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

Mini Bike & Go-Kart Parts

#45
With my press brake backordered for a month, I had time to consider alternatives. Looking at the mounts massacre posted, I decided to pivot and go with a similar, bolted-up alloy setup, rather than the folded steel box I had imagined previously. I ordered the supplies needed and they're trickling in. I don't have a chop saw or band saw, and I wasn't looking forward to hacksawing through 8 inches of 1/2" thick 6061 aluminum. Several people online had good results with circular saw blades designed specifically designed for cutting aluminum. I was skeptical, but I figured for $20 it was worth a shot. I figured even if I just able to get a good, straight, perpendicular score across the metal, it would help me cut straight with the hacksaw.

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I swapped out the blade in my sliding miter saw and used the adjustable depth stop to make a series of approx. 1/8" deep passes. That was probably conservative. It cut effortlessly—no bogging, no burning, just plenty of little chips flying out the back of the saw. The resulting cut was really clean. I'm really surprised how well it works.

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Here's the base plate, ready to drill and bolt into the frame. To this I will add angled vertical plates similar to Massacre's suggestion. I have 7/8" thick 6061 arriving today.

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#46
I cut the engine mount verticals this morning. I started with the circular saw and fine-tuned them with the bench sander. I eventually got everything straight, true, and even without wasting any metal stock, so that goes in the W column as far as I'm concerned. The left mounting plate looks undercut, but I accidentally inverted it for the photo below; the angle at the rear actually goes the other way.

I plan on using socket head through-bolts at the front. At the rears, I will drill the aluminum for 8mm helicoils. Likewise at the bottom, where the vertical blocks will bolt to the base plate.

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The engine has to sit in one specific location where the starter motor, the bottom of the CVT plate, the spark plug cap, cylinder, and the intake/exhaust ports are all clear of the frame, and the drive sprocket aligns with the idler and rear sprocket.

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Tanshanomi

Active Member
#48
Trying to find a space for my carb that won't be occupied by my right leg. I'm not sure how successful this arrangement is. And yes, I know that silicone hose downstream of the carb is a no-no. I'm just temporarily jiggering this for now. The hose actually has hard contact with the frame, so this is no bueno on that count, too.

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I am considering making up a 180-degree intake pipe, similar to what Mike Festiva did on his XR100 build:

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Tanshanomi

Active Member
#49
Since the engine mount only bolts to the frame towards the rear of the base plate, I am adding these link rods between two mounting bosses on the front of the crankcase and the original downtube gussets below the steering head. It's not the most robust point on the frame, but that's not the point. The whole engine is cantilevered pretty far above and in front of the lower mounting points. Without any other constraints, that's a pretty big lever. These are not turnbuckles (right-hand thread at both ends), so they won't be highly tensioned. However, since they're angled inward on each side they should limit gross lateral deflection. I just want to prevent the mount and lower parts of the frame from fatiguing. I am also optimistically hoping this will help damp vibrations. Obviously, I need to cut and thread steel rods to replace the wooden dowels in the photo.

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#53
I'm working on the intake, and it's taking more effort than I expected.
I did find a commercially-available plug-and-play option, but it puts the carb so far outboard that I would have to run the cable outside of the tank, and I want to route the throttle cable through the tank tunnel in the conventional manner.

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I tried a straight u-bend, but putting the carb close to the center of the frame also put the float bowl pretty close to the cylinder fins — really not ideal.

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I slapped the 45° hose bend I had tried previously, and it moved the carb forward into a good position.

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I verified that I will be able to get to the choke with the tank on.

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So, there: desired configuration settled. But there's still a long way to go. The hose section will need to be replaced by an additional metal section; that silicone hose isn't fuel resistant, and even though it's molded, it allows the carb to sag a bit. But that's okay; I need to start fabrication again from scratch anyway. First of all, I was overconfident about my welding skills. After taking a great deal of time to fabricate a flange and fit it to the U-bend, I totally gobbed the welding. Totally — as in, I'm too embarrassed to show any close-ups.

Secondly, one of the mounting screws for the exhaust is right behind a frame tube. Installing and torquing it properly requires un-bolting the engine. It would be better to have the intake tract mounting bolts more accessible. The engine's intake is that odd D-shape, so I have an adapter flange to smoothly transition it to round (the red anodized plate visible in the photos). I'm going to make my own version of this adapter, similar to one that I made for my Honda CL125S:

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  • It will be thicker than the anodized one on there now (1/2" alloy) so the transition in shape of the interior hole will be less abrupt.
  • It will have countersunk holes to mount to the intake, like above, and a second set of studs clocked to resolve the frame interference issue.
  • The intake pipe mounting studs I'm adding will be slightly farther between centers. One of my problems welding was that there was very little clearance between the 1.25" tube and the bolt holes in the flange plate. The new studs will also be centered on the intake tube. The existing holes are offset slightly.
  • The design is shaped so that I have three equidistant points at 120 degrees, so I can mount in my 3-jaw chuck to cut the taper in the center hole.
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#54
I whipped up the adapter plate for the intake this morning before work. I simplified it a great deal from the drawing I originally made, by simply using a pre-cut 2-1/4" dia. x 3/8" thick steel disk. While not absolutely necessary, this doohickey has some advantages:
  • A gradual transition between the D-shape intake port and round intake — theoretically better flow than just slapping a flat plate on it.
  • Matches the intake dia. to available 1.25" dia. 18ga tube.
  • Intake mounting holes are now clocked to avoid frame tube interference.
  • Intake mounting holes are now symmetrical, instead of being slightly offset from center.
  • Greater center-to-center distance between the mounting holes, which will provide more room for a weld bead around the flange/pipe joint.
I originally planned to thread the flange mounting holes, but at the last minute I simply drilled 6.5mm holes and will put nuts behind the plate. Unfortunately, I positioned the lower hole right in front of a cast fin on the head, which will need to be ground back a small amount. I also need to soften the transitions between the main center hole and the smaller "D" holes. In fact, the whole inner surface could use some smoothing; my boring bit was a bit duller than I thought it was.

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#57
Tanshanomi, I read your post with great interest. You do very nice work. My history is working on mostly hot-rods but also basically anything motorized. In my collection is a mid 70's Honda Trail 70. The motor is hung but not running. I'll do all the normal checks but if the motor turns out to be a dud I'm going to follow your path. Thanks for sharing.
 

toomanytoys

Well-Known Member
#58
Tanshanomi, I read your post with great interest. You do very nice work. My history is working on mostly hot-rods but also basically anything motorized. In my collection is a mid 70's Honda Trail 70. The motor is hung but not running. I'll do all the normal checks but if the motor turns out to be a dud I'm going to follow your path. Thanks for sharing.
If it's a trail 70 just buy a lifan replacement.
 

Tanshanomi

Active Member
#59
If it's a trail 70 just buy a lifan replacement.
100% agree. I recently saw photos of a Predator-powered CT70 online, so it's do-able — but it wasn't a simple or elegant swap. The Predator/CVT combination doesn't fit the space very well. On the other hand, a clone Honda motor would be a virtually bolt-in solution, and probably about as cheap in the end. You can get a 110cc or 125cc for about the same price as a 70 or 90, if you want some more oomph.

http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=324503552424

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Tanshanomi

Active Member
#60
I realize that hydraulic brakes are not at all an "old mini bike" thing, but I began rebuilding the bike's goofy Honda Inboard Disk this morning and figured I'd post a couple photos.

The caliper was already seized solid when I got the wheel almost 16 years ago, and it had been sitting dry, with no line connected, in a dusty corner of my garage ever since. Clearing the line took both master cylinder pressure from one side and a mityvac pump pulling on the bleeder from the other. Eventually, a big black plug of gook appeared in the bleeder tube. Once I pushed that through, I closed the bleeder and had no problem pumping the pistons out. Overall, it's in surprisingly good shape. There was a lot of crusted-on crud in all the crevices and some jellied residue inside, but I had been prepared for much worse. The pistons are probably reusable, but I already purchased new ones, along with new seals and boots. Now it all goes into the ultrasonic cleaner!

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