Chainsaw Porting Theory

[drf256]

They actually just welded everything, but close enough.

I have it backwards. You know the story.

I knew one of the old architects. He told me the story 10 years ago. Still remember the lesson, maybe not the details exact.

 

[Mastermind]

Don't know what that means. Even looked for it in a dictionary before I made myself look stupid by posting this...lol. guessing it means "owned"? If so, many more times coming

Long story.......but it means I'm giving you reputation points. That's a good thing BTW.

 

[exSW]

I have it backwards. You know the story.

I knew one of the old architects. He told me the story 10 years ago. Still remember the lesson, maybe not the details exact.

I find it amazing the architects listened. Not something in my personal experience the craft is known for.

 

[merc_man]

Don't know what that means. Even looked for it in a dictionary before I made myself look stupid by posting this...lol. guessing it means "owned"? If so, many more times coming

Thanks for taking one for the team. I been wondering what that meant too.[emoji6]

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[czar800]

That's what I'm saying, if it gets past the rings it would pump it back through the transfers and leave residue.

I'm always a page behind....

 

[XP_Slinger]

Long story.......but it means I'm giving you reputation points. That's a good thing BTW.

Thanks for the explanation and thanks

Thanks for taking one for the team. I been wondering what that meant too.[emoji6]

No problem

Back to the discussion...I think we can all agree the rings are the most likely culprit given we were told the saws that had carbon in the transfers were old and worked hard. Combine worn rings with a restrictive muffler and it will be even worse.

 

[drf256]

Thanks for the explanation and thanks



No problem

Back to the discussion...I think we can all agree the rings are the most likely culprit given we were told the saws that had carbon in the transfers were old and worked hard. Combine worn rings with a restrictive muffler and it will be even worse.

Not so sure on that. I think it's a combo of both.

But then again, why wouldn't transfers be washed clean like a piston top? They provide the wash for the piston, don't they?

I think it's heat "cooking" the residue of unburned oil for thousands of cycles. In the very top of the transfers, maybe it's from exhaust gas, maybe.

I could be 100% wrong. Just makes sense to me.

 

[XP_Slinger]

Not so sure on that. I think it's a combo of both.

But then again, why wouldn't transfers be washed clean like a piston top? They provide the wash for the piston, don't they?

I think it's heat "cooking" the residue of unburned oil for thousands of cycles. In the very top of the transfers, maybe it's from exhaust gas, maybe.

I could be 100% wrong. Just makes sense to me.

No wrong answers here, everyone seeing things differently is what helps us learn. I absolutely agree that heat plays a factor in forming carbon deposits in the transfers. The fuel air mix should wash the transfers but if the rings are letting exhaust blow by then more heat from cumbustion is getting to the transfers. I would've liked to see the Pistons from the cylinders that were posted. I bet there's carbon on the wrist pin sides of them. I may be 100% wrong too. It seems like it would have to be the perfect storm to get carbon fouling in the transfers, or blow down is simply too short.

I'm glad I'm not the only one who gets up at 0530 on a Saturday and immediately gets on OPE

 

[drf256]

I can see a restrictive muffler playing hell with transfer pressure. Good answer Joey.

I'm gonna go a little further and suggest that more blowdown time would be needed with those stopped up cans.....

This statement is confusing to me

So we have a restrictive muffler. We know that the OEM responded by increasing exhaust durations.

So now we have more exhaust in the chamber when the transfers start to open, this is where my confusion lies....

So you go with less blowdown, so there is more transfer duration to fill the chamber better and push out any remaining exhaust?

Or, do you go with more blowdown, physically lower transfers, so there's less exhaust pressure to potentially back fill them?

Quads vs. duals would play a hand here as well. Case volume as well. A generality may not exist.

I think that the factory 262 jug is an example of the first above. It's got a restictive muffler, an exhaust at 103, and transfers at 115-118.

I remain confused. I see it both ways.

 

[drf256]

No wrong answers here, everyone seeing things differently is what helps us learn. I absolutely agree that heat plays a factor in forming carbon deposits in the transfers. The fuel air mix should wash the transfers but if the rings are letting exhaust blow by then more heat from cumbustion is getting to the transfers. I would've liked to see the Pistons from the cylinders that were posted. I bet there's carbon on the wrist pin sides of them. I may be 100% wrong too. It seems like it would have to be the perfect storm to get carbon fouling in the transfers, or blow down is simply too short.

I'm glad I'm not the only one who gets up at 0530 on a Saturday and immediately gets on OPE

100% no wrong answers. It's a discussion. I want to be disagreed with, and told why. What would be the point otherwise?

 

[drf256]

Here's a pic that intrigues me. Look at the roof of the exhaust port on the new 261 Stihl. I wouldn't let one this square leave my bench.

This would allow for some seriously fast exhaust venting and a lot of port area vs. time.

 

[XP_Slinger]

100% no wrong answers. It's a discussion. I want to be disagreed with, and told why. What would be the point otherwise?

Exactly...that's why this forum is the place to be. I've yet to see a chest thumping session in any threads I'm active in. Threads like this one would be especially prone to that kind of conduct in another place.

 

[XP_Slinger]

This statement is confusing to me

So we have a restrictive muffler. We know that the OEM responded by increasing exhaust durations.

So now we have more exhaust in the chamber when the transfers start to open, this is where my confusion lies....

So you go with less blowdown, so there is more transfer duration to fill the chamber better and push out any remaining exhaust?

Or, do you go with more blowdown, physically lower transfers, so there's less exhaust pressure to potentially back fill them?

Quads vs. duals would play a hand here as well. Case volume as well. A generality may not exist.

I think that the factory 262 jug is an example of the first above. It's got a restictive muffler, an exhaust at 103, and transfers at 115-118.

I remain confused. I see it both ways.

Establishing a generality for variations of port timing is as you stated...hard to do. My theory is in the context of a port layout that doesn't cause inversion into the transfer ports and thinking of other mechanical causes of it. You could say I'm thinking on a smaller scale. Didn't mean to apply a generality to all saws new or old. Port timing, whether stock or modified will certainly effect how much inversion is present. And it is present to an unknown degree in all 2 strokes...isn't it?

 

[drf256]

Where are you located XP?

I wouldn't believe any inversion at all, but Blair's book does show a pressure change in the transfers upon initial opening in a chainsaw engine.

Does that pressure change just compress the clean mix that's at the transfer tip, or does actual reversion occur? That I'm not clear on.

 

[merc_man]

Here's a pic that intrigues me. Look at the roof of the exhaust port on the new 261 Stihl. I wouldn't let one this square leave my bench. View attachment 12987

This would allow for some seriously fast exhaust venting and a lot of port area vs. time.

So how would you fix that? Would you have to raise the roof to round it off whitch would change timing?

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[Keith Gandy]

So how would you fix that? Would you have to raise the roof to round it off whitch would change timing?

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He would raise it anyway if cutting squish and porting it

 

[merc_man]

He would raise it anyway if cutting squish and porting it

Ya i figured that. I guess i should have mentioned if not gonna deck it. Im gonna start my first port job (without decking) so was just curius if it could be fixed just kind of keeping it simple for something like my situation if i came accross that.

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[Moparmyway]

Here's a pic that intrigues me. Look at the roof of the exhaust port on the new 261 Stihl. I wouldn't let one this square leave my bench. View attachment 12987

This would allow for some seriously fast exhaust venting and a lot of port area vs. time.

Where are the ring pins, I'm guessing intake side, just about opposite direction from the exhaust port to minimize the rings from trying to open into the port

 

[Deets066]

Here's a pic that intrigues me. Look at the roof of the exhaust port on the new 261 Stihl. I wouldn't let one this square leave my bench. View attachment 12987

This would allow for some seriously fast exhaust venting and a lot of port area vs. time.

It's probably fine like that at stock width, but once you start widening you better have a little arch in it.

 

[drf256]

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