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OLScrew

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Hello everyone!

I have been dreaming of a one-off bike build for a few years now and its recently been gnawing at me a bit harder. I had at one time, years ago, a JAWA "Top Tank" modified scooter. Immediately after purchase it melted down due to main seal leakage and so I ended up rebuilding it completely into a mildly modified version and enjoying the machine very much. It had a form factor/size and a riding style that was very fun and enjoyable to me.
What I am considering building is very different animal indeed, but whats important about the JAWA is the general layout and style of the machine. I essentially want to build a super scooter: Horizontal large 2-stroke engine, custom frame and fairings, modern motorcycle tires and suspension. Small, lightweight machine, big power, and classic styling.

The situation I find myself in is:
-I am not an engine builder.
-I am not well financed.
-I have access to, but do not own any machine tools.

-I have 3D design (solidworks) experience.
-I have solid fab skills in both metal and composites.
-I am resourceful.
-I have raced and rebuilt many 2 stroke machines.
-I have a great home level shop. (Primarily woodworking equipment)

Reason for posting:
I am seeking guidance in making the tough decisions about how to bring this horizontal engine into reality. To me this is the most complex part of the project. The number of questions I have feels staggering. I do not have any firm size or power demands at this time.

My initial thoughts are air-cooled for simplicity and similar look to the original impetus. Though I believe there would be advantages to using as many "off the shelf" parts as possible and liquid cooled 2 strokes are far more common in the larger sizes.
There are lots of classic air cooled 2strokes, but I am unsure if relying on 50 year old used parts or parts supply chains is a good idea.

Engine Goals:
Reliable
Electric start
6 speed gearbox (5 if its significantly easier)
Oil injection
Inexpensively maintained (relatively)
Smooth power

One path forward I am considering is purchasing a common production engine like a Honda CR250 or Yamaha YZ250, perhaps Kawasaki KDX 200, and then looking to have custom cases made up to make the engine horizontal. This seems to have several advantages: case volume and engine geometry is well known and understood. Donor engines and parts are and will be readily available for a long time to come.

The same could likely be done with an air cooled engine. Yamaha WR500 is a big one. Many 350s I could look into. The IT200 commonly found in the Yamaha Blaster might be a contender.


At this stage, I would really like to hear comments and suggestions from people with experience in this type of engine modification/development. I am sure some of you have been down this road before and might offer some insight into where to begin.
I look forward to hearing your thoughts!
 

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Last edited:
I suggest looking for anything available, with parts, from current dealers.
Then adjust your expectations based on price and stuff.

Oil distro, hydraulics, may make some production engines a bad idea-horizontal.
Maybe go see a long-term big reseller (honda, yamaha) in your area, often their boss is a long-term enthusiast and helps free.

I think budget-limited, reliable, 6 speed, special, tend not to coalesce.
 

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