Chainsaw Rubber Dampers Four of Them Take the Shake

The engine shakes on its own, and four pieces of rubber take that shake before it reaches the handle. The MS381 anti vibration kit is exactly those four.

Is the engine of a chainsaw hard-mounted or soft-mounted? Hard on the frame, and the shake runs up the frame straight to the handle, and the hand goes numb. The four rubber dampers sit right in between, the engine on one side, the handle frame on the other, and the rubber squeezed in the middle. The engine shakes, the rubber flattens and springs back, and most of the shake is eaten at the rubber, what arrives at the hand is what is left. That is isolation.

Why four, and why do they look different? The engine meets the frame at more than one point, and the force at each point runs in a different direction, so the rubber at each point has a different shape. Three ring cylinders each take one point, the bore size, the hole size, and whether the top face carries small holes all matched to their own seats, and the fourth, the one with the metal bracket, takes the point with the biggest load, the metal seat carrying the bolt force, the rubber taking the shake. Four together, and the engine is held.

What is the ring groove on the rubber for? The groove around the side of the cylinder is not decoration, it splits the solid rubber into two spring sections, so it deforms more evenly under squeeze, and it seats into the housing more easily. When the groove wears flat, or the rubber hardens and loses its spring, the isolation is gone.

When to replace them? The rubber cracks, it is squashed and will not spring back, it has gone hard and sticky, the metal seat is cracked, or its hole is worn round, and the isolation between engine and handle has a hole in it, the hand going more and more numb, that is the time. The four age in the same batch, and when you open it and find one rotten and the other three tired, swap the whole set, do not mix new and old.

What to watch when fitting them? Lay the old pieces out as you take them off, and match the new ones against them, each to its own seat, do not cross them. On the one with the metal bracket, check the direction of the holes, line them on the bolts, then press the rubber home. Once fitted, idle the saw, listen to the sound, feel the handle, and the shake should be less than before, that is how you know it is seated right. Saw families mostly fit, but fit is not guaranteed for every one, so comparing against the old pieces is the safe way.