Shaved the bottom of the cylinder where the scavenging ports are

[BikeBuilder43]

Ok. So in the quest for power I thought it would be beneficial to open up the scavenging ports by taking off about a 1/2" of metal from the bottom of the cylinder the width of the scavenge ports. It isnt pulling like it did before. What did I do?

 

[crassius]

perhaps left a rough spot or bent cylinder a bit out of round so that piston is now dragging just a bit?

 

[Steve Best]

Ok. So in the quest for power I thought it would be beneficial to open up the scavenging ports by taking off about a 1/2" of metal from the bottom of the cylinder the width of the scavenge ports. It isnt pulling like it did before. What did I do?

Can you show picture or even a drawing?
I am guessing you widened the cylinder (or engine case?) transfer ports?
1/2" of metal off anywhere on these engines sounds like a lot to me.

This could be negative if:
1) it reduces the crankcase compression (ccr)
2) the larger cross-sectional area reduces flow speed (fuel drops out of suspension and air loses momentum)
3) the match or mismatch of ports does not work with the flow and resonance of the engine. Sometimes a mismatch can be helpful.

Just a blind guess, I'd love to see a picture.

Steve

 

[Deleted member 12676]

?you shortened the cylinder skirt?

 

[Deleted member 12676]

Did you cut the sleeve off at the red dotted lines?

That exists to separate the downward motion of the piston from the upward motion of the intake charge in the transfers.

 

[BikeBuilder43]

Jag thats exactly what i did. Also took a drill bit and widened the transfers a bit

 

[Deleted member 12676]

did you accidentally change the transfers to allow them to angle more towards the exhaust?
see http://www.dragonfly75.com/motorbike/transfers.html

 

[BikeBuilder43]

I did raise the transfers a bit by drilling the middle of the top transfers a bit. I am about to take it apart to see if i drilled the sides. I will take pics.

 

[BikeBuilder43]

 

[BikeBuilder43]

Used teflon as a head gasket. May shave the head a bit more now that i have a sheet of glass and use the stock gasket.