How to use and read timing degree wheel?

[idiotwithasaw]

I have just purchased a timing wheel because I want to see what some of my saws are setting at. And I may in the future decide my hand at this fad I've heard called porting.

So how does one go about both setting one up. Then get some readings, then understanding those reading.

Please feel free to link any videos or post any pictures. I'm starting this thread not just for myself but for anyone in the future looking to learn like me.

Also I understand that knowing the numbers means nothing if you don't know what they mean. What is desirable and why. What makes more torque, more rpm.

I know I'm asking alot from one thread but I know there is a lot of smart people here with a lot of knowledge. And anyone willing to share is appreciated. I hope this place becomes a wealth of useful information that is easy to find.

 

[Brewz]

Do a search on YouTube
Mastermind has some vids up of how to do it.
Search on chainsaw timing or chainsaw degree wheel or something like that

A vid is better than a text description

 

[Brewz]

 

[idiotwithasaw]

I agree a video very helpful. However all of the ones I have seen do a great job of showing how to set up a degree wheel and find top dead center. It's the finding of the port numbers that are confusing. I've seen some guys employ funny math that isn't explained real well to get some numbers. Then there are things like blowdown and port durations that I don't understand the math to find. Mastermind explained a few of these things to me in another thread on another forum. But I'm looking for a refresher and to learn something new.

 

[Brewz]

Ahhhh yes, thats the tricky bit.
I recently made a degree wheel with a printout glued onto a bit of plywood.

I am still at a bit of a loss as to exactly what the most important numbers are but my interpretation is this, and I am happy to be corrected and further educated!!!

With the piston at TDC (Top Dead Center) rotate the crank so the piston starts to move down. Don't do this by touching the degree wheel.

The first reading you will get is when the exhaust port first opens. Shine a torch in the spark plug hole, it helps.
The next one to check is a bit further down when the top of the transfers open
The amount of degrees between the exhaust port opening and when the transfers is your blow down
Now where to measure the intake has me stuffed. I have never been able to get a clear decisive answer on it.

People who know this stuff well usually quote 3 different figures.

I would also love to know exactly what they are referring to.

 

[drf256]

The intake closing is measured from degrees before/after BDC. That's why it's confusing. So a lower (physical) intake has a higher numerical value.

The intake is also measured at the port floor and the bottom of the piston skirt, also backwards from the other two readings.

Edit:see below.

 

[Brewz]

Ahhhh so the 3 numbers usually quoted would be:

TDC down to Exhaust open
TDC down to Tranfer open
BDC up to intake closed

???

 

[drf256]

No,

Maybe I think I mislead you and wrote wrong, it's early here. Think I explained Backasswards.

It's piston skirt from TDC down. So at TDC, the piston skirts above the roof. Start counting going down. Duration is the other way.

So you rotate crank, piston drops, skirt fully closes intake floor, that's your closing point in degrees.

 

[drf256]

So if your intake closes at 80*, you have 100* more before BDC. So you've got 100* of case compression and 160* of total intake duration.

 

[Brewz]

Ahhhhhh gotya

So Ex And Tr reference to opening at top of piston on the way down from TDC
Intake references to bottom of skirt closing on the way down from TDC

If so.... that makes posts like this make sense
Am I right?

All set up for timing measurements.



The port timing on this jug stock.....

Ex: 94*
Tr: 124*
In: 81*

 

[drf256]

I believe so.

My brain starts working from bottom dead center (on the thrown) everyday. By the time the coffee got to TDC, I realized I posted wrong info.

There's a lot of interpretive error though. You can read a degree wheel at an angle, you can read a port opening different than others.

Shining a flashlight in the plug hole in a dark room to look for exhaust opening gives me 1-2* less opening point than what I observe viewing the piston crown opening directly through the port.

Which is correct is highly debatable.

Makes me wonder if @David Young methodolgy of measurement may be more exact than a degree wheel.

 

[czar800]

I'm no teacher but maybe this helps. It takes playing around with a wheel to start getting it.

 

[czar800]

 

[czar800]

It all fails if you do not find top dead center correctly. I find top dead center the exact same way Randy did. I really need some cool music playing in the background of my next video!

 

[Landmark]

Great thread keep the info coming. When i first saw how to do this it blew my mind. I am fortunate enough to live near @rattler and he has taught me alot in last couple years. If you can get some hands on experience it will be far more beneficial than vids. Thanks to all the porters who will share their knowledge.

 

[mdavlee]

I start by getting the intake. I set the wheel to be symmetrical to the intake. So both ways it reads the same say 74 or 106 depending on how the wheel is made with the numbers. Then get the exhaust and transfers. Should read the same going either way on the rotation. I use the edge of the bevels as the port opening. Exhaust when I can see the bevel and light through the plug hole through the port.

 

[super3]

So if your intake closes at 80*, you have 100* more before BDC. So you've got 100* of case compression and 160* of total intake duration.

Case comp is intake close to transfer open.

 

[SixGun]

The only way to really understand is by practicing .
If your numbers are way off, you know you're doing something wrong.
Also try not to get confused when guys post duration numbers as opposed to actual open numbers.
I use a calculation to get from duration #s to open #'s for exhaust and transfers
Duration # divided by two and subtracted from 180= actual number
Intake just divide duration number by 2
(To convert initial degree wheel numbers to duration, do calculation in reverse)
( guys please correct me if I mis typed this)

 

[idiotwithasaw]

A lot of good information here guys keep it coming.

Here's the next question, what is duration and how is it figured on a wheel?

Also when looking at a degree wheel it has essentially two sides that read up to 180° why does it not just go all the way up to 360° and when you are looking at timing numbers how do you know what side of the wheel the numbers come from and does it matter?

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[idiotwithasaw]

I start by getting the intake. I set the wheel to be symmetrical to the intake. So both ways it reads the same say 74 or 106 depending on how the wheel is made with the numbers. Then get the exhaust and transfers. Should read the same going either way on the rotation. I use the edge of the bevels as the port opening. Exhaust when I can see the bevel and light through the plug hole through the port.

How do you achieve this?

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