What small cam do I have???

Pull it clockwise towards you and it is engaged. CCW Toward engine is disengaged. Spring is a return for it. Should be a bolt hole on front of head that it secures to.

 

Three good batteries and you won’t really need the compression release. It does let the starter spin over a little faster. It holds the valves open so it will not fire until it is released.

 

You only use it as a starting aid. Compression was higher and batteries were weaker back then. All 6V in banks to make 12v and 24v. Many trucks used 24v to crank and then you had to flip a switch back to 12v to run.
The compression release rod runs next to the push tubes (push rods) and lifts them up to open valves to allow the engine to crank without compression. Once it gets spinning pretty good you release the handle and the valves close like normal and it fires up. Easier on starter and batteries. Don’t pull that release during anytime after the engine is running above idle because bent push rods will happen. It is not a Jake. BUT the old Cummins shop manuals did say that at IDLE ONLY it can be pulled to be used for an emergency shut-down if the fuel shut-off solenoid stops working. Without damage.