Moving this over from the regular chainsaw forum.
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. Current numbers with .018” gasket after taking .028” off the base:
(47mm bore)
Int : 82* = 156* duration. Widened to 28mm from ~22mm
Exh : 102 for 164 duration, thinking I will need to raise more for more RPM and even out duration ratio to intake - 100? Widened Exh to 30.5mm = 65% of bore.
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?
For reference, 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 open the lower transfer ports out to gasket size like the 357, they are wide open now.
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.
At this point, I'm planning to machine to squish band a bit because there is a little ring around the outside .010" tall x about 1/8" wide which is limiting my "true" squish. I want to get rid of it and get the "roof" flat. Then machine the base a hair more to get squish to .018"-.020". Then I will have to go ahead and raise intake. I'm seeing a trend of recommendations to not go over 80* on the intake port. Probably 120-122* upper transfers and widen a little. Going to have to measure and map it all out, I may be getting close to freeporting with the exhuast port at that point.
Any and all input appreciated!
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. Current numbers with .018” gasket after taking .028” off the base:
(47mm bore)
Int : 82* = 156* duration. Widened to 28mm from ~22mm
Exh : 102 for 164 duration, thinking I will need to raise more for more RPM and even out duration ratio to intake - 100? Widened Exh to 30.5mm = 65% of bore.
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?
For reference, 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 open the lower transfer ports out to gasket size like the 357, they are wide open now.
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.
At this point, I'm planning to machine to squish band a bit because there is a little ring around the outside .010" tall x about 1/8" wide which is limiting my "true" squish. I want to get rid of it and get the "roof" flat. Then machine the base a hair more to get squish to .018"-.020". Then I will have to go ahead and raise intake. I'm seeing a trend of recommendations to not go over 80* on the intake port. Probably 120-122* upper transfers and widen a little. Going to have to measure and map it all out, I may be getting close to freeporting with the exhuast port at that point.
Any and all input appreciated!
