Minimalist FD

cannonball2

cannonball2

Well-Known Member
In keeping with my addiction to put a motor on anything with 2 wheels is a plan to motorize my pedal only bike with a small FD. I wanted a 4stroke. There are many out there but most are designed to run a centrifugal clutch and mount to a heavy bracket. Not a bad thing but my target is to add a unit weighing 10lbs or less as it will be on the front. Also have in mind to make it quickly removable for use in restricted areas/bike paths. Idea is to pedal the bike most of the time and use the FD when I'm pedaled out.

The victim in this build is a composite bike built from parts left over from other builds or scrounged off the side of the road. The basis of the drive centers around an Echo curved shaft head. It uses ball bearings instead of bushings like a lot of trimmers. The engine is a Briggs Fource 34cc Flattie oil in sump engine. This engine got a lot of use in R/C aircraft conversions, where it had a good reputation/reliability. Not a real power house but has enough for what I'm wanting.
Initial drive roller is a Lawnboy 7/8 LH roller. 7/8 is small for a roller, but I'm not after speed. Should run easily 10/15mph. Engine should be here Thursday.

Pics are of all I have so far.
 

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KOOOOOOOOOOOOOOL ! Got to watch this, just love home brew. Where do you get the motor from? ...................Curt
 
Sounds interesting. When I first started fooling with gas motors on bikes it was with the old Tanaka friction drive motors popular in the 1970's. These were marketed under several names including "Free Spirit" through Sears and "Bikebug". If I remember right they produced a whopping 26cc and were 2 stroke. They were well made and easy to use, but let them sit for awhile and fuel parts developed problems. I look forward to following your thread. Simple is good.
SB
 
Thanks yall!

SB its really good to hear from you! Hope things are going well!

Curt found the motor on ebay.

So heres the basic drive. The motor will clamp directly to the pipe as close as possible. Should touch the trimmer head. Hope there is room in the angle to support the motor. If not it will cantilever on the pipe just as on a trimmer. The slotted piece is the lift arm. It will have an adjustable eyebolt with the spring on bottom the cable on top. The cable pulls the spring directly lifting the motor in the process. Will have a CG clutch lever with thumb lock to allow clutching(motor is direct drive) and pedaling when motor is off. Pipe and angle will be cut to length once I have the engine. Mounting bracket will be welded to the fork once all is settled. That's a socket filling in for the Lawnboy roller.

Motor is totally self contained and weighs according to Briggs 8lbs. I believe I just might make my 10lb target.

Will add throttle cable pulled from handle bar by a ratcheted thumb lever. That's it(I hope). Unit will quickly remove by removing the nut on the pivot shaft, cables and spring. The whole system is easily transferred to another similar bike in a few minutes by swapping the fork. So far its taken longer to think this out than make it.

Interestingly the engine has a 360 degree oiling system. The R/C fellas found out the engine could be mounted and run inverted, with the cylinder to the side, and of course upright.
 

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Got the clutch basically finished. Spring will hook in a hole drilled into the bottom of the eyebolt and go to a tab that will mount on the axle. Will link the spring with light chain. That will make it easily adjustable just by moving up or down the chain. Fitting on the stem is split making the cable quick to remove. Figure unit removal in 3-5min.

Throttle and drive roller(in shipment) next.
 

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Almost Curt.

Engine is on the UPS truck and the roller is in the mail truck. What wont be here until tomorrow is a 3/8 helicoil kit to adapt the roller to the trimmer head(and fix the outboard on my Boston Whaler).

Heres a link to the engine though I didnt buy here.

http://www.brandnewengines.com/21032-0111.aspx

If all this works out this is an MB build well under $200 as was discussed in the general topic area.
 
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WOW! THANKS!
Nice little motor, should make a nice compact unit. Like the idea as not so temperamental as 2 strokes.
Although i have a "Bike Machine Motor" seemed quite reliable, sorta like a cag engine on it.............Curt
 
Man i love minimalist friction drive. I just pulled mine apart to donate my frame to a buddy. Chainsaw motor, bike peg, and heavy duty gate hinge. That was it. Took more time to figure out than a full scratch built 4 stroke setup. Looking really good tho bro.
 
Thanks Yall!

Well its up and running, just not as I expected. The Briggs was apparently in a bowling tournament somewhere along the way in shipping. The damage was enough for me to refuse it. Sad thing is I negotiated a really good price as it was the last one the seller had. The available replacements cost much more. Will have to look around.

So being all dressed up and no place to go so to speak. I got the old Echo power head from the donor trimmer. Hadn't been run in years but was put up properly. Cranked in a few pulls and settled down to running good as always. Some how I thought it was a 24cc. Nope its the little 21cc. Didn't expect much. Was quite surprised how well it pulled. You have to pedal it to 5+mph then add throttle and its off and running. I'm guessing 12-15mph. That's pulling the throttle cable end by the right hand and steering with the left, not an ideal test!

It really is pretty cool. Not nearly as ungainly/unbalanced as it looks. Once riding you really notice nothing unusual in handling. Its with in the confines of the handle bars so if they fit the engine will too. The little 21cc was always noted for being silky smooth. its a very pleasant little engine. The Lawnboy roller is perfect in design and the size(7/8) works well with the little engine. These rollers drove the mowers in damp/wet conditions, maybe it will work as well with the Hookworms.

So living in the flats this thing is going to work great. Doubt it will climb much of a hill, but bet the Briggs might.

Have to keep looking for another Briggsey, in the mean time I high rollin on 21ccs! Too funny!!
 

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Makes for a sad moment when that happens, think the rest of use feel the same. Looks good though, the Briggsey would have more pulling power.............Curt
 
Whilst accepting this was made to be ultra simple, I wonder if your belt experience will eventually result in a similar motor with a large diameter roller underneath it and reduction drive set, similar to te old French bima a galet system.
 
Strangely LII

I have a 49cc HS engine with a 3:1 reduction that I almost inframed driving a big roller probably jackshafted behind the seat post in some manner. This build was more about having a good hybrid(pedal/power) bike.

Its still very light. More bicycle than MB. Got the throttle cable made and hooked up. Will ride a bit today to see how it all works out. Cool thing is almost any of the consumer trimmer motors should hitch right up. Saw a stack of 26cc trimmers in the Depot yesterday for $79. In theory I should be able to take any small trimmer out of the box, remove it from the shaft, mount it on the bike, hook up its throttle cable and go. This build is well under $100(save for the new tires). If one can use a lower power MB this is pretty easy to do.
 
Is there something compact that turns the drive through 90 degrees? I'm thinking of something like the connection between the motor and the disc on an angle grinder.

On sale in Australia:

WA-PT5500-PT5900.jpg
 
The RYOBI 30cc 4 CYCLE has an external belt/pulleys for the OHC.
If the friction roller could be mounted on the pulley, it could be 4 times larger.

Many Walmart 20" trick bikes have 2.3" wide street tires
that would give a lot of contact area for small rollers.

The last one I bought at Goodwill was $5, painted in girl colors.
 

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Wow those are really interesting motors, Particularly the Ryobi. Last one I had was OHV. This one must be the current MTD 4stroke? Cant believe they would go to that trouble. Must be having to compete with Honda.

Went on a 8mi test ride. Pedaled out 4, powered back. Worked very well with no issues. Hardly noticed it was there pedaling. The little Echo is surprisingly powerful for its size(relatively speaking). I'm betting its easily making close to 20mph. The smaller roller suits its power band very well and lets it rev out completely. A BMX peg would kill an engine this size.

20mph may not sound impressive, but you can actually get somewhere if you aren't in a rush. Heck when I was in Germany as a student in the late 60s people were riding Velosolexes all over the country at 20mph, pretty loaded down too. Its engine was rated at .8hp.
This little engine is the last of the Japanese Kioritz engines, they were extremely high quality. Don't know who makes Echo now. The color changed to orange(which it was long years back) with the new ownership.

With the many newer designed engines out there a trimmer powered FD might be worth a second look. Heck if you were trying to stay legal with the 49cc law you could run two of these engines with 7ccs to spare!
 
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So after putting a good many miles on the bike the little Echo began 4stroking. Cleaned the air filter, checked the exhaust screen. All was well. Finally figured when under load it ran fine. As soon a the engine unloads it four strokes. You can actually eliminate the 4stroking by riding the brakes. I'm guessing the carb was a bit restricted in the main jet from sitting and cleaned out richening up the mixture.

So this means its more of a load trimming grass with a string head than moving a 170lb person down the road on a bike. It never four stroked as a trimmer.

This means also that the roller is TOO small. I remembered Lawnboy had a high speed commercial version, the difference in the drive is the rollers size. After researching I found one its 1 1/8 and on the way! Imagine the 21cc had too much power. I bet this will straighten it out.

Incidentally the Lawnboy style roller woks the best of any steel roller I have tried, which were the knurled style. You cant break it loose even when super loaded. At least with this engine. A Cag would be another story probably.

All this fine tuning will perfect the system for a Briggs when I can find one.
 
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Tom Bartlett produced Zipcycle from 1993-2003.
Using a belt reduction Friction drive powered by a Homelite 25cc String Trimmer.

"Most bikes would run from 23-25 mph. We experimented with different gearing and found that although we could run a higher gear and obtain slightly higher speeds, the bike had no reserve and the speed fell quickly on hills. So we compromised for a slightly slower speed and moderate hill climbing ability. Basically, the bike was rev-limited at the top end."

Factory Rev-limited by too small of a carburetor to protect the motor is my speculation.

"We used polyurethane rollers that were just slightly harder than the tire compound (this was so that the majority of wear would be on the tire). The result was a roller that gave an excellent grip, but was long wearing. We found we could ride in the rain or morning dew without slipping.
The driver roller was suspended at both ends by sealed ball bearings."
 

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