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Piston Ramps for Chinese 2-stroke 80cc Bicycle Engine

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Piston Ramps for Chinese 2-stroke 80cc Bicycle Engine

Post by Fabian on Sat Jun 30 2012, 05:38



This piston modification will improve crankcase evacuation of air/fuel mixture through the transfer ports on a centre mount, Chinese 2-stroke bicycle engine.
As standard the piston only uncovers half of the transfer port when at bottom dead centre; restricting the time window for air/fuel transfer.
The modification has a 45 degree chamfer cut into the piston (above the top piston ring), lining up with the transfer ports so as to increase opening and closing duration; allowing a greater charge to enter the cylinder.

It's a very simple and sneaky way to easily increase transfer port timing without having to modify the cylinder.

This link will take you to a vendor who professionally remanufactures new OEM piston with transfer port ramps and exhaust port ramps for the 80cc Chinese 2-stroke bicycle engine:

http://motorizedbikeforum.the-talk.net/t340-twin-spark-plug-cylinder-head-for-80cc-happy-time-engine















Fabian
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Re: Piston Ramps for Chinese 2-stroke 80cc Bicycle Engine

Post by James Cagney on Mon Dec 15 2014, 18:51

I'm not one to claim knowing how the 2 stroke engine works but. The factory set ports are best not altered. The best way to get power out of these 66 cc engines is the correct size expansion chamber. This will keep the combustion chamber charged by increasing back pressure enough to allow the fuel that is pushed out of the combustion chamber into the exhaust /expansion chamber ignition as well block it from escape. This sounds to simple but the math is likely estimated on this basis. I'm working on an old bike that has offered much difficulty currently. I'd say the cast aluminum engine will likely tolerate the slight increase in fuel with the expansion chamber I've linked to the engine without much effort. Enlarging the ports on it is not an option for me with this I'd suggest it only for those who have a billet of forged aluminum to punch out and one piece steel crankshaft with a two piece connecting rod and forged piston at the very least with this light engine case. It's possible to to decrease the counter weights and port fuel to bypass the smaller crankshaft and assembly as well and create a wet sump in this case you can toss out the needle bearing a solid bearingless wrist pin will oil well enough and with this setup likely outlast the engine itself the piston will need long enough to block the ports top through bottom dead centers.Well if you've got all day and are good at math own a machine shop it might work if it did it would likely work to well.

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Re: Piston Ramps for Chinese 2-stroke 80cc Bicycle Engine

Post by Fabian on Mon Dec 15 2014, 19:08

A wet sump 2-stroke would be an impressive project. I would like to see you make it happen, then make the engine available to anyone who wants to purchase it.


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Re: Piston Ramps for Chinese 2-stroke 80cc Bicycle Engine

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