Chainsaw Repair

I borrowed a Ryobi 40 cc chainsaw RCS 4040A and all was going well until there was a bang and the motor stopped. Closer investigation revealed all of my body parts still attached to me but the starter cord was broken and there was a crack in the casing on the starter side.

Opening the side revealed that the motor had grabbed the starter under full power and wound the spring of the starter backwards until the spring and string broke.

The starter can be purchased as a single block with the starter cord and handle, this is relatively simple to switch out, although there is a trick. First take the top panel off (2 Torks at the back, lift and slide back). Unplug the spark plug and then work on the side. The fuel and bar oil caps need to be off to get the side off and there is a screw under the handle that is a complete pig to get out. It is fixed with a nut on the back, so I used a pair of pliers to hold this, but it was still stupidly hard to get off. The new side slots in and away you go. Check that the spade connecter from the spark plug to the magneto is still attached, it fell off when I opened the case and this will really annoy you if you miss it.

In my case a whole lot of pieces of aluminium fell out, so I needed a second part. In this saw the driveshaft extends out of both sides of the motor, on one side driving the chain, on the other a thing called a flywheel is bolted. This does four things. It acts as a flywheel, it acts as a fan to cool the engine, with scoops on it to pump air, it contains a magnet that passes a coil to fire the sparkplug and it connects to the starter cord.

To grab the starter two little arms are sprung against the plastic of the starter spool, which has a series of wedges on to engage them in one direction only. As the motor spins up they are flung away by centrifugal force. The problem was that they push off the cooling fins and these had broken. It looked as if one of the arms had spun right round, engaged backwards and wound the starter backwards. As a chainsaw motor runs fast this quickly resulted in disaster.

The flywheel is also available as a spare, I used Mower Magic, who ship to Germany for less than I could get the part from a German company.

Taking the flywheel off is not so simple, it is attached by a recessed nut and is wedge shaped. I used a clamp to hold the old flywheel still and turned the nut with a socket spanner. There is a washer under the nut that you do not get in the spares bag so do not lose it. Once the nut is off the flywheel was still well attached. There are no stable things to lever it off against, at least I was not happy levering against the fuel tank. Luckily a few taps with a hammer on the outside edge of the wheel were enough to loosen it.

I should have taken pictures of the inside, but as the one screw is so hard to remove and attach I have no desire to take it apart now just for fun.

The cracked and broken casing, my fingers are glads that the spring did not escape.

The spring part after its brutal reverse winding.

What the ratchet looked like after the motor stripped the teeth off

The flywheel as it was supposed to be.

The broken flywheel, the missing fins allowed the arm to swing completely across.

The pile of wood, admittedly much of it was done with a Bosch electric chainsaw, but the big cuts were done with the Ryobi. The electric chainsaw is good, but has difficulty with harder woods, such as holly and cuts deeper than half the bar length. The Ryobi also could have done with a bit more power but cut the full length of the bar in my elm trunk before struggling on the heartwood.