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Stihl MS650 NEW mysterious behaviour!

popopboat

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My MS650 what i already made a thread or two about... developed a new mysterious behaviour!

A few days ago, I was cutting logs when two pieces caught the chainsaw chain, one rolled and stretched it significantly. Despite wearing earmuffs, I heard a "HRRRT" sound (similar to gear grinding but different) , and the chainsaw died. For whatever reason my first thought was that the PTO side bearing might have spun. After inspecting it, I started it up, and it fired right up, although the idle speed was slightly higher than usual. Otherwise, nothing seemed different. Since I didn't find any issues, I continued using it over the past few days. It idled and ran fine, but something felt a bit off.

Today, however, I noticed some awkward vibrations while decelerating after throttling out of a cut. I quickly removed the clutch cover to check for side-to-side play on the crankshaft, and there WAS play, could also be heard when I wiggled the crankshaft end. I then removed the clutch drum for a better grip on the crankshaft and comfirmed THERE WAS A PLAY, but only forward and backward, not up and down (not axial). I decided to remove the clutch and oil pump to see if the bearing had indeed spun, but once I disassembled it, the play completely disappeared. (i guess as the saw cooled down)

After reassembling everything, I used the chainsaw a bit more and then checked again. After that, there was again no play at all.

My question is : What do you think what might have happened? As there was definitely some radial play on the crankshaft end.
It really bothers me as it is my absolute favourite saw... Its been serving me for past 4 years without any issues.

Have i missused it in this 4 years of owning it? Absolutely not, never cut with a dull chain, used high quality oil on richer oil/fuel mixture, used decompression valve for starting.... you name it...
 

64poncho

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When you had it apart, did you pull the seal and check to see if the bearing cage was intact?
 

popopboat

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Thanks for the reply.

Yes, i figured plastic cage might have fallen apart so it caused intermittent odd vibrations as balls rearranged, but it is intact.

Also, after first dissasembling I have marked a line on the crankcase that aligns with markings on the bearing, and it has not rotated a bit after checking it.
 
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