McCulloch PM 105, SP105 and the SP125 Chainsaws I see the above models of McCulloch sell on Ebay.com quite often with some sellers uncertain which one the saw is, now if as in a lot of cases the ID tags are missing along with there ID stickers, theres really only one external clue as to which one it could be and thats the location of the decompressor and the hole in the cylinder shroud. Note the cylinder shrouds do not interchange because of the relocation of the decompressor valve

Left is the location of the SP125 Decompressor ....................................Right is the location of the PM 105 and SP105 Decompressor. Another giveaway is the depth of the fan housing as the PM / SP105 used a shorter crank on the ignition side .