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Old 02-22-2010, 07:21 PM
wildemere wildemere is offline
Motorized Bicycle Elite Member
Join Date: Feb 2008
Location: Newcastle
Posts: 269
Default Re: How to rebuild and balance these engines

Tadd, as I say, its all in those old texts as they are from the era of racing 2 strokes. When reading these texts just remember a few things about the happytime, they are piston ported, 66cc or 48cc, 6,000 or 7,000 max rpm.

They are not 12,000rpm+ race motors. There are no dowell pins, bearing retainers, shims, or anything that promotes power or reliability in these engines as delivered. Including any standards between numerous factories that bang these kits together. Power and reliability is as random as the build quality and gear noise/vibration.

An engine tuner needs numbers to work from, a base standard or blueprint.

And a dyno...

It is not a Yamaha YZ or Honda CR where all these numbers are available in a workshop manual. That is why there is no "guide " to blueprinting these old fashioned, low tech engines.

Regarding balancing, run the engine first, some HT's are smooth out of the box, others vibrate. If yours is not smooth then look into balancing. A 2 stroke single is never balanced, there is always a rocking motion.

The other problem we have is a lack of a real blueprint. Things like port heights, durations, ignition settings, compression ratio and even torque settings are all up in the air. Evey barrell I have inspected is different slightly, eapecialy in the transfers

Some forum members here are achieving great things though, through good research and trial and error. Other members make here great bolt on parts too.

You can't make a guide for random chinese engineering, just do the best with what you got, run a spare bike or engine when pushing the envelope and have fun.
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