Here is the results of years of collecting parts and building it in my free time. I'll be posting more pictures. I'll explain what I did as I post the pictures. Basically I built this with found or collected parts with minimal cash. I spent less then 200 on parts/supplies. This runs very well with a top speed of about 40mph. It's geared well enough that I don't even need to pedal at all. I have about 300 miles on the bike now and just minor issues here and there but nothing like my first build which was a 2 stroke. The cost between the two builds are also drastically different. I learned allot from my first build and applied allot of that knowledge to this one. Like I said I'll be posting pictures of the progression of how I built it. I've been using this as my daily commuter for the past month or so now and I love riding it. Not only is it about as quick as traffic but is great on gas and is a head turner for sure. I've even had a lady get out of her car at a red light to come check out the bike. It was a fun build that is like to never do again. J/k I'd like to do another.
Briggs 3hp stretch build
- Thread starter Motakitty
- Start date
Mocking up the top bar. This bar came from one of those kid trailer bike things. I had to remove a riser from the tube and patch two tiny drill holes. I also decided at this point to flip the rear of the frame upside down as it would allow a bottom bar to fit nicely between the two bars and the seat tube. I addressed the drop outs later.
I got the engine on there. I just cut the original mounting plate the engine was on and weekend that straight to the frame and added gussets underneath for strength. I also had to reroute the chain. I used skateboard wheels and cut groves in them for the chain to ride in. It clears and pedals just fine. I also had found a rear hub adapter on a bent up bicycle wheel at our trash so I snatched that up and it for my wheel perfectly.
I got it in primer for now. Mainly to keep it from rusting and plus flat black is my favorite color. I bought a jackshaft kit which fit great. Gives me the adjustability I wanted and best part is no chain tensioner. I went with a max torque clutch. I found this seat too. It's a full suspension seat as in there's springs running under the seat and makes this a very comfortable ride. I also found these tires . The front is a marathon plus for ebikes but it's a bit narrower than the rear. I added a kick stand that I had laying around.
Here it is fully ready for its first test ride. The drive chain cover is from a planter box just cut down. I added a front caliper brake just for the time being but I did go to a disc setup later. I got the front light and rear light from AliExpress. The rear light is under the seat. I used a 3 cell lipo battery from a RC car I had and don't use. I got a pencil case that fits the battery perfectly and wired it all up with a switch under the front half of the seat. The lights are bright, they last a long time and I can change the battery. The first ride went good. Nothing broke but I did have some engine issues. I completely went through the engine. Replaced every seal and cleaned the carb. That fixed all the issues it had. I also later took the head of and cleaned all the carbon off and lightly polished the combustion chamber. Cleaned and reoiled the air filter. The first ride out went about 25 but felt like it had more in it for sure. I made the throttle with linkages from my rc parts.
Also because I flipped the rear half upside down the drop outs became drop ups which was not good. So I fitted some plates that go around the axel and screw into the frame so I'm the event an axel but comes loose the frame doesn't just drop to the ground. I want to do the same for the front or at least get new locks. So far I've got about 300 miles on the bike and very little had to be fine besides the normal tuning things that one has to do after a new build. I had to readjust the drive chain but it now runs smooth and straight. The engine has plenty of power. I had added a small engine tach/hour meter and a speedometer to keep track of things and it can go top speed 40mph but I like to cruise around 32 but go up to 38 in traffic just to keep up. I didn't even have to use the pedals even from a dead stop. It's great on gas but I'd like an option to be able to fill up at a gas station. The best I can think of is always carry a gas bottle I can fill up or get a piece of tubing that fits over my gas tank so I can seal the pump to it cause right now my tank is so small that the gas nozzle would bottom out before the seal happens. It's been a fun build that took me 4 years to finish. I had collected parts over the course of like 5-6 years. I found stuff on Craigslist, nextdoor, literally the side of the freeway. I even collected car batteries to get credit for paint supplies.
I also built my own muffler too after the stock one feel apart. I used a straight pipe and drilled small holes then added an larger outer shell that's filled with steel wool and wrapped it in header wrap with a small chrome tip welded on. It definitely doesn't sound like a normal bicycle anymore. It's loud but a good loud. You can see the muffler in the pictures with the red wheels.
Sidewinder Jerry
Well-Known Member
First of all great build. Those look like 26" tires but I'm not sure since a girls step-through frame was used they may've been 24" tires. ?????
I'm going to assume the B&S engine is a 130 cc since you said it was rated at 3 hp. I'm not sure what kind of hills you deal with. You have more than enough room to install a CVT and keep the Jackshaft. In order to do 40 mph on 26" wheels with your engine doing 3600 rpm you'd need a reduction of almost 7\1. Installing a CVT you'd get a reduction range of 21\1~7\1. Meaning you could climb almost any hill.
Another option would be to install a Strumey Archer S3X IGH as a jackshaft transmission. 1) Could be a climbing gear. 2) A level ground gear. 3) A down hill gear. This'll give you the following reductions and speeds:
1) 11.14\1 [25 mph]
2) 9.28\1 [30 mph]
3) 6.96\1 [40 mph]
The ultimate setup would be to run a CVT to the Strumey Archer S3X IGH for a reduction range of 33.42\1~6.96\1. Then this'll be the reduction ranges and purposes for the 3 gears:
1) 33.42\1~11.14\1
Steep hill climbing/ heavy load pulling.
2) 27.85\1~9.28\1
Around town general use.
3) 20.88\1~6.96\1
Open road/highway use.
Years ago Cannonball did a build using a S3X as a 3 speed gearbox. The S3X is no longer in production but you can still find them with a bit of searching. The good thing is the chains can be kept on the left side since the S3X is a fixed gear IGH. There's no pawls in the hub due to it being a fixed gear IGH.
Thread 'Cannonballs Abbynormal 3Speed.' https://motorbicycling.com/threads/cannonballs-abbynormal-3speed.58233/
Just some thoughts if you seek more challenges with the build. Consider triple tree or springer front forks. Along with a suspension seat post for a more comfortable ride.
I'm going to assume the B&S engine is a 130 cc since you said it was rated at 3 hp. I'm not sure what kind of hills you deal with. You have more than enough room to install a CVT and keep the Jackshaft. In order to do 40 mph on 26" wheels with your engine doing 3600 rpm you'd need a reduction of almost 7\1. Installing a CVT you'd get a reduction range of 21\1~7\1. Meaning you could climb almost any hill.
Another option would be to install a Strumey Archer S3X IGH as a jackshaft transmission. 1) Could be a climbing gear. 2) A level ground gear. 3) A down hill gear. This'll give you the following reductions and speeds:
1) 11.14\1 [25 mph]
2) 9.28\1 [30 mph]
3) 6.96\1 [40 mph]
The ultimate setup would be to run a CVT to the Strumey Archer S3X IGH for a reduction range of 33.42\1~6.96\1. Then this'll be the reduction ranges and purposes for the 3 gears:
1) 33.42\1~11.14\1
Steep hill climbing/ heavy load pulling.
2) 27.85\1~9.28\1
Around town general use.
3) 20.88\1~6.96\1
Open road/highway use.
Years ago Cannonball did a build using a S3X as a 3 speed gearbox. The S3X is no longer in production but you can still find them with a bit of searching. The good thing is the chains can be kept on the left side since the S3X is a fixed gear IGH. There's no pawls in the hub due to it being a fixed gear IGH.
Thread 'Cannonballs Abbynormal 3Speed.' https://motorbicycling.com/threads/cannonballs-abbynormal-3speed.58233/
Just some thoughts if you seek more challenges with the build. Consider triple tree or springer front forks. Along with a suspension seat post for a more comfortable ride.
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Thank you for your reply. It does okish on hold but where I ride there aren't to many so I'm happy with it's performance. It'll hit 40@3600 so it's fine and I don't go that fast anyhow. The seat post is actually welded into the seat post so that's fixed but the seat is very comfy. I had thought about swapping the front fork. I like the double spring springer fork. My last build had a classic springer fork and it rode great and would look great on this bike too but I always liked the double spring ones. Oh and yes they are 26" wheels and yes it's the 127cc b&s.
Sidewinder Jerry
Well-Known Member
I'm a large person 245 lbs, live in a mountainous region, and have health issues. I built a shifter bike that uses a Robin Subaru EH035 engine (33cc) along with a Staton Inc triple chainring shiftkit. The reduction range on my bike is 66.79\1~16.25\1.
At 1.6 hp and a total weight of 350 lbs you must have multiple engine driven gears where I live. Hills can be up to a 30% grade. In the near future I'm wanting to build my girlfriend a stretch cruiser using a CVT to a Jackshaft for an extra reduction point. I plan to use a 79cc Predator engine. The top level ground speed will be 30 mph.
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