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Old 05-21-2014, 04:19 PM
Theon Theon is offline
Motorized Bicycle Elite Member
Join Date: Jan 2014
Location: FNQ Australia
Posts: 1,440
Default Re: Making a custom bike engine

The standard China girl cranks run a 15mm main journal and 16mm big end pin.
I guess it all depends on what bearings you plan to use, what stroke you use, and how you plan to connect the 3 case's and crank sections.
Are you planning on splitting the cases verticaly or horizontaly?
Do you plan a single crank or three cranks that join?
I would be thinking splitting the cases verticaly and making the cases as 2 halves that have all three barrels each rather like a Volkswagen Case, (I use to work on VW's). These would then need to be align bored as VW cases do. I would then run loose needle rollers for main bearings, However this would require hardened split shells.
But allow you to run a larger Dia main Journal.
Also the standard rods need to be pressed between flywheel discs, I'm not sure how you plan this on a multi cylinder engine, and would require some tricky alignment.
However split big end rods such as out of a chainsaw are going to cost!
A very challenging project! Currious to see what you come up with.
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