Briggs and Statton 3hp trash picked bike

S

suzukirider

New Member
i just finished this bike the other day and wanted to share it with you guys. it has an old briggs that i've had for a few years just sitting around not doing anything. i found an old bike at the dump and brought it home, did some welding with some scrap steel square tubing i had lying around, bolted a sprocket (from ebay) onto the wheel, threw on a clutch and there you have it.

top speed was 57.5km/h, but that was before i modified the camshaft. it'll probably do 2 or 3 more clicks now. there's only one brake, but i'm going to put on the front tire from a mountain bike and some better pads to get a bit more stopping power.

this thing is geared reeally tall. at 57km/h it's only turning 2800rpm. still another 800rpm before it even reaches its rated horsepower.

P1000245.jpg


ol'reliable
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here's after i removed the "easy spin" feature. what it does is pop open the intake valve during the compression stroke, and while that makes it easier to pull over, it's bad for power, especially low down, so i ground the lobe off the cam.

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i'm gonna have fun cruising with this thing. i might even go on a road trip or two. already put 80km on it
 
Looks great! Only advice I can offer is find a better way to attach the sprocket to the wheel. Broken spokes at 60 kmh isn't my idea of fun. Even a rag joint would be better, what you have unevenly puts strain on only some of the spokes and will damage the wheel. Everything else looks good though! Have fun!
 
Yeah, I would mount that sprocket differently. I have never seen such a monster on a rack mount before. what an amazing find.
 
Hi suzukirider

I think you are right about the gearing:

bicycle with 3 hp briggs engine motorized bike 44mph
http://www.youtube.com/watch?v=HWeHW3GyFbc

The easiest fix would be to try a straight pipe to replace the muffler.
From:
http://www.diygokarts.com/vb/showthread.php?t=1118

On the 5 hp motor

"stock exhaust chokes the engine of 1/2hp, even at 3600 rpm"

3600 rpm 8.44% increase in torque


The next easiest fix might be to slap a 5hp Briggs in. It should
have more bottom end torque.

Also using a 24" wheel would help gearing.

Great work.

Speaking of "Massive Racks":
 

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mat_man said:
Hi suzukirider

I think you are right about the gearing:

bicycle with 3 hp briggs engine motorized bike 44mph
http://www.youtube.com/watch?v=HWeHW3GyFbc

The easiest fix would be to try a straight pipe to replace the muffler.
From:
http://www.diygokarts.com/vb/showthread.php?t=1118

On the 5 hp motor

"stock exhaust chokes the engine of 1/2hp, even at 3600 rpm"

3600 rpm 8.44% increase in torque


The next easiest fix might be to slap a 5hp Briggs in. It should
have more bottom end torque.

Also using a 24" wheel would help gearing.

Great work.

Speaking of "Massive Racks":
Click to expand...

that video link was actually my inspiration for this bike.

as for straight piping it, that's a no-go since i'm riding it in town. don't want any complaints or the law might become interested in my rig.

i do have a 5hp briggs but the shaft is too short for the clutch, plus it's kind of an antiquey keepsake, not for messing around on a bike and possibly damaging it. if i can find another 5 horse i will slap it on in a heartbeat.

but perhaps a better option would be a ~5hp ohv chinese clone engine. anyone know any links to ebay auctions?
 
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I believe a better option would be to keep the engine that you have, and just add jackshaft to the rack and get the gearing right. Right gearing is a way better fix than just slapping on a bigger motor.

You'll find that the lil 3 horse will be plenty powerful for a bike. Especialy if you get the revs up to about 4800, that's a good bit more than 3 hp.
I would gear it for about 35- 38 mph at 4800. Use the gear calculator stickey in the DIY forum.

I found that the 8 hp 3/4" muffler lets these motors run a lot better than the 1/2" size one.
 
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meh, i like the gearing where it is. apart from strong headwinds and uphill, it cruises just fine, and i don't want to make it buzzy at high speeds. a 5hp would combat hills and winds better while keeping the revs at a minimum. i'm about torque derived power, not rpm derived.
 
If you were going to do the rag joint mod, I would consider doing it on a smaller wheel like 24".
This would lower the gearing, change the rake to slow the steering down, more stable at high speed. Maybe get some drop bars to cheat the wind.

If your Briggs 5hp is 1952 or older, it will be cast iron and heavier than newer aluminum ones.

Best of luck
 
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Suzukirider, I was wondering that bike brake for just one (the front wheel) was the way it was made originally.

For thoughts, I felt that I’d show the bosses I made for the mounts for v-brakes ( the original Shimano V’s) from trash picked stuff.

You do welding then you could try this. My bike had coster brakes and now that there are no pedals anymore (not trying for on road legal only OHV an Parade) there would otherwise be no brakes.

One picture a little fuzzy shot at night shows the rear welded on angle brackets without the v-brakes yet installed.

The rear pair of brackets I welding in the position a nut that has a flange. They were fit in and stamped in to a tight fit to a hole I drilled in them. To hold them securely I weld a few spots on the flange to the angle bracket. Then the brackets were attached with these threads so that would be in the right position for the mechanism to move the brake pads to match with the rim*.

The nut threads are the size that fit the threaded portion I scavenged off the bike the v-brakes came from. That is the post that makes the bearing surface that allows the brakes to pivot and clamp the rim with the pads.

All went well until I found that the pulley attached to the rear wheel needed to clear the frame in the back. With a spacer on the left side which fixed that problem, it had caused another. The left rear brake pad shoe had to have a little extra length to rear the rim. I made special extra length onto the shoe to the v-brakes which I made a spare to keep on hand*.

This I don’t think you would run into this depending on how much clearance is needed with chain and sprocket, but if I had known in advance I would have shimmed the left side rear boss so a modified brake pad would not have been necessary. I may still cut the left side boss and adjust it someday.

I have ridden a belt drive without any clutch or jackshaft for special reduction ratio for torque on a 24 inch wheel bike using 3hp, and it ran fine. Chugged at start up, but went fast. The thing I am doing with a multiple jackshaft for a 44:1 reduction is just a mod that allows use in parades that restrict speed to 5mph or less and I want to keep my clutch cool by not needing to pulse the throttle to achieve slow speed. The use it would be when fish art cover removed is to be a dirt bike and I would half that ratio to 22:1 for speed but still able to climb hills.

The mount to the spoke with a washing machine pulley with plywood covered resorcinol epoxy type glue and painted sandwich might stress the spokes, but I never broke a spoke with my build that was a similar type but more crude way back when I built a motor bike when in my teens. If you could spread the pressure of the rag joint over more spoke surfaces it may lessen the chances of wear and tear on the spokes. If you are think about it, even though the old Whizzers clamped spokes clamped differently, it could possibly be adapted to a sprocket.

MT

My thread on page 4 of 5 so far:

http://motorbicycling.com/showthread.php?t=29678&page=4
 

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sorry for the late reply. i didn't get a notification email. the bike did have rear brakes but i removed them because they were in the way of the motor frame. it only has front brakes. i put new pads on though and the stopping power is sufficient, though it wouldn't hurt to rig up a rear brake. the bike also has new mountain bike tires that work better on gravel.

as an update to the bike: i found a 5 horse and rigged it up. boy does that thing fly now. worlds better than the 3 horse. i got it up to 76km/h. during one speed run the throttle stuck open at 70 but i managed to stop the bike with the brake and then the throttle unstuck. i really need to rig up a killswitch on the handlebars.

dirtbikemike, the ratio is 6:1 with a 12 tooth clutch and 72 tooth wheel sprocket.

76km/h is terrifying on a bicycle. this was on gravel too
 
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