1973 build with grom forks

Discussion in 'Projects/Builds' started by fatcaaat, Dec 2, 2019.

  1. fatcaaat

    fatcaaat Well-Known Member

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    Well i picked up a pc orange frame and an otherwise disassembled stocker as an aborted project in october. Here it is complete thus depleting the remaining stock of spares. I no longer enough to reasonably start another.

    1973 frame
    Honda grom forks
    Kepspeed stock swingarm
    Over copy stainless pipe with tri oval can
    Jailing 140 with tb v2 head, taky s25 decomp, vm26-606
    Full wave dc stator setup
    Stock rims with heidenau 110/90-10 k58
    Gps 2-wire speedo
    Bmx bars
     

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  3. airblazer

    airblazer Active Member

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    Great looking bike, too bad we all missed the build progress and only get to to look at the finished product ;)
    Is a Grom front end really plug and play with the stock tube of a CT70?
     
  4. kirrbby

    kirrbby Well-Known Member

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    My hat is off to you sir (y)
     
  5. fatcaaat

    fatcaaat Well-Known Member

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    Yeah, sorry about that as this was put together in about 6 weeks time and I honestly didn't think it was much of a project other than getting the forks together. For someone that wants to swap out the grom forks, it's a bit of work and will require the use of both a lathe and a mill. You'll need to mill the top tree to remove the ignition stuff...approximately 1.25" deep across the 7.5" length of the tree. You'll also need to mill the backside of the lower tree so the steering stop works correctly. You'll need to rut the weld on the bottom tree out and then press the old stem out. Then put a different stem in there. I had a G'craft stem here I purchased a few years ago...and the bottom area designed so it won't slip through the lower tree was only 1mm larger than the hole, so instead I made a sleeve that fit over the stem in the same diameter and put it in the lathe to cut it down to the same diameter as the lower hole. I drilled and tapped the bottom of the stem to 1/2"-20 threads 1.5" deep. I then pressed the stem in and used a thick washer and a grade 8 bolt in the bottom to prevent stem pull-through. Lastly, I used taper bearings and at the top I took an original spanner bolt and put it in the lathe and cut it down to about .35" thick with the last 1/4" trimmed to stick up into the top trees so that it fits tight.

    There was enough room to have the bottlenecked grom fork legs fit correctly in the lower trees but the bike sits about 1/2" taller in the front. I can move the forks in the trees up about another 1/4" but that's it which splits the difference. I am running 335mm rear shocks, so it will even out perfectly when I do this.

    For the front wheel, I am running a chinese billet hub and wheel star mated to the stock rims with a 220mm disc and the stock Nissin caliper from the grom. Other than custom wheel spacers to get it aligned, no funny business was needed.

    I cheaped out on the headlight, which was a mistake. Anyone that ever sees a Krator LED headlight, avoid them at all costs...I dont' think this thing throws any more light than a stock 6v CT70 headlight. I'll fix that at some point.

    Other neat parts on this build include a custom footrest assembly from Racerx, which is the best setup available for these bikes. I have another set on another bike. Also, the original Jailing stator assembly was a two-lead AC setup where you have to put one end to ground...the leads are together but grounded. I had a cheapie setup I purchased a couple of years ago that is actually a single-line wrapped over 5 prongs that's floating...hence can be used for a full-wave DC conversion at about 55 watts.
     
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  6. racerx

    racerx Administrator
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    Pretty cool use of surplus parts. Grom fork legs are a substantial upgrade over CT70, especially the K0 pogo sticks...and light-years beyond the cheap Chinese inverted fork legs that are becoming a defacto standard among customizers. There are some really good upgrades for the Grom fork...valving kits as well as high-end (high-dollar) "plug & play" aftermarket fork legs.

    That sounds like a lot of painstaking work to the triple tree assembly. I can't help but wonder if it wouldn't make more sense to go with different trees, eventually. Fork trees are a lot more complicated than seems possible, at first blush, aren't they?

    You've again piqued my curiosity about full wave stator configuration. Intuitively, an even number of coils, wound CW-CCW, in-series, is logical; the bridge diode rectifier taking half of the stator output on each side, then phasing the two opposite waves into DC. But, this is where there's still a gap in my electrical knowledge...one which, so far, allows a basic question to remain an enigma. Think about the results; we've seen virtually full alternator AC output delivered as DC, meaning a minuscule loss due to rectifier inefficiency. If a fullwave rectifier was turning half the AC waveform into waste heat, then combining what's left into DC, wouldn't there be a huge (~50%) power loss? To me, it indicates that, in laymen's terms what the full wave rectifier does is "bounce" half the waveform to the opposite input pole...and then combine the two inputs phasing...voila!... DC output with virtually no loss. If this is correct, then it doesn't matter if there is an even number of coils, or not. So, here's a true $64(K?) question. If the only requirements are properly phased winding + series wiring and a floating ground, this could be a very easy conversion. OTOH, if an even number of coils is needed, then a 5-pole stator would have to "lose" a single coil...more work but, at 11W per pole, the power reduction would be small enough to not be a problem.
     
  7. fatcaaat

    fatcaaat Well-Known Member

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    I don't pretend I know how the electric works on the conversion...electrical engineering in College resulted in a "D" for diploma...glad I never needed to really apply that in my work. Anyway, what I can say is that I have successfully wrapped TRX90 stators to 4 poles and wrapping the 5th pole independently...and I've also done the same for a honda xr200 setup. The 4 poles wrapped as you stated, floating, fed into a full-wave rectifier producing DC voltage at approximately a 3% loss. The leftover pole can be run as direct AC current which is good enough to power...well, not much of anything to be honest, but it does produce some juice. IN both instances, I have left that extra wrapping not connected to anything.

    However, this is now the second chinese 5-pole floating ground I have wired up to be full wave DC. First one was on a Cheap chinese $225 110cc that went into the CT/CL70 hybrid I built and sold this year. That one basically took the two leads, ran them into a regulator, and then ran those into a square radioshack style bridge recifier and then onto the DC accessories...no battery was used on that one. This spare stator that's been sitting in the parts bin for at least 2 years seems to be the same design, except in this case I purchased a normal motorcycle full wave rectifier and took the white and yellow as inputs, and have a single red output and ground direct to the battery. And everything comes off the battery instead of having separate DC and AC circuits. Its wired the same using the stock 3 position key but the lighting circuit input comes from DC battery. Last one made about 52w DC power, and I assume this one will produce about the same.

     
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  8. fatcaaat

    fatcaaat Well-Known Member

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    Well, today at lunch, I actually got to fire it up and ride it a little bit. It's geared a little to low...as in, it has a lot more power than I was expecting it to have. I think that V2 head definitely makes it pop. Anyway, it power wheelies with 17/33 gearing...so I'm going to bump that to 17/31 since I have the sprocket and that should be about right. These have 18/67 prime ratios and 24/22 4th gear ratios so my gearing would otherwise have been fine for a stock 140 i think.
     
  9. racerx

    racerx Administrator
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    That's a very logical assumption, imho. I've guesstimated ~12.5W per coil, with the radial-array stators. On the extreme generous end, let's imagine 15W per coil, at the weak/stingy end 10W per coil...that's a range of 40W - 90W. The low end of that is sufficient for road use, anything beyond that minimum level just plushes-out the system. And, full-wave DC power just has all the advantages.
     
  10. hrc200x

    hrc200x Active Member

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    Nice looking custom ct70. The '73 atc70 gas tank decal looks like it belongs on there.
     

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