Piston direction?

[45u]

Every two cycle I have worked on the arrow on top of the piston faced the exhaust port. Is this how these engines are or does the arrow face the intake port? The reason I asked I just received a motor and the arrow is facing the intake.
Thanks
Jeff

 

[Greg58]

The ring gaps go to the rear, they will be between the intake and transfer ports. That's what I go by, we have found all kind of markings on pistons.

 

[45u]

Thanks but the cylinder is on and all I can see is the arrow. Thanks Jeff

 

[butre]

you have to take the cylinder off to flip the piston anyway. the arrow doesn't mean anything it's the ring ends that need to face a certain way

 

[Greg58]

Some pistons have arrows, some triangles. Others have a square or nothing at all. If memory serves me correctly if the piston were in backwards you would see the ring gap on the left side looking in the exhaust port.

 

[Greg58]

Jeff if you do any porting going a little wider will help, just de-burring all ports will help. If you open the ports from top to bottom it will change port timing, if you use the search box near the top of the page you can find a lot of useful info.

 

[45u]

I want to run it all most stock to start with then make changes to see the difference. I just looked at another piston I have and with the ring gap between the intake and boost ports the arrow it pointing forward. Going to check the one in the motor now.

I am going to get another cylinder and do some porting and timing changes. Going to try this.

Just remove 1.6mm from the piston intake skirt and use your rotary tool and cutting disc to raise the exhaust port by 1mm increments till you achieve the speed you want. Use a small file to round off the newly formed lip where you removed metal. That is to prevent the piston rings from snagging on that lip.
Thanks
Jeff

 

[45u]

OK all thanks I see the arrow means nothing as the piston in the motor was totally different from the extra I had.
There is so much shavings grit and other stuff I am going to take it all down and make sure it is spot less.
Thanks
Jeff

 

[sbest]

On the Grubee engines I have the ring gaps are safe from falling into the exhaust port, so you won't see them through the exhaust port.

This was the same plan I followed Jeff, bought the motor with spare gaskets and cylinder with a plan to do mods one at a time to verify what works and what doesn't. Has been enlightening. Intake portmatch did not work. Worked better with the mismatch.

Steve

 

[45u]

Steve,
I all ready bought many spare parts including 4 gasket kits as I know I am going to be taking apart and assembling many times. Mater of fact I have not finished my first build but have a SkyHawk aluminum bike frame GT2-A on the way. LOL I am hopping on building two more bikes one with a 4 cycle motor.
Thanks
Jeff