Yeh, the transfers on my 5100 where really nice to, not much casting flash at all. Overall, I was pretty impressed with the casting in general. The worst part of my saw was the squish, was at .046" from the factory with a .026" base gasket. I cut .028 from the cylinder to set the final squish at .018" with the oem gasket.
The exhaust port on mine was almost as wide as you would want to take it because of the narrow skirt. The one side had almost exactly a 2mm margin before cutting. The other side had a 3.3mm margin. It was like the port was not centered exactly. I widened the side that I could to leave a 2mm margin on that side and straightend the sides up for a max. area as quickly as possible, with a generous arc on the roof as to ease the rings back into place.
The intake had alittle room to be widened, the margin was about 3.5mm on both sides. I made the original hole more of a rectangle shape than an oval, just because I wanted more area and the single ring doesn't come down in the bore far enough to risk snagging....You cannot get close to the general rule of 60% of the bore on the intake or exhaust becaust of the narrow skirts on the piston.
On the bottum of the cylinder, where it would set upon the crankcase, there was a pretty big mismatch in the transfer area. I used the oem gasket to scribe each surface and match them up.
These are my oem timing #'s
Intake 71.5
Exhaust 110
Transfer closest to Exh. 133
Transfer closest to intake 130
Squish .046"
These are the #'s I ended up with
Intake 77.5
Exhaust 98
Transfer closest to exh. 123
Transfer closest to intake 120
squish .018"
This saw cam with a 18" 3/8 pitch bar new. I pulled the muffler and modded it before it ever seen any wood. The saw handled the 18" square ground fairly good for a small saw...Basically, it was pretty stout.
For someone just wanting to widen the ports and clean them up, I don't know if there is all that much room for improvement because of the narrow skirts and the clean castings on the cylinder. I think this is why some saws tend to yeild better results after modding then others?....If I knew what I know now, I would off taken the base gasket out and tossed it in the trash and put the saw back together. Of course, I figured that while I was in there I would try for alittle more, just to make it worth while...I wasn't thinking that I would have that much time into it, I was wrong..
Did I make it any better? Did I totally goof the #'s? Don't know yet, I read as much as I could on here about porting and gave it a shot. It's all back together with a new piston and ring, updated gas tank vent, updated metal ring in the intake and filled with fresh premium gas and oil. I will try and put a couple of tanks threw it tomorrow.
I am no expert on this, just my 2 cents worth.
