Originally Posted by Master-shake
What is this I hear about chromed piston rings or sanded down ones? I have an extra set that I'd like to experiment with. Also, these wrist pin bearing things, would I be able to take em out, take em down to Home Depot and find an upgraded set or do I have to have bearings specific to the grubee gt5 sky hawk? I polished the inside of my cylinder with scotch bright when I first got it, got it to almost a mirror shine. I guess it helped?
anything you ever need to know about replacing these motors hardware: https://docs.google.com/document/d/1...it?usp=sharing
As for the OP... thats sweet, I had been toying with the idea myself but not having the tools to do so (and a dremel would be notoriously difficult to do with) I never got around to it. However three suggestions: For the intake and exhaust ports, make em wide. if you use a 40mm intake spacing, make the intake port 28.1mm wide. If it's a 30mm, then 20mm wide (leaves 2mm walls between the port and the screws, if you widen it on the inside, you'll lose intake velocity, just make it 20mm all the way in). Exhaust port make it ~30mm wide with a 40mm bolt spacing. And the transfers, match them to the base like you planned but when it comes up to where the transfers meet the combustion chamber, aim them toward the intake side of the cylinder, this'll reduce short-circuiting allowing a more efficient flow and give more power. Also if you can figure it out, make the transfers enter at a sharp 30 degrees on the Y axis (so the airflow skims the piston). I'm not sure how to design for that, but our stock motors enter at 60 degrees on the Y axis and doesnt allow for complete exhaust evacuation.
Port heights (timing) depends on your application but generally speaking, match the grubee cylinder. They produce good power at low RPM's and aren't designed for high RPM's anyway, so making high ports may only hurt them.