I have a couple of the new style Dynatex blank firing grenades (BFG’s). One of them started to go off almost as soon as the pin was pulled rather than after the normal 5 second delay. So I decided to take it apart to see what was going on. Sorry, no pictures at the moment, but next time I take one apart I’ll get some pics.
First, how to get in to them. The metal top of the grenade is press fitted into the plastic body. To remove the top, warm the upper half of the grenade with a very hot hair dryer for a few minutes or place the grenade in a warm oven (100c). Once the plastic is warm it is a lot more flexible.
Remove the cap where you stick the blank and instead of a blank inset a long bolt so that the shaft of the bolt passes through the hole in the cap. Screw the blank housing back into the top of the grenade and use the protruding long bolt shaft to lever out the entire top of the grenade from the warmed up plastic shell. You will only be able to get the top off if the plastic shell is hot, if it’s cold it won’t come out and you risk damaging the grenade.
Once the top is off the internal mechanism is very simple. The issue with mine was dirt under the upper (smaller) O-ring. This O-Ring acts as a one way valve to help you prime the grenade, any dirt under it will let air back through in effect keeping the valve open and the grenade will fire prematurely.
I recommend removing and cleaning both O-rings and then apply a very small amount of silicone grease to them. You only want a very, very small amount of grease as any excess grease will attract dirt and dust and could lead to more problems in the future.
You will also find a small allen head grub screw in the nylon shuttle. You can use this screw to adjust the timing of your grenade. Screw it in (clockwise) to increase the delay and turn it anti-clockwise to decrease the delay.
Reassemble the grenade by again warming up the plastic body and gently tap the top back into the body. If the body is warm enough it doesn’t require much effort to get the top back in.
For replacement pins you can buy split pins from any good car spares store and use a key ring ring for the pull ring.