The railways in Gensokyo usually import their coal from the outside world, what would happen was that with the help of Yukari's gaps, a crack team of youkai will go out and steal wagon loads of coal. Sometimes from Japan, sometimes from other parts of the world. However, Yukari's recent disappearance meant that some coal from nearby would have to suffice. So both the narrow gauge railway and the somewhat larger standard gauge railway had to use a mixture of low quality Japanese coal and low-grade charcoal. This in turn creates more ash and gives all the engines bad indigestion.
One day, Kenta was pulling a train from Mayohiga to the Kappa Valley yards. He wheezed and coughed the whole way through. He even accidentally caused a small accident and sneezed black soot all over one of the signalboxes. Trains could not past by until proper visibility was had again.
"When will we get there!" gasped Kenta.
"Once we get to the yards, we'll give you a proper washout." replied his driver.
Kenta had to make a stop to pick up some goods from the Human Village before he had to make his way to Kappa Valley. But when Kenta tried moving again, he couldn't breathe. He tried to blow some ash out, but there wasn't enough air.
"That's done it." said Kenta's driver.
"What's...done?" replied a breathless Kenta.
"Your smokebox door is bent. Its those hot ashes that did it."
"How..." Kenta weezed, "...can we fix it."
"Hmmm...I'll be right back."
Kenta's driver left and within a few minutes came back with some flour, a bucket of water, and some old copies of the Bunbunmaru Newspaper.
"How is water and...newspaper going to help?" asked Kenta.
"Me and the firewoman are going to make paper mache and we're going to patch the hole the bend in the firebox makes." replied the driver.
Soon, the driver and the firewoman ripped the newspaper into strips and mixed the flour with the water. Dipping each paper strip into the bucket, they laid them across the area that Kenta's bent smokebox door created. Kenta felt a little better after that.
Kenta made the journey back home without any issue. That night in the sheds, half of the other engines were moaning about their aching boilers. Kenta was just about to fall asleep when he heard some breathless noises.
"Stop that!" he shouted, the engines that were awake looked at Kenta crossly.
But the silence was followed by a quiet chuckling, it was coming from Hachirou, Kenta had heard this.
"Insolent engines." grumbled Kenta as he fell right to sleep.