Originally Posted by CooperMan
Interesting that they are compression ignition diesels (can't do a spark or glow plug small enough?)

The smallest spark-ignition engine in my collection is a replica pre-WWII German Felgiebel that I bought at auction. Champion made plugs small enough (1/4" x 32tpi) but not for those miniature engines by Ronald Valentine. Some scratch-builders do make them, a real labour of love and not always with successful results.

[Linked Image]