Chainsaw Repair

at BDC

.......  the longer rod shown in these comparison graphs is 4x the TOTAL center to center length of the shorter rod.

all of these graphs above reflect this exaggeration.

had to do this to show some difference in the velocity and acceleration graphs.  ie.  there would be a gnat hairs difference in 3 mm.

for what its worth......ccase volume:

using approximate numbers for a 460ish.  i don't have of these saws.  numbers reflect just a guess to show that ccase vol. remains unchanged.

assuming this:
ccase BDC volume = 150 cc
swept volume cylinder under piston = 75 cc
cccase TDC = 150 cc + 75 cc

using the twisted new method:

for a stock rod

= (150 + 75)/(150)
= 1.5
 
adding approximately 6 cc for the stroker plate..........and longer rod

= (150 + 75 + 6)/ (150 + 6)
= 1.48

--------------------
the way the folks who invented this did it this way:

= (volume ccase)/( swept volume cylinder)

stock
= 150/75
=2

long rod stroker plate combo
= (150 + 6)/(75)
= 2.08

...the piston velocities (and/or acceleration) are not symmetrical around TDC and BDC.   faster and slower, respectively.  hope someone gets my drift.  long rod or not.

find where the actual dwell is.  helpful?  benefit (if any) is elsewhere.

It's easy to see dwell if you overlay the piston position vs. crank angle of the two rod lengths. You'll see that the longer rod stays close to the top of the stroke longer (within 2x squish clearance).

People often miss that the piston forces due to acceleration are decreased with a longer rod. F=MA, so with your example it's a 10% reduction in the force due to acceleration. Which doesn't sound like a whole lot but it's really significant in fatigue life of a part.

Got a sort of off topic question.  The poulan partner jonsered crankshafts used in the 415 425 445 475 505 2077 2083 660 710 7700 are similar to the husky 371 but with coarse threads.  Saws are built in the husqvarna plant using alot of husky parts.

I have at least 4 of them now with bad big end rod bearings.  Being the cranks are NLA, I am wondering if a redneck could some how push apart the crank to be able to replace the bearing and some how true these back up?

Betting the 372 big end replacement bearings would work?