeg
 
Last edited:

Tanshanomi

Active Member
#20
You know that whole part about swapping the engine in without cutting the frame?

boris-didntwork.gif

No matter how I reoriented the engine and torque converter, something ended up bumping into the frame somewhere: the flywheel, the cylinder head, the starter motor. At one point, I was willing to lose the electric start if that would have allow things to go into the frame, but ultimately that wasn't a magic bullet.

So, after a bit of measuring and a long time staring at the frame and trying to think things through, I bit the bullet and whacked the down tubes off. With that done, I could prop the engine up on wooden blocks to figure out where it had to go, in order to figure out where the frame could go.

IMG_2614.jpg

This view gives you an idea of the tubes' original path. Even without the starter, the flywheel and torque converter would have been in the way.

IMG_2616.jpg

It took a lot of jockeying around, but once the engine was sitting properly, I got out the angle cube and did some measuring.

measurements.jpg

The engine was inclined at 10.9° forward, nicely within the normally accepted 0° – 15° "safe" range for a GX clone/Pedator engine. As the bike sits, the lower frame tubes of the SST frame are –9.1° from level. The forward seat tube is 36.05°, and the top of the cylinder head is "eyeball close" to parallel. The GX/clone engines have the cylinder inclined 25° from horizontal, so my numbers all check out:

GX200_DD.jpg

So, my next step is to make an engine mount with an included angle of 20°, and get everything bolted up with the torque converter sprocket properly aligned.

After that, I will have to figure out how to configure replacement frame tubes. For this, I'll be using the Ridgid #368 bender (3/4" OD x 3.75" radius) that I bought to modify Bultakenstein's frame. I got a cheap score on a few 3-foot remnants of 0.75 OD, .065 wall, unspecified "carbon steel" tubing. The existing frame tubes are 7/8" OD x 0.95" wall, so these are thinner and the smaller OD will be a visible mis-match, but so be it. For what a different mandrel bender would cost, I am super okay sticking with the OD that matches my tool. Even the tools for this project are whatever I have lying around. And even though my bender is rated for up to .120 wall, the 0.65 will be just fine for this application (and as a bonus, super easy to bend!).

IMG_2615.jpg

Stay tuned!
 

Top