"Valmet" is the name of the original Finnish manufacturer. "Jyskän Tehdas" means "factory in Jyskä", which is where the engines were manufactured. Click on the image for a closer view of the serial number.
If the engine identification plate is missing, don't worry. The serial number is also etched into the top edge of the forward buttress, on the starboard side. (Note that the photo is of a partially-dismantled engine, showing only the front part of the crankcase)