In military service, it was +5 to -3.
From AP 101B-5510-15 (Chipmunk T Mk10 Pilot's notes) Part II )limitations Section 3 (c):
'Normal Acceleration. Accelerometer readings are permitted within the range +5 to minus 3 g.'
Although, I (or my students!) managed to overstress on more than one occasion. The engineers didn't start their checks until +6g. I defy anyone to push more than -3g in a chippy!
There was always a lot of 'fokelore' regarding the stopping of the engine under negative g. The common misconception was that the engine was starved of fuel while the aircraft was inverted. However, the design of the Hobson carburettor meant that the float floated to the bottom of the float chamber (upside down!)and the metering valve was fully open, therefore the cut while inverted was a rich cut and not fuel starvation. The advice to close the throttle was to reduce the ammount of fuel entering the cylinders allowing a quicker pick up when positive g was restored.
I never subjected the aircraft to anything more than hesitation slow rolls in the neagtive sense. The key to successful Chippy aeros was maintaining your energy. I saw too many people trying to impress by pulling hard - the net result was that they ended up at base height sooner!