motorhedfred
New Member
- Joined
- Mar 8, 2012
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Greetings everyone.
My name is Fred. I'm 56 and have aspirations of building my own small engine. I've been fascinated by internal combustion engines and the machines they power for as long as I can remember.
The main reason I joined several months ago was to pick up a few ideas for a project I've been fiddling with. I found this forum on a Bing search (my preference to Google) for small v-twin, 4-stroke gasoline engines. In the spirit of full disclosure, this engine is for a motorized bicycle and would need to have an output of at least 2.5 horsepower. Since I've yet to find a commercially available engine that would meet the requirements, I turned to this forum.
To be legal in my state, the discplacement would have to be around 3 cubic inches or between 49 and 50cc. I may ignore that and claim I don't know the engine size if stopped while riding the contraption.
Because I have no lathe or mill, any machine work will have to be hired out. With that in mind, I've been collecting parts from Craigslist and eBay. So far, I've puchased a small SpeedAire 90 degree v-twin compressor and a couple of Honda GXV120 cylinder heads. The bore and stroke dimensions are 1.75" by 2". The long stroke should yield good low RPM torque, which is fine since I don't want to rev it very high.
The heads are a pretty good match for the cylinders with two of the head bolts matching the center to center distance of the original heads. The other two will have to be worked out. The spark plug hole ends up right at the edge of the cylinder and the pushrods would drop down between the "V", intake ports to the inside, exhausts to the outside.
The next big challange would be the camshaft. I had thought of making a camshaft box with an external octagon shape and bolting it to the block using steel or aluminum angle from the cylinder bolt location. I found a couple of gilmer belt pulleys where I work (Summit Racing Equipment) that would have the correct 2 to 1 ratio to drive the camshaft, one of which is the correct bore size for the compressor pulley shaft. A camshaft for a Briggs, Kohler...ect. 90 degree v-twin should have the proper lobe orientaion for valve actuation.
I know there are many other issues such as oiling, ignition and even the strength of a machine that was designed to compress air, not burn fuel and contain combustion pressures, so please tell me if I'm crazy or wasting my time.
Perhaps the pump is best used for parts such as crank, rods and cylinders.
Long winded introduction.....sorry.
MHF
My name is Fred. I'm 56 and have aspirations of building my own small engine. I've been fascinated by internal combustion engines and the machines they power for as long as I can remember.
The main reason I joined several months ago was to pick up a few ideas for a project I've been fiddling with. I found this forum on a Bing search (my preference to Google) for small v-twin, 4-stroke gasoline engines. In the spirit of full disclosure, this engine is for a motorized bicycle and would need to have an output of at least 2.5 horsepower. Since I've yet to find a commercially available engine that would meet the requirements, I turned to this forum.
To be legal in my state, the discplacement would have to be around 3 cubic inches or between 49 and 50cc. I may ignore that and claim I don't know the engine size if stopped while riding the contraption.
Because I have no lathe or mill, any machine work will have to be hired out. With that in mind, I've been collecting parts from Craigslist and eBay. So far, I've puchased a small SpeedAire 90 degree v-twin compressor and a couple of Honda GXV120 cylinder heads. The bore and stroke dimensions are 1.75" by 2". The long stroke should yield good low RPM torque, which is fine since I don't want to rev it very high.
The heads are a pretty good match for the cylinders with two of the head bolts matching the center to center distance of the original heads. The other two will have to be worked out. The spark plug hole ends up right at the edge of the cylinder and the pushrods would drop down between the "V", intake ports to the inside, exhausts to the outside.
The next big challange would be the camshaft. I had thought of making a camshaft box with an external octagon shape and bolting it to the block using steel or aluminum angle from the cylinder bolt location. I found a couple of gilmer belt pulleys where I work (Summit Racing Equipment) that would have the correct 2 to 1 ratio to drive the camshaft, one of which is the correct bore size for the compressor pulley shaft. A camshaft for a Briggs, Kohler...ect. 90 degree v-twin should have the proper lobe orientaion for valve actuation.
I know there are many other issues such as oiling, ignition and even the strength of a machine that was designed to compress air, not burn fuel and contain combustion pressures, so please tell me if I'm crazy or wasting my time.
Perhaps the pump is best used for parts such as crank, rods and cylinders.
Long winded introduction.....sorry.
MHF
