8 speed 79cc revival

Discussion in 'Motorized Mountain Bikes and Road Bikes' started by xXNightRiderXx, Sep 2, 2019.

  1. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    Hey guys, I know it's been a while since I posted here. Ive been working on that mongoose with that 79cc predator and shift kit a lot lately, and just wanted to share some updates:

    I've removed the transmission plate that comes with the kit to reduce friction and noise. Ive also moved the 23t sprocket to the jackshaft, and am replacing the current cassette with one that has a 42t-11t range. The stages are now as follows:
    10-23
    9-44
    36-38\11 soon to be 36-42\11

    I have also moved the exhaust pipe through the center of the rack to clean up the look some. It certainly looks better and more thought out.

    I have gotten a new carb with a slide, but need smaller jets for it. The ones it came with either seem to be too large, or the same size (65-85, increments of 5, same amount of exhaust smoke, other than the stock jet). Regardless, throttle response has improved.

    I finally sanded down the cylinder head. There turned out to be a gouge near one of the pins, so I sanded with 1000 grit paper and cutting oil until that was gone. Compression has definitely increased. I can feel it in the starter rope. Along with the head sanding, I replaced the valve springs with 18lb springs. I will soon replace the pushrods if I can find em, just to be safe. The lifters shouldn't be an issue.

    I will be fabricating a fairing for it. On this fairing will be a speedometer, a tachometer, and, of course, all the switches I don't need on the handlebars, such as parade lights, headlights, and ignition switch. The kill switch, high/low beam switch, horn button, and turn signal switch will be on the bars at the grips.

    I will also be building new wheels for it. I am going to upgrade the tires to maxxis hookworms (so I can have a chicken strip. Like seriously, that tread is almost halfway down the sidewall), and use a 36 spoke double wall mtb rim, and of course, mtb hubs. What can I say, mountain bike wheels are built for abuse.

    Oh, I almost forgot about electrical. The last post I made, I was going to put an alternator on it. I've since ditched that plan. Instead, I'm just going to attach a quick connector to the battery for a trickle charger. That keeps the build cleaner, and lets me plug it in wherever I find an outdoor outlet, or can run an extension cord.

    41312217-68c7-4c9b-86de-9f0888c636d7.jpg 20190822_160221.jpg 20190822_160233.jpg

    Don't worry about the paint damage. That's getting replaced. I'm having the frame chrome plated so I can add a transparent emerald finish for that anodized look. The headset, tank, and fenders will get a green metal flake finish. The box is getting retorched, and sealed with high gloss spar varnish, and the seam will be sealed using black silicone caulking. Oh, and that little bottle opener on the box? That's getting a green LED put behind it.

    All in all, it sounds like a small motorcycle now, when it just sounded like a lawn mower before. It is also beginning to look a lot cleaner. I just have to reroute the cables and heat shrink them together.
     
  2. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    Just got my 30t in yesterday. Haven't mounted it yet, but I'm going to. The thing is a BEAST! I swear, this one sprocket weighs as much as one and a half centrifugal clutches! Time to go get my chain resized again to fit the additional 7 teeth (I'm going to need quite a few links, haha).
     
  3. waynesdata

    waynesdata Active Member

    Joined:
    Jul 10, 2017
    Messages:
    253
    Likes Received:
    104
    Did removing the transmission plate give you anymore speed or acceleration? Is that the CNC short head? What is the box for battery for lights horn etc?
     
  4. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    Removing the plate reduced chain noise significantly, however, I need to compensate for the loss of gear reduction with a larger jackshaft sprocket, which is why I got the 30t. As soon as I can get the chains installed, I can do a 0-30mph time test and a top speed test.

    Yes, it is the short head. I need to put a vent in it though. I think it's causing some emissions issues cause I'm getting some cold vapors coming out of the air filter.

    The box is essentially a fuse box with a battery compartment. My entire electrical system stems from that box. I have my tail light bolted onto it because it was convenient, and gave the bike a high spot to mount it, increasing visibility.
     
  5. waynesdata

    waynesdata Active Member

    Joined:
    Jul 10, 2017
    Messages:
    253
    Likes Received:
    104
    I am still trying to design a electrical system. If you post your work other users can build on your design. Been looking at youtube videos on how to build battery packs.
     
  6. waynesdata

    waynesdata Active Member

    Joined:
    Jul 10, 2017
    Messages:
    253
    Likes Received:
    104
    A few users have posted that some of the jackshaft plates have crap bearings in them. I will be spending the extra money to get a GTC plate. I wonder if the bearing in your place can be replaced? Will you be adding any kind of chain guards for extra safety?
     
  7. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    Yes, the moment I get a metal brake, I will be fabricating some chain guards. As it is, I already have to cut, grind, and drill an 8" steel disc to separate my right side chains.

    Yes, the stock bearings are crap. My 79 shattered the shell of the left bearing, forcing me to get a new set of bearings. I have to get a new set now for high power applications.
     
  8. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    Alrighty then! I got my 30t sprocket installed, got a new chain to fit it (had to go #40), and now she rolls like a champ! I think I could further optimize with a 32t, which would also take the slack out of the clutch chain. I've almost got it pullin wheelies. Next is the wide ratio cassette (40-11t) and derailleur hanger extender.

    I still need to do some ACSheriff approved tests, as my rear brake isn't put putting as much power into the ground as it should be, and idk why. My front works great. I think hitting it with some brake cleaner and sanding down the pads will help. Hopefully the pads aren't contaminated. If they are, I won't be riding for a while, cause contaminated pads means destroyed pads. I can't afford new ones right now. I think I'll have a caliper/rotor guard 3d printed soon so chain oil doesn't get flung onto them until I get some chainguards. I will be making these fully functional with a shallow oil bath. It will help keep the chain clean while also keeping it lubed. The guards will be 3/4 enclosure to prevent spray from flung oil, but allow easy access to replace the oil with a hinge, which will also be kept lubricated by the remaining flung oil.

    Aside from the malfunctioning rear brake, everything is working wonderfully. Chains are aligned just right, so there's no more binding on the right side, and shifts are smooth. I'm getting what feels like 35mph out of it now, but I need a proper gps speedometer to truly know.

    I still need to sand down the cylinder head some more. The sanding I did feels more like a honing than anything functional. No noticeable power increase. I will be using 400g with cutting oil and finishing with 1000g with cutting oil.

    Edit: Pads are contaminated. Gotta get a new set.
     
    #8 xXNightRiderXx, Oct 19, 2019
    Last edited: Oct 19, 2019
    waynesdata likes this.
  9. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    So, I just realized something when talking to my dad yesterday. My valve lash is off. When I did that last bit of sanding, I tightened the valve lash via material removal, so that may, in concert with the film left by the cutting oil, be contributing to my performance problems. I'm going to do a full disassembly and clean the parts, remove the governor, ensure piston ring alignment, set my valve lash, and put every part that needs it into an oil bath so they aren't dry when I reassemble the engine.

    And when I say "clean the parts," I mean taking an old toothbrush and some degreaser and scrubbing down every single part in that engine. This way, I know there will be zero grit causing wear in my engine, and I can be sure that my oil won't collect that grit and send it everywhere.

    Anyone know the bolt torque values for the conrod, case, and flywheel?
     
  10. xXNightRiderXx

    xXNightRiderXx Active Member

    Joined:
    Jan 12, 2017
    Messages:
    383
    Likes Received:
    54
    I've decided that I NEED MORE TUNING! Gonna swap the Piece of Shallot Runtong for a pbhg 19mm, so that I not only have a mixture adjust screw, I can also supertune for any mods I do in the future. Not to mention, I would FINALLY be able to use my 35mm ram air filter (looks like a high bypass turbofan with the cone in the middle). I haven't quite figured out how I'm gonna mount the carb yet. Maybe I'll slip it on over the intake (19mm od) and secure it with 19mm ID silicone hose and hose clamps (stretching it over the carb). I feel like that would also eliminate any air leaks. Any thoughts from the peanut gallery?
     

Share This Page