MS361 blew up again

[poulson01]

I haven't checked it out yet. It's still in the cab of my truck because I'm too depressed to even look at it right now.
I was working on a couple of wild cherries this morning. I was using it on some oak last week and noticed that the rpm would hang for a second or two after a cut. I didn't get through one tank of gas today when it lost compression very suddenly. Stuck rings and scored piston pro'lly.
I was given a box 'o' 361 a couple weeks ago, with a bad rod bearing.
The P/C is decent. A chunk of needle bearing had gotten by the piston, scratching it and sticking the rings. The file on my Swiss Army knife happens to fit the ring groves perfectly and I cleaned it up. It'll be fine.

Before I waste it on MY saw, just to lean it out and kill it, what went wrong with mine?

I had the carb set rich enough to flood it on cold start and it still acted lean.
Like I said, the rpm would hang after a cut.
I changed the carb with no improvement.

Crank seals?
I checked the fuel line, carb boot and cylinder bolts. All look good.

I killed my old Homelite 360 in the same exact way and wound up eBaying it off.

 

[watsonr]

You have an air leak somewhere... find it before you tear it down and fix it, then replace the top end.

 

[Lank Thompson]

High speed jetting should have nothing to do with the starting of the saw. You must be lean on the high speed circuit. Did you use a tach to set it?

 

[jus2fat]

Yeppers..that 'hanging rev's' before going back to normal..you got an air leak.

J2F

 

[stihl for life]

try checking the crank seals on the clutch and flywheel side and also do a vac test to see where the air is coming/leaveing

 

[Philip Wheelock]

...I was using it on some oak last week and noticed that the rpm would hang for a second or two after a cut...

That means you're running lean due to an air leak.

 

[DexterDay]

X4 on the air leak.

Vac test and find the Original Problem. Otherwise it will continue on like the plague.

 

[poulson01]

Rainy days here.
My "box "O" 361 is cleaner (maybe newer) then my saw.
If it didn't need a crank and rod, I'd retire mine.
I would need to order bearings and seals either way so I'll bring mine in tomorrow.

 

[poulson01]

Never even got to really run it.
I bought it blown up. Unstuck the rings and did a couple jobs. Stuck the rings again.

Bought a big bore P/C and ported it. Ran it a few more times. Always was worried about an air leak but wasn't sure.
Killed it again. I was sure I had scratched up my new cylinder so, disgusted, I shelved it for two years.

Someone gave me another blown up 361 so I got motivated and took mine apart.
Turned out, the P/C was perfect. I (think I) set squish too tight and popped the two rear cylinder bolt heads right off. Put it back together and vroom!

The air leak was feeling pretty bad this time so I was going easy on it.
I was in the cut and it died, just like I hit the kill switch. Not even one full thank of fuel.:bang:

View attachment 298988View attachment 298989View attachment 298990

That's what we call "FOD".

 

[poulson01]

High speed jetting should have nothing to do with the starting of the saw. You must be lean on the high speed circuit. Did you use a tach to set it?

I had to fatten the low speed screw up a lot. It would hesitate as if lean.
It's an air leak for sure and it has gotten worse.

 

[ZeroJunk]

It takes a bad leak to make the RPM actually hang. You should be able to see it. Hole in the intake or spun the insert out of a seal maybe.

 

[Mad Professor]

So you pooched a new AM P/C because you did not do a vac/pressure test. LOL.....

1) Do a vac/pres test, fix what is pooched.

2) Find a OEM cyl, get a meteor piston, check piston and rings for fit. OR just buy OEM, better....

3) Tune the carb right , WITH the mix you run...

ENJOY making chips!!!

 

[tilenick]

I'll tell you the story of my ms-360 pro. I bought it for forty dollars in known blown up condition. I looked it over and after taking the cylinder off I decided that it needed a new one. I bought a new aftermarket piston and cylinder assembly (among other things. As it had itself been used as a parts saw.) then I ran it for a minute. It sounded funny. So I ran it next to my ms-361 and definantly sounded wrong. So I took it apart and I inspected it harder and it had a crack in one of the lobes of the crankshaft which caused it to rub on one side of the crankcase. I wound up buying a whole crank assembly on the bay and swapped all the parts over from the saw and it has seemed to run ok now for about twenty tanks to date . I don't know if this helps, but, it seems to me It is the progression of one Part leads to another and another and finally the only thing left is the tank handle assembly, chain brake, and the oil pump off the original saw.
P.s. Sorry about your ms 361. Iove mine.
Just my .02
Nick.

 

[poulson01]

So you pooched a new AM P/C because you did not do a vac/pressure test. LOL.....

1) Do a vac/pres test, fix what is pooched.

2) Find a OEM cyl, get a meteor piston, check piston and rings for fit. OR just buy OEM, better....

3) Tune the carb right , WITH the mix you run...

ENJOY making chips!!!

Laugh at a guy when he blows up his saw?
Anyway....no. It didn't blow up because of the leak. It obviously ate a wristpin clip. Everything was well lubed with no sign of overheating.

 

[SawTroll]

You have an air leak somewhere... find it before you tear it down and fix it, then replace the top end.

Yes, sounds like an air leak!

 

[poulson01]

I put it back together with the stock jug and piston from the other saw. I made a half hearted attempt at a leak down test. The only soap bubbles I made were around the muffler (not sealed very well) and the decompression valve.

I started the saw and it sounded pretty good.
I think my air leak might have been at the base gasket. I dunno. I'll tune it tomorrow but, for right now, it revs quick and four strokes at around 13k rpm.
I emailed a pic to Tammy at Bailey's. The circlip is still stuck in the cylinder, right where I found it. Maybe they can do something for me. I should have clipped the danglers off those circlips when I first put that piston in.