Part Three: The Transfer Ports

[Terry Syd]

Is that a picture of the 'someone' or the actual cylinder/piston?

 

[David Young]

Is that a picture of the 'someone' or the actual cylinder/piston?

I have seen that type of mod on saws. Normally not firewood saws. The pictures I have are not my work so without permission I prefer not to share terry.

 

[Terry Syd]

I understand David, no problem on sharing the pictures. As far as the mod, it would be interesting to see how some guys have done it.

It appears to me that not only would it be easier on the rings, but with less grinding on the jug the finger ports could be deeper without compromising the strength of the jug.

 

[Nutball]

I see what you mean now, great idea

 

[Wonkydonkey]

I don't like what I see above the exhaust port

That’s a factory made groove full of carbon, I believe it’s to help releave compression on starting.

 

[David Young]

I understand David, no problem on sharing the pictures. As far as the mod, it would be interesting to see how some guys have done it.

It appears to me that not only would it be easier on the rings, but with less grinding on the jug the finger ports could be deeper without compromising the strength of the jug.

Most chainsaw cylinders don’t have enough real estate

 

[Terry Syd]

Most chainsaw cylinders don’t have enough real estate

Yeah, I understand that the jugs need to be thin in order to keep the weight down. Sometimes you have to improvise, on my Husky 450 I had to grind out the back of the transfer covers and build them up with fiber glass and GB Weld in order to get the flow I wanted.

On a jug, a more vertical transfer port wouldn't weaken the structure as much and after the port was roughed in the surrounding area could be filled with GB Weld to build it up again.

A more vertical port would also assist the flow (like a rear boost port on a bike cylinder) as it directs the flow upwards along the back of the cylinder. A rear boost port is generally about 1mm lower than the side ports and at an upward angle of 50-70 degrees.

 

[Ketchup]

How about a lower transfer wall with cutouts? Is the triangular shape to increase flow to the outside of the transfer tunnel and then top of the upper port?

I think a lot of us scratch our head the first time we see these.

 

[Nutball]

I wonder if the decomp port on the exhaust could be filled with JB and if it would add a worth while compression increase, or if the decomp port is nearly invisible at high rpm? Unusually low stock compression in that saw. It's hard to say how much of it is from the decomp port.

I see the triangle port as either a vortex generator for better mixing and flow performance over a sharp angle. Similar devices involving triangles before control surfaces or right angle cerrations in the leading edge of a wing prevent the air flow from stalling and becoming turbulent. The vortex easily expands and follows sharp angles.

OR it could simply be a square port at an angle so it is inline with the normal flow direction for that spot in the case possibly caused by the crank motion.

 

[mettee]

Dolmar 7910...

Talk to me about staggering the transfer ports vs not. I've had suggestions both directions. Im a rookie but I wrapped my head around the porting theory a little bit.

I figured the stagger would continue to direct the charge up into the squish/combustion chamber better than having them flat.

But I'm also considering the timing and the charge going out the other side...

 

[huskihl]

Dolmar 7910...

Talk to me about staggering the transfer ports vs not. I've had suggestions both directions. Im a rookie but I wrapped my head around the porting theory a little bit.

I figured the stagger would continue to direct the charge up into the squish/combustion chamber better than having them flat.

But I'm also considering the timing and the charge going out the other side...

I always try opening the primaries first. 3 or 4° later, about the time the primary charge reaches the intake wall, the secondaries open and roll the leading edge of the charge up into a loop.

That's what I try for anyway...

 

[Nutball]

One could try 3 saws: normal, primary side high, and secondary high.

 

[mettee]

That's potentially a 300 buck science experiment...

 

[mettee]

I always try opening the primaries first. 3 or 4° later, about the time the primary charge reaches the intake wall, the secondaries open and roll the leading edge of the charge up into a loop.

That's what I try for anyway...

Thats along my chain of thought, but I really don't know.

 

[Redfin]

I always try opening the primaries first. 3 or 4° later, about the time the primary charge reaches the intake wall, the secondaries open and roll the leading edge of the charge up into a loop.

That's what I try for anyway...

This right here is why the quads are so much easier to get to run than the duals. Scavenge loop is key.

 

[Redfin]

Of course there are others that have way more experience that can up on the duals.

 

[huskihl]

Thats along my chain of thought, but I really don't know.

I've tried them every which way. This way seems to have a bit more torque, possibly at the cost of hp, and possibly not. I think you'd need to run the saw every day of the year to he able to tell much difference. It's the right way in my mind, so I roll with it

 

[huskihl]

Of course there are others that have way more experience that can up on the duals.

Gotta hold your tongue just right in the corner of your mouth to picture it and do it on duals, lol

 

[mettee]

I'm gonna try and draw it out later so we can see it

 

[Stump Shot]

Like to concentrate the most effort here, when, how long and where the transfers are directing the fuel/air charge are all worth exploring.
When washing the last of the JMS particles out in the zink, I like to run water through the transfers to see how they look. Two spigots on a quad port will shed some light.