Does anyone know if the Holliday's "cinder discharge port" (pictured below) on the smokestack actually "works" by opening/closing? Or is it just a welded on static decoration?

I've been thinking that since the engine actually burns diesel, there's no need for it to work. In fact, she doesn't even have a spark arrestor device. But, you never know what Walt was thinking back then

Back before Engine 1's most recent complete refurbishment, the base of the spark arrestor near the ash vent was bulging outward from all the built-up cinders. At least that was the cause mentioned here back then. If that was truly the reason for it bulging outward there, that would lead me to assume that the cover was not removable.

But, that was back then. The handle for the cover was broken off for the longest time too before the refurbishment. Maybe the lack of a handle made it difficult to remove, not that it was impossible to remove or nonfunctional.

But, those are 100% pure speculations on my part and I fully admit that.

In the Disneyland Railroad video from Ape Pen, an engineer said that they couldn't use it because the handle was missing but recently (this was recorded in 2007) that they found it (or cast a new one) and use it to clean the stack.

I think it was bulging just because of the weight--not because of cinders (Oil burners don't really produce cinders). I'll try and check w/ my contacts on the roundhouse.

Thank guys. Does the port open by pulling out the door like a plug? Or does it swing open on a hinge? The picture I posted as a long bar on the side as a handle, so it looks like you'd pivot the door open.

Yes, and the dynamic loading due to operation. That stack has serious inertia, and wind might contribute, too.

What material is the stack pipe made of in the area where it buckled, and how thick is it? And, is the cleanout pipe base welded all around?

The stack is sheet metal welded construction, so it's probably no. 10 (or so) sheet metal.

Other pictures show that the port is base welded to the stack.

I'm guessing that your illustration of the stack interior, in the modeling section, is correct for the Holliday. It certainly doesn't appear to have any way of preventing the release of burning wood cinders.

The thing is, the Central Pacific lower stack pipe diameter is quite a bit smaller than funnel and Radley-Hunter type stacks. I know the latter has an annular space around the exhaust pipe, where ash collects. The ash is removed via a cleanout, which looks similar to the capped "port" on the C.P. stack. But the smaller diameter of the C.P. lower stack pipe suggests to me that there is no such ash trap there. Could the port have a different function, such as a connection for bellows to induce draft?

The cap is functional in that the lever is used to remove the cover. It is just a detail that is not really meant to be used as it would have back in the 1870s--just like the Holliday's headlight has the detail of a chimney--clearly just a cosmetic detail to makle the headlight appear correct, and not functional when used with an electric lightbulb.