Bar's sprocket is freezing

[muddy42]

I have had similar issues to you – seized bar nose sprockets. This was a Stihl 088 and MS460 with OEM Stihl bars (20, 25 and 36 inch Stihl Rollormatic stihl bars respectively. The bars are pretty new and are still on their first chains. I do as you do and clean the bar grooves out regularly. I also cleaned out and checked the oil tank and oil pumps everything was fine. Similar to you the bar threw off oil from the tip. Odly a smaller saw (MS260 with a 16 inch bar) was unaffected by this issue.

It remained a bit of a mystery that was only solved when I switched brands of bar oil. I was using rotatech and have moved back to Oregon. I am not sure but I think the rotatech oil was too thick and it wasn’t oiling the middle of the bar nose sprocket properly.

Hopefully I havn’t caused any long term damage. I soaked the bar noses in diesel and bar oil combination. I always have adjustable oilers set to maximum

I thought I'd provide an update on my particular issue, after a few more weeks of cutting and investigation. All three saws are now working again after the same treatment. I am now confident the bar oil was to blame. On all three saws I removed the sprockets and oil pumps, cleaned everything out with solvent. I'm now using Oregon chain oil rather than Rotatech - for a few weeks there have been no more seizures. What's weird is both oils are ISO 100, the rotatech oil looks darker but that's all, just one of those little quirks. I'll thin the rotatech oil with diesel and use it in the aux oiler for milling.