Narrow Gauge SP 4-6-0 #18 on loan to the Durango and Silverton blew a cylinder head, ...she’ll be out for a while.

Another view

My goodness! I hope no one was hurt.

Any idea as to what happened, or is it too early to say?

That's unfortunate. Looks like a nice clean break in the casting. No clear sign of a prior crack/flaw.

Looks like a hydraulic failure, someone forgot to open the cylinder cocks, or the cocks were plugged ?

Good luck, Kevin

I'm thinking if it had been water in the cylinders it would have blown the entire head off. I'm thinking something else let go and the piston overtraveled into the cylinder head.

Looks like the piston came loose and hit the head....very similar to the damage incurred on the hiesler that was running in Arizona in '09...rod end came off, piston hit the head, blew the cover off and shattered the head....
If you look close, there's probably cracks radiating from the center hole....

Whatever happened, it does not look as simple as someone forgot to open the cylinder cocks. Looks like the piston itself shattered as well as the head...appears something worked loose allowing the piston to contact the cylinder head.

Well, if it had to happen it happened at a railroad with a shop more than capable of dealing with this kind of relatively simple repair. I'm sure the D&S will have her back in service soon after they get the castings from the foundry.

That's not something you see everyday even in the steam era. However in today's world it is a WOW event.

The piston fragments show that they struck each other as the thing disintegrated, and that tells me that the cylinder bore got gouged and roughed up by those big chunks as they hammered the cylinder head.

I see a boring machine in that engines future.

This thread on the NGDF contains a number of images showing the damage, etc.:

SP 18 run, piston failure, and rescue 4-9-19

I was riding this train during the break down. Official cause was a broken lubricator.

Surprised they've nailed it down so fast. However, I suppose the lack of lubrication could have caused the piston to bind up, which caused it to slide on the piston rod or do something that effectively made the piston rod longer than it should be by moving some adjustment point. That could in turn cause it to strike the cylinder heard. So it's seems plausible that's what happened.

Per Jeff Taylor post on NGDF...

"Here is the inside scoop. It is believed that a partial ring failure caught a port and destroyed the piston. The piston fragments then punched a hole in the cylinder head."

More information can be found at their forum.