026 build running a bit lackluster

[NateSaw]

@Mastermind ,@drf256 ...
Am I visualizing this right? :
Is the goal with later exhaust timing to have a more productive power stroke? And the lower blow down... I picture better scavenging... Gasses flowing out of the cylinder are at a higher velocity when the uppers open, perhaps drawing on them harder? (keep in mind I'm not imagining a vacuum). Is it that there is an offset (in theory) of pressures between the jug and the case, and that what I'm trying to catch is when it's in flavor of the case? Bear with me fellas. I'm the mind of an inquiring child. I want to understand! This way I can apply to other builds.

 

[drf256]

The exhaust.

You want to vent it before cylinder pressure is too low, but not before you use all the pressure you can. You also want the most fully charged swept volume possible before you close the roof off.

The transfers.

You want them open early enough to fill as much of the cylinder as possible. Open too early and they will backstuff with exhaust. Open too late and you’ll get less charge and less loop scavenging.

If you have more case pressure, you can open earlier. A wide exhaust with a generous muff mod will allow for earlier effective opening.

It all has to work together. What sounds like it will work in theory doesn’t necessarily hold true in the real world. There are some basic rules that we all follow, and then we fine tune from there. A lot of it is experimentation. All of the events that occur in the cylinder are interrelated to each other. I’ve seen saws with beautiful porting that wouldn’t rev higher than 12k unless the muffler was closed off more. Try to figure that one out.

Again, there are some general rules, but they don’t work perfectly in every application. I hope I explained correctly.

Easiest to try to think of each event separately and later on, all together.

 

[NateSaw]

The exhaust.

You want to vent it before cylinder pressure is too low, but not before you use all the pressure you can. You also want the most fully charged swept volume possible before you close the roof off.

The transfers.

You want them open early enough to fill as much of the cylinder as possible. Open too early and they will backstuff with exhaust. Open too late and you’ll get less charge and less loop scavenging.

If you have more case pressure, you can open earlier. A wide exhaust with a generous muff mod will allow for earlier effective opening.

It all has to work together. What sounds like it will work in theory doesn’t necessarily hold true in the real world. There are some basic rules that we all follow, and then we fine tune from there. A lot of it is experimentation. All of the events that occur in the cylinder are interrelated to each other. I’ve seen saws with beautiful porting that wouldn’t rev higher than 12k unless the muffler was closed off more. Try to figure that one out.

Again, there are some general rules, but they don’t work perfectly in every application. I hope I explained correctly.

Easiest to try to think of each event separately and later on, all together.

This is great stuff... I'm feeling less and less like I'm adrift.. So I just took the timing numbers again. As expected from my last decking/squishing (lol). Every thing retarded one degree.
101
127
72
I'm going to try and raise the uppers to 120,keep em nice and flat/straight. I'll widen and taper slightly on the intake side. It appears I have a step in the top of the intake flange still, so I'll match that out to the boot. And in theorizing I should open the intake a bit sooner, say to 74btdc. I'm all for taking nibbles. Then seeing what gives. If I wait to lower the jug again, I still can lol. As always, your thoughts are much appreciated!

 

[Mastermind]

This is great stuff... I'm feeling less and less like I'm adrift.. So I just took the timing numbers again. As expected from my last decking/squishing (lol). Every thing retarded one degree.
101
127
72
I'm going to try and raise the uppers to 120,keep em nice and flat/straight. I'll widen and taper slightly on the intake side. It appears I have a step in the top of the intake flange still, so I'll match that out to the boot. And in theorizing I should open the intake a bit sooner, say to 74btdc. I'm all for taking nibbles. Then seeing what gives. If I wait to lower the jug again, I still can lol. As always, your thoughts are much appreciated!

The 101 ex is too high for a 50cc saw in my opinion. It's not an easy thing to get it a lot lower on an 026 though. In that era, Stilh made a lot of saws with the ex too high. 105, 122, 75 would be a great place to be....but since you are at 101, then I'd follow your plan to go up to 120 on the transfers.

 

[NateSaw]

The 101 ex is too high for a 50cc saw in my opinion. It's not an easy thing to get it a lot lower on an 026 though. In that era, Stilh made a lot of saws with the ex too high. 105, 122, 75 would be a great place to be....but since you are at 101, then I'd follow your plan to go up to 120 on the transfers.

Then I need to bite the bullet and drop the jug... Sans lathe. That'll almost cure the high exhaust roof and late intake in one fell swoop. And it seem I have more grinding to do than my cutoff wheel method will support. Taking the blowdown to 15 degrees I'm afraid mean raising the uppers quite a bit. 90 handpeice on the way!

 

[NateSaw]

The piston is traveling the fastest per degree of crank angle at the middle of its stroke, no? I'm I retarded in visualizing also, more stroke per degree in that range? I'm thinking small adjustments to the upper = greater degree in timing change, versus intake opening time, due to piston travel per degree being less at the top and bottom of stroke... Or am I just complicating a fart here....?

 

[NateSaw]

Based on what you fellas are teaching me, this thing woke up after I set the squish and decked the base, more because the timing was heading the right way, than because the compression went up....

 

[NateSaw]

Can you see the smoke pouring from my ears?

 

[Mastermind]

The piston is traveling the fastest per degree of crank angle at the middle of its stroke, no? I'm I retarded in visualizing also, more stroke per degree in that range? I'm thinking small adjustments to the upper = greater degree in timing change, versus intake opening time, due to piston travel per degree being less at the top and bottom of stroke... Or am I just complicating a fart here....?

Exactly.

Based on what you fellas are teaching me, this thing woke up after I set the squish and decked the base, more because the timing was heading the right way, than because the compression went up....

Right again.

 

[Mastermind]

This might help you with landing on your desired numbers in the future.

 

[NateSaw]

This might help you with landing on your desired numbers in the future.

So simple, yet genius. Thank you! So... I already sanded 10k off the deck. My numbers didn't change. I reset the wheel twice to make sure. I'm guessing I have to take somewhere in the neighborhood of 40k of the base to get close... Man I need a lathe setup.

 

[huskihl]

@huskihl , I have to test this, but what you were saying is spot on... The more I looked at the physics of those dogs, the more clear it was to me that the moment the chain pulled in that bottom dog, the harder it tried to pivot the saw down into the woods. So I raised that dog and shortened them all. Really, I'd be wise to, as you pointed out, start the chain in the wood till the bar is deep enough to engage the center dog, then let it pull in. The fulcrum of the center dog is now slightly above the chain curf. That lower dog will be useless until/if I get more power out of this thing. I'd have raised it further, but alas, the chain catcher is running out of room lol.

It’s just an 026, though. You’re probably only running a 16-20”bar. With your chain set up properly, you shouldn’t really be dogging in anyway.

 

[NateSaw]

It’s just an 026, though. You’re probably only running a 16-20”bar. With your chain set up properly, you shouldn’t really be dogging in anyway.

20" with an Oregon 22lpx full chisel. I use the dogs when bucking and sometimes limbing. I clean up a lot of trees with thick rotted bark and cambium.

 

[NateSaw]

024 with 44mm jug and 044 carb.
View attachment 369711

Sound like you’re getting it.

There‘s always a balance. Like Moobs said, no “wrong” way. Kevin is trying to say that your uppers/lowers might work if you used your engine for an airplane and ran it at 20k. You lowered case pressure, have too much blowdown and your uppers lack direction.

Bigger isn’t always better. Think of the transfers as a garden hose spraying water (charge) into your cylinder. Now imagine you want to wash your car. If you try to use the hose with no nozzle it flows more water overall, right? Would you wash your car with it with no nozzle (why not, it flows more water)? You‘ll use a different nozzle setting to spray a car off vs filling a bucket vs shooting a spray the furthest distance. See where I am going here?

Buy a meteor piston for your oem 44mm jug. You should be able to find an oem 44mm jug here for pretty cheap. I have used pistons here if you wanna go that way.

There is more than one way to skin a cat. For an 026, I use Treemonkey’s recipe. I cut the band flat, cut the piston dome flat, and time it at 105/120/78.

Here's where I am:
I was able to sand 030 off the base and get to 103 exh. I used Randy's method to hit 120 on the transfers using a dremel cutoff wheel. Doesn't look horrible but I know it's not ideal. I need to take around 031 from the piston/squish. The sandpaper method is a joke for this much material. I also learned the hard way I need to chamfer the barrel to avoid catching the nikasil, which I did and it peeled. I used a diamond burr to chamfer the boogers but now I am less than confident that hyway nikasil has good adhesion to the jug. I made a profile gauge, and I COULD take all 031 off the piston using a lathe. It would lighten the piston quite a bit, however, it would put the compression ring close to the top like a dykes type . So my options... My oem 44 jug is very glazed... The way that one failed was the piston smacked the lip in the squish crushing the ring lands, and it was run that way long enough to eat the skirt on the exh side.
Option 1:
Push forth with what I have, cut the piston to get my squish. Bite fingernails for rest of builds life worrying about nikasil coming off and tearing up the bottom end.
Option 2:
Buy a meteor piston for the 44, and a proper hone. Still, without a fixture, cutting the squish flat is not feasible, so I'd be taking off the piston... Also, biting my nails due to cylinder wear from previous piston damage.
Option 3:
What do you guys think about meteor cylinders? I buy the whole kit, start from scratch, but still have no reasonable means to cut the squish...
I'm excited to do this right. Anyone have a lathe fixture for sale?
At the end of all this, this will be the most expensive 026 I could have bought in to lol.

 

[drf256]

If you cut your piston crown, your exhaust will open higher. You’ll defeat the sanding you did on the base.

 

[redline4]

There is, or was, a lathe posted in the for sale section here.

 

[Mastermind]

Option 4:

Make a request for a used cylinder on OPE forum. Then send the piston and cylinder to me to have the piston crown, and squish band cut flat.

 

[NateSaw]

If you cut your piston crown, your exhaust will open higher. You’ll defeat the sanding you did on the base.

I'm dull. Yes, just like cutting the skirt to advance the intake timing. With you fellas I'd be cornering myself with dyslexia lol.

 

[NateSaw]

Option 4:

Make a request for a used cylinder on OPE forum. Then send the piston and cylinder to me to have the piston crown, and squish band cut flat.

Randy, can I dm you?

 

[NateSaw]

There is, or was, a lathe posted in the for sale section here.

Thank you Ed!