First Build, 4-stroke 3.5 hp on a Schwinn Bike

Ive been having a really disappointing day. I did not know that this sprocket will not work and I may have lost my $23 on that sprocket. I bought it from "boygofast" on ebay, do you think he will take it back?

I wanted to put the engine inside the frame, but it didnt seem reasonable. I would have to have my legs really wide open, and I like riding bikes normally.
Ive tested riding the bike with the engine on the back and I cant even feel the weight. I will have to build a V-shaped kick stand of some sort. Anybody have any good designs for a kickstand?

What is the max RPM for this engine? Is this a Tecumseh engine?

I want to be able to cruise at least around 40mph, what would I need to do that without shelling out more money that I dont have?
 
This engine is likely governed at 3600rpm. If you de-govern it, let it breath more and use a header the RPM should increase to about 5000 -5200prm. Using a 12 to 1 reduction you will get about 40-42MPH.
 
Is it safe to de-govern?

With a 12:1 ratio, at what speed will the clutch engage?
My clutch is rated @ 2000rpm.
 
I am sure that is a Techumseh engine, the carb is the same as used on the 2 stroke Toros from years back (s200) - good to know the diapharam carb will work on the four stroke.
As for safe rpm, I am not sure except yours is aluminum and I think the cast iron ones can blow up from over-reving.
With a ten tooth clutch sprocket, you would need a hundred twenty tooth drive sprocket to get 12 to one. Kinda big. If you do a jackshaft, you still could use that 36 tooth sprocket on your wheel.
Are both the clutch and drive sprockets you have the same pitch?
 
professor said:
If you do a jackshaft, you still could use that 36 tooth sprocket on your wheel.
Are both the clutch and drive sprockets you have the same pitch?
Click to expand...

Yes, same pitch. #41 chain. How much is the cheapest jackshaft and corresponding sprockets?
 
(Is it safe to de-govern?

With a 12:1 ratio, at what speed will the clutch engage?
My clutch is rated @ 2000rpm.


There is no real danger of over reving with only minor mods as long as you only rev it with a load on the engine. The stock valve springs will float and limit the RPM to about 5000 to 5200 max. By float, that means they will not allow the valves to open and close quick enough for the RPM to go beyond an unsafe range.
The clutch will still engage at the same RPM. Ifr you use it on the jackshaft instead of the output shaft you should go with lighter springs. These can be found at a kart supply site. I would just go with the clutch on the output shaft since your engine will have plenty of enough power for a bicycle.
 
I meant to ask at what mph will clutch engage? but it doesnt really matter, because this thing wont even run until I get a jackshaft for a good price. I dont think I have a kart supply store near me, so I will have to order online. But I dont know where.
 
You might consider running a belt on the primary side. Pulleys and belts are easier to get in smaller sizes(though Grainger has about any size you want). You would have to get a pulley clutch, these generally have a 3" pulley. If you couple this with a 6" pulley along with a 10t/60t chain set up you will have a 12:1. I would rather have a belt behind me on the primary than a chain that could come whizzing by me if it broke. Enter the word Veteran in the search feature and it will take you to my 3.5 Tecumseh in frame bike that has this set up.
 
cannonball2 said:
You might consider running a belt on the primary side. Pulleys and belts are easier to get in smaller sizes(though Grainger has about any size you want). You would have to get a pulley clutch, these generally have a 3" pulley. If you couple this with a 6" pulley along with a 10t/60t chain set up you will have a 12:1. I would rather have a belt behind me on the primary than a chain that could come whizzing by me if it broke. Enter the word Veteran in the search feature and it will take you to my 3.5 Tecumseh in frame bike that has this set up.
Click to expand...

Thank you, I hope I can afford this setup.
 
professor said:
Well Scotto, I suppose doing the heavy motor on a tandem, it won't flip over backwards as readily as on a normal bike. Sorry I didn't recall your ride.
Click to expand...

No worries man, was just havin some fun with ya. Yes that is a big, heavy 124cc Kow and I would not put it on the back of anything other than a tandem. It could however be put in-frame without much trouble at all....4+hp and 34lbs. dry, and it purrs like a kitten.

Kristof, don't get dicouraged, your build will come together.....just take your time and think things through, you're almost there (^)
 
Is it even worth doing this build or should I get a Grubee kit? (How would I get a kit shipped to California?)

Will this 100cc haul ass compared to a Market 80cc kit?
If I de-govern this thing it will only rev @ 5000rpm.

Ive found this jackshaft kit: Will this work?
All I would need is a 20T + 10T sprocket + another master link.

I will also need to build a throttle of some kind or buy one for really cheap.
 
Last edited:
IMO that jackshaft will work for your project. It's made for mounting that type engine. The bolt holes should match the pattern of the engine's. You may want to call BMI to determine the diameter of that shaft so you can order the right sprockets for it. If you use the 36T sprocket on your wheel you will still need about an aditional 3.33 reduction. This can be done with an 8t on the engine to a 24T on the jackshaft then the 10T clutch drives the 36T on the wheel. These are in #40/41 chain. You could use #35 chain from the engine to jackshaft reduction. There are too many different options to list here. If you ride up hills you may want a different ratio. Where I ride it's flat, so my bikes are all geared for level ground.
I have used several kits 47cc, 49cc, and 66cc. I have done a few DIY bikes with 4 strokes and like them best. The HF 79cc, 2.5HP will haul my 190lbs all day at 40MPH
 
No doubt what you are doing (if you continue) will be bullet proof when done. You can make a throttle out of a bike derailer friction shifter (what I use- love it). But you still have to do the jack shaft and sprockets (some guards too) and a stand of some kind.

The two stroke kit - you will need to massage (look at the stickies) has more reliablity issues, but is much simpler. Tough choice?
By the way- your emphasis on speed makes me think you haven't injured yourself very much yet.
One of the difficulties with going fast is car drivers will never think you are doing that when they look at a bicycle coming down the road, they are very likely to pull out in front of you, besides being non legal.
 
professor said:
By the way- your emphasis on speed makes me think you haven't injured yourself very much yet.
One of the difficulties with going fast is car drivers will never think you are doing that when they look at a bicycle coming down the road, they are very likely to pull out in front of you, besides being non legal.
Click to expand...

Ive fallen of a cliff mountain biking before...

I hate cars very much, even if Im cruising at 20 with my regular bike, sometimes they dont even notice me.

This is not legal? or not advised? will cops pull me over for this?
 
My modded Whizzer easily makes 50, cruises nicely @ 40-45, yet I find myself usually riding at 35. Just seems more comfortable there. The extra top end also equates to added power on hills and acceleration. What you will have with the Tecumseh is torque, it has a rather large bore for its displacement which is good. Besides, the old USofA engines of the past will run just about forever with little trouble. Id say stick with what you have and expect a cruise of 35. If hills dont figure in then you can run a higher ratio(lower #) for more top end.
 
Your gearing is way too tall.
I plugged it into a gear calculator & its around 87 mph.
You'll strain the clutch & engine never getting into the engines sweet spot.
-lowracer-
 
What kind of ratio will get me cruising at 40mph @ 5000rpm?

I do live in a hilly area, so what kind of ratio should I be looking at, a 12:1 or 10:1?

I will have to overcome air and ground resistance wont I?
 
Kristof,
I have a Lifan 98cc 2.5hp 4 stroke & am running a 3.2" engine pulley to a 22.25" wheel pulley 8.4:1 with a 1.9 mtb slick & hit 45mph at around 4500rpm. The torque is great & I have lots of power anywhere in the rpm range.
-lowracer-
 
lowracer said:
Kristof,
I have a Lifan 98cc 2.5hp 4 stroke & am running a 3.2" engine pulley to a 22.25" wheel pulley 8.4:1 with a 1.9 mtb slick & hit 45mph at around 4500rpm. The torque is great & I have lots of power anywhere in the rpm range.
-lowracer-
Click to expand...

Do you live in a hilly area?

8.4:1 is a pretty tall ratio. Youd have to be going 18mph for clutch to fully engage, no?
 
You must log in or register to reply here.
Back
Top