Chainsaw Repair

at the lower left of this pic, it shows a broken insulator.  this was my first attempt at cutting to find where the ceramic meets the metal.  was a little high, and broke the plug.

this will most likely take a couple of tries to find the correct cut off point.

pencil is pointing to the 'fuel ring'

in each photo, the position of the cut off ground electrode and threaded portion is oriented as if it were attached to the plug.

the bright silvery metallic color below the pencil point, is actually ceramic.  this is very hard material, and will not be cut.  the bright metal was worn and got deposited on the ceramic, came from the HSS cut-off tooling.

things fuel ring:

-widest portion of fuel ring = 0.116 inches
-narrowest portion of fuel ring = 0.067 inches

so what to do... with this info.....

need the average.  average = 0.0915 inches.  this is about the width of the ring at the other two sides of the plug on either side of the plug.

going to call this number the 'reference plug'.

assuming that the computer controlled injectors are doing their thing correctly, the factory picked the correct heat range for the spark plug, etc.

going to use this width as a target for the 2 stroke plug.

things are clouded up here, threatening rain....after i woke up from a nap......postponing a brake job.

imo.......

top photo: 
looking at the bottom of the threaded metal portion exposed to combustion.  portion of one side looks clean.  the remainder has black deposits.  shows uneven heat distribution.  if this was wet with fuel after a hot shutdown, rich.  clean area possibly rich washed.  should be colored and color should be uniform around its entirety. 

top photo, 2nd down, 3rd down:
looking at curved ground electrode.  in top photo is is bare of any deposits....getting too hot.  should show deposits about half way on flat section exposed to combustion.  the pencil is pointing to the first signs of deposits on the side of ground.  notice it's down in the curved portion.  electrode is getting too hot in these views as well.

the rest of the photos show a very wide fuel ring.  it will be wider than the dodge plugs.  showed the dodge plug width to establish an example of proper ring and minimum width.

the saw plug was black on on one side of the insulator due in part to ground electrode shrouding coupled with the minuscule distance between the insulator and threaded metal portion of the plug.

the plug in question, is an ngk bpm8y.  going to look for a colder #9 plug replacements and try some different tunings at this point.

don't think the saw will ever see higher loads and heat than it seen in those last 2.5 tanks.  i want to make sure to tune for the most heat soaked and heavy load conditions.

more to come after i get some more plugs.

hope it helps
-joe

Ngk cmr6h.  562xp. Three tanks on plug

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Better...

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