You'd have to tap into the crankcase in a location where the nipple you thread in will not interfere with moving internal components, and where you will not weeken the crankcase. If there's a conventional backplate, I'd drill in the centre of it, and be sure to file the nipple flush inside. I'd avoid anything in the bearing area, or in the arc of the conrod.

Looks like the SPE40 is an engine with a crank bearing in front of and behing the cylinder, with a pto shaft stub out the back. That makes things more difficult. Don't weaken the mounting lugs or bearing housings.

The crankcase is an open volume, so the whole crankcase sees similar pressures at any given moment. It won't matter from that perspective where you drill.

Think about this though. For the cost of a smoke pump, you're voiding the warranty of and risking the integrity of your engine. You're running a gasser, and you're gonna be carrying a second tank for smoke. Is the 60 buck, 2 oz smoke pump really that big a problem that you're gonna risk your $300+ engine? I'm sure it could work OK, but what are you gaining, really?

I don't quite get it, I guess.

J