Piston wash patterns

[NightRogue]

I’ve seen interesting wash in the combustion chambers on a few saws too. Stock wash 395: View attachment 298870

This is a good example, and exactly the product of tongue wash. Proof of scavenging ends near plug, which should give max fuel economy. Low to none fuel escape out exhaust port

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[huskyboy]

This is a good example, and exactly the product of tongue wash. Proof of scavenging ends near plug, which should give max fuel economy. Low to none fuel escape out exhaust port

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Makes sense, I remember it being good on fuel for a 90cc saw when it was stock.

 

[huskihl]

Vertical flat angle should give more rpm and higher hp, slope should give more low end tq.

I’ve read this in the books also. I figured I was misunderstanding it.
Try raising just the edge of a saw’s transfers in a straight line back in to the existing swoop. And then after running it go back in and hog the ceiling out without raising the plating so that they blow flat across the piston dome and actually wash the crown off. It makes way more difference than 2-3° of timing difference. The former will rev much higher and not have nearly the felt torque as the latter

 

[huskyboy]

I’ve read this in the books also. I figured I was misunderstanding it.
Try raising just the edge of a saw’s transfers in a straight line back in to the existing swoop. And then after running it go back in and hog the ceiling out without raising the plating so that they blow flat across the piston dome and actually wash the crown off. It makes way more difference than 2-3° of timing difference. The former will rev much higher and not have nearly the felt torque as the latter

I flattened the roof on the transfers of a 572 in the process of porting it. Didn’t change the transfer timing at all, just the roof. It had “interesting” wash stock. Just a flat black piston top with no pattern. Saw gained a good amount of power and showed good wash after a gallon of gas. Was my results because of the flattening the transfer roof or the portwork? Or even opening the muffler to allow more efficient scavenging? Idk. I can’t prove anything. But with what you said it makes sense.

 

[huskyboy]

I do feel like a saw with removable transfer covers would be a great testing ground for a lot of these transfer theories. You can grind exactly the shape you want easily and quickly.

 

[huskihl]

I flattened the roof on the transfers of a 572 in the process of porting it. Didn’t change the transfer timing at all, just the roof. It had “interesting” wash stock. Just a flat black piston top with no pattern. Saw gained a good amount of power and showed good wash after a gallon of gas. Was my results because of the flattening the transfer roof or the portwork? Or even opening the muffler to allow more efficient scavenging? Idk. I can’t prove anything. But with what you said it makes sense.

This is only my opinion, but a 5 series only has about a half inch of roof even with the covers on. I think most of the charge blows hard to the intake and up just a little, regardless of what the roof does. I play with the angles in them trying to find a difference but I can’t really tell. The cylinders with wide swoop will show the differences more. Like a 365

 

[NightRogue]

I’ve read this in the books also. I figured I was misunderstanding it.
Try raising just the edge of a saw’s transfers in a straight line back in to the existing swoop. And then after running it go back in and hog the ceiling out without raising the plating so that they blow flat across the piston dome and actually wash the crown off. It makes way more difference than 2-3° of timing difference. The former will rev much higher and not have nearly the felt torque as the latter

If im following you right, in that particular subject. They called it effective port time/area, by making the roof flat you're actually giving more area while keeping everything else the same. So it should rev more and hold power at higher rpm

On the slope/angle transfer you mentioned 2 things can be happening, it revs almost the same but the power is developed at much lower rpm. Now some saws are generally designed to run at certain rpm, due to the intake/case volume/exhaust and etc being designed that way. Tweaking just the transfer angle might change the balance and cause the power being developed at rpms where the saw is not "comfortable", seems like huskies are often sensitive to this kinda approach.

So what you described is actually not wrong, you raised the transfer edge to get the angle/slope. Which means you've increased time but area doesn't get much, so it'll rev hard empty and deliver power at current or lower rpm under load. Also might feel boggy less power due to rpm change out of load to in load



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[Bjorn]

Huskihl say, I think most of the charge blows hard to the intake and up just a little, regardless of what the roof does.

The crankcase compression only reaches like 10 psi. If you think about the engine running at 50-250 revolutions per second or 3000-15000 rpm, think about how long the transfers are open for each stroke. If you have an air hose pressurized to 10 psi, and could open the gate for 1/50th of a second, and that is a full stroke of the engine at idle, how much air is coming out of that hose?
The only way these engines can pump efficiently is from the energy produced by the burning mix.
At first the expanding gases push the piston down, then as the exhaust opens and the gases hit the muffler can and expand, it created a pulling effect on the rest of the cylinder, vacuum. And a lot of it. So the transfers want to open just as the pressure is changing to a vacuum for the most efficiency.

After pondering this for a bit I see this as the only way to get enough transfer to run the engine. The crankcase compression combined with a vacuum on the other side means the transfer port sees a much greater differential than just 10 psi to atmosphere.

My question is does the transfers blow or the vacuum suck fuel from the transfers. Or is it a combination that i belive and others too?

 

[legdelimber]

A couple of pics from an Echo pb-500 blower.
These units are an interesting thing, But would need a separate thread to get into the intake tract and multiple reed locations though.

I Shot these images through the spark plug hole.
On the second image, I shot multiples and then found an image stitcher to put them into one broader view.

1st pic: Stock cylinder with base gasket delete. Unit actually lost around 900 rpm vs having the gasket in.
I thought it interesting that the "wash" pattern was actually located in front of the divider.

2nd pic: I made a little effort to get the transfers cleaned up and back above the piston top when at BDC.
Got the rpms back up to spec!
Didn't degree the ports, just looked at things, marked some lines and went with enough to get the transfers un-blocked and pointed to the combustion chamber & rear of cylinder, at first opening.

These pb-500 were notoriously lean tuned from factory (the Echo hallmark...)
Yes the piston is a bit "gooey" here.
I did a bit of carb tweaking back then, but still need to go back and get the mid-range fueling dialed down a bit.
Red Armour oil at 3.5oz to gal, in all of the pics.

 

[RI Chevy]

I have an ECHO PB500. It's ugly looking inside. Ready to blow at any given time...

 

[NightRogue]

Huskihl say, I think most of the charge blows hard to the intake and up just a little, regardless of what the roof does.

The crankcase compression only reaches like 10 psi. If you think about the engine running at 50-250 revolutions per second or 3000-15000 rpm, think about how long the transfers are open for each stroke. If you have an air hose pressurized to 10 psi, and could open the gate for 1/50th of a second, and that is a full stroke of the engine at idle, how much air is coming out of that hose?
The only way these engines can pump efficiently is from the energy produced by the burning mix.
At first the expanding gases push the piston down, then as the exhaust opens and the gases hit the muffler can and expand, it created a pulling effect on the rest of the cylinder, vacuum. And a lot of it. So the transfers want to open just as the pressure is changing to a vacuum for the most efficiency.

After pondering this for a bit I see this as the only way to get enough transfer to run the engine. The crankcase compression combined with a vacuum on the other side means the transfer port sees a much greater differential than just 10 psi to atmosphere.

My question is does the transfers blow or the vacuum suck fuel from the transfers. Or is it a combination that i belive and others too?

That is the answer to the million dollar question, you nailed it.

These days when i degree a saw/blower or whatever the first thing i see is CC and BD, CC is your positive pressure and BD is your negative pressure. Both this numbers work in a harmony, you can play with numbers by increasing/decreasing charge pressure and volume.

A friend called me up couple weeks ago and gave port timing on his 60cc dolmar, and without looking at his saw i told him your muffler is clogged. And he goes how the hell you know that?!

After studying variety of models and makes, I've came to a conclusion. This high CC and BD designs are actually to give fuel economy by keeping as much fuel as possible in and they clog the muffler up to give egr effect, thus it meets epa standard.

And when you muffler mod this type of engines without changing anything else, it tends to overshoot mix out into the muffler. On these designs muffler mod has to be very conservative unless you're grinding inside the cylinder to drop pressure.

That's why you have to consider everything else before modding, you want to drop CC and gain volume. It can be achieved by increasing intake timing and giving it some area, when you do that. You've decreased pressure and increased volume, that way it becomes less violent and moves more charge per revolution. Increasing charge saturation per stroke will increase power

For example ms880, it usually comes like this 98/122/65. CC is 57, BD is 24. When you port and go to something like 98/120/75, CC will be 45 and BD is 22, now charge will be moving in bigger volume and pressure lost will be recovered by muffler mod. Thus giving the saw more power, you'll lose a little fuel economy during idling and low rpm

 

[drf256]

This one makes me wonder if wash really means anything. It’s totally wrong and anyone would say, based on the wash pattern, that the saw is inefficient on fuel and should be a dog with no power. It’s the piston on the 036 I did for @dall . May not be the fastest but it runs damn well and isn’t terrible on fuel. Go figure.

 

[drf256]

See if anyone can guess the amount of BD in that jug and which side of the upper opens first. Both the intake and ex side of each upper and the PTO vs Fly side.

 

[MustangMike]

That was a darn good running saw ... why is it back in the shop???

ps I love the way my MOFO 360 runs!

 

[drf256]

That was a darn good running saw ... why is it back in the shop???

ps I love the way my MOFO 360 runs!

It isn’t in the shop. It came back because Dall was kind enough to let me uncork it and measure/mic the entire cylinder. It went right back together. Nothing is wrong with it.

 

[MustangMike]

Good to know, that was nice of him.

 

[MustangMike]

Pulled the cylinder on a near new 461 with a burned piston.

The plug looked like it had not even been used, but the whole top of the piston was black.

Called the owner (a tree guy) and told him it looked like he was running Stihl oil (which he was) and recommended he switch to Saber.

At least the cylinder is not bad and will clean up, so I ordered a meteor piston.

Will also mod the muffler and pull the carb limiters. That procedure seems to help these saws a lot!

 

[Wonkydonkey]

Plug could have been changed ? Could be the exhaust screen clogging it up (if there is one) Maybe change that 461 coil as well

 

[MustangMike]

Plug was not changed, he told me it was a fairly new saw.

With a stock saw (just muff modded) the stock coil usually does just fine.

 

[Ronie]

Echo 600p after about a 1/4 tank.