79cc MTB official build thread

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ultralight01

ultralight01

New Member
Oct 30, 2016
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Hood River, Oregon
I was posting some updates in one of my other threads, but it was off topic.
The bike will have
A 2000 lumen headlight
203mm rotor and hydraulic brake for front wheel
Suspension fork
CNC sprocket adapter
Jackshaft disc brake
79cc predator engine (governor removed)
Turn signals and brake lights
Fancy lights (el wire and el strip)
Comfort seat
Purchased exhaust with muffler (whoah, I'm buying an exhaust? This time, yes)

I'm 3D printing mirror parts and more. I printed the intake manifold for the engine. I have nearly all parts except for the fork, rotor, lights, exhaust, handlebars and seat. The headlight is incredible and lights up entire fields at night. I'm running it off a 4.5amh battery which I will try to charge with a DIY alterrnator setup. The frame is a 90's steel Schwinn MTB frame with a 1.125 headset.
Mockup? Kind of
IMG_4161.JPG
Is like to name it, but I'm bad at namemaking.
 
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ultralight01

ultralight01

New Member
Oct 30, 2016
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Hood River, Oregon
Some more pictures. Parts, the headlight, and some 3D prints. The one on the right is an intake manifold, the others are mirror pieces. I'll show how that goes together soon.
IMG_4162.JPG

IMG_4166.JPG

IMG_4165.JPG
Edit: I cut off the old fork
 
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ultralight01

ultralight01

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Oct 30, 2016
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Hood River, Oregon
Ok, I'm sold on 203s.
I got the seat out, it was stuck in there really well. I sanded it down and lubed the seat post and the inside of the frame. I put t it back in with my turn signals an fender attached.
 
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ultralight01

ultralight01

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Oct 30, 2016
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Hood River, Oregon
I got my suntour 1 1/8" fork today. I was positive that I got my measurements right, but I didn't. It's too big for the headset. The old fork steertube actually fits inside of the suntour steering tube. What do I do now? Return the fork or replace the headset? 1" suspension forks are rare. And how do I know which headset would be correct for my bike?

Thank you...

Heck, I'd have to get my current set out too. But I really should do this. The bearings are a little tired and choppy.
 
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scratchbuilder

scratchbuilder

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Jan 17, 2015
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ca.
That's the problem I have because I use old beach cruiser's. When you place the 1 1/8 cups on your bare headtube, they are the same diameter. I've done one by cutting rings to slip over the head and cup. The build I'm doing now I just cut 2/3 of the headtube off and put an 1 1/8 headtube in. The fork will slip into your headtube now, with no cups. I know there has to be an easier way...seems like I read here somewhere. Always swap meets. I found a couple nice 1"forks.
 
ultralight01

ultralight01

New Member
Oct 30, 2016
337
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Hood River, Oregon
scratchbuilder said:
That's the problem I have because I use old beach cruiser's. When you place the 1 1/8 cups on your bare headtube, they are the same diameter. I've done one by cutting rings to slip over the head and cup. The build I'm doing now I just cut 2/3 of the headtube off and put an 1 1/8 headtube in. The fork will slip into your headtube now, with no cups. I know there has to be an easier way...seems like I read here somewhere. Always swap meets. I found a couple nice 1"forks.
Click to expand...
I have a lathe, I was going to turn the cuosmdown to fit. Maybe there's 1/8" or 1/4" of room?
 
M

Mikey_

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May 15, 2016
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I can't wait to get reports of how it rides. I like the idea of a mountain bike frame and a strong engine. It is going to be nice and flickable and fun around the bends.
 
ultralight01

ultralight01

New Member
Oct 30, 2016
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Hood River, Oregon
I wrote a whole response, and when I clicked post reply it sent me to a random thread. Well, a summary:
I'm a little concerned about stability because the frame is a little low and has a short wheelbase, but I love MTB frames. The aggressive riding style is perfect. This build should take 1-1.5 months to complete, since Im going on vacation to CA again for two weeks and I'm still waiting on some parts. It's funny, this bike is really a commuter, that I'm converting to a suspension MTB. No one ever does that in the cycling world. Haha!

I'm doing it because the frame has plenty of room.
 
ultralight01

ultralight01

New Member
Oct 30, 2016
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Hood River, Oregon
Still working on the bike. Got the mounting plate welded, fabbed some plates to sandwich it onto the frame, and bolted the engine in. I'm fitting the two pillow block jackshaft behind the engine and right in front of the back wheel, with about an inch of clearance. The #41 chain will be very short, since it's such a short bike in terms of wheelbase.
I'm finding a place to mount the battery, alternator, and headlight. I still need my fork stem, handlebars, alternator, motor, step down converters, gas tank and the headset.

I'm using a 34mm 1.125 headset and turning it down to fit in my headtube. I'll need to get the current headset out, which I'll be doing with a homemade tool.

I tested the engine, it runs great. It doesn't sound lean but I'm assuming it is just because of the mods.

I'm back to making my own exhaust for the fun of it. But I've only got two days before I take a vacation. Darn you California relatives. :p
 
ultralight01

ultralight01

New Member
Oct 30, 2016
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Hood River, Oregon
By the way, I think this guy and I would be friends:
212cc insane bike.jpg
I found that on Imgur. Notice he cut the frame and welded some steel AROUND the engine to make it fit. But hey, full suspension! Lol

Wait, and a jackshaft? I hereby decree this bike to be named "Suicide"
 
M

Mikey_

Member
May 15, 2016
37
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GA
ultralight01 said:
By the way, I think this guy and I would be friends:
View attachment 84881
I found that on Imgur. Notice he cut the frame and welded some steel AROUND the engine to make it fit. But hey, full suspension! Lol

Wait, and a jackshaft? I hereby decree this bike to be named "Suicide"
Click to expand...
LOL I would be afraid that the frame couldn't handle it. That thing has to be scary fast!

I want to try a Lifan or Predator on my build.
 
ultralight01

ultralight01

New Member
Oct 30, 2016
337
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Hood River, Oregon
That thing... Scares me.
Meanwhile, I'm leaving tomorrow morning, printing out some intake manifolds, and I got to work on my bike last night.

This is how it's going to look for the next two weeks:
1.jpg

I removed the cups. Since I have 1.125 cups on the way with a 34mm flange, I'm going to need to turn it down it my lathe till it's very thin. I believe it will still be strong enough.

Meanwhile, I mounted the jackshaft. Since the frame is chrome moly steel I decided to bolt it into the frame. Time will tell if that was a mistake or not.

I'm gonna need a paintbrush and spray paint to cover over all of these scratches.

I used two pillow blocks, a mini hub from MFG supply, 36T #35 aluminum sprocket, 11t #40/#41 sprocket.
2.jpg
3.jpg

Final gear ratio is 12:1.
Ouch
I mistakenly thought my 36T was a 39T, and thought I would get 13:1.

Well, I'll ride it for a while and then change something. Maybe a 10T out or a larger wheel sprocket. I'm using the CNC adapter and sprocket, which is being delivered today:http://www.ebay.com/itm/262519605753?_trksid=p2057872.m2749.l2649&
ssPageName=STRK%3AMEBIDX%3AIT

with a 44T CNC aluminum sprocket.

How can I make my bike a single speed? Or at least keep the chain from slipping into different gears? I may need wide pedals too, or some kind of pedal extension. So far the cranks clear just fine, but I have to reach around the engine with my legs, which I don't want to do, to reach the pedals.
 
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