Stihl 039 muffler mod

[Brewz]

Hi Folks

First post........ but I have been lurking for a while and decided to join up.

My 039 never really felt like I ran like it should.
It used a lot of fuel and would stall in the cut if I worked it too hard.
A bit of googling started bringing up threads here and I started looking into what could be done to improve performance.

I left the baffle alone and opened up the holes around the face of the muffler outlet.




I borrowed a tachometer from a friend and after a lot of reading and you-tubing, had a go at a carb re-tune this morning before I started to cut.

I let the saw warm up and adjusted Idle to 2700 RPM
I opened up the throttle and the saw was running at 10900 RPM. Leaned it out and brought it back to the rough till it just 4 stroked and gave me 12500 RPM

WOW....... its a different saw!

Throttle response is much better, It ran cooler, used less fuel, was not any noisier, and fell through foot thick eucalyptus like it was butter.
A nice 4 stroke burble in the cut, and no more stalling under load.

I am a happy man!

 

[Brewz]

And just for the hell of it....... the saw

 

[Jimbo209]

Welcome aboard from Perth Brewz
great result with that saw, where are you down under

 

[Brewz]

Welcome aboard from Perth Brewz
great result with that saw, where are you down under

I am on the other side
Hunter valley, NSW

 

[farmerward]

Nice saw, how many inch bar is that hanging off it?


Sent from my iPad using Tapatalk

 

[Brewz]

Its a 20" bar and I use Oregon full chisel 3/8 chain on it.
The tree shown above was as hard as nails. Once I got through the smaller forks I bolted on a 30" bar (pic below) to buck out the main trunk that was about 30" thick. It was even harder and would dull the chain to the point of smoke on the 3rd cut. Chain was Oregon semi chisel 3/8 chain
In its previous form before the mod, it did it, but only just. If I asked it to dig in it just slowed or stalled. It was slow going but fantastic burning wood which made almost zero ash.
As you can see, the bar made the saw front heavy and it would fall on its tip........ way out of balance


I have since bought an 066 Magnum to take care of this big stuff as I just don't want to kill the 039 by asking to much of it.
Since i have upped the 039's go go button, I cant wait to put it up against the 066 Magnum in a head to head timed race through a bit of wood.

Here is a question i have........... The spark screen!
It is fine and looks restrictive.
I have ordered some slightly courser less restrictive SS mesh to replace the stock screens in both the 039 and the dual port on the 066.

Does the screen have to be super fine to stop the risk of a spark?

 

[Stihlofadeal64]

You should receive better gains if you perforate the baffle face. Not sure you're getting the max out of it as is because the cover plate may be restricting your flow on the obround slots. I'd put a single 5/16" hole in the front or opt for a few 1/4 inch holes and retune it. Ditch the screen, and trim your cover plate back a bit. There are plenty of muffler mod pictures here with various ideas if you try a search. Others may chime in.

 

[Stihlofadeal64]

http://www.arboristsite.com/community/threads/porting-a-hutzl-stihl-039-cylinder.277638/page-2

muffler mod pics in this thread as well.

 

[Brewz]

Yeah.... everything I read said to drill or remove the baffle, but I didn't want to take it all the way on the first go and find it was a nightmare to tune or use.
You cant believe everything you see on the net!
I have a 2nd brand new aftermarket muffler so I might give that the full works.
I keep looking at that face plate on the muffler thinking it can be done sooooo much better.
The other option I have considered is fitting a bit of 1/2" pipe to the side of the muffler body to point the hot gas out the side safely.

The other thing I have read is that one larger hole offers less resistance than multiple smaller holes, hence why I slotted. I'm no expert though, but geez it made a difference!

Plan is:
Drill the new muffler as per the linked images..... it looks good to me.
Only thing I plan to change is to drill one 1/2" hole in the baffle center, and then using the 1/2 drill bit in the hole, angle the hole to vent the gas in the direction of the outlet. Same with all the smaller holes. Curved directional holes can only help.
Then the fave plate...... thinking of opening up the hole to a nice round and also cutting some fine slots longways in the raised leadup to the exit hole, and open them up to be small round directional holes, pointing the gas in the same direction as the main exit.
Them maybe a 1/2" vent pipe on the side of the muffler body to reduce pressure and gas flow through the front, but it will be only if deemed needed, and I doubt I will need it.

 

[Jimbo209]

Its a 20" bar and I use Oregon full chisel 3/8 chain on it.
The tree shown above was as hard as nails. Once I got through the smaller forks I bolted on a 30" bar (pic below) to buck out the main trunk that was about 30" thick. It was even harder and would dull the chain to the point of smoke on the 3rd cut. Chain was Oregon semi chisel 3/8 chain
In its previous form before the mod, it did it, but only just. If I asked it to dig in it just slowed or stalled. It was slow going but fantastic burning wood which made almost zero ash.
As you can see, the bar made the saw front heavy and it would fall on its tip........ way out of balance
View attachment 451773

I have since bought an 066 Magnum to take care of this big stuff as I just don't want to kill the 039 by asking to much of it.
Since i have upped the 039's go go button, I cant wait to put it up against the 066 Magnum in a head to head timed race through a bit of wood.

Here is a question i have........... The spark screen!
It is fine and looks restrictive.
I have ordered some slightly courser less restrictive SS mesh to replace the stock screens in both the 039 and the dual port on the 066.

Does the screen have to be super fine to stop the risk of a spark?

I saw it mentioned in another thread here, something about its carbon bits and pieces that haven't fully burnt and they had some bigger mesh. Might have been a build thread for one of the secondary builders with a custom light bar.......

 

[anlrolfe]

This one is opened up under the deflector almost exactly as you have done.
The screen is OEM but as you can see the outer deflector is opened a bit more.

 

[Brewz]

I am avoiding opening up the front deflector as above due to the heat and dry dusty nature of a lot of the wood I cut. Just look at the nature of the bark in the pictures I posted above.
I often cut in food deep long dry grass and really want to avoid pointing hot gas at the timber.
Here is what I have done tonight.
I drilled a hole just under half inch in the center of the baffle depression, and opened up the 4 smaller holes on the baffled section.
I then used slightly smaller drill bits than the size of the drilled holes to bend the holes creating directional ports to get the gas moving in the general direction of the exhaust exit.
I figured if the gas has to hit the front deflector at 90 deg and change direction, it is added restriction. getting it moving in the general direction of the exit can only be better.
I then opened up the outlet on the aftermarket front deflector plate by about 50%, rounding it to smooth exit gas passage.

Cant start it up now as the kids have gone to bed, but I cant wait to see how it sounds

Question, does anyone know a good source of small aftermarket deflectors that can be used to screw onto the muffler?
Edit: Not to replace the muffler deflector, I am thinking more to screw onto the side of the muffler body to cover a hole made in the side