Open port cylinder grinding

[Reesedlightning]

I’ve been trying to look around and do some research and haven’t come up with a straightforward answer about this so I’m putting it out for the pros.

I’ve noticed on most open port cylinders there is a middle vane or blade if you will that runs the length of the transfers. When putting the cylinder for performance purposes, is there any value in grinding out that middle vane?
For example, on an MS 290 or 390 where that middle blade is really thick. Cannot be thinned or just removed all together?

I started playing around with a cheap little Warhawk cylinder for an ms180 and I noticed the blade was rather thin and tapered once it reached the upper transfer are. I’ve attached a picture of the 180 cylinder
You will see where I started to widen the lower transfer a bit but then I decided to pause and run this question by the forum before I took any more material out

 

[The Shooters Apprentice]

following to learn

 

[Reesedlightning]

For what it’s worth, my plan is to push the limit on the intake timing so I’m thinking about what needs to happen with the transfers to get that air moved.

I am participating in an MS 170 build off and I’m playing around to see how much I can squeak out of this thing without getting into machining

 

[Sierra_rider]

I’ve been trying to look around and do some research and haven’t come up with a straightforward answer about this so I’m putting it out for the pros.

I’ve noticed on most open port cylinders there is a middle vane or blade if you will that runs the length of the transfers. When putting the cylinder for performance purposes, is there any value in grinding out that middle vane?
For example, on an MS 290 or 390 where that middle blade is really thick. Cannot be thinned or just removed all together?

I started playing around with a cheap little Warhawk cylinder for an ms180 and I noticed the blade was rather thin and tapered once it reached the upper transfer are. I’ve attached a picture of the 180 cylinder
You will see where I started to widen the lower transfer a bit but then I decided to pause and run this question by the forum before I took any more material out

That middle divider provides ring support. I'd work on blending mostly, widening the exhaust port etc. I think you're probably on the right track to increase intake duration.

IDK you plan for the exhaust port, but I'd also be careful with the exhaust timing...it seems like a lot of the clamshells have wide squish clearance and low compression. There really isn't an easy way to machine them for more compression, so if you go with a tall exhaust port, you end up with a peaky powerband.

 

[Reesedlightning]

The exhaust is most certainly going to get widened. I don’t think I’m going to raise it as I’m going to need all the compression I can get. I’ve considered welding up and then machining a pop up onto the piston to get my squish where I want it. I ordered a couple different pistons last night and I will go through them all when they come in and see which one gets me closest to what I need.

I am going to continue blending then I might put some epoxy in the upper transfers then sculpt that to aim the air more towards the upper intake rather than the 90° turn that the transfers are at now. I’ve seen some really good saw builders use that trick.

I might try to thin that middle blade or even take it out and see what happens. If I hang a ring then at least I am only ruining a cheap Chinese cylinder. I kind of bought it for testing purposes anyhow lol

 

[Sierra_rider]

The exhaust is most certainly going to get widened. I don’t think I’m going to raise it as I’m going to need all the compression I can get. I’ve considered welding up and then machining a pop up onto the piston to get my squish where I want it. I ordered a couple different pistons last night and I will go through them all when they come in and see which one gets me closest to what I need.

I am going to continue blending then I might put some epoxy in the upper transfers then sculpt that to aim the air more towards the upper intake rather than the 90° turn that the transfers are at now. I’ve seen some really good saw builders use that trick.

I might try to thin that middle blade or even take it out and see what happens. If I hang a ring then at least I am only ruining a cheap Chinese cylinder. I kind of bought it for testing purposes anyhow lol

Sounds good getting rid of the sharp bend in the transfers. I still like to have the roof of the transfers to be flat rather than angled up, but they need some sort of transition rather than just a sharp elbow. I haven't had too much experience with clamshell/open port cylinders, but on the close ports, I try to have the volume of the transfer gradually shrink as it gets get closer to the upper window.

 

[NSEric]

The china 52-62cc saws I ported have a divider in the open transfers too.
I remove the bottom of it below where the rings hit it, the divider doesnt need to go to the bottom to support the rings.
I put the piston at bdc and marked the divider by the wrist pin of the piston, removing everything below that mark.

 

[Reesedlightning]

Awesome! Thanks! I’ll try that before I grind the whole dern thing out. I appreciate that tip.

 

[Lightning Performance]

@Reesedlightning

Don't remove any material in the lower case area. Nothing is happening there. Thin the divider to the transfers at the port window exit area next to the piston only when it is up near TDC. You want the entry from the main case area and under the piston to be smooth into the side tunnels. Grinding any lower adds case volume and that hurts your case pressure. In fact you can fill in the lower potions of the transfer port ducts. With the piston almost at top dead center smooth out the sharp edges at the transfer port slots on the edges. Do lift the roofs and blend them back into the 90 up there. You can fill the corners just a bit if you do real good prep work the epoxy won't come loose. If you cannot work the roofs higher easily, remove 0.030 from the piston on the primary transfer ports and go in 0.005 increments if you want more but like not needed. Trim your intake skirt 0.040 and bevel it 30 degrees or more. Do Not leave thin or sharp edges on anything. Doing carb work is pointless when the air filter is the real restriction on those saws. Fix that issue by tossing it and then toss on an 025/250 carb. Buy a cheap 250 carb and swap them is your best bet. Widen the intake and smooth out the casting marks if you have any but watch your ring end. Toss the second ring and do not port the intake roof area or remove material from the port runner. Stay near the port window if you widen the intake. Advance the ignition timing by removing half of the crank key or toss it and time the engine from TDC. Set your lead ignition advance from that. You can use a timing light, a degree wheel or a dial indicator. Anything more is getting down into the case area and filling in any voids to increase case pressure by reducing volume. Piston work isn't recommended on the windows. Welding it up or buying a popup piston will help compression just a touch but you pay a price for a heavier slug. Higher compression also increases pumping looses at high RPMs. Many just flat out overlook that fact. You won't have that problem here but be aware if it on pro models when cutting the base and combustion chambers.

This is all go fast work and will reduce your midrange ability to pull more cutters or a very aggressive chain.

Get NK 043 or 050 chisel chain or buy one from somebody who knows how to modify the cutters for faster chip ejection. Square is faster if you can sharpen it correctly. If not just go with round filed or round ground cutters. Pro rim and drum adds weight so skip it and use a spur.
Removing a portion of the flywheel fins on the flywheel reduces drag.

No point in quoting degree wheel numbers or crank angles if your not using a degree wheel on it.

Don't use race fuel go with pump gas for max torque.

The rabbit hole goes much much deeper but you won't need to know about that.

K.I.S.S.
GL

 

[Reesedlightning]

That is some awesome information. Thank you for sharing that. I appreciate that greatly.
Fortunately I haven’t done much with the cylinder yet besides some thinning out of the lower transfer area. But I’m seeing that may be a mistake.
I have had some decent success with porting closed port cylinders but this open port business is totally new to me.
I do have a degree wheel and have been getting much better at understanding how the numbers work together but your post is a perfect example of how the numbers are just a small part of it all. I’ll post an update once I get projects out of the way and get a degree wheel on it. Should be this month.

 

[Reesedlightning]

Update.
I got the cylinder ported to my liking.
Stock, the Warhawk cylinder was at
80, 124, and 103

Squared and opened the intake within tolerance of the ring ends. Lowered to 82°
Widened the exhaust to about 70% of bore diameter and set at 102. Cut and bladed the lower portion of the transfers and opened the passage to the impulse a little.

Modified an adjustable carb from an ms250 to fit.

Here is the port work roughed in. Needs chamfered and polished and all that but you will get the idea of what I did.

 

[Lightning Performance]

Update.
I got the cylinder ported to my liking.
Stock, the Warhawk cylinder was at
80, 124, and 103

Squared and opened the intake within tolerance of the ring ends. Lowered to 82°
Widened the exhaust to about 70% of bore diameter and set at 102. Cut and bladed the lower portion of the transfers and opened the passage to the impulse a little.

Modified an adjustable carb from an ms250 to fit.

Here is the port work roughed in. Needs chamfered and polished and all that but you will get the idea of what I did.

Why did you cut out the lowers?

That was good place to fill them in and lift the roofs while narrowing the diver up where it matters next to the piston. You added case volume and removed most of the side support. What was the thinking here?

 

[Reesedlightning]

Why did you cut out the lowers?

That was good place to fill them in and lift the roofs while narrowing the diver up where it matters nextvto the piston. You added case volume and removed most of the side support. What was the thinking here?

I only removed the lowers up to where the piston hits BDC so no support was taken away.
I’m at 22° of blowdown which is what I was aiming for. I did indeed think about filling them but to be honest, I kind of wanted to see how this thing would run without too much tampering of the uppers. I’m planning on experimenting with this saw a good bit so that is probably something I am going to go back in and do so I can compare gains if there are any to be had there.

I have been reading a good bit of the two-stroke tuners handbook, and they talk about case volume and how you can make it work to your advantage, depending on what part of the power band you are looking for.

 

[ballisticdoughnut]

Nice work. What have you done for a muffler mod?

 

[Lightning Performance]

I only removed the lowers up to where the piston hits BDC so no support was taken away.
I’m at 22° of blowdown which is what I was aiming for. I did indeed think about filling them but to be honest, I kind of wanted to see how this thing would run without too much tampering of the uppers. I’m planning on experimenting with this saw a good bit so that is probably something I am going to go back in and do so I can compare gains if there are any to be had there.

I have been reading a good bit of the two-stroke tuners handbook, and they talk about case volume and how you can make it work to your advantage, depending on what part of the power band you are looking for.

Support was taken away in a critical area but you didn't answer the question, why?
What is your reasoning for increasing case volume?

 

[Reesedlightning]

Nice work. What have you done for a

 

[Reesedlightning]

Support was taken away in a critical area but you didn't answer the question, why?
What is your reasoning for increasing case volume?

What was the critical area? If the rings aren’t touching that area and neither is the piston then what is there to support?

According to the author, increase in case volume with an increase in intake timing can lead to better held rpm under load.
It makes sense to me because I figure if you are allowing more charge in, in a larger space, it leaves a larger volume of air to be compressed and pushed up through the transfers.
Then, again, I can see why keeping case volume small could lead to that same amount of air being compressed in a smaller space

 

[Lightning Performance]

What was the critical area? If the rings aren’t touching that area and neither is the piston then what is there to support?

According to the author, increase in case volume with an increase in intake timing can lead to better held rpm under load.
It makes sense to me because I figure if you are allowing more charge in, in a larger space, it leaves a larger volume of air to be compressed and pushed up through the transfers.
Then, again, I can see why keeping case volume small could lead to that same amount of air being compressed in a smaller space

It has nothing to do with the ring.
My bad for offering advice.

Good Luck

 

[Reesedlightning]

Roger that. I’m sorry if I came off the wrong way.
Didn’t mean any offense by raising questions. I’m trying to better understand the dynamics of what’s happening and get better at porting

 

[NSEric]

If you had the time and can get an extra cylinder it'd be nice to see the difference between the two different styles/approaches to porting these saws.
One is the way you did it and what comes up when you search how to port them.
Open up the lowers as much as you can, big open intake, 80ish degrees of intake timing, 20-25 degrees blowdown.
The other way (what ligthning performance suggested)
Fill the lowers as much as you can without hurting flow, small intake, less intake timing(guessing 77-78), less blow down(guessing 15 degrees)

When I started porting cheap china saws, I went with making everything big, not touching the blow down numbers, lots of intake timing and they ran better than stock but not great.
Now I dont open up the ports much and run 15-16 degrees of blow down, they are just as fast, snappier and run better this way.