One More Briggs Bike

M

msrfan

Well-Known Member
Well here's another Briggs and Stratton bike. This one was built by a friend of mine a couple of years ago. He had one of those cheap repro springer forks from ebay. He tried to get a little air over a speed bump in front of his house and the forks collapsed sending him over the bars and breaking his arm. While he healed up I took the bike home and installed a good solid moped front fork with cool headlight/speedo combo, added a more attractive fuel tank, re-did all the cables, and smoothed out a lot of ugly welded on brackets and mounts. He never felt comfortable on it since his crash so it just sat in his garage until I offered him a handful of cash. Now it's mine but still in the pre-assembly stage. Plan on finishing it up after a few more projects take priority. Hope you enjoy the photos. Another good use of old moped parts.







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These motors are amazingly reliable and easy to start. I just pull the compression release lever, pedal a few strokes while sitting on the seat, let the lever out and it immediately comes to life. The automatic clutch has a one-way bearing in it so all forward motion turns the motor, unless, of course, it's running in which case it just out runs the bearing. Very nice set up. Have been using them for years with not even a hint of wear or problem.
 
Hey msrfan,

Can I ask you how fast this bike will go? I am very interested in using a Briggs and Stratton motor, but with just one speed, I wonder how fast a 5 hp motor will go. I realize that different motors and different bikes with different sprockets will produce different results, but I just wanted to know how fast a particular set up (like this one) will go.

Thanks for the pictures and information,

Gilbert
 
Before I started using the automatic clutches, I had a 2.5'' motor pulley which netted around 35mph. When I went to a larger pulley the top speed increased but it took a few more pedal strokes to get it going enough to engage the slipper clutch without belts squealing. Now I use a 3.5" motor pulley and top speed approaches 50mph and take-offs are no problem. The automatic slips just the right amount, making it more of a pleasure to ride. It disengages when I stop and the motor idles nicely. I love the chinese two stroke motorbikes, but my four strokes are the ones I take on long rides, just for the comfort and low end torque. No vibration buzz on my hands or butt. As far as going faster, there are a ton of hop up parts for these motors. I haven't used any but plan to get a performance cam, bigger valves, tuned exhaust, jetted carb and some port work on a future build. You can double the output with not much investment. I hope you decide to build one. I have a few buddies working on Briggs bikes, but there's will just be stockers. I would love to see a hot rod Briggs bike. Thanks for your interest.
 
Love the moped/Schwinn look. Got me thinking a bit about the Briggs approach, too. It looks to me like you've worked out a good system. I like the China girls, too, but find now that when I want to ride I almost always pick a four stroke. As you say, less vibration and nice to feel like you're going to get where you're going. And you know, the idea that the Brigs is an American motor just rings my bells! If a person was looking for a used one to tinker with, what should you be looking for?
SB
 
Hey silverbear, look for an upright, or horizontal shaft, aluminum motor commonly used on reel mowers, tillers, pumps, compressors, etc. The I.D. # is usually on the shroud. a 5hp starts with 13. Try to get a fairly late model with pointless ign. It will likely say magnetron on it somewhere. But an old point style will accept the pointless coil. Also a float bowl carb is a good idea. If you find one that says IC, it's an industrial-commercial and will have ball bearing crank mains and an iron cylinder. I forgot to mention flathead style motor.
 
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Thanks for the information msrfan, I really appreciate it. I am leaning towards powering my bike with a briggs and stratton engine. And now hearing your speed numbers, I will probably be getting one soon.

I am not a speed demon by any means, but I would like my bike to be able to go 40 or 45mph without being at its maximum speed limit. I am very interested in hot rodding a briggs engine, but I will probably try to just get the bike running first. I would like this project to span out over a fairly long period of time (like a hobby kind of thing), but I want to ride it right now! So far I am working out making it a riding bicycle, then I will take it back apart to modify the frame to my liking.

Again thanks for the info and the great pictures.

Gilbert
 
Thanks, and good luck with your project. I can't stress enough the importance of a compression release for starting. There's a couple of ways to set one up. Let me know when you get that far along.
 
msrfan, a couple of questions. What is brand/manufacturer of the clutch. Does it come with the pulley mounted to it. What is the brand/manufacturer of the engine mounted pulley. Thirdly, how do you tighten the belts? I know I must be missing something, like another plate, but it looks like if you adjusted the pulley/clutch to tighten the engine to clutch belt, it would loosen the clutch to wheel belt and vice versa.
 
I think the rear tightener shows in the last pic along w/the sliding the motor for the front belt,I am just thinking ,,a height adjustable cent clutch braket on the seat post w/a top pivot bolt and a lower lock bolt for doing both adjustments at once
 
4everblue said:
msrfan, a couple of questions. What is brand/manufacturer of the clutch. Does it come with the pulley mounted to it. What is the brand/manufacturer of the engine mounted pulley. Thirdly, how do you tighten the belts? I know I must be missing something, like another plate, but it looks like if you adjusted the pulley/clutch to tighten the engine to clutch belt, it would loosen the clutch to wheel belt and vice versa.
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The clutch is made by 3rd Millenium Energy, who said they're not making any more. So the next one I bought is a late Whizzer item. These auto clutches have both pulleys made on them and spin on a sprag bearing so you can pedal start. It is mounted on a pivoting plate and the motor mounting holes are slotted. The adjustments show in the last photo. This bike was made from an instruction book I provided to my friend, but he made the engine mounting and clutch adjustments a little different than me. I normally mount the motor solid and have up and down plus sideways pulley adjustments built into the clutch mount. A spring pulls up and the clutch self centers, tightening both belts at once.
 
Sure, MotorCrazy. I break the fins off with a hammer, then grind them down on a pedestel grinder, and finish it off on a lathe. I have a stub shaft from a junk crank I put into the lathe chuck and bolt the flywheel to it. It will need to be re-balanced , so I use a lawnmower blade balancer. Hope that helps.
 
Alright, sweet. Im sure ill be able to break the fins off :D but i needa get acess to a lathe... And what do you think about a Briggs 3hp with and manual tensioner primary belt, to a jack shaft, then to a sheave on the rear wheel? Im not keen on using a centrifugal clutch, doesnt seem to fit the "vintage" theme.... I have heard rumrours about belts stretching etc. So im wondering if its worth it.
 
Update on the bike. Here's what it looks like now. I made it into a race bike for the Willow Springs race last june. Put a drum brake on the rear so I wouldn't have to pedal in the corners, installed a smaller pulley on the motor to gear for the track, put on a better ignition wire, made a header exhaust pipe, changed the bars to shorties with a better twist grip throttle and added rear axle adjusters. I also reinforced the frame in a couple places and made a set back seat post with a skinny seat.



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MotorCrazy said:
Alright, sweet. Im sure ill be able to break the fins off :D but i needa get acess to a lathe... And what do you think about a Briggs 3hp with and manual tensioner primary belt, to a jack shaft, then to a sheave on the rear wheel? Im not keen on using a centrifugal clutch, doesnt seem to fit the "vintage" theme.... I have heard rumrours about belts stretching etc. So im wondering if its worth it.
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That sounds great. Nothing wrong with a 3hp. In fact it is a little smaller and will fit into the frame easier. If you get good industrial or automotive belts, you won't have a stretching problem. Stay away from the fhp belts. That's fractional horse power and they work great on low demand applications but stretch considerable on motorbikes. Check out harry76. He's using that motor in a girl's frame and it looks fantastic. There are a dozen or so Briggs bike builders on the forum. Take a look at them. Lots of good ideas.
 
Thats why i figured 3hp, i got three 5 horses sitting rouind and they all seem to big and a bit overkill :P Thanks alot for the info, ill start a build thread, and if i need anymore help, ill let ya know, cheers. Oh, those bikes look great in the update, how do you start them? Thanks for your help :)
 
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