Stihl 026 rebuild

[Brewz]

Thanks mate, as always really appreciate your input and knowledge.
I have been looking at my 066 Magnum recently thinking..... Mmmmmmm, I wonder what I can do with that carb, but that's for another thread.

I have been putting a lot of thought into the perfect bar and chain for this saw. I just cant seem to decide.
At times I cut clean green timber and in this situation the .325 chain is going to shine, but quite often (more often than not in blown down eucalyptus), the center of the wood is full of rot and/or termites and this has proven to take its toll on the .325 chain faster than it does on 3/8. It is often like a core of wet dirt that can be from 1" to 1' thick and is hard on chains

I am thinking that I already have a 16" .325 bar with 2 chains, I might get a 16" 3/8 bar and run semi chisel chain on it.

That way I can switch between the 2 depending on what I am cutting.

I also plan to get the gear to make my own loops soon, so its more cost effective running everything on 3/8 063 chain.

Thoughts?

 

[Terry Syd]

Well, considering you have an issue with the clutch that needs to be resolved, if the existing torque causes a good clutch to slip with 3/8s, then going to a chain with less resistance in the wood may be an answer.

I remember a bloke on AS about 5 years ago that liked 3/8s on his saw because it 'pulled' better. It didn't cut any faster than his .325 chain, but he liked the way it pulled the saw into the wood. I think what he was noticing was the bigger cutters giving more resistance as it moved through the wood.

I go back to my earlier comments about NK chain. A standard .325 chain has cutters that are 1.25mm thick. The NK chain cutters are only 1mm thick. Think about driving a wood chisel into a piece of wood, a thicker chisel takes more effort to drive it into the wood than a thin chisel. Most people think NK chain cuts faster because it has a slightly narrower kerf, but I expect that the real reason is the thinner cutter.

As far as longevity, the NK VP95 chain has exactly the same curvature on the corner as standard .325. The chrome thickness is also the same. In other words, it wears at the same rate as the standard .325 Oregon semi-chisel.

If that clutch won't hold the torque you are either going to have to raise the cutting speed of the engine with some mods (the torque will be the same, it will just be at a higher RPM) or you will have to decrease the resistance of the chain in the wood.

You also may be able to mod the clutch by increasing the mass of the shoes. If you've got access to a welder you could weld some extra material on the shoes.

 

[Brewz]

Na I recon a new clutch and sprocket will grip. The old ones were very worn.
Where do you get the NC chain and bars from?
I have done some looking and they dont seem to be common.

How does the thinner cutter go in dirty rotten centered wood?

 

[Terry Syd]

I got mine from Bailey's. I noticed they have various lengths up to 20" in NK for Stihls.

Even on my NK stumping chain with the cutters filed all the way back to the witness marks, I still have all the cutters on the chain. Of course, just like on any chain, if you hit dirt with them the edge will disappear real quick.

 

[Brewz]

I looked at buying some stuff from Bailey's recently but they don't accept international transactions and I have to "ring" them.
With the current exchange rate, that's not going to happen when i can get an Oregon bar and chain for under $95 AUS delivered in Australia

I guess for now, I dont need to buy a 3/8 bar for it as much as I would like one.
I will use the 16" .325 bar and burn the 2 chains I have and make a decision based on how it goes.

 

[Brewz]

Link to a very cool breakdown of the Walbro WT carbs

http://www.acresinternet.com/cscc.n...35294bc0259ec77888256e19001c6e30?OpenDocument

 

[drf255]

I'd personally stay with .325, but I don't cut the wood that you do there.

3/8 slows it down, 3/8 picco, that speeds yer up.

 

[Brewz]

Yeah I will stay with 325. Its the logical choice for the cutting I will be doing with it.

If i find dirty wood is killing the chain, I will just use the 066 with 404..... that chain can take a beating.

I got my new sprocket today and I have a new elcheapo aftermarket clutch on the way.
I also found an old but un-used OEM clutch on evilbay in the states for about what I paid for the aftermarket one, so I bought it as well for insurance.
Both clutches still cost me less than half what a new one would cost

Also got a text from the Stihl sho[p saying my chain catcher has arived

Its all coming together. Cant wait to run some timed cuts with a 7 and 8 pin sprocket and up against my dads stock saw.

 

[MattG]

Cant wait to run some timed cuts with a 7 and 8 pin sprocket and up against my dads stock saw.

Looking forward to your carburettion mods write-up!

 

[bikemike]

I got to say I'm happy with a 3/8 full chiz have put some thought into a 3/8 skip cause I have a 18 or 20 inch bar and a skip will help unload the drag and let rpms take over. They love to piss rev

 

[Brewz]

Speaking of the carb, I just went and fitted the new chain catcher and thought I would play with with the carb tuning with the heavy Spring fitted.

First I wound out the LA screw to get 3300 rpm at idle.
Then I tried to drop the rpm's back to 2800 by making the L circuit richer. Couldn't do it! With the heavy Spring, it will not supply enough fuel at idle to flood and stall the saw.
Also when I wind it lean, it does not gradually drop rpm as fuel flow decreases. It goes from idle to a lean stall in 1/8 of a turn.
This means I need to use the LA screw to set idle.

Now this has me thinking.

When I get it out bush next (I have to be reasonably considerate in suburbia with a fricken loud saw) I am going to see how much difference adjusting the L screw will make at WOT. If I can drop the rpm,s with more fuel from the L circuit to fine tune the WOT 4 stroke rps's, then that should let me tune the fuel ratio in the cut with the L circuit without changing idle speed.

 

[Brewz]

On the other hand, I am a bit concerned with the lack of adjust-ability at idle.

There is not much I can do to set the idle fuel to an optimal setting to get the best throttle response.

Throttle response is good but fine tuning is out the window compared to what you get with a lighter standard spring.

It will certainly make for some interesting testing.

 

[Terry Syd]

I see where you're going with this. Yeah, see if you need to increase the L circuit when you are out in the field to get the best powerband for cutting. If increasing the L circuit doesn't help with the performance, then you might consider cutting the spring back a bit so you can get more adjustment at idle (or find a slightly weaker spring).

That stronger spring is really holding the metering valve down on the seat. I've never run into an idle issue like yours before.

The pre-load on the spring acts similar to lowering the fuel level in a float bowl carburettor. It takes more 'suction' to get the fuel flowing, in other words, it makes the fuel mixture leaner.

 

[Brewz]

Yeah, I am thinking that the spring may be too stiff.
Further thought has me feeling it may end up hampering things like low down torque when getting the saw going again in the cut as the fuel delivery will likely be peaky

I might change the spring back to the standard spring and run the saw in with that.
As shown by others with a few 026 builds under their belts, they are strong saws with the stock carb.

When I have the saw fine tuned and have a good feel for what I can do, I may play with some spacers under the stock spring to stiffen it up a bit and see what happens.

Undies before pants, crawl before walk............

 

[Brewz]

Ok, stock spring is back in the WT-394
As soon as the WT-194 shows up from the states, I will pull them both apart and compare their internals.

As for the carb, I'd love to hear more on your theories on this. I set my carbs to the highest idle rpm, then richen until throttle bOg goes away. As for the H side, I set it so it just doesn't 4 stroke in the cut at intended bar pressures. I can get it overly rich easily that way. It's just richer when piss revving, but who cares.

Mate, may I ask you to elaborate of a couple of points from the above just so I fully understand what your talking about?
When you say you set the carb to the highest idle RPM then richen till bog goes away, I am interested in your method of achieving highest RPM and exactly what you mean by that. There is a great carb tuning vid on youtube where the bloke tunes an MS460 to 3300 rpm with the LA, leans it to get to max RPM's then dials back to 3300 RPM again with the LA. He then richens it out to 2800 rpm idle speed which is what I tried to do today.



I am interested in your tuning procedure details, and anyone else's, to add more knowledge to this thread !

Also, this being my first ported saw, and first saw under 64cc, I am having trouble working out when it starts to 4 stroke from the tone.
My other saws are easy to tell as there is a clear change in note from the high clean 2 stroke whine to when the rougher burble kicks in, but with the 026, it gets the high clean 2 stroke whine at between 15000 and 16000 RPM, and as I richen it out, the revs drop but I cant really detect that rough burble I am used to listening for.
What should I be listening for to indicate where I should set my WOT speed?

Lastly...... I have no idea what "piss revving" means

 

[drf255]

Not saying my way is right, just how I do it.

Piss revving is when you just rev with the bar and chain on, but not in wood. Pisses oil everywhere.

The way I do it, from what I was taught is this:

Set idle L screw (with brake off) to highest rpm. Wait a few seconds with each change. When I get the highest rpm, I lower the LA screw down till the chain is just barely spinning. Then I do it again.

There's no accelerator pump on these carbs, so unlike a carb on a car that has one, the mix will lean out initially when you hit the throttle. I richen the L mix just until all throttle hesitation goes away. Then I set the LA screw for the final time, to where the chain just stops moving.

For the H, tune it fat a few times and you'll hear it. Piss revving and in wood.

Go rich, start cutting. Turn the screw 1/32 at a time until the sound with bar down pressure is clean, but it's not clean when you pull the saw up in the cut.

Brad Snelling had a nice video here of tuning in wood. It's really the safest way to do it. I do all of my saws piss revving and then in wood. If you do it this way, and with the bar you'll be using and in the wood you'll be cutting and with the max pressure you'll be pushing with, the mix should be good enough without all the fancy carb mods you are attempting.

Don't get me wrong, I'm fascinated with what you guys are doing with the carbs. I just know I'd likeLy proud space a saw that ran worse.

 

[drf255]

Tuning in wood is the safest in general because a lot of newer saws have limited coils too.

The sound of a saw hitting the limiter and 4 stroking is supposed to be pretty hard to discern.

You won't hit the limiter in the cut.

 

[drf255]

Here's an 036 I did. Listen when I pull it up in the second cut. This is a dry red oak stump. About as hard as wood gets by me. Concrete.

 

[drf255]

Hear the "fat" sound when I'm piss revving it?

You will get it. They just start to get a musical muffled sound when they are tuned rich enough.

Takes a bit to get it.

 

[Brewz]

Yeah that vid clears a lot up

I hear the fat burble and how it cleans up in the cut.
That's what I will aim for.

I am trying to train myself to be able to tune correctly without needing a tacho as speeds are irrelevant.

That timber looks similar to what we have here. Hard as hell.
A lot of Eucalyptus cuts like that green.
I remember trying to cut into a very old dead bit of red Ironbark (several decades dead old) and it was so hard I had sparks coming from the chain after 3/4 of a cut in 20" timber so I gave up.
That was with my dads 026 years ago.
It needed 90cc's and 404 chain!