MS361 Problem - Oil/Fuel Leaking from Under the Muffler

[WACutter]

I have a new to me 361 that is in pretty nice shape, except for one issue. It seems to be leaking an oil/gas mixture of some sort from under the muffler. I pulled the muffler and took a couple of pictures before I cleaned it up.

I can see no external damage to the saw. It starts and runs fine, then within a minute or so black oily stuff starts dripping/running from underneath the muffler.

The piston looks good. I don't see any visible damage from where the case halves meet.

Any ideas? My wrenching skills are not that great, and before I continue troubleshooting I thought someone might recognize the issue or give me some tips to get to the root cause.

Happy New Year!

Thanks

 

[s219]

May simply need a new muffler gasket. Though if it's leaking a lot, it could also be set way too rich.

 

[wheelman]

Are you sure that there is any gas in that leak?
It looks to me like you are leaking bar oil from between the case halves.Probably loose screws that hold the halves together.

 

[Kenskip1]

I hate to ask but what oil ration are you using? What type of oil are you using? From the limited information given it appears that it has not gotten hot enough to burn the oil out of the muffler.Short running and shutting off has allowed the oil to accumulate in the muffler.I would take it out with 40/1 mix and find something to cut and let er rip.I bet that it would smoke like hello for a bit.Use some FRESH mix.Ken

 

[WACutter]

Ok, thanks for the tips.

I tightened down the case halves, but they seemed pretty tight. I'll tune it after I put it back together. As to the mix that was used, I have no idea what the last guy used. I drained the saw, idled it dry, and then put in some Stihl premix just to remove that variable. I cleaned out the muffler, and will mod it a bit before reinstallation.

Going out to work on it now. Still recovering from last night.....:msp_thumbsup:

 

[Austin1]

I am thinking it is just oil goo for lack of a better word from running too ritch a mix. You did good buy running a good oil at 40/1 or 50/1 I bet it goes away once you burn out the oil in the muffler.

 

[Monadnock]

I already know I whacked, but does that first pic give anyone else anxiety?....in a that looks nasty sort of way? I don't mean filthy. I mean in a disturbing gimmie a file or torch so I can scrape/burn that stuff off sort of way?!

I've seen some disgusting stuff but that's freaky. I have a bit of trypophobia and that pic sorta triggers it. Do a search. You may be a trypophobic too, lol.

As far as the oil leak, it's hard to tell but a ripped gasket/loose bolt comes to mind.

 

[Kenskip1]

One thing for certain, the muffler bearing are well lubricated! LOL Ken

 

[z71mike]

Even if it was a bad muffler gasket, a properly-proportioned mixed will burn itself out so no liquid exits at all. Either the mix ratio is like 25:1 or the carb is set WAY rich. My money is on the mix ratio.

OP, you mentioned you ran some new Stihl mix through it, but I didn't see a ratio. Can you clear that up for us?

 

[nmurph]

Maybe it's me (or maybe it's Maybelline), but I can't see a ring on that piston.

 

[Jacob J.]

Maybe it's me (or maybe it's Maybelline), but I can't see a ring on that piston.

I see a ring, but all of the 361 pistons I've seen had two ring grooves?

 

[z71mike]

Maybe it's me (or maybe it's Maybelline), but I can't see a ring on that piston.

oh **** i didn't even notice that

 

[nmurph]

I see a ring, but all of the 361 pistons I've seen had two ring grooves?

I was thinking 361's had two rings. I still don't see a ring.

 

[nmurph]

I blew it up a few hundred percent and I'm reasonably certain there is not a ring in that piston.

 

[WACutter]

Even if it was a bad muffler gasket, a properly-proportioned mixed will burn itself out so no liquid exits at all. Either the mix ratio is like 25:1 or the carb is set WAY rich. My money is on the mix ratio.

OP, you mentioned you ran some new Stihl mix through it, but I didn't see a ratio. Can you clear that up for us?

I used the Stihl Moto Mix in a can which is 92 non ethanol gas premixed at 50:1 with Stihl synthetic ultra. I use this in my trimmers every now and then.

 

[WACutter]

I blew it up a few hundred percent and I'm reasonably certain there is not a ring in that piston.

I ran out to take a look, and yes it has two rings intact. You are right though; it looks like it is missing a ring in the picture.

Refinishing the muffler now....and if I get off of work in time will put it back together tomorrow night and fire it up.

Btw, two of the screws near the clutch were not completely tight, so I torqued them down a bit.

 

[z71mike]

This is getting interesting. Good mix. Good rings (hopefully). Hmmmmmm.

 

[WACutter]

Resolved!

Ok, I put it back together, fired it up and tuned it. It was actually a bit lean. I only had time to run it for around 10 minutes, but it looks like the oil leak has disappeared.

What I did:

1) Tighten case bolts (they were pretty tight already).
2) Remove, refinish, and reinstall muffler correctly with Loctite on bolts. I painted the muffler and baked it in the oven; it was smoking like a chimney. The wife was pretty unhappy!
3) Tighten bolts around clutch/oil pump assembly (these were slightly loose, and the likely culprit).
4) Used all fresh Stihl premix and fresh bar oil.

It's running like a champ.

Thanks for everyone's help.

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