Closed port v.s open port (education) calling all saw techs

[slipknot]

Like most members on this great site I contribute what I can when I can. Im the first to admit I dont know everything. I've learned almost everything i know about saws here at arboristsite.com a.k.a chainsaw university online..atleast to me anyways. I always do a search BEFORE i start a new thread...and i looked for what im about to ask and didnt find it. The title may lead you to think this is a debate..it is not. To those that are gifted with the knowledge please school me and Im sure alot of others whats the difference in design. I know one is closed and one is open...but lets go into detail about it. I believe that sometimes contributing to this site is to..ask a question that hasn't been asked before to gain knowledge...others get to read it and gain it too. So if you take the time to contribute your knowledge it will earn some of those new rep points i keep hearin about. (new to me..as that wasnt thought of yet when i joined) Its been a while since ive contributed to this site..like 2-3 years i think. Boy does it feel good to be back. good to see that AS mainstayes are still here...hopefully that Thall guy will respond to this...he's informative and makes a crappy thread good just by how he handles his business...lol..just dnt say anything bad about stihl...dayyumm!

 

[slipknot]

I guess I'll be the first to reply...what inspired me to start this thread? I have a efco 952 w/ a scored piston and jug...i bought it that way hoping to breath new life into it. Im having a hard time finding a replacement piston(45mm) It does not look like any on bailey's..they all look "open" while mine looks like it came out of briggs & stratton. what i mean is..it looks like a closed design? its not hollowed out around the pin area..if that makes sense? So thats how this came about. If you happen to know of an alternative..pm me please. I aint buying OEM..id have to sell the saw to afford those prices. emak has to be the worst saw to buy parts for..it makes no sense to repair..just go buy another. But I like them, they are unique and Im the only one in the county where I live that runs exclusively efco or even has one for that matter.. I like being different!

 

[spudulike]

http://www.episan.com/

http://www.meteorpiston.com/eng/cataloghi.php?catalogo=gardening

http://www.aippistons.com/

These sites have plenty of dimensions of pistons - check diameter, wrist pin size, piston height and pin to piston crown height.

Spud

 

[GASoline71]

Who let you out of the "politics" forum?

Gary

 

[GASoline71]

I meant it in jest mang... no blood no foul...

Gary

 

[TRI955]

"slipknot is a glorious beacon of light" LMAO!!! Who comes up with this stuff!?!?


Mike

 

[berryman70]

To those that are gifted with the knowledge please school me and Im sure alot of others whats the difference in design. I know one is closed and one is open...but lets go into detail about it.

Good Post,This could be a interesting thread if we can somewhat keep it on topic. I've been wondering the pros & cons of open/closed ports myself. From what I know open port is less expensive to manufacture, it is easier to modify but how much less performance potential? lets hear it.

 

[pioneerguy600]

opcorn:opcorn:
Pioneerguy600

 

[parrisw]

From my reading and learning from the pros, closed port is better for modifying I think!!

So for your piston you just need a piston, the cylinder is ok? Why not post up some measurements, post some pics of it, you main measurements you need are crown height and bore dia, crown height is from the top of the pin bore to the top of the piston, a little taller won't hurt at all, measure your squish stock and see how much room you have.

 

[berryman70]

From my reading and learning from the pros, closed port is better for modifying I think!!

Better to mod as far as better performance potential,I said maybe a little easier as far as opening the transfers. Was hoping to have more discussion on this topic.

 

[troutfisher]

I guess I'll throw in my 2 cents here.....I think the roof of the transfer port is what matters. The transfer port needs to re-direct the flow, it needs to turn it and send it out across the piston. A nice deep closed loop transfer port does this well, a shallow open port has less roof to catch and re-direct the flow. I think the deep transfer ports work better, but weaken the structure of the jug, therefor the bridges are needed to strengthen it. It also makes it more expensive to make. Just an opinion, maybe I'm wrong.

 

[J.W Younger]

Intresting thread, I have a question. Is a 6400 mikita open transfers and when its upgraded to a 7900 or larger are those cylinders open or closed?

 

[berryman70]

I guess I'll throw in my 2 cents here.....I think the roof of the transfer port is what matters. The transfer port needs to re-direct the flow, it needs to turn it and send it out across the piston. A nice deep closed loop transfer port does this well, a shallow open port has less roof to catch and re-direct the flow. I think the deep transfer ports work better, but weaken the structure of the jug, therefor the bridges are needed to strengthen it. It also makes it more expensive to make. Just an opinion, maybe I'm wrong.

:agree2:

 

[slipknot]

A look at a EFCO 952 jug.

So would this efco 952 jug be a closed port design? This thing came from a saw I bought for parts...looks like they ran pure gas and siezed it up. Im hoping to salvage this jug after I do all my research on how to...here on the AS archives. I think it could be cleaned and maybe opened up a little. It will be my first port if I can bring it back to life.

 

[thomas72]

One good thing about closed ports would be the decrease of volume in the crank case.

 

[Andyshine77]

Intresting thread, I have a question. Is a 6400 mikita open transfers and when its upgraded to a 7900 or larger are those cylinders open or closed?

The 6400 has open transfers, both the 7300 and 7900 have closed transfers.

I'll guess that closet transfers also provide better charge velocity, and direct the flow more accurately.

 

[billmartin]

I'm awfully green here but I'm thinking that the closed must be better as it is seen on the pro type saws. While the open is on the weaker type saws.

What I would honestly like to know is the best way to deal with transfers in an open port cyl is?

 

[slipknot]

Thats good info..I can actually say i learned a thing or 2.

 

[CHEVYTOWN13]

I guess I'll throw in my 2 cents here.....I think the roof of the transfer port is what matters. The transfer port needs to re-direct the flow, it needs to turn it and send it out across the piston. A nice deep closed loop transfer port does this well, a shallow open port has less roof to catch and re-direct the flow. I think the deep transfer ports work better, but weaken the structure of the jug, therefor the bridges are needed to strengthen it. It also makes it more expensive to make. Just an opinion, maybe I'm wrong.

I think you're on to something here.

Here is a picture of the open ports on a 510 cylinder. The roof's of the transfer ports are flat and at 90º to the port.

A curved closed transfer offers optimum FLOW fo show!

 

[fredmc]

I've seen a few saws apart and the open transfer models I've seen generally have scoring where the piston meets the transfers. I would say you may have to rebuild an open design more often than a closed design. Longevity may play into this also.