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MS361 - Diagnosis?

odin

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Broke down an MS361 today looking to see if it could be salvaged. This is what I found. To my untrained eyes the jug looks fine other than some transfer (finger nail could barely feel it). Question is, what in the world causes all the discoloration in the transfers???

Clutch side:


Flywheel side:


Intake:


Exhaust:


Wide shot of ex side:
 

AlfA01

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Little history on the saw? Mix ratio/ mix oil? Ethanol/ non ethanol gas? Tuning?

The jug should clean up pretty easily. Use Mastermind's method on his YT channel. Worked for my scored 550Xp cylinder that looked worse than yours.
 

odin

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Was told this was a fence builder's saw, meaning ranch fence around these parts. That could also mean pasture clearing saw used to cut endless Eastern Red Cedar in ranch pastures. Saw was fairly greasy when I got it and was told it was left out with an oily rag over it. Was also told that it wouldn't turn over when it was brought in (I turned it over in the shop prior to being told this). Not sure how much of the story I believe as it seemed to be sitting in old-man Duggan's shop for quite a while by the buildup of dust and grime on its exterior. And Duggan is old enough to have forgotten most of the story, that's for sure.

My thoughts were this - Old rancher used it to clear pasture and fenceline, prefering 32:1 because that's what we've always used... Until the day his grandkid went out to clear a bit and forgets to put any oil in the mix at all.

Ran real good for about half a cut, Grandpa... :flamethrower2::facepalm:
 

smokey7

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The staining is from the transfers back stuffing. A restricted muffler will cause it and cheap oil mixed at a heavy ratio will cause the varnish to show up more heavily quicker.
 

odin

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I think thats blowback down the transfers when they open. A good way to know exactly where the windows in piston are haha

What causes blowback?

I could probably guess... but I don't wanna guess...

edit - sorry, slow typing. thanks @smokey7
 

odin

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Haven't pulled the screen on the muffler yet... I was actually trying to part out an 064 carcass and this 361 was in the way.
 

cus_deluxe

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Stuffed up exhaust. Exhaust port opens, exhaust gas has a hard time escaping, when blowdown period is done, combustion chamber/exhaust still has higher pressure than crankcase, exhaust gas flows down transfers momentarily then is forced out.
 

odin

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Couple more questions for anyone tuning in. Not really a worry, just looking for knowledge.

Why is the buildup of varnish heavier (but different) on the PTO side?

Is there any way to clean the varnish out of the transfers (or is it not really a worry)?

Is there any way to clean all that buildup out of the chamber? (it's like black goo in person)

And related to that... there's a band of buildup about 3/16 wide on the cylinder wall at the top of the chamber. Would this be evidence of the area where the chamber gasses wrap around the top of the piston (up until it reaches the first piston ring)?

Plan at this point, since I've now got a bad piston, is to sand squish (if necessary) and delete the base gasket, advance the timing a bit and apparently drill a big f*cking hole in the flywheel side of the muffler...
 

huskihl

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Couple more questions for anyone tuning in. Not really a worry, just looking for knowledge.

Why is the buildup of varnish heavier (but different) on the PTO side?

Is there any way to clean the varnish out of the transfers (or is it not really a worry)?

Is there any way to clean all that buildup out of the chamber? (it's like black goo in person)

And related to that... there's a band of buildup about 3/16 wide on the cylinder wall at the top of the chamber. Would this be evidence of the area where the chamber gasses wrap around the top of the piston (up until it reaches the first piston ring)?

Plan at this point, since I've now got a bad piston, is to sand squish (if necessary) and delete the base gasket, advance the timing a bit and apparently drill a big f*cking hole in the flywheel side of the muffler...
The buildup is worse on the right side because it's burned on due to that side being hotter. The fan being on the left while the right side does the work makes it hotter
 

JonCraig

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Looks like my father-in-law’s 041. He’s been using the cheapest outboard oil he can find for years...
 

MustangMike

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I had a lot of carbon on top of an 044 P+C, someone had stuck a .040 base gasket in there! Carb cleaner helped, but I also did some gentle scraping with a screw driver. I dropped the intake a bit and installed the P+C on an Asian 440 and it runs just great!
 

drf256

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That’s coking.

That’s from mix sitting on a hot surface for a long time, and not being burned or scraped clean by a ring.

I disagree that it’s backflow. It’s simply mix sitting, that’s why there is a ring around the top of the cylinder and the PTO side has more.

The area around the sides of the piston crown before the ring doesn’t have any burn.
 

AlfA01

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Couple more questions for anyone tuning in. Not really a worry, just looking for knowledge.

Why is the buildup of varnish heavier (but different) on the PTO side?

Is there any way to clean the varnish out of the transfers (or is it not really a worry)?

And related to that... there's a band of buildup about 3/16 wide on the cylinder wall at the top of the chamber. Would this be evidence of the area where the chamber gasses wrap around the top of the piston (up until it reaches the first piston ring)?

How'd the bar and chain look? I'm guessing it ran quite often with a dull chain, which causes excess heat, especially on the PTO side. Is that where the scoring is?

Yes. You can sand or polish it out or use some chemicals to soak it out. I've heard of some folks using acid and such, but I stick to mechanical means versus chemicals to remove crud. Well, besides brake or carb cleaner.

That collection of gunk is in the area of your squish and probably wraps around the top of the piston until the ring. As doc said above the ring is not wiping that area clean during operation.
I would fully clean that also before adjusting squish and messing with a new piston in there. You can cause some of that crud to come loose and end up scoring the new piston/cylinder also.
 

odin

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That’s coking.

That’s from mix sitting on a hot surface for a long time, and not being burned or scraped clean by a ring.

I disagree that it’s backflow. It’s simply mix sitting, that’s why there is a ring around the top of the cylinder and the PTO side has more.

The area around the sides of the piston crown before the ring doesn’t have any burn.

Would this/could this be caused by boat oil + bad tune?? I guess I'm asking what is the cause of coking. My assumption is bad mix and bad tune leaves mix sitting in the transfers and causes mix to not burn well in the chamber. Evidence in this jug is varnish in the transfers and baked on goo in the chamber (plus piston crown and ex port).
 

odin

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How'd the bar and chain look? I'm guessing it ran quite often with a dull chain, which causes excess heat, especially on the PTO side. Is that where the scoring is?

Yes. You can sand or polish it out or use some chemicals to soak it out. I've heard of some folks using acid and such, but I stick to mechanical means versus chemicals to remove crud. Well, besides brake or carb cleaner.

That collection of gunk is in the area of your squish and probably wraps around the top of the piston until the ring. As doc said above the ring is not wiping that area clean during operation.
I would fully clean that also before adjusting squish and messing with a new piston in there. You can cause some of that crud to come loose and end up scoring the new piston/cylinder also.

Bar is/was a 16-inch Stihl E laminate bar. Chain looked fine and I was kinda stoked to get a bar with the saw... then I looked closer. The bar rails are worn unevenly with one about 1/16-inch lower than the other. I quit looking at it after I saw that. Not really worth the hassle to fix IMO considering a Raisman is <$20 and I've got other Stihl bars that would pair well with this head.
 
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