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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...
 

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.
 

popopboat

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Update for those that have been dying waiting !

Well I'm glad I was right, but I'm not glad for anything else...

Fortunately, the bearing didn't spin in the crankcase. I marked a line that corresponds to the middle "1" on the bearing, and it hasn't moved.
IMG_20240628_202845.jpg

Perhaps it spun on the crankshaft, or even better, the bearing just failed.

 

popopboat

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Forgot to mention, theres play only when the saw is hot, cant hear/feel any play on cold saw.

Any ideas why this may happened?
 

popopboat

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Yeah, its... okayish...

But im pretty sure it shouldnt be this noticeable, besides, chainsaw starts running a bit strange as it heats up, and it didnt do this before.
 

MG porting

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Yeah, its... okayish...

But im pretty sure it shouldnt be this noticeable, besides, chainsaw starts running a bit strange as it heats up, and it didnt do this before.
Time to take it apart and split the case and put new bearings in and new seals she'll run like new again.
 

popopboat

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Yep, will replace both bearings and seals, not a big job, but... a bit of a pain in the butt as i put new bearings in not 3 years ago
 

MG porting

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Yep, will replace both bearings and seals, not a big job, but... a bit of a pain in the butt as i put new bearings in not 3 years ago
If it has plastic cage bearing on the PTO side that will happen for over heating and over tightening the chain metal cage bearing will do the same thing but take a lot longer to do so.
 

popopboat

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OEM, NTN bought at the dealer.

Yes, plastic cage, however i always run chain just ever so slightly on the looser side, and completely loosen it when not in use :/

Guess i'll just pretend it has too much power as I did too good job porting it :smash2:
 

Bigmac

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It also depends how you use your saw, I have a friend that is always forcing the saw in cuts. He will stall the saw constantly making cuts, and his PTO bearing wears out pretty fast.
 

Wilhelm

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It also depends how you use your saw, I have a friend that is always forcing the saw in cuts. He will stall the saw constantly making cuts, and his PTO bearing wears out pretty fast.
^^^==== THAT ====^^^

Most chainsaw operators don't even realize they do that!
They consider it a normal thing/practice.
 

popopboat

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It also depends how you use your saw, I have a friend that is always forcing the saw in cuts. He will stall the saw constantly making cuts, and his PTO bearing wears out pretty fast.
Can bet I could count on my fingers and still have some spare left how many times it stalled in the past 2 years using it.
Also, I like to keep RPMs in higher range while cutting.

Thats why I'm actually surprised..

Saw ran perfectly fine until it really snagged a chain, problems occurred only after that.
 
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