So I bought a rebuilt 2159. Top end is a $40 Ahlborn China kit. Didn't have any power, only 100psi compression. I got a new 357 top end for it but in the meantime I decided to play around with it at work (machine shop) and see if I could get it to run decent. Squish was .050" so I took .028" off the base and got it down to .022". Of course that lowered the ports and turned it into a low RPM torquey tractor. I don’t have much frame of reference for a 60cc saw but it’s defintely better, plug looks good 4 stroking at 12,500RPM. I want to raise the powerband. Initial numbers with .018” gasket after taking .028” off the base:
(47mm bore)
Int : 82* = 156* duration. Don't really want to try to raise it. Widened to 28mm from ~22mm
Exh : 104 - raised .020" to 102 for 164 duration, thinking I need to raise more for more RPM and even out duration ratio to intake - 100? Widened Exh to 30.5mm = 65% of bore - could go 33mm.
Xfer : 120 - think they need raised and widened, but don't have tiny tooling to get in them. Might get some.
Blowdown is 18* get - closer to stock numbers by raising exhaust?
A factory cylinder with no base gasket:
103 exst - 154° duration
79 intake - 158° duration
Blowdown - 20°
Figured out since I don’t have removable xfer covers, I could blow the lower transfer ports out to gasket size like the 357, they are wide open now. Also knife edged the leading edge of the port divider. Die grinders I have are a big too big for this, bull in a china cabinet. Rough, but quick.
Compression is now 150psi below sea level. Little disappointed in that. Cheap ring methinks. Found a Caber for $8, on the way.
Swiss cheesed the muffler baffle and made it dual port exh.
Any and all input appreciated!
(47mm bore)
Int : 82* = 156* duration. Don't really want to try to raise it. Widened to 28mm from ~22mm
Exh : 104 - raised .020" to 102 for 164 duration, thinking I need to raise more for more RPM and even out duration ratio to intake - 100? Widened Exh to 30.5mm = 65% of bore - could go 33mm.
Xfer : 120 - think they need raised and widened, but don't have tiny tooling to get in them. Might get some.
Blowdown is 18* get - closer to stock numbers by raising exhaust?
A factory cylinder with no base gasket:
103 exst - 154° duration
79 intake - 158° duration
Blowdown - 20°
Figured out since I don’t have removable xfer covers, I could blow the lower transfer ports out to gasket size like the 357, they are wide open now. Also knife edged the leading edge of the port divider. Die grinders I have are a big too big for this, bull in a china cabinet. Rough, but quick.
Compression is now 150psi below sea level. Little disappointed in that. Cheap ring methinks. Found a Caber for $8, on the way.
Swiss cheesed the muffler baffle and made it dual port exh.
Any and all input appreciated!
