Beginner01's first build..

Tony01

Tony01

Well-Known Member
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************************ Original post

Hello,

MB newbie here just getting started on my first build. Found a Briggs & Stratton 3.5hp motor for $30, and a '79 Chicago Schwinn bike for $60. My goal is to build something reliable, heavy-duty, fast, and cool looking. Meaning, flat bars bobber style.

Motor mount is cut from some .187" steel plate. Plate is not yet welded in the photo.

The frame seemed a bit small, so I hacksawed through the chainstays between the BB and the kickstand mount (to keep the strength) and proceeded to straighten out the seatstays and bend the chainstays with a C-clamp and a couple of strong beams. On Friday, made a part from some stainless tubing to connect the chainstays.. and dropped everything at the welder's.

The plan is to have a tensioned belt jackshaft setup with clutch lever, disc brake on the front, possibly a multi-speed rear internal gear hub.. or even a such hub mounted externally.. under the jackshaft.. so that I can swap it out quickly in case it breaks down ;)

Or even... a locked up 5-gear freewheel on the back with a heavy duty derailleur spring? It would drag sure... but it would be like driving a manual transmission almost... :)

The stretch is going to force my BB much lower to the ground. Anybody know of any wide cranksets with short crank arms?

And what to do about mounting that cruiser seat?? ahhh decisions... decisions...
 

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Check out msrfan's post another Briggs build,he usees 5 hp briggs without cutting the frame.
You can get shorter cranks from a 20" bike or have your welder bend and cut some regular ones.............Curt
 
Yeah check out msrfans stuff ..He is THE Briggs guy here. There are lots of guys selling laid back seat posts to get that seat back and you can flip the guts of the seat tonget it lower.
 
Cool, I checked out msrfan's bikes, they are badass! The welder did a great job on my frame. Mocked up the bike... now I can start measuring for belts and other parts. Lots of room in front of the rear wheel! The stretch didn't alter the rear tire size requirements too much like I thought. I can still fit a 2.5" tall tire on the back rim, though with a max width of 2.2" and still have a quarter inch clearance per side at the chainstays.. Thinking of getting 2" wide rims front and back now :)
 

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this is going to be a sweet ride when you are through!
I like the unique lines of the frame now that you have redone the back end. It looks long and low.
 
I concur with GN, nice!

I'm going a bit of a different route with a dirt bike / art vehicle.

The old style frame before you moded it to be a rad looking machine is quite like what I started with. The JC Penny Foremost 26 inch wheel frame from the 60's era I had a time fitting the 3hp Briggs 80202 0430 70's era engine in the middle.

I can't tell yet, but is the carb going to change to a float bowl type to make room fitting the engine? Ya know then gas tank is up above on the top bar.

Great to see this goin on!

MT
 
Thanks, What would be the least expensive means, for my setup, to gain more torque on takeoff ? 3 1/2" motor pulley to 6" jackshaft pulley, otherside of jackshaft is 10 tooth sproket to 48 tooth rear sproket ? I thought about going to a 24" rear wheel or larger rear sproket. has a belt clutch I made.
 
If you already have the 24" wheel that would be cheapest way.
A 56 tooth sprocket would most likely cost less than a new wheel if you go the other way.
Keep in mind that either way you go it will reduce your overall top speed.
 
Thanks guys, I really like how the stretch came out too. I have some issues I need to solve, however:
Need short cranks. Due to the stretch, the BB shell bottom is less than 5" off the ground with flat tires.
need a wide crankset or BB to clear the motor.
Need to decide on a jackshaft setup, namely how to mount it to the seat tube.
Need to decide on a front brake (disc or drum, whatever cheap deal i find first really)
Need to decide on gearing or cvt.
If gearing, do I go with a IGH or derailleur? if IGH which one? must be at least 5 spd.
If CVT, do I go with the $200 comet original CVT or a cheap knockoff ebay CVT for $120? motor is a briggs 3.5hp. if the cheap ebay CVT is good, which seller should I buy from? Are all the knockoffs the same?

Sorry I haven't updated, I got laid off from my job last week.... so yeah.
 
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Well, It's been a month since my last update.. and I've started getting my unemployment checks and still have too much time on my hands. I have to keep track of how much I'm spending on this project. So far:

Motor 30
Bike 60
forks 50
Front wheel/rotor 40
Hayes Hydraulic disc brake $44
Pillow block bearings (jackshaft) $18
V-belt, pulleys, some hardware $55

That's around $300.. my original budget!! New budget, $500 ;)

I've decided to go with a hydraulic disc front brake, tensioned belt clutch, and derailleur gears (6-speed megarange). The current disc is 160mm, later on I will get a 203mm when I get the rest of the bike dialed in. The jackshaft will ride on two pillow block bearings mounted to a plate to clamping u-bolts on the seat tube. Still need the wide BB, BB adapter, and some other stuff from SBP, head/brake lights, CA plate, gas tank, some home depot hardware, tires, and lots of tuning. Next week will be jackshaft time... I can't wait!!
 

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Been a while since an update, been busy. Got a lot of parts in the mail and have made some progress.

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I cut the chopper forks, set up the headset and was able to get it tight which was kind of tricky with the dual clamp setup.

Set up my jackshaft, two pillow block bearings supporting a 5/8" shaft with 7" v-belt pulley, 10 tooth drive sprocket, and freewheel adapter for the pedal input. Shaft still needs to be shortened.

Got an 8" disc brake rotor with adapter and installed the caliper. Man oh man, setting up the front double clamp fork and aligning the brake caliper parallel to the disc was a REAL PITA. It looks way cool, though! Tomorrow I will be shortening the hydraulic brake line, as this unit is for the rear wheel. Hopefully it can be done without needing a re-bleed.

Got my rear wheel in the mail, of course this cheap freewheel thread wheel was spaced for 135mm... I thought it was standard for them to come in 120mm or so? Freewheels don't usually go bigger than 5 or 6spd. Fixed the spacing to as much as I could remove.. down to approx. 125mm and dished the wheel somewhat to center it out again.

The drive sprocket I received turned out to be much fatter than I expected.. For a very wide 1/2" pitch chain. No problem, turned that baby down from a .225" thickness to a .090", to fit 3/32 bicycle chain. Hardened steel and interrupted cuts... my favorite...

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.090" thick:
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It looks like I will have little clearance for my rear chain movement.. which means use of only 3 or 4 bottom gears out of the 6-speed cluster. The derailleur is hooked up and ready to go. After considering my gearing and top estimated RPM of 3600, it looks like I can go up to 25mph in first gear... hill climbing torque!! and somewhere around 60 in 6th.. :D


I still don't know what to do about an intake manifold. I have a Honda-style 22mm slide carb waiting to be fitted.. but no intake.. Home depot and their limited selection did nothing for my creativity in modifying their parts. Looks like the only option is to machine a part. Or DIY cast one at home in sand and drill and face on two sides.. hmmm....

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