I wanted to cover this issue in detail. The ms201t isn't the best design really, the oiling system is also quite bad. On mine, part of the oil pump is corroded and leaking oil. The crankcase block that the bar mounts onto is also corroded and not making a tight fit in the area where it feeds oil into the bar. This was partly my fault for not cleaning it, especially from the corrosive effects of palm debris. I fixed this corrosion with automotive high temp gasket sealant. Having said that, these surfaces lack any type of chromate coating that protects against this. I thought the MS200 was the Lamborghini of chainsaws.
Then there is the issue with the alignment screw that keeps the bar aligned on the crankcase block. It is of insufficient length, has ripped out and the thread is gone, so a new screw can't be reinserted. Now the crankcase block has to be replaced. Instead, I corrected Stihl's catastrophic mistake, by drilling a deeper hole and tapping a new and deeper thread. The alignment screw keeps the bar straight but also keeps the oil entry and exit channels aligned.
Once you have corrected the defective nature of the saw's oiling system, then you need to look out for simple things. The chain expanding and coming loose is the notable sign of no oil inside the bar.
Remove the bar, check oil is coming out the channel on the block
Turn screw clockwise on oil pump to maximize oil output
Go back to using original stihl oil
Clean the oil filter
Check for dirt particles inside the oil pump
Check blockages around oil hoses
Clean oil channel on bar
Check alignment screw
Check for leaks around oil pump
Check worm drive for wear
Check air release valve
Clean surfaces
Ensure inertia clutch mounts onto worm drive correctly
The pump may be delivering oil, but not a sufficient quantity. Not enough
oil causes the chain to expand and the bar to get hot. Eventually the chain
will come off or sometimes it snaps.
