dbabcock
Hi Tech Redneck
As many of you know, later models of the 3120 XP have rev limiters built into the CDI/coil. On my 1999 model, the thing cuts in at about 11,500 RPM. On newer models, Ken has told me that he's seen something like 9,000 RPM! This really sucks when you're looking for any edge you can get on a screaming, unlimited 088 KD at close to 15 grand. In a large fir log, this isn't necessarily a problem because the revs of both saws fall below this in the wood. In smaller logs and cants, however, the inertia carried into the first few inches of the wood by higher RPM can mean the difference between beverages all around or a lengthy trip behind the bushes for some relief.
So here's what I did for my '99. First you order up a "-02" suffix flywheel for a 3120. Watch out if you have a 2000 or beyond model as you may not have to change the flywheel. More on that later. This is about $100 US. Then get hold of a 394 coil, which has no rev limit. These are about $75 US or so. The 394 coil has a two-legged pole piece, while the 1999 3120 coil has three legs. It is because of this that the position of the flywheel magnet relative to the crankshaft keyway will be different between the two. For models after 2000 or so, this will not be the case. As to when the changeover was made, I don't know, but you can look at the attached picture to see the relative positions of the magnets on the flywheels. The 1999 original flywheel and coil are on the right and the -02 flywheel and 394 coil are on the left. Note that the keyways are at the 3:00 position. The coils were placed so that they are in the position where they would just pick up the magnet for a counterclockwise crank rotation.
So here's what I did for my '99. First you order up a "-02" suffix flywheel for a 3120. Watch out if you have a 2000 or beyond model as you may not have to change the flywheel. More on that later. This is about $100 US. Then get hold of a 394 coil, which has no rev limit. These are about $75 US or so. The 394 coil has a two-legged pole piece, while the 1999 3120 coil has three legs. It is because of this that the position of the flywheel magnet relative to the crankshaft keyway will be different between the two. For models after 2000 or so, this will not be the case. As to when the changeover was made, I don't know, but you can look at the attached picture to see the relative positions of the magnets on the flywheels. The 1999 original flywheel and coil are on the right and the -02 flywheel and 394 coil are on the left. Note that the keyways are at the 3:00 position. The coils were placed so that they are in the position where they would just pick up the magnet for a counterclockwise crank rotation.
Ive used those things for many aplications. Trenching , popin out small stumps, . never thought that using it along with a BFH would be able to remove fly wheeles . ya learn something new everyday !
