Port timing question: bevel or port wall

[Ketchup]

How do you guys read your timing? As soon as the bevel is visible, or do you try to judge the distance from your bevel to the actual wall?

In my own stuff I just try to be consistent. I read numbers from the first hint of a bevel. But all bevels aren’t the same. And they cloud the waters of duration and port area.

Is there a standard practice?

 

[Bigmac]

I go to the port edge, at 10k rpm. The bevel doesn’t have as much of an effect on timing imho. And the bevel shouldn’t be huge anyway. There is some controversy over giving the anything but the exhaust port a chamfer at all. Some think there isn’t enough area in the transfers to have any ring issues, and there is power to be had by leaving then fairly sharp. Some feel there needs to be some bevel on the port edges. I like to have a bevel, even if it’s small!

 

[jacob j.]

I use a strong flashlight to help me gauge the timing, when I can first see light really coming in. I usually look at it both ways.

One thing I've noticed - a big bevel on the exhaust port of a modern saw seems to make the motor "lazy" - i.e. it loses some torque in the cut.

A few years ago there was a trend among saw builders on the west coast to really bevel the exhaust port out good - most of those motors
I had in my hands were not very good runners. Early 064s had almost no bevel at all on any of the ports.

 

[MG porting]

I normally have little bevels on all ports just to make sure that the rings have a smoother path checking timing I normally go buy just when the port start to open your going to find out everyone has their own way of checking port timing it's just the way it is I guess.

 

[drf256]

I measure it at the bevel edge. Gets confusing at times when there are huge bevels. A huge bevel is kinda like an in between/fudge factor. Some bevels can be up to 3-4* in some saws.

I can say that I have done saws where I dropped the jug .040 and got the same roof height in degrees as the bevel was before. All the drop did was eliminate the bevel. It gets annoying because you tend to wind up with plating in your port from the bevel. The saw ran better with the smaller bevel.

I hope that made sense and isn’t as clear as mud. For example, the Stihl 462 has a big bevel. Pretty sure I dropped the jug over .040 and you can still see the bevel remnant in the port.

 

[Ketchup]

That’s exactly what I’m talking about. A 4 degree fudge factor is way too much. And a bevel that big lets light through. Plus most pistons have a bevel. It makes me feel like my numbers aren’t accurate. Especially the transfers, which are hard to see anyway.

To make it worse, a large bevel will make durations even less accurate.

Maybe try reading the numbers with a feeler guage? Or at least take numbers before grinding the final chamfer?

 

[Bigmac]

I feel you need you need to take the bevel into consideration, but if a port is over beveled, your numbers and results won’t make sense if you address that issue. If the bevel is .040 and you test the performance between an unaltered port and a port that has been lift lifted .035 and beveled is .005 the numbers would be the same and performance would be quite different. So any method you use, there is more to numbers, than just numbers!

 

[Mastermind]

Don't come at me with pitchforks......but.

Unless you are using a ring moved upward by the piston to get your port timing numbers on the exhaust port and the transfer ports......you have no idea what the opening points really are. Bevel or not.

 

[Ketchup]

Don't come at me with pitchforks......but.

Unless you are using a ring moved upward by the piston to get your port timing numbers on the exhaust port and the transfer ports......you have no idea what the opening points really are. Bevel or not.

I do that to set my own mumbers, but not to take stock numbers or check my own upon reassembly. Not sure how a ring would work for that.

 

[Bigmac]

Don't come at me with pitchforks......but.

Unless you are using a ring moved upward by the piston to get your port timing numbers on the exhaust port and the transfer ports......you have no idea what the opening points really are. Bevel or not.

True! But then what, bevel or not on the numbers? I know it’s a saw forum but on other 2t’ with removable heads, you can see the effect of the bevel on the port as it opens.

 

[Mastermind]

True! But then what, bevel or not on the numbers? I know it’s a saw forum but on other 2t’ with removable heads, you can see the effect of the bevel on the port as it opens.

Port opening. The bevel will matter not at high speed.

 

[Ketchup]

Hmm...

Use the tools you have...



So by eye I read 105.5/123/79
With the feeler I read 106/125/78.
If you take the .030” feeler into account the readings are basically identical. I guess it’s easier to read around the bevel than I thought.

That’s reassuring. I was afraid all my notes were trashed.

 

[MG porting]

Port opening. The bevel will matter not at high speed.

Thank you I wanted to say that but I know I would have been throne to the wolves.

 

[Wonkydonkey]

I was gonna say, randy has shown his method many times over how he works to get the number. Using a piece of card. I guess that’s how his work is unlike anyone else’s. It’s repeatable over many saws. Unlike the eyeball way on the trans.
So you find the way that works for you that’s it.. test the same and get it repeatable..


if you try someone else’s numbers and you use randy's way or even your own , you will get a different result..
as for the bevelled bit, it’s just a small edge, most of the time, and a small part of a bigger picture

 

[Fullkip]

I have been making spacers out of old pistons. Once you come up with timing numbers that perform well on saws you port often cut spacers . Write data on the spacer like what was taken out of the squish and the port timing it gives you. Very repeatable, the spacers can be shimned to change timing.
I have always timed before chamfering. I admit I still have lots to learn...

 

[Fullkip]

If you look at a 562 factory jug they don't have much chamfer. I think as you get to wider ports on 70cc plus size bores giving them a better chamfer is a good plan. Max width exhaust ports need some care.

 

[00wyk]

I go to the port edge, at 10k rpm. The bevel doesn’t have as much of an effect on timing imho. And the bevel shouldn’t be huge anyway. There is some controversy over giving the anything but the exhaust port a chamfer at all. Some think there isn’t enough area in the transfers to have any ring issues, and there is power to be had by leaving then fairly sharp. Some feel there needs to be some bevel on the port edges. I like to have a bevel, even if it’s small!

The direction, design, and timing are far, far more important than a tiny bevel.

 

[Lightning Performance]

Welp why not.
I should get a lot of *s-word for this.

I use a wire... any thickness. Find out how many degrees the crank rotates the thickness of the wire in the transfer port. Just shove it in... coming in the spark plug hole. Subtract that and you have the roof number. I have been doing it like that for over forty years... just remove the rings first if your porting to your desired heights by using a piston jig or a set up case for checking the the duration timing. The piston is my stop and the port roofs. The intake gets eyeballed.

The bevel is removed from the equation. A bevel in the center fifty percent of the exhaust port don't do *s-word imo. The rings would never touch it.
Transfers need little bevel on the exit ends. No need for a burr there.
Intakes need bevels and I see many with none that were ported on a lot of stuff over the years. It tears up the piston imo with a flat floor there. I sand the plating just a bit to a V or U shape to capture the piston skirt with some oil on it. Maybe 3-4 ten thousands dropping a 16th down the center a quarter inch wide. No more streaks from fines getting in.

Most Stihls made after 1990 have way too much bevel margin imo. You can get four degrees out of the average 361 transfer port clean-up to the bevel. The intake is done at the factory bevels and the roof is perfect most times untouched.

Skinny rings are less forgiving imo.

Flat port floors clip rings with no bevel and pull off piston tops lol.

 

[Lightning Performance]

The direction, design, and timing are far, far more important than a tiny bevel.

Read my last statement.
How does any of all that *s-word you said matter if the rings are fugged and piston looses it's head?

 

[Wonkydonkey]

I think I read things a bit differently, but I could be wrong,, well sometimes, i is & sometimes i is not