49cc piston

Hashbrown

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Jan 15, 2018
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I know that there are two different size pistons, is that only for 66/80cc or does the 49cc have two differant sizes? I just bought a reed valve and wanted a windowed piston (or modify one) but everywhere ive looked they don’t specify if it is a 40mm or 38mm.
The place where i bought my kit from says its a 38mm stroke
 

crassius

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Sep 30, 2012
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I haven't seen every possible configuration of these motors, but I doubt there is a 40mm stroke on any of the small motors. Knowing the size of your piston, you could measure distance from skirt to wristpin hole on a pic at site you are ordering from and see if it is same as measurement on your actual piston.
 
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Hashbrown

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Jan 15, 2018
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I haven't seen every possible configuration of these motors, but I doubt there is a 40mm stroke on any of the small motors. Knowing the size of your piston, you could measure distance from skirt to wristpin hole on a pic at site you are ordering from and see if it is same as measurement on your actual piston.
Now can i use the reed valve without a windowed piston, Or will it just run like crap?
 

crassius

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most folks seem to get best result with cutting windows - probably works that way for any reed setup, but a reed user would know more
 

Hashbrown

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So zeda made 2 youtube videos using bolt on reed valves. They put the motor on a dyno, they first tried it with just the reed valve and it cut the hp by more than half then they tried it again but added a windowed piston and it barely made 1hp.
So it looks like the bolt-ons aren’t worth the money.
 

MotorBicycleRacing

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I know that there are two different size pistons, is that only for 66/80cc or does the 49cc have two differant sizes? I just bought a reed valve and wanted a windowed piston (or modify one) but everywhere ive looked they don’t specify if it is a 40mm or 38mm.
The place where i bought my kit from says its a 38mm stroke
A 48 cc piston is 40 mm OD and inly comes in 38 mm stroke.
Some 48 cc pistons have a flat top and others have a dome which are the only differences I know of.
What kind of reed valve?
 

Hashbrown

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Sorry if i wasnt clear I meant that the 2hp motor lost 1hp in both tests.
It was with the RSE reed valve.
 

crassius

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Sep 30, 2012
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there was one report of reeds too stiff to fully open, but not sure if that was a flaw or true for all