chainsaw's new engine
Monday, January 5 2009
My Stihl 029 (Farm Boss) chainsaw has been out of commission for weeks now as it has awaited the arrival of a brand new engine to replace the trashed one inside it. That replacement came yesterday, and since then I've been trying to rip out the remains of the bad engine to make room for the new one. It had been relatively easy to remove the cylinder head and piston, but the new engine was a complete unit that included its own crankcase, and it seemed prudent to keep it intact through the swap. This meant I had to get the old crank case out, but I was stymied by two difficult procedures: the removing of the flywheel and the removal of a double-threaded bolt (a stud) serving to physically attach the saw bar to the engine. To bust that flywheel loose would require some sort of puller to get it off the engine's crank shaft, so I tabled that problem while I worried about the stud, which seemed like the only thing keeping the engine in the chainsaw.
I'd learned in my childhood that headless bolts could be turned by locking together two nuts on its threads (this was a procedure required in an electric motor kit I'd built). But this stud, which was about eight millimeters thick, didn't want to turn last night when I'd tried the technique on it. So I'd done as much web research as I could, eventually finding a great reference on Google Books called Chainsaw Service Manual. I'd thought Google Books was mostly useless, since it only contains excerpts of copyrighted material. For this particular book, though, only about 20 percent of its content had been redacted. Being a reference for numerous models and makes of chainsaws, much of the content was fairly repetitive, so I figured I'd be able to find something about how to get that stud out. As it happened, the place in the book discussing my chainsaw hadn't been redacted, and this was how came to learn about the thread compound used on the threads of that stud where they entered the crankcase. The book suggests using heat, though it didn't say how much. Today I did some more research to learn about the removal of engine studs more generally and found a good reference. Armed with this information, this afternoon I went out in the driveway with the chainsaw and my MAPP gas torch and started heating that bolt. (I thought it best to work outdoors, since the saw's fuel tank still contained several cups of gasoline.) After both of the mated 13 mm nuts on the stud had changed color from gloss to matte, I began backing out the bolt using two spanners, one on each nut. Happily, the stud began to turn and eventually I was able to get it out. But the engine still wouldn't separate from the saw; the flywheel was too bulky to allow the two to separate.
But now the engine was loose enough for me to thread bolts up through the flywheel's fan blades into the flanges of an old automotive steering wheel puller. I've had that steering wheel puller for ten and a half years now. It had originally been bought on my recommendation by my friend Matthew Hart in hopes of removing the steering wheel of his Ford Taurus (back when we lived together at Kappa Mutha Fucka in Charlottesville, Virginia). The tool had failed us then, but somehow it had found its way into my tool kit and survived all the moves since then, allowing me to get that flywheel off my chainsaw today. When it broke loose, it did so in an instant with a loud soft-metallic "crack!" sound, throwing my right hand into something sharp and tearing a gash across the back of my thumb. This matched a similar gash I'd gotten yesterday on my left thumb when breaking loose the chain gear on the other side of the crank shaft. (The chain gear tightens backwards, as in lefty-tighty, righty-loosey, something I'd known before I began because, suspecting that this would be the case, I'd carefully inspected the threads.)
It didn't take too long to get the chainsaw all back together. This time I was very careful with the oil-to-gasoline mixture as I refueled the saw. Then I took it out and tried it out on some of those White Pine pieces salvaged from the windfall across the road a week before. The saw started much more easily than it had ever in the past, and it ran okay for a bit. But then it died and refused to start.
Suspecting the carburetor, I removed it and replaced the rubbery parts I'd replaced weeks ago when I'd initially blamed it for all the saw's problems. (I'd used a refurb kit that hadn't exactly fit my particular carburetor and I'd had to cut additional holes through the rubber. It was a goofy thing to attempt, but that's how I roll.)
With the carburetor restored to its original state, the saw worked flawlessly. It started easily and didn't stall. Indeed, it was behaving as it never had in the past, confirming my suspicion that (possibly) when Gretchen had bought it as a gift for me two years ago, the guys at Herzogs had taken advantage of her gender and sold her a known lemon.
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