Exhaust port question

[I Know Something]

My piston at bdc is just a smidge past me exhaust port. Would it make sence to lower it to where the piston stops? I did widen it a bit. But, I did not I lower or raise it. Please educate me.

Thank you all.

 

[Wilhelm]

A whole lot of info in this thread

http://opeforum.com/threads/part-one-the-exhaust-port.7279/

Also, intake

http://opeforum.com/threads/part-two-the-intake-port.7290/

 

[I Know Something]

Thank you

 

[Nutball]

Whatever improves flow, just don't go too far. You don't want the exhaust port to open again at TDC

 

[I Know Something]

I'm ASSuming that as well. There is a small (being new, it might actually be big) lip from bottom dead center and the bottom of the exhaust port. My thought is to level that out for better flow.

I'm reading threw the posted thread and loving the info. I can go threw a 4 cycle engine all day doing whatever I want. But, 2 cycle, until lately, I've never had the opportunity to. So. Thank you for the help.

 

[Chainsaw Jim]

The escaping charge should be gone by the time the piston gets that far down.

 

[I Know Something]

Yeah. Lol. Thought of that shortly after I posted my last response.

Also a thought. Seems like that's the intakes air pooling spot. Where it has a small window to collect incoming air before it starts compressing?

 

[Dub11]

I wouldn't do it. Might be free porting at TDC.

 

[mettee]

You really do not want freeport if you can help it.

Throw the piston in, time it, and go to the BDC and use a sharp sharpie to trace the port on to the piston. From your line down is the room you have to work with in cutting squish and base on the cylinder.

 

[XP_Slinger]

I wouldn’t worry about it either. Like stated above, the exhaust port is done with its job well before the piston reaches BDC.

 

[I Know Something]

Lol. Read my name. You'll understand. Lol

What exactly is Freeport?

 

[Chainsaw Jim]

Visible opening below or either side of the piston skirt.

 

[MustangMike]

Exhaust timing is dictated by the top of the piston on the way down, passing the top of the exhaust port. Freeporting occurs if you lower the bottom of the exhaust port too much, when the piston is at TDC, the skirt would open the exhaust, something you don't want to happen.

That is also why the exhaust port has to be narrower than the piston skirts (the skirt keeps the port closed).

A flat exhaust roof may provide the best performance, but is not recommended for a work saw as it makes it easier to hang a ring. Generally, a broad arch is what is used on work saws. Make sure you bevel your edges if you change the size of any ports that rings cross.

That is kinda the basics.

 

[XP_Slinger]

Lol. Read my name. You'll understand. Lol

What exactly is Freeport?

We all started with the exact same name brochacho. Gotta start somewhere.

 

[I Know Something]

I should probably inform you all. Since I forgot to mention it. It's a clamshell engine. I dont know what my squish is as of yet. But. I'll know soon.

 

[MustangMike]

Clamshells limit your ability to drop the jug (you can't) because you can not mill the base. They do make pop up pistons for some models if your squish is not tight. Different pistons may also give you slightly different port timing and squish.

 

[I Know Something]

I have hand massaged car parts like this clamshell to get 30 thou that got screwed up. It's a pain in the rear and very time consuming. The only difficult part is getting the bearing housing close for its rubber boot seal. Its doable. And something I will do someday. Just not this year. That was a headache.

I think it's a 43.8ish mm piston. I'll look around when I get off work. I've freed up a lot of air flow on my Craftsman already. Still waiting on a new OEM piston.

And thank you. Your helping me go threw this learning curve. Its awesome. I love learning new things.

 

[MustangMike]

Do not use anaerobic gasket sealer on a clamshell, it will not work around the seals.

 

[I Know Something]

Figured to go with whatcha know!

3 bond 1184

 

[I Know Something]

I've got room before the freeporting takes place. Lol. And if for a work saw it's not needed. I'll just ignore the idea.