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

[Kristof]

Hi,

This is my first build. Any tips, concerns, or help is accepted.

Parts:
-Schwinn Ranger 2.6FS with 26 x 1.95 in wheels
-3.5 Hp Sears Companion Motor
-Hilliard Max Torque Clutch 5/8 drive 10 teeth
-#41 Chain
-36T 9-hole sprocket #415 <-apparently this will not work...hopefully I can get my money back (***Ok, well Boygofast made an exchange and I now have a #415 60 tooth sprocket, I had to pay $11 for exchange.)--from eBay
-Jackshaft kit, with 14T and 10T sprockets.

http://motorbicycling.com/showthread.php?t=27165

Video is here.

I will have a 8.4:1 ratio when this project is complete.

Speed and other info:
-Clutch fully engages around 18mph
-Has so much torque it wips chain around like crazy at low speeds
-Currently top speed of 33mph.(Flat surface)

!!!THREAD CLOSED!!! Project has been cut up (literally) and is no longer in existence, but if you want to see the video go on ahead.

 

[Kristof]

Here are the first bit of photos:

 

[Kristof]

Second:

 

[scotto-]

Looks like a fun build.....nice pics, keep it coming!

 

[cannonball2]

You gonna fab some sort of reduction? That would be a mighty tall ratio as is!

 

[Kristof]

I thought 36T would get me more speed, I don't really care about low end torque. I ride my regular bike everywhere with a heavy backpack so this will be no problem. 1 to 3.6 ratio sounds fast, this 100cc should be able to handle it.

 

[cannonball2]

A good average ratio is in the 15:1 area. I have a Tecumseh 3.5 powerd bike I have been riding for years. Its ratio is in the upper 16s as I remember, crusies around 30 and climbs average hills like crazy. In reality what you have wont work as is, that would be a pretty tall ratio for a mini-bike. You can easily fab a jackshaft and run the larger 54 tooth final drive sprocket.

 

[Gator Wrestler]

IMO you will need about a 12 to 1 gear reduction. You may get it to work with a bit less maybe 10 to 1 but what you have now isn't going to work. The clutch will be destroyed shortly.

 

[cannonball2]

12 is a little high for hill country(at around 3+hp) would be killer in the flats though.

 

[Kristof]

I don't understand, why are people switching to 36T sprockets then?

I just found out that my clutch needs to have a bolt and nut in the crankshaft in order to keep it on. Should I drill a hole into the crank and put a bolt in it?

I am currently building an exhaust. Is it better to have straight pipe or a muffler on it? If so, can someone give me internal design of best muffler design.

 

[cannonball2]

If you can exchange the clutch, there are clutches that use set screws, otherwise drill and tap the crank. The exhaust is personal preference, some form of muffler is better these days, but I see a lot of straight pipes too. For the engine to pull the bike direct as you have it the sprocket would have to be huge, probably approaching the wheel size. You have to use a form of 2 stage reduction. The 36t sprocket is used with the china girl engines which are already internally reduced.

 

[Kristof]

So my build will not work with a 36T sprocket?

 

[cannonball2]

No not really. Would not want to pull away from stop. Would have a 75+mph@3600rpm though! You will have to reduce the ratio to 12:1 or higher range depending on what you want out of the bike.

 

[Gator Wrestler]

I have had good results with this jacksfaft: Torque Converter Backplate & Jackshaft, www.bmikarts.com : BMI Karts & Supplies : Go Karts Parts : Racing Go Kart Parts : GoKarts : Versailles, Ohio : USA : Indoor Track : Tips

This will bolt right up to most modern 4 stroke engines in the 2.5 to 10HP range. The supplied 20t sprocket when used with a 10t clutch gives a 2 to 1 reduction. From there if you use a 10t to drive the rear sprocket you will have a 12 to 1 reduction.

I use the 60 tooth rear sprocket from BGF on Ebay and #41 chain. The gearing options are many. The jacksfaft will accept up to about a 30t #41 or even higher tooth with #35

I believe the EZM will also be a good choice with that engine. You may want to check on that first. I have not used that gear box yet.

 

[Goldy]

IMO, the guys are giving you some very good advice as to the need to increase your overall reduction...it just won't work the way it is (goodbye clutch!). Anyhow, that aside, this looks like a Tecumseh engine, the exhaust note on these is amazingly quiet, so you could run with an open pipe if you want without bothering the neighbours.

 

[professor]

Run a muffler- the less of an irritant you will be when you ride- the less interest you will have from police. Wear a helmet. Look responsible.
I found the cigar shaped briggs 3 hp. muff is a bit restrictive on my HF79. Will use 2 on a "T" or a single bigger muff.

That engine on back is very heavy. Riding is not a problem, the difficulty is putting it somewhere where it won't fall over when you are not riding. Even holding the bike up by the handlebars, the weight can get away on you.
It would be a lot better on a 20 inch bike, but even better inside a frame.
This is why you don't see big engines on the back of bikes.

 

[scotto-]

I don't understand, why are people switching to 36T sprockets then?

I just found out that my clutch needs to have a bolt and nut in the crankshaft in order to keep it on. Should I drill a hole into the crank and put a bolt in it?

I am currently building an exhaust. Is it better to have straight pipe or a muffler on it? If so, can someone give me internal design of best muffler design.

Here's a couple pics of a pipe I made using 2 stock header pipes, some straight tubing and a small 2-stroke silencer. This pipe works well.

 

[scotto-]

That engine on back is very heavy. Riding is not a problem, the difficulty is putting it somewhere where it won't fall over when you are not riding. Even holding the bike up by the handlebars, the weight can get away on you.
It would be a lot better on a 20 inch bike, but even better inside a frame.
This is why you don't see big engines on the back of bikes.

You don't ?

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This looks like a pretty big engine to me.....

 

[cannonball2]

He would have to drill and tap or replace the side cover, to use the torque converter, as well as drill and tap the crank. Not a huge deal but some amount of work. The way the rack on the bike is, a jackshaft could easily be added underneath, foward of the engine. The 60t sprocket advised from BGF would work nicely. Its not a big deal to add the jackshaft to what is already fabbed.

 

[professor]

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.