They were troublesome to say the least. Do a web search. There are many places that have tidbits of unfavorable history on these. Some ran very well with the right TLC and hap-hazard quality in the same package. Put out around 1936 to about the mid 50's I think. Started at about a $1.50 and ended near $6-8. Mostly sold in the back of hobby mag's. There used to be kits sold as a replica not too long ago.Originally Posted by T.L.A.R. eng
If you can do searches that include (GHQ + "model engines") or the like. You should have reasonable luck in wringing out something useful.
The consensus was that these made better paper weights than model airplane engines.....