I don't have any answer besides...When they are worn. Subjective at best since there are no wear indicators on the sprockets. Seems like I can feel when they start wearing the drive links funny on my chains when in the hand.
But really. I’ve cut approximately 60 cord with my MS362 and only changed the rim sprocket maybe once. Also the spur drum on my ms251.
When the chain stops-a-turning, I replace the sprocket. Well, maybe not THAT long, but I go a long time.
I picked up this 372xp a couple months ago without knowing too much about it. As circumstances would have it, I recently bought 2 new 3/8 8T sprockets so I decided to put one on this new used saw. The 7T sprocket that was on there is definitely the most clapped out I’ve ever seen. It’s probably seen a lot more than 2 chains on it
I would change it. It’s going to go downhill fast from there and at some point the chain will be damaged. Once there is a decent groove worn it’s on borrowed time. Before I knew what FHC was I ran my spur sprocket until it was completely annihilated. Didn’t change it out until I head crunching and destruction. I now change things prior to their catastrophic failure. I even check my air filter with regularity. You could change it out now and save it for an emergency if u find yourself with a roached spur drum at a later point.
I would at the very least get a spare for your inventory so you can swap it straight away when it does become and issue.
Also, keep in mind that running a new chain on an old worn sprocket, or vise versa, new sprocket with and old stretched out chain, will destroy the new part a lot faster than if they were both new, or both worn. If you have ever ridden a motorcycle where someone has a mismatched chain/sprocket set wear wise, it sounds horrible!
You could also take this as an opportunity to change the spur sprocket over to a rim sprocket. I prefer a rim sprocket. Echo Cs 590 Timber Wolf, 600P, 620P Clutch Drum And 3/8 7 Tooth Rim Sprocket
Happened across my sprocket stash this weekend after finding a couple of 3/8-7's I had bought and forgot about. Am good for forseeable future with at least 5ea of .325-7 & 3/8-7. Have a few 'oddballs' as well....325-8's, 3/8-7 small hub, and a couple 3/8-8's I forgot about. All say Oregon on them as I'm scurred to trust the off brands.
Off the top of my head, I have one saw with the spur sprocket, and it’s only been changed when I can no longer keep tension on the chain cause there’s a groove word down the middle. Takes a lot more that two loops of chain to get there. Rim sprocket saws haven’t been changed yet.
