OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters McCulloch Chainsaws McCulloch 10-10 chainsaw chain tension problem

Those grooves in the center of each sprocket tooth are wear - they were not part of the sprocket.
While people often talk about chains stretching, they do not actually stretch, they wear, often due to inadequate lubrication, but also due to abrasion associated with exposure to dirt (including dirt embedded in the wood you cut). Some of the wear is to the rollers, but most is in the pivot pins and side plate pivot holes. This causes the chain to become longer, but much more importantly, it has more length for the same number of links, so each link has increased in pitch. Unfortunately the sprocket still has its original pitch, so the chain and sprocket pitches no longer match. This causes serious damage to the sprocket teeth, such as yours show. Putting a new chain on old sprockets is just about always a false economy, since the damaged sprockets then apply uneven loads to the chain links, and cause premature wear to the new chain. To summarise, you need a new sprocket as well as a new chain, and then you need to keep the chain and sprockets clean and properly lubricated by chainsaw bar oil, not by another kind of oil. The bar oil contains an additive that makes it super-sticky, and this is essential. You should remove the chain, clean it in solvent, re-oil it, and reinstall it, at frequent intervals - especially if you ever cut fallen trees or other deadwood. Contact with dirt doesn't just blunt the chain and strip the chrome off it - it also sticks to the chain and gets into the pivots.