1st project. Which engine?

jared8783 · #1 (**permalink**) 05-21-2009, 04:48 PM

Hello my name is Jared.

I am getting ready to build my first 4 stroke motorized bicycle. I originally wanted a 2 stroke for looks but I can't find one that is not form china so I'll need 4 stroke. I have never done this an am unsure which engine to buy. I just ordered a Trek Calypso cruiser style bike.

I want to keep it under $600 for the engine. I prefer frame mount but will settle for rack mount. I would like to be able to buy/order parts from my local moped/lawnmower/small engine shop. I also would like it to go 25-35 mph. It MUST be chain driven.

Also I heard that my stock spokes would mabye last a summer and would need to upgrade rear wheel to heavy duty spokes. Is this true? What are the major differences I will notice between a 35 and 50 cc motor? Will a 35cc still reach 30-35 mph? If I buy just a mount kit with gear box can I go to my local small engine shop and buy any 4-stroke?

If anyone could share their advice and experiences with me that would be appreciated.

HoughMade · #2 (**permalink**) 05-29-2009, 12:37 PM

Frame mount or rack mount for Honda GXH50:

4-Stroke Engine Kits

Engine source- the used to list a $210 engine without tank, but maybe they are out.

http://www.smallenginewarehouse.com/product.asp?PN=GXH50QXA&desc=Honda%20Engine%20%202 .5hp%20Horizontal%205/8"x1-5/8"%20Keyed%20Shaft,%20Overhead%20valve%20LOS%20700 0%20RPM

Another good source for chain drivin kits, but rack mount:

Staton-Inc motorized bicycles, bike kits & gear drive kits.

The Honda GXH50 will get you your 35mph. Don't know about the smaller engines, but I highly doubt under 35ccs would be close.

ocscully · #3 (**permalink**) 05-29-2009, 01:06 PM

Jared,

The most common frame mounted 4-stroke is the chinese copy of the Honda GXH50. The Honda and its chinese clone are the motors that the available gearboxs fit. The smaller cc weedwacker type motors use a smaller mounting pattern on the output side of the motor and the reduction gearboxes that fit them are not interchangable to the larger motor with its larger mounting pattern without the use of an adapter. The Honda GXH50 and its clones are pretty unique 4-stroke motors. The biggest difference is its max rpm 7800rpm vs 3600 rpm for most industrial small 4-stroke motors. The idle speed of the Honda/clone is higher as well 2000rpm. Another area where the 4-stroke motors run into problems in frame mounting is the overall width of the motor and its primary reduction gearbox/drivetrain. The grubee kit and its gearbox comes in at 9 ins. +- The EZ set-up is close to the same. This width is only a problem if you intend to or have to maintain the ability to pedal the bicycle. To the best of my knowledge no one offers a frame mounted kit for any of the smaller cc 4-stroke motors so if you opt to use one of these you will need to fabriacte your own motor mount and perhaps other parts to make one of these smaller motors work as a frame mount. The fact that you want to be able to get parts locally would seem to me that you would want to go with the Name Brand Motors Honda or Robin/Subaru rather than the clone motors. The differences you will see between the 50cc motor ad the smaller 35cc - 25cc motor is going to be max speed and how much you need to pedal assist. The 50cc motor has quite a bit more torque and cand operate from a dead stop to low to mid 30's mph without pedal assist.

As for the rear wheel /spoke problem? The best solution is to get the driven sprocket off the spokes and onto the rear hub. Look into the Sprocket adapter offered by Manic Mechanic (see sponsors add to the right) SPROCKET ADAPTER

ocscully