Porting stihl ms361

[t4driller]

I'm gonna port my 361. I'm the second owner of this saw and doesn't have alot of use. This is the saw that led me to find all of you and one that I probably will never sell.

lastnight I took it all apart and got some numbers in stock form.

I came up with..
Ex 104
Trans 132
Intake 74
Squish. .024
I checked the numbers a couple times and got the same results. Didn't think the intake would be that low. Do these numbers seem right?? I'm not asking for numbers, I want to do some research and try to come up with my own game plan. But I'm sure I will be asking for some help eventually though. This is probably gonna take me a while to do also, as I'll work on it when time allows.

The one question I do have is.. I noticed for the first time on the muffler there's a little hole where exhaust comes out and a metal tab that can be pulled in and out. What is this for and does it do anything?

I also have a AM cylinder kit from hlsupply that I was gonna port while doing the oem to try a couple different things on without messing up my oem jug. So this is the start, hoping it turns into a nice runner. [emoji4] [emoji4]

 

[huskihl]

That's the screen that pulls out. There's supposed to be a screw holding that tab in. If you're going to open the muffler, you'll probably need to split it. Decide if you're going to utilize spark screens. I gutted mine and relocated the screen a bit. And I added a 2nd port.

 

[t4driller]

There's no screw there. There's a 1/4 inch hole with that tab that slides in and out. Can not remove it. On the fw side I added another port awhile ago. I will probably have to open it up more once ported.

 

[Gunn]

That tab is the spark arrestor screen. The screw kept it from falling out. Yours is probably locked in by carbon build up. Grab some pliers, it'll work free.

 

[t4driller]

alot more carbon then I thought would be in it. When I first got it I ran stihl ultra, then switched to Benol at 40 to 1.

 

[Definitive Dave]

Ultra is bad
Benol is bad
I would avoid those two but not sure what to suggest.
I think there is an oil thread around here somewhere

 

[Chainsaw Jim]

Anything rated "FD" is a good oil to use. It must say fd or higher on the bottle.
My first thought when I saw the pic of the piston was Stihl ultra. I don't know all fd rated brands, but Husqvarna, shindaiwa, and echo are and Stihl is not. Stihl must have bought too much fb and refuses to discard it to replace it on the market with higher rated quality.

 

[mdavlee]

That looks like a lot of ultra build up.

You got this thing ported yet?

 

[t4driller]

That looks like a lot of ultra build up.

You got this thing ported yet?

Nope. Lol... need someone to cut chamber for me. But... the am cylinder with base gasket removed has the same port timing numbers as stock but the squish is at .018. The oem jug with base gasket removed , the piston hits thecylinder. I'll have to measure how much needs cut out of the squish band to get me to .020. So I might try the am jug first to see how it does.

As for the carbon buildup , I don't know what the previous owner ran in it. I ran a couple gallons of ultra then switched to Benol. I use to run Benol in my cr25p and 500 and really liked it.

 

[mdavlee]

That can be a problem. How thick is the base gasket .022"? What bore size is a 361?

Benol protects like crazy but needs heat to burn clean.

 

[Chainsaw Jim]

It sounds like the squish is right where it needs to be with the oem gasket. If I'm wrong then go through your house with a caliper in hand to find some paper with the perfect thickness. Usually the cover of a calendar is perfect.

 

[jmssaws]

I've never had benol look like that but it's exactly what ultra looks like.

Is it done yet?

 

[Jswanson]

I'm gonna port my 361. I'm the second owner of this saw and doesn't have alot of use. This is the saw that led me to find all of you and one that I probably will never sell.

lastnight I took it all apart and got some numbers in stock form.

I came up with..
Ex 104
Trans 132
Intake 74
Squish. .024
I checked the numbers a couple times and got the same results. Didn't think the intake would be that low. Do these numbers seem right?? I'm not asking for numbers, I want to do some research and try to come up with my own game plan. But I'm sure I will be asking for some help eventually though. This is probably gonna take me a while to do also, as I'll work on it when time allows.

The one question I do have is.. I noticed for the first time on the muffler there's a little hole where exhaust comes out and a metal tab that can be pulled in and out. What is this for and does it do anything?

I also have a AM cylinder kit from hlsupply that I was gonna port while doing the oem to try a couple different things on without messing up my oem jug. So this is the start, hoping it turns into a nice runner. [emoji4] [emoji4]

Combustion chamber and muffler pictures looks like benol usage to me.

 

[t4driller]

That can be a problem. How thick is the base gasket .022"? What bore size is a 361?

Benol protects like crazy but needs heat to burn clean.

Base gasket is .023, and bore size is 47mm. Comparing the 2 jugs, would the am be a little better? You stay with stock timing numbers but the squish is tighter. I know am cylinders don't run as good as oem generally but of I clean the aftermarket up and widen ports I think it would run good. So at this point I think I will find some kind of paper to make the oem cylinder squish a little tighter, widen/ smooth ports out, advance timing and gut muffler. Do the same for both cylinders and compare the 2. What you guys think??

 

[mdavlee]

You can do that. I'm going to guess the transfer tunnels are different sized in between them.

 

[t4driller]

this is the oem jug. There's alot of casting flaws in the transfers. I'm still debating what to do with the oem cylinder. For the AM cylinder I started grinding on it. The first thing I noticed, was that the aluminum seems softer. The burr cuts through it like butter. I'm shooting for.
Ex 100
Trans 127
Int 74
Squish .018

 

[mdavlee]

As long as the lining doesn't chip I'd try it. The composition there I've not got a clue how hard it should be.

 

[t4driller]

The lining looks ok. There's no pitting, or chips around the ports. The cross hatching isn't as good. But this is just for kicks and giggles. More of a learning experience on how it all works.

 

[drf256]

I don't like your numbers.

The AM may have thinner plating? That's why you're cutting through faster?

I've found that OEM KS jugs are a tougher material than Mahle. In fact, on the 026, I don't like KS.

What are your starting numbers on bothe jugs?

 

[paragonbuilder]

I don't like your numbers.

The AM may have thinner plating? That's why you're cutting through faster?

I've found that OEM KS jugs are a tougher material than Mahle. In fact, on the 026, I don't like KS.

What are your starting numbers on bothe jugs?

He said 104/132/74