So I read Jenning's Book.....

[Mastermind]

I like to see about 40 degrees from the point the intake closes, till the transfers open. With that in mind, for a transfer height of 118* ATDC I'd want 78* as my intake opening point. That's not always possible though. The MS660 is one example......it normally closes at 83* after I get done with my machine work. I put the transfers at 120*, for 37* of case compression. This is also the reason a 064 will spank a MS660.......it's intake floor is much higher.

 

[EvilRoySlade]

Here's a read for that.

http://www.dragonfly75.com/motorbike/PCR.html

I like threads like this, it's all about learning. When do we get lab day with all the tools and spare cylinders?

 

[Mastermind]

I just tore a saw down that was ported by some other guy........it was at 117* on the transfers, and 85* on the intake. It only has 32* of case compression.....it sounds great, but is weak as a kitten in large wood.

Now for a race saw that is gonna be spinning at 16,000 RPM or so........a lower case compression is a good idea. It frees up power that could be lost to the pumping action in the case. On those engines, opening up the transfers......and adding to the case volume helps them spin way on up.

 

[Mastermind]

I'm a long way from being an authority on two stroke theory........but I have spent a bunch of time, energy, and money testing what works, VS what doesn't.

For instance, I just ported a few 064s. I did up a "special" jug to test alongside the "normal" ones.......

 

[EvilRoySlade]

Have you done 036/360 with the bridge ports?
I have a Durand saw and was curious about having him add those.

 

[drf255]

I'm a long way from being an authority on two stroke theory........but I have spent a bunch of time, energy, and money testing what works, VS what doesn't.

For instance, I just ported a few 064s. I did up a "special" jug to test alongside the "normal" ones.......

View attachment 392147

Do you reverse the piston with that porting?

What keeps the rings on the pins?

 

[Mastermind]

Do you reverse the piston with that porting?

What keeps the rings on the pins?

I do run the piston backward......the pins end up on each side of the exhaust.

 

[Mastermind]

Have you done 036/360 with the bridge ports?
I have a Durand saw and was curious about having him add those.

Better leave that Durand saw as is.........he builds a really good running saw.

 

[nmurph]

Here's a read for that.

http://www.dragonfly75.com/motorbike/PCR.html

I like threads like this, it's all about learning. When do we get lab day with all the tools and spare cylinders?

Using JB in the crankcase for a stuffer??? What happens if it comes loose?

 

[redfin]

I'm a long way from being an authority on two stroke theory........but I have spent a bunch of time, energy, and money testing what works, VS what doesn't.

For instance, I just ported a few 064s. I did up a "special" jug to test alongside the "normal" ones.......

View attachment 392147

Those look niiiiice!

 

[drf255]

I do run the piston backward......the pins end up on each side of the exhaust.

Do you limit exhaust port width because of this?

Any longevity issues with flipping the piston?

 

[EvilRoySlade]

Using JB in the crankcase for a stuffer??? What happens if it comes loose?

I agree, good theory but I wouldn't do it without a pile of parts saws or deep pockets.

 

[Mastermind]

Do you limit exhaust port width because of this?

Any longevity issues with flipping the piston?

I rarely ever widen the exhaust anyway. Proper height is far more important than width.....at least in my opinion.

No issues running it backward.....

 

[drf255]

I rarely ever widen the exhaust anyway. Proper height is far more important than width.....at least in my opinion.

No issues running it backward.....

Sorry to pick your brain too much, but if its not revealing too many trade secrets, what kind of exhaust numbers do you like?

Do you swing the rings around in most setups, or just that radical jug you posted above?

 

[Mastermind]

I normally run the piston in the standard configuration. Only backward if finger ports are used.

I used to post my timing numbers for everyone to see.......but I have stopped doing that because it causes arguments.

I will tell you this.......I use a displacement rule for exhaust height. Smaller engines get a lower height, and higher compression than larger engines.

Send me a PM......I'll gladly share.

 

[SS Sniper]

Why don't Randy or someone write a book specifically for chainsaws? May put ya out of business... but what the heck

 

[Mastermind]

I've got 33,425 posts here about chainsaws, and other BS.........that would likely fill a small book.

The thing is.......I'm still learning more everyday. The things I was sure about a couple of years ago......I'm wondering about today.

It seems like the more I know......the less I really understand.

There is a guy that should write a book on saw engine porting though.

Scott Kunz......AKA Treemonkey.

Hell, Scott has forgotten more about these engines than I'll ever know.

 

[SS Sniper]

And that's what makes a better man... the will to learn more about something you probably know too much about
There's other things that make a better man, but we'll save those for another day haha
But what the hell do I know?

 

[Dennis Cahoon]

I'm a long way from being an authority on two stroke theory........but I have spent a bunch of time, energy, and money testing what works, VS what doesn't.

For instance, I just ported a few 064s. I did up a "special" jug to test alongside the "normal" ones.......

View attachment 392147

Hey Randy, did you ever try the 064 cylinder I sent you?

 

[Mastermind]

I've still not put it on a saw. I have three jugs sitting here I want to try Dennis. Yours, one with just bridge ports, and the one I posted a pic of.

I need to clone myself.......then I could get some stuff done. Hey Randy #2......get that damn saw together ya slacker.