It's a Mac 3-25 with a serial number somewhere in the mid-to-late production range around 50000-100000... two-piece fuel tank, later starter, missing the rubber plug cover (which Mac issued a special service bulletin warning people not to run a saw without that plug cover -- engine can overheat), and with a seldom-seen chain guard sticking out over the bar to somewhat protect the operator against backlash from a derailed chain.
Only the 3-25 has a frame (top-handle) which curves around on the left side and enters a hole in the fan shroud with a rubber grommet to hold it in. Neither the 4-30, 4-30A nor 47 have that type of frame.
The model and ID tag should be riveted to the bottom left side of the rear handle. If the metal tag is not there, you'll find the two rivet holes about 2 inches apart where it once was.
People in the woods had a tendency to take the chain guard off and forget it somewhere... Ditto the plug cover, until they found out their saws developed heating problems without that rubber cover. Later, Mac took to riveting the plug cover onto the cylinder shroud. You'll find the hole where it was riveted-on.
Don't break this saw up for parts. It's a whole, complete antique saw made (in this saw's case) between late 1951 and March of 1953. They're not really uncommon (after all, Mac did make over 112000 of them between October 1949 and March 1953), and they don't command a big price on the antique chainsaw market like a Reed-Prentice model 50 or a Homelice 26LCS made during the same era, but the McCulloch model 3-25 is an iconic and under-appreciated collectible chainsaw. It's introduction to the forestry industry revolutionized chainsaw making. This model of chainsaw introduced so many innovative changes to saw-making that I won't even start to list them here. But, one example... Mac put a diaphragm carb in this, his first one-man chainsaw, in 1949, while many chainsaw makers (Reed-Prentice, Titan, Lombard, Homelite, and many, many more) were still putting float-type carbs in their saws even as late as 1957.
Keep it and restore it and be proud of it.
Be very careful when cleaning it with that instructions decal on the diamond-shaped cover on the right side of the oil tank. Very few surviving 3-25's still have that decal.
Or see to it that it gets, undamaged and complete, into the hands of someone who can appreciate it for what it is.
With the model 3-25, Robert Paxton McCulloch stood the chainsaw industry on its ear! And everyone else was years trying to play catch-up to Mac... until he sold the company to Black & Decker in 1973 and the sad story of the decline of McCulloch chainsaws (and American-made chainsaws in general) began...
