Well, whaddayaknow...

Obviously, it's for the fuse.

Ken Cook wrote:       Obviously, it's for the fuse.

!!!!!!!!!!!!!!!!!!!!

Time for some searching. I remember something about the Pipe Bomb Engines and the mysterious hole somewhere not too long ago. When I get a few minutes later, I will see if I can did it up.

Ken Cook wrote:       Obviously, it's for the fuse.

Now, that’s Funny , said like Larry the Cable Guy!

I've seen a hole in the plastic case version with a tank in about that spot. It was actually a front rotary valve version and a long tube ran from the tank and sat in the intake hole at right angles. This version doesn't have a tank, plus it has a reed valve back end, so it's a mystery to me

Ok. So I stand corrected. I found the article in question that I referenced earlier. However, it was not a Pipe Bomb engine, but rather the nylon version. The hold was a 4-position fuel metereing valve. Anyways, here is the link and teh description is approximately 1/2 way down on the first page.

https://www.coxengineforum.com/t1590-testors-plastic-crank-case-engines?highlight=testors

I found it interesting Bill Netzeband's explanation on the creation of that multi-position fuel metering valve, especially his comment that there was never time available to do things right the first time but always time to do it over. (This statement about never enough time seemed to apply also to the aerospace industry I worked for some time back. ) I gather that marketing must have gotten involved to use a manufacturing moulding process that was inferior (but cheaper) to the engineer's precisely machined valve. The prototype metering valve must have been a work of art.

I suppose if one had the resources and time with access to machine shop equipment, could come up with a press fit plug with a specially crafted needle valve assembly inserted, to bring the front hole reed valve pipe bomb engine back to life. But then these were after all, inexpensive product engines to be tossed after the RTF product was destroyed (usually after first flight ).