Stihl 026 rebuild

[MattG]

My only view on the chinese parts affair - I bought a cheapo carb for my 200t. It was horrid. Cost 20 english pound. It'd start cold, but once hot I could not tune it or restart it very easily. Eventually I bite the bullet and bought the pricey stihl one. Which of course just works ....

 

[MattG]

Hey Brewz

Have you thought of just dismantling the clutch and giving all the moving parts a good clean? Perhaps there's some gum in the mechanism?

 

[Brewz]

mmm

The clutch looks good but the sprocket drum is quite worn.
I will replace the sprocket first and see how it goes.
If I still get slip I will replace the clutch.

 

[Brewz]

Hey Brewz

Have you thought of just dismantling the clutch and giving all the moving parts a good clean? Perhaps there's some gum in the mechanism?

Yeah will do that now...... it cant hurt!

 

[Terry Syd]

Maybe you can try your Dad's clutch and see if it holds any better. If not, then I think your carb mod has done more than you expected. - (I wonder how much an o39 metering spring costs?)

If the torque is now too much for the clutch, then the only thing I could recommend is to raise the cutting speed. A centrifugal clutch holds better at higher rotation speeds.

 

[13TreeWorks]

I have a who knows no name china clutch on my ms361 no complaints there fit and works good also I had a forester clutch for my ms390 ( probibally chinese also ) so i could have the same drum rim sprocket and bearing as my other saws.... was not happy it said large rim it was a goofey sized rim and had no bearing with it probibally be ordering one for my 440 shortly as that ones shoes are starting to " ramp " I'll go chinese again because I beat the clutch on the 361 pretty hard with no issues. it was dirt cheap and there easy enough to replace if there is a problem

Jesse

 

[Brewz]

Well maybe and maybe not.
It did run like a little torque monster, smashing through hardwood at speed, but I couldn't test what it did under a lot of load as it just slipped.

Pics of the inside of the sprocket and of the clutch face are below. The sprocket actually has a groove in it which is why I have a replacement ordered. I did order a new one initially but it showed up as the lower older 026 sprocket and didn't fit.
I had the same issue with my 039 when I got it. It would pulse in the cut, slip, grab, slip, grab, slip, grab.
I replaced the sprocker and it still slipped though not as bad. The clutch had the same shiny uneven wear marks on it.
A new clutch and it has never slipped since, even running a 30" bar.

I think I will just order a new Stihl clutch and be done with it.
I have a feeling once I get some grip in the clutch, this thing is going to be a little beast.

When the clutch grips, I will do some comparisons with the springs in the carb

 

[Brewz]

Now..... back to the carb.

Terry, you said increasing the tension of the metering spring changes the fuel curve of the L circuit. I incorrectly thought it was the H circuit it controlled.

So, in theory, with the stiffer spring I have made the L circuit richer without flooding the saw from idle as it accelerates. This should give me more fuel in the cut once I already have revs up, but keep things leaner down low to give good throttle response?

To be able to modify accurately, one must first understand accurately, and I am getting there.

keep the fine tuning coming Terry.

Cheers

 

[13TreeWorks]

I would be more concerned with the " witness marks " on the side of the shoes those will tell you how worn the clutch is or if there " ramping " if the clutch shoe shows more wear on the leading edge then under load the shoe is tipping back causing uneven contact pressure also means the shoes are worn on the hub as that's what holds them true let them wear to far and they blow up..... My 440 looks similar but still grabs fine with a 24" bar also look at the springs to see if there worn into the shoes another good indicator of the condition of the clutch ..... If your worried about the shiny spots on those shoes scuff it with some emery cloth see if that gets your grip back untill the new parts come cone in

Jesse

 

[Brewz]

Yeah i tried the emery scuffing on the 039 and it did bugger all.

Looking at the cheap units on Ebay, I just get a bad feeling. All the cheap chainsaw parts I have tried this far have a higher fail rate than win, and then they were a win it was only just.
You get what you pay for.

I think with the extra power this puppy will have warrants a bit of extra cash for an OEM clutch.

 

[drf255]

Those clutches and covers are a dime a dozen here mate.

If you bite the bullet and buy some covers from here, have the seller throw a few clutches in the flare rate box.

BTW, great job on the build. Not being able to use it right now must be killing you. It would kill me.

 

[13TreeWorks]

" did bugger all " ...... Is that code word for it worked or failed or was a cob job ?? ..... I agree with the china parts im not a fan of the them either and there's a lot i flat refuse to try but the clutches worked well for me so far I noodled out 2 good sized trees with the 361 with no issues ..... That being said all the knockoff parts work great for some ppl .... Different standards for what constitutes " opinion of quality " is my guess .......

Jesse

 

[Brewz]

"did bugger all" is Australian for "failed to operate" ,"did not work","would not start"

But as we say..... She'll be right cobber!

Not worrying me too much at this stage. I cant access the tree's that need cutting due to all the rain and having just ordered a 42" bar for my 066 to cut up a lot of 4' thick timber, I plan to concentrate on cutting this up, and this will also give me some nice big bits of timber I can use to do testing on the 026 when I get it home.

Once I have the big bits home, I will be able to make some uniform slabs to bury the bar and test cut speeds.

Its going to take a few weeks to get happening but will be worth the wait.

I really enjoyed spinning it up in some timber for a half dozen cuts today.
Short but sweet.
The motor is VERY strong and the aim of the day was to find out if there was a weak point.

I am fairly confident this little saw will make my 64cc saw all but obsolete, it shows that much promise!

 

[Terry Syd]

So, in theory, with the stiffer spring I have made the L circuit richer without flooding the saw from idle as it accelerates. This should give me more fuel in the cut once I already have revs up, but keep things leaner down low to give good throttle response?

Yep, you got it. (although the stiffer spring did not make the L circuit richer, you did that with the needle)

The whole ramping in of the low speed circuit is much more complex in boat and kart racing. Take a boat or kart coming out of a turn, the fuel mixture has to be spot on to give the best acceleration out of the turn as the throttle is opened. However, in chainsaws we have a lot more leeway - just hit the throttle, get the revs up and start cutting.

The biggest concern is getting the flow rates for both the low and high speed circuits working to give the best fuel mixture for the revs. If it bogs a bit off of idle, so what? It is what the saw will do in the cut that counts. (having said that, I do like a crisp throttle response)

 

[13TreeWorks]

Right i need the Aussie urban dictionary ...... I'm anxious allreaddy ..... Waiting to see how it turns out before I dig into mine lol ...... I think that makes you ginny pig for the carb tinkerings

Jesse

 

[Brewz]

Thanks Terry...... I am content I now have an more accurate understanding of how the fuel is delivered.
I am still not 100% on how the H circuit works though

Jesse, You dont need a dictionary....... just apply the term "She'll be right" to any issue you have in life and you may make it as an Aussie!

 

[Terry Syd]

I should add that having a good throttle response is desirable when you stop the saw buried in the cut and you have to get the saw cutting again. For example, if you are working a back cut and stop to check the hinge, being able to get the saw cutting again from a dead stop without moving the saw is a desirable trait in a saw.

Get the low and high speed circuits working at the right flow, then worry about getting the best throttle response. If you go back to the '7900 carb upgrade' thread, you will see Rich and I joking about how anal we get about throttle response. We both liked a 'light switch' type response. Once you know you can get that kind of response, you tend to tweak the carb to get it.

 

[MattG]

The clutch looks good but the sprocket drum is quite worn.
I will replace the sprocket first and see how it goes.
If I still get slip I will replace the clutch.

Sorry, I missed the earlier discussion, (out sawing and splitting logs), but yeah, I agree. Change the cheaper stuff first (i.e. the drum). See how that works first.

 

[Brewz]

I had a better look at the clutch and have decided to replace it. The 3 shoes rock back and forth more than I am happy with. I recon its right proper stuffed!

I have ordered a cheap AM clutch to see how it goes. We are back to a single income so times are a tad tough....er.
I got it from a local supplier via Ebay so if there is a problem, I can send it back. Fingers crossed!

I was thinking about how the saw went today. I remember on the first cut, when the clutch and sprocket were still cool, it gripped well and really dragged me and the saw into the cut. I was a tad shocked at the power.
It then got worse and worse each cut as it got hotter and hotter.
After half dozen cuts, It suddenly felt like the chain was blunt, with a much slower cut and any downward pressure resulted in the chain stopping with the saw carrying on as normal.

I am busting to get it loaded up with a new clutch and sprocket and see what it will do.

Terry, is the carb H circuit controlled only by the H screw/needle on the side of the carb?

 

[Terry Syd]

Sorry Brewz, I didn't see your question about the H screw. In most cases, yes, the H screw controls the flow to the main discharge nozzle.

However, there are variations of carbs that have an auxiliary jet to add additional flow to the High speed (venturi) circuit. You ran into that on the 039 when you had to remove the auxiliary jet and plug it with GB Weld. On some carbs the back of the main discharge nozzle has a jet drilled in it. Rich had to block several of those on the Zama carbs he was building.