a loooong time ago, I bought a Skoda of 1966 vintage. It was a quite sophisticated vehicle, considering the antiquated materials they were working with leather or cork oil seals ,for example.
Car went,very suddenlyonto 3 cylinders,so I limped it the half mile home and guessed a stuck valve....removed rocker-box and sureenough one pushroddisplaced and valve partway down.
"repair"....Remove sparkplug, poke something (wire/ screwdriver) down hole and turn engine so piston is well down the bore. get big hammer and smite rocker above stuck valve.....after a few blows,it returns fully.smite a few more times and time it to shove the pushrod back under the other end of the rocker
engine ran faultlessly therafter.
bit of a redneck yee-haaa repair but saved rmoving the head,etc. took about 15 minutes all in.