skirt trimming w/ windowed piston

jwr3k

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So. I have a 66cc 2-stroke with dio reed valve and windowed piston.

I ported my cylinder, mainly dropping the floor on the intake and a little widening. Anyways, I had the reed valve removed from my cylinder and was looking through the intake as the windowed piston moved up and down.

I noticed that the bottom of the piston skirt doesn't fully clear the intake, so I thought 'what is the point of wideniing my intake if it doesn't fully open?'

I would normally trim the piston skirt a little but I don't have a whole lot of material beneath the windows to work with. If I was to trim it, it would leave very little material and I would be afraid of it weakening and perhaps even breaking off.

So what should I do? Make my own windowed piston and compensate for this? And in doing so, would the bottom of the window have to be higher than optimal in order to leave sufficient material for durability?
 

Street Ryderz

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So. I have a 66cc 2-stroke with dio reed valve and windowed piston.

I ported my cylinder, mainly dropping the floor on the intake and a little widening. Anyways, I had the reed valve removed from my cylinder and was looking through the intake as the windowed piston moved up and down.

I noticed that the bottom of the piston skirt doesn't fully clear the intake, so I thought 'what is the point of wideniing my intake if it doesn't fully open?'

I would normally trim the piston skirt a little but I don't have a whole lot of material beneath the windows to work with. If I was to trim it, it would leave very little material and I would be afraid of it weakening and perhaps even breaking off.

So what should I do? Make my own windowed piston and compensate for this? And in doing so, would the bottom of the window have to be higher than optimal in order to leave sufficient material for durability?
By the time the piston skirts bottom edge is left in the port the intake charge is complete, it's not an issue. In a piston port (non reed) setup this would be more of an issue as the bottom skirt edge is what controls the timing/duration where the reed setup see's most of it's flow through the window and is not effected much by this obstruction, and you are right if you make that area too thin it will most likely break from stress.
 

jwr3k

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Local time
11:52 AM
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Jul 24, 2019
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Ok tht makes alot of sense. the more I've been thinking about it, the intake charge is taken through the window in piston, and the window is plenty big to fully open the port.

Thanks guys!
 
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