I'm a porting idiot.....

[Trent Curtis]

If it makes you feel any better, I've been there myself. I believe I can say most of us have.

Big ports dont always make big power. Always need to remember, the engineers that designed these saws weren't idiots. Think of how much they spent on design alone.

What they did was make a nearly perfect saw in terms of endurance, performance, emissions, noise and economy to list a few.

All you do when you port a saw is trade one of the above balanced factors for another.

It's a good thing to keep in mind before you touch a burr to any jug.

Al,

Was chuckling when reading your replies.

First of all your completely right. I was laughing because my father is a very accomplished mechanic and a smart cookie.... and concerning 2 strokes he said exactly what you just reiterated "the engineers who design the saws aren't idiots".

So I have no desire for a race saw. Just want a really strong work saw. I believe I have plenty of room to fix my flat port work- I actually didn't take much off the exhaust. Mostly from corners, but I didn't think about the curved top/bottom helping the rings. The have plenty of room for correction.

When you say that carving on the intake floor causes case pressure, I'm assuming this is when carves too low and exposes past the piston skirt.

I think I'm going to do the following- and please give me your feedback.

1. Clean up the ports, nice bevels on jug side, and radius to the top/bottom of exhaust port. The exhaust port is not free porting, but I'll map the cylinder the get exact measurements before grinding again.

2. Measure squish and delete the gasket if room allows.

3. New piston and ring. Between the new Piston and deleted base gasket i hope to get compression back up to 165-175.

My regret on my terrible first dabble is the work I did on the intake. As you said, I hurt the intake velocity. Trading that for volume may not have been the best idea. There certainly is a happy medium.

Thanks for the good advice Al, appreciate it.

 

[Trent Curtis]

Go for the single ring piston. You will get better performance and see no lost in compression. The rings create a lot of drag.

It's a known fact that the top ring wears faster than the bottom ring. It's common practice to swap top and bottom rings to pick up some compression in an old saw. The only thing the second ring is good for is being a bandaid when that top ring is worn out. If that top ring is worn out, both it and possibly the piston should be replaced, not relying on a second ring to do the job. You're never going to know the difference in the real world.

As far as heat displacement...I've never seen evidence to suggest that. Most of the saws I build run only a single ring and have never had issues with heat.

Makes sense, I never considered the extra drag from a second ring.

Single ring it is!

 

[blsnelling]

My regret on my terrible first dabble is the work I did on the intake. As you said, I hurt the intake velocity. Trading that for volume may not have been the best idea. There certainly is a happy medium.

I don't see where you hurt a thing. Opening up the intake is always part of a proper port job. If I were porting it, I'm sure a lot more would be coming out.

My best advise is to not do another thing until you've set the squish and the degreed the ports.

 

[Chris-PA]

When you say that carving on the intake floor causes case pressure, I'm assuming this is when carves too low and exposes past the piston skirt.

Actually the problem is with increasing case volume and thereby decreasing case pressure. When the piston rises it creates a low pressure in the case and atmospheric pressure outside pushes air into the case to equalize the pressure. Since gas is compressible, and the cylinder only has a fixed displacement volume, if the case volume is larger then the pressure in the case will not be as low and you won't pull in as much air. IMHO a smaller case volume is always better in these non-piped 2-strokes.

There are issues on the other side as well, when the piston is pushing the air up the transfers. However, here the case is closed and the pressure can be higher than 1 atmosphere. A larger transfer volume will reduce transfer velocity, but it may also reduce restriction. I'm more concerned with filling the case than pushing the air up the transfers, so I consider anything that increases case volume to be a net negative. But having said that I doubt the grinding you did on the transfers will matter much.

My regret on my terrible first dabble is the work I did on the intake. As you said, I hurt the intake velocity. Trading that for volume may not have been the best idea. There certainly is a happy medium.

I would not worry about opening the top of the intake port at all. Intake velocity matters in terms of keeping fuel mixed in the air, and if there is a nice column of moving air with a good mass you could get some intake charge inertia. But here the intake is very short and it feeds into a crank case with a bunch if spinning bits and I doubt it matters at all.

I don't think you ruined the cylinder. You should check the timing before you decide what to do next.

 

[jmssaws]

Flow will trump what little bit of velocity there is,where people mess up and make a turd by hogging out the transfers is they don't do enough,
You have to do all of it not just the lowers.
However much you raise the transfers you have to maintain the roof angle and entry angles or you most certainly will make a stinker.

A 044/046 hybrid is a "velocity" saw and they sat hogging one out will kill it but that's not true at all.

There's jb weld filling the holes where I ground through in the transfers.
They can't be any bigger.

Makes for a very smooth tourqey hybrid and that's something most are not.

 

[Trent Curtis]

There are issues on the other side as well, when the piston is pushing the air up the transfers. However, here the case is closed and the pressure can be higher than 1 atmosphere. A larger transfer volume will reduce transfer velocity, but it may also reduce restriction. I'm more concerned with filling the case than pushing the air up the transfers, so I consider anything that increases case volume to be a net negative. But having said that I doubt the grinding you did on the transfers will matter much.

I would not worry about opening the top of the intake port at all. Intake velocity matters in terms of keeping fuel mixed in the air, and if there is a nice column of moving air with a good mass you could get some intake charge inertia. But here the intake is very short and it feeds into a crank case with a bunch if spinning bits and I doubt it matters at all.

I don't think you ruined the cylinder. You should check the timing before you decide what to do next.

Chris thank you for the reply- one thing you said that doesn't make sense- volume does not exactly equate to pressure. And whatever pressure is built in the crank from volume, would be a good thing.
Should the the transfers be enlarged that would allow this pressure/volume to be efficiently moved to the combustion chamber, preventing the "trapped" pressure in the crank that you're referring to.

 

[Trent Curtis]

I don't see where you hurt a thing. Opening up the intake is always part of a proper port job. If I were porting it, I'm sure a lot more would be coming out.

My best advise is to not do another thing until you've set the squish and the degreed the ports.

This whole porting endeavor has shown me how much I don't know!

I clearly have no idea about checking port degree, or timing.

I always referred to timing as simply when the the plug fires in relation to the piston stroke.

What is yalls version of checking the timing?

 

[jmssaws]

Once running and everything is full it won't matter if the transfers are the size of a 5 gallon bucket, "velocity" and pressure will be the same.

There's not enough velocity in a saw to worry about.

You want as much as possible going through the transfers and dumping in the cylinder at the right angle to increase loop scavenging.
The more efficient at removing exhaust with the fresh charge you can get it the better it will run.

 

[jmssaws]

This whole porting endeavor has shown me how much I don't know!

I clearly have no idea about checking port degree, or timing.

I always referred to timing as simply when the the plug fires in relation to the piston stroke.

What is yalls version of checking the timing?

You want to think of port timing like a cam I a 4 stroke/car motor instead of like a plug firing.
Think duration and learn to talk duration instead of openings and you will be better off.
There's a 1000 threads on setting up a degree wheel

 

[Trent Curtis]

You want to think of port timing like a cam I a 4 stroke/car motor instead of like a plug firing.
Think duration and learn to talk duration instead of openings and you will be better off.
There's a 1000 threads on setting up a degree wheel

Ok underatood- so duration that the intake is open, transfers are open, exhaust etc etc.

I'll be back after some research

 

[Trent Curtis]

You want to think of port timing like a cam I a 4 stroke/car motor instead of like a plug firing.
Think duration and learn to talk duration instead of openings and you will be better off.
There's a 1000 threads on setting up a degree wheel

Just got done picking at my face and reading a bunch of threads on a timing wheel.

Makes total sense- actually puts a science behind the madness.

Now I have a question- I'm sure guys have ruined a lot of cylinders and or pistons figuring out the ideal durations for different model saws. Have any baselines been found to hold true for pro series saws (i.e. Saws that are frequently modded)?

Ordered the timing wheel, can't wait to try it out.

 

[Cease232]

You can print one out for free online. Glue it to a piece of wood or cardboard. Nothing wrong with buying one but it'd get you started today.


Sent from my iPhone using Tapatalk

 

[blsnelling]

Just got done picking at my face and reading a bunch of threads on a timing wheel.

Makes total sense- actually puts a science behind the madness.

Now I have a question- I'm sure guys have ruined a lot of cylinders and or pistons figuring out the ideal durations for different model saws. Have any baselines been found to hold true for pro series saws (i.e. Saws that are frequently modded)?

Ordered the timing wheel, can't wait to try it out.

Every model is an individual, although there are some general guidelines that hold true for MOST saws. Find out where you are first and then go from there.

BTW, you can download a picture of a degree wheel, size it to your flywheel, and glue it on.

 

[Chris-PA]

Chris thank you for the reply- one thing you said that doesn't make sense- volume does not exactly equate to pressure. And whatever pressure is built in the crank from volume, would be a good thing.
Should the the transfers be enlarged that would allow this pressure/volume to be efficiently moved to the combustion chamber, preventing the "trapped" pressure in the crank that you're referring to.

Once running and everything is full it won't matter if the transfers are the size of a 5 gallon bucket, "velocity" and pressure will be the same.

Picture two extremes, one with a very small case volume and one with an enormous case, like a 5ga bucket. The same small cylinder is on each. When the piston rises on the small case the volume in the case might go up by 50%. That causes a large drop in pressure in the case (relative to atmospheric) and so it pulls in a lot of air.

On the large case that same rising piston only increases the case volume by a small percentage, and so the drop in case pressure will also be smaller. A smaller pressure difference means less force to drive air into the case at a lower velocity, and you get a lower "Delivery Ratio" (the volume of air delivered to the cylinder relative to the displacement).

It isn't much different than why a large combustion chamber give a lower cylinder pressure.

 

[blsnelling]

Picture two extremes, one with a very small case volume and one with an enormous case, like a 5ga bucket. The same small cylinder is on each. When the piston rises on the small case the volume in the case might go up by 50%. That causes a large drop in pressure in the case (relative to atmospheric) and so it pulls in a lot of air.

On the large case that same rising piston only increases the case volume by a small percentage, and so the drop in case pressure will also be smaller. A smaller pressure difference means less force to drive air into the case at a lower velocity, and you get a lower "Delivery Ratio" (the volume of air delivered to the cylinder relative to the displacement).

It isn't much different than why a large combustion chamber give a lower cylinder pressure.

Exactly. And the same applies to case compression, as the piston moves down, forcing the charge through the transfers.

 

[jmssaws]

On the large case that same rising piston only increases the case volume by a small percentage, and so the drop in case pressure will also be smaller.

Am i not adding case capacity by enlarging the transfers?
Your explaining to me what I already said.

You have to close the intake sooner to make it work and then instead of a filter soaking pig you have a saw with almost no spit back.

 

[blsnelling]

Am i not adding case capacity by enlarging the transfers?
Your explaining to me what I already said.

You have to close the intake sooner to make it work and then instead of a filter soaking pig you have a saw with almost no spit back.

How are you going to fill the added volume if you close the intake earlier?

 

[jmssaws]

Exactly. And the same applies to case compression, as the piston moves down, forcing the charge through the transfers.

I'd say as a whole the saws you build have the least amount of case compression than anybodys so you should keep everything as small as you can.
You have to with big intake duration

 

[jmssaws]

How are you going to fill the added volume if you close the intake earlier?

How are you going to make case compression if you dont?

 

[blsnelling]

I'd say as a whole the saws you build have the least amount of case compression than anybody's...

Where did you get that?