Honda GX-160 In An Extra-Long Bike

Discussion in '4-Stroke Engines' started by MikeJ, Jun 12, 2011.

  1. MikeJ

    MikeJ Member

    Hi Everyone -

    Just another post, mostly for entertainment value... Attached should be some photos. (It is amazing what other riders in this forum thread have done with other sizes of Honda engines!)

    I made a major improvement to my bike recently. Some you of you may recall that I had a 79cc Harbor Freight engine (2.5 claimed HP) on my very-much-modified bike. The engine proved marginal at best at this >5500 feet above sea level altitude with its thinner air. I am sure it would run great at below 3000 feet. But I just don't have that option.

    So I went to something overkill... A Honda GX-160. It is a 4-stroke, 163cc, horizontal shaft commercial grade engine. (I did a lot of measuring, reading and test fitting in a mock-up before ordering from Tulsa Engines. I did not want to make a very expensive mistake!)

    Honda used to claim 5.5 HP from this stock engine; randomly selected production engines test out at 4.8 HP according to a new international standard for small engine testing.

    So the engine arrived a couple of weeks ago. What is the second thing I do (after I examine it)? Take it apart, of course. Remove gas tank, remove muffler, and remove air cleaner. Then check it for fit. It fits in the bike!

    Then I order parts from Affordable Go Karts. They sell up-performance parts for select Honda engines. After parts arrive, I remove the flywheel, remove all governor parts, replace flywheel, and remove the crankcase oil level sensor and associated wires. I install a higher-lift cam and stronger valve springs, and test fit a low restriction air cleaner and a low-restriction exhaust system. (One can safely assume Honda will no longer honor their usual three-year warranty.)

    The engine gets mounted; hooked up the muffler, air intake, and provide fresh gasoline. 18 ounces of Castrol 10W-30 SJ oil goes into the crankcase. I pull and pull on the rope, but it just won't start. It backfires a few times. Now what? (Old-heads may know the answer....)

    So I take the engine all apart again, front, back, and top WITHOUT removing the engine from its mount points (nice discovery!). I found the problem... I installed the new cam gear off by one tooth to the crankshaft. DUH! How careless! Fixed it, double-checked every nut, bolt, and gap again, then reassembled. Replaced oil and gas and pulled the rope. It fired! And sounded good! This is a really responsive engine; it has a really short throttle plate arm.

    I let it fast idle for two hours just to listen for any strange noises and start the break-in process. This morning, I prep the bike frame (tires, look for loose nuts and bolts, adjust brakes, etc.). Put on riding gear (helmet, bright jacket, etc.) and take the bike out to local streets.

    This engine has a LOT of pulling power, even at this altitude. I am impressed! Of course, that should be expected, also. The first ride was for only 20 minutes. Lessons learned: More adjustments are needed. The air filter is in the way of peddling, it needs relocating closer to the centerline of the bike frame. Have to work that. The exhaust needs relocating closer to the frame because my leg rubs against it when peddling; maybe routing it forward is the answer. Even with muffler wrap; the pipe gets much too hot for safe riding. (A replacement run-forward pipe from Affordable Go Karts has been ordered.) Third, the throttle control needs to be toned down. Right now, just a little twist of the throttle means big acceleration (don't need that mistake when approaching an intersection). The fix to that one is easy.

    What will top speed be? Answer: Way too fast for me to even try. I intend to hold my speed to 30 mph. If I need to go faster, I will drive my quarter-ton pickup truck.

    The first photo shows my build after this morning's run. This engine has a really hot exhaust; see the color of the pipe.

    The second photo shows the engine, mounts, and clearance. The hard-to-see little stub of yellow wire near front of the engine is all that remains of the oil level sensor circuit. The red knob is the ignition kill switch. I should route the wire to a kill switch on the handlebars.

    The third and fourth photos are of the right-hand side of the bike.

    The fifth photo shows the protuding air cleaner and exhaust pipe. I have to get them closer to the centerline.

    I worked on this bike and electronic circuits and flat tire problems as time permitted. There is always some little feature that can be incorporated. I intend that after the intake and exhaust problems are fixed, more riding time will follow. Will post more later.....


    Attached Files:

    Last edited: Jun 12, 2011

  2. bigkahuna

    bigkahuna Member

    I love it! The way you added the second "half" bike frame to stretch your frame and the wooden motor mount are brilliant! Some day I hope to assemble the parts to build something like it. Some very inspirational ideas in this build. :)
  3. nwohater

    nwohater New Member

    Wow I've never seen a bolt on tandem thing like that, that is cool. Did you make that or is it a kit?

    I bet you doubled the hp on that engine... I guess if you ever do have a passenger and need to climb a hill and tow a truck, you're set.
    Last edited: Jun 13, 2011
  4. MikeJ

    MikeJ Member

    Hi Guys -

    There was a lot of thought going into this build. And a lot of mistakes in the building process; some were a bit expensive. But you have to expect that once in a while. The back frame portion is part of a Rockhopper Extreme mountain bike which I hacksawed up. I purchased it for $5 from a bike rebuilder. The downtube is what you see; its length was important. Its bottom bracket got augmented with more bottom bracket shell pieces from a third bike frame, which I think I got just for the asking. And there is more to it than that, but that is for another day....

    I did not like the limited options for motor mounts from vendors, so I thought I could make my own by laminating lengths of red oak with glue, bolting that block to the bike frame, and then filling the voids with JB Weld epoxy. I was concerned that the engine torque would break the wood apart. Then I found a site that stated the tension strength of red oak is 30 times that of what the engine would require. There are no stress cracks yet....

    I read just today that a good, reliable motorized bike can be costly. How true that is! Cost can be in dollars or maintenance hours. But if you are careful, cost for a fun and useful bike can be pretty inexpensive.

    I expect this engine to provide some serious hill climbing ability; I trust it will. And handling of the long frame? It takes a big radius to turn it around. But because my seat is in the physical center of the frame instead of right over the back wheel, big bumps are much less severe. Tires are run at 55 psi, not upper limit of 65 psi, so that helps as well.

    This bike will be my weekend vehicle. I hope to accomplish one or more 200-mile daytime runs. But I will refrain from bragging until that goal becomes history.