To piston skirt or not to skirt

[Mark 1971]

Today I looked into my intake and saw that the piston skirt hung about 1/8" to 1/16" of the piston skirt impending my intake when piston is TDCThe ports look really good for a cast AL head( one piece jug and head). Is it worth it to skirt the piston? And if so, do I go ahead a bevel both the cylinder ports ? Polish the exaust side too..? Im a new builder. Just built 1st bike 2 weeks ago.I am looking for torque. Top speed is not my main goal. I do 36mph all stock so far

 

[Chainlube]

Today I looked into my intake and saw that the piston skirt hung about 1/8" to 1/16" of the piston skirt impending my intake when piston is TDCThe ports look really good for a cast AL head( one piece jug and head). Is it worth it to skirt the piston? And if so, do I go ahead a bevel both the cylinder ports ? Polish the exaust side too..? Im a new builder. Just built 1st bike 2 weeks ago.I am looking for torque. Top speed is not my main goal. I do 36mph all stock so far

Did you have the jug off before? You should always bevel the edges of the ports before you put it back together. Put the piston at TDC and trace the port on the bottom of the skirt with a sharpie. Then take it apart and carefully and cleanly file off the sharpie mark.

 

[Mark 1971]

Did you have the jug off before? You should always bevel the edges of the ports before you put it back together. Put the piston at TDC and trace the port on the bottom of the skirt with a sharpie. Then take it apart and carefully and cleanly file off the sharpie mark.

Got an example of a properly beveled port? Brand new motor just broke in. Running 32 to1 fuel. Ngk plug. Cut big hole in the stock air cleaner cover. 40t hub mounded sprocket. Runs good just want more torque!

 

[DAMIEN1307]

40t hub mounded sprocket. Runs good just want more torque!

Then you would probably want a 48 tooth rear sprocket then for more torque...I think i mentioned that once before sometime back...larger sprocket equals more torque, but less top end speed...DAMIEN

 

[Mark 1971]

True, but trying to stay at 35+mph with a cruise of 30mpg at lower rpm

 

[DAMIEN1307]

True, but trying to stay at 35+mph with a cruise of 30mpg at lower rpm

You do, of course need to be realistic of your expectations from a stock "China Girl" here...What you want to do, of course can be done, but how much time, effort, and money are you willing to sink into this for slight gains ???...lol...its all relative to this...DAMIEN

 

[Mark 1971]

Time and effort is on my side atm..cash is not unfortunately

 

[Chainlube]

Got an example of a properly beveled port? Brand new motor just broke in. Running 32 to1 fuel. Ngk plug. Cut big hole in the stock air cleaner cover. 40t hub mounded sprocket. Runs good just want more torque!

Unfortunately I do not have a sample, but it doesn't take much. A little sandpaper to just take the sharp edge off. Did you look into the ports when you had it apart? Some times the casting will run into the port and this has to be taken off as well. If the edge of the port feels sharp, then just sand it until the edge goes away.

 

[Chop-chop]

If you're after more usable torque, install a thicker base gasket between the cylinder and the crank case, this will alter the port timing for more torque, however this will also increase the cylinder volume hence reducing compression, that is why you must counter act by using a thinner head gasket or by shaving the mating surface of the head to reduce combustion chamber area in order to achieve a respectable squish band also restore compression. Hope that helps