Chainsaw Repair

re-read my other thread, just now:  http://chainsawrepair.createaforum.com/ported-saws/port-mapping-old-school/

clear as mud it is.  hope to wash some of the mud off in the next few days.

this is where the story starts:  http://www.bridgestonemotorcycle.com/documents/aspirin_takers6.pdf

first thing that i would do is figure out 'angle area'

you need a couple of things before a number can be had.

looking about, most folks here and elsewhere talk in degrees.

seems where the port opens in degrees is talked about more often than port durations.   (opposite is true most everywhere else).

going with that.

looking at a typical exhaust port:

degrees where the port just starts to open, for example is 97 degrees ATDC.  ATDC = after top dead center.  TDC is top dead center, where the piston is physically located at the uppermost point of its travel. (at TDC = 0 degrees).

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to find 'durations'.........the amount of angle degrees a port is open can be done a few different ways.

Port Open Durations:

Exhaust Port Opens @ 97 degrees ATDC.  so, 97 x 2 = 194; then 360 degrees - 194 degrees = 166 degrees duration.
Transfer Port Opens @ 121 degrees ATDC. so, 121 x 2 = 242; then 360 - 242 = 118 degrees duration

Blowdown is simply: Degrees Trans first opens - Degree Exhaust first opens = 121 - 97 = 24 degrees duration.

Intake is a little different, because most it seems measure the opening degrees BTDC in saws.  (before top dead center).

Intake Port Opens @ 75 degrees BTDC.  so, 75 x 2 = 150 degrees duration.

in my opinion, the 'mean port angle' carries more weight, than where a port first opens degrees.  not talked about, but hope to show why.

Cool stuff , wish my brain worked like yours does with math!!!  63PS Chain and a few good beers coming your way via UPS in AM

this brain is shot.  trying to keep numbers to a bare minimum.

will put together two very small programs that will do all the numbers for yall.

still, some degrees will be needed to be had.  so a wheel will be necessary.

one version, you will need the find connecting rod length.

another version, where connecting rod length is not needed.  this will not be as accurate, but close enough to be in the wheelhouse.
so all that you need is a wheel and calipers.

both will use an extended version of the jennings graph.

beer....ya man.  pesos and beer back at ya.

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