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Please accept my humble apology...



It was not my intent to create a controversy or offend anyone with my casual post; however in my haste it would appear that I have done just that. Please allow me to explain. I will start by addressing your response and end by explaining in more detail my original statements.

Yes, with the standard 10 tooth front sprocket and a 36 tooth rear sprocket in a single drive ratio configuration, it is not only doubtful that this engine would power any bicycle to over 50 mph, it is not possible. Using a 12 tooth front sprocket and a 32 tooth rear sprocket 50 mph is not only possible, it reduces top end rpm's considerably for nominal power output (average speeds of between 30 and 35 mph). No, I was not abusing this engine, and have actually expended considerable time and effort to improve this power plant to determine if factory modifications would be feasible within the manufacture's cost constraints. Driving the engine at high (not excessive) rpm's for extended periods of time (1 to 2 hours) is part of my test plan to expose possible component failure, e.g. improve durability.

Allow me to introduce myself. Without going into exhaustive details about my education, background or other self indulgent displays of bragging rights, suffice to say that I'm a fairly qualified mechanical engineer. I have earned several graduate degrees in advanced science, have a considerable background in many fields of engineering, and have been modifying internal combustion engines (2 and 4 stroke; considerably bigger and far more complex than this particular power plant) for the better part of 4 decades. Now that, that is out of the way please allow me to explain my previous statements.

I have been searching for a cheap, lightweight, efficient power plant for a specific task. Not finding off the shelf components up to spec., I have been looking for something that can be practically modified (by this I mean inexpensively and simply improved) to meet the following requirement:

Power a practical vehicle with a single adult passenger, 3000 miles, in 30 days or less while consuming, 50 gallons of pump gasoline or less. This vehicle can not experience any major failures during this journey and all of the fuel and passenger supplies must be loaded on the vehicle from the start. Sounds simple doesn't it? It's not. Many have tried, but no one has yet succeeded. Not even close.

The two (2) stroke power plant in question started out as a promising candidate, however after extensive testing, I discovered the following issues that although correctible individually, represented a sum total of problems that clearly indicated low quality manufacturing and an unacceptable cost of improvement for "my specific" application:

1.)Engine surface machining is extremely poor and engine gasket material of very low quality, resulting in numerous compression leaks. Corrective action required re-machining of cylinder and cylinder head surfaces, and engine case center seal surface, and improved gasket material.
2.)Magneto is of low quality with the windings not properly sealed allowing moisture to corrode and decay windings and welds. This unit is also highly prone to heat damage from extended operating times, (greater than 1 hour at nominal power output). Further, the only alignment provided with this design is a function of the four (4) mounting screws, which can and eventually will allow for contact between the center magnet and the armature as the engine wears (from inherent vibration). A satisfactory correction was not found for this issue.
3.)The sealed and specific ignition module is prone to damage from vibration. Corrective action: shock mounting and modification of spark lead connection to prevent separation with silicone water sealing.
4.)Carburetor is of fair quality, however the choke mechanism can wear and loosen over time, allowing the choke to engage and significantly alter the fuel mixture while operating at nominal power output. Corrective action required a redesign of the choke mechanism.
5.)The entire engine is balanced so poorly as to introduce considerable vibration and loss of overall performance. Correction required extensive internal component modification.
6.)Piston wrist pin clearance is too high allowing for piston slap that will eventually cause engine seizure under load or at high rpm's. See item (5) for corrective action.
7.)Intake and exhaust ports are not properly located in the cylinder allowing for high temperature and/or high rpm pre-ignition. Not correctable without casting a new cylinder and machining for replacement intake and exhaust mounts.
8.)Fly wheel, needle bearing and connecting rod assembly are all prone to oil starvation after extended operating times. Not corrected. Engine candidate abandoned.

Granted, this application is far beyond what normal users will be expecting from this power plant; however, the items described above represent "poor quality control" undeniably and further, represent issues that will affect even the standard user application over time.

In short, all I was trying to say was simply this:
There are better power plants available for a motorized bicycle application, period.

It is possible that the units I received and tested are somehow inferior to the units the vast majority of enthusiasts are obtaining. I doubt this, but even if these units are "defective", the overall design of this engine, from a specific "design perspective" does not lend itself to long term, durable and reliable use in a low maintenance rough duty application of any kind.

Your mileage may vary, and probably will. Again, my intent is not now and was not previously to offend anyone or encourage even the slightest controversy. With this I will close and withdraw from any future forbearance of opinion or thought to this forum.

Thank you for your time, interest and indulgence,

Sincerely, Dr. David A. Gray,
BS IEEE, MBA, Ph.D. Electrical Engineering, Astronomical Physics, Quantum Mechanical Physics
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since this seems as close as we're gonna get to an intro from you, i moved it.

welcome...read your private message about forum ops, please.


DON'T DO THAT...don't "withdraw from any future forbearance of opinion or thought to this forum"......i/we want your opinion and u have just as much right as anyone else here to voice that opinion.People may not necessarily agree with what u have to say or the way u said it so they also have that right of rebuttal.It's human nature to disagree and nobody likes a "yes" man.....Yes!

BTW,Welcome man to MBc.
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Large Filipino

You get what you pay for. A good quality 2 stroke you would design would probably run in upwards of 600 dollars. Might as well get a moped or something.
But I think the whole point of a Happy Time is just that. Happy Time. HAPPY!!
"UNDER 200 DOLLARS FOR THE ENTIRE KIT??? NO WAY!!!" people would say.
And people have taken the Happy Time many many miles. But they are designed for going under 20 mph for it's a bicycle for crying out loud.
Nevertheless,I like your input for were always modifying stuff in our minds always.
Keep us in mind,at least. Maybe build yourself a motoredbike for pure recreation. Not for testing and please share!
(I bet it may not be too difficult to design a better magneto with the right tooling for example)
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I'm probably getting in way over my head but here goes anyway. I believe I could build an Indy car using a stock 4 cylinder street car engine. It would run but I'm not gonna win any races. The Happy Time is probably not suitable for your specifications but there are other power systems available that cost more but are far more robust. The Japanese engines are some of the highest quality around and for the application you describe, I would think a four stoke might fill the bill better than a two stroke. The power / torque curve will be much lower allowing your machine to achieve the needed cruse speed at a lower RPM. This should give you longer engine life, less vibration and less stress on drive components. Something in a rack mount with a chain drive and a robust gear box might meet your criteria.


Welcome David. I think you can contribute a lot to this forum.


Active Member
Feb 14, 2008
Welcome David, it seems to me this is a group of average guys/gals with tons of talent in a thousand different areas. In life, some drive a Mercedes some a Lexus. Some a Chevy some a Ford. We are all about having some inexpensive fun and hanging out with a bunch of guys/gals with a common interest. If I can get 2 years out of my H.T. engines and they go to the scrap heap, big deal. For only $150.00 I can be back on the road in a day for a few more years of fun.
If I was going on a journey, id fork out some "ching" and spend a couple $grand. Were all about getting educated. So contribute to the group so we can learn. And in return you'll pick up some info from our talents in a thousand different areas. Welcome new friend, graucho
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Welcome David. Sounds like you have a lot offer. IMHO most of this fourm is dedicated to the fact that these Happy Times are pretty poorly constructed and we spend all our time figuring how to improve them or at least get as many miles out of them as we can. There's a lot of us who have never held a screw driver, some are shade tree mechanics, real mechanics, inventors and engineers. 1,500 members have points of view about one little motor. LOL
30 mph is plenty fast for my bike. But your idea of a 3000 mile 30 day troble free trip on 50 gallons sounds awesome.


Hope you stay around, but seems like all hat no cattle. But welcome to MBc from the Giant Side of Texas!