Exhaust Port Bridge

[NPKenny]

I haven't come across the answer to this in searching and reading over the last 6 months. Someone please enlighten me...

On some of the older saws with the bridge in the exhaust port, the dual pane approach to an exhaust port, is there any reason not to cut it out to resemble a single port exhaust and increase the flow.

The saw in question is a little Mac tophandle that was given to me. I have it all apart to clean it am of the thought that I might as well do some touchup work.

 

[Jacob J.]

The bridge is for stability, especially in saws that have a factory thin-ring piston (like the McCulloch CP-125). I'd leave it in.

 

[mattinky]

Yep, I'd leave it in, you're asking for a snagged ring if you remove it

 

[RaisedByWolves]

Thats a No No.....

 

[PES+]

If the rings are pin stopped you can remove it and eyebrow/chamfer the top of the port.....if they are not pinned do not remove

 

[Freakingstang]

I have seen where the pin ends at the bridge on some engines, removing the bridge would like cause a snagged ring because of lack in ring support.

Just port both halves. A lot of times you can thin the bridge up, just don't totally remove it.

 

[PES+]

Partner usually pinned at the bridge on the intake.....Stihl does too but only a partial bridge....I'll have to look at the mini mac....To my knowledge no engine ever pinned at the exhaust bridge because the heat there would make the pin loosen and fall out.

 

[NPKenny]

Good counsel. Thanks to all who have posted. I haven't checked to see if or where the rings are pinned.

Out of curiosity, why would certain engines need the ring support over the exhaust port and others not. Are the thin rings just not very rigid. The reason I ask is it sure seems like all of the saws I have been into have the rings really spanning some large gaps on the ports.

 

[mattinky]

Good counsel. Thanks to all who have posted. I haven't checked to see if or where the rings are pinned.

Out of curiosity, why would certain engines need the ring support over the exhaust port and others not. Are the thin rings just not very rigid. The reason I ask is it sure seems like all of the saws I have been into have the rings really spanning some large gaps on the ports.

In order to make the port wider for better performance, the bridge is there to keep the ring(s) from snagging, very common on 2-stroke motorcycle engines

 

[Crofter]

On a single port about the absolute maximum size is 70% of bore diameter and that would be very hard on rings. They are usually much less on stock saws. With a bridge in the middle and twin ports you can span a larger percentage of cylinder. Piston scuffing has sometimes been a problem as the bridge runs hot if you push performance. See where the ring gap locator is before you cut the bridge out and also make sure that the resulting single port would not be too wide. Stock port widths are more in the 60% of bore range.

 

[Duke_Spinner]

its there for ring snag ..