M2HB Crankfire Installation Instructions
Installation instructions for the M2hb Crankfire Systems unit:
1. Remove the back plate from the receiver.
2. The original butterfly trigger and spacer will need to be removed from the back plate and replaced with the new trigger and spacer provided. The trigger is retained in the back plate by a 3/16" diameter cross pin that can be pushed out from either side of the back plate. You will need to apply some upward pressure on the trigger against the return spring to allow the pin to slide easily and to prevent the trigger return spring from taking flight when the pin is removed. Once the pin is clear of the trigger let the spring extend slowly and then remove it. You will reuse this spring and pin with the new trigger. The original butterfly trigger and spacer can be withdrawn to the rear of the back plate at this point. I have found the easiest method of getting the pin/trigger/spring/spacer all gathered up and in place; is to use a pin punch inserted from one side to get the pieces roughly in line. Then "Chase" the punch back out with the trigger pin as it is installed.
3. Installation of the new trigger and spacer is essentially the reverse of the above, however the new trigger can be inserted from either the front or rear of the back plate.
4. Remove the two 8-32 button head screws on the top of the Crankfire unit and remove the dust cover.
5. Remove the two 1/4-28 socket head cap screws from the mounting clamp and remove the clamp cap.
6. Position the Crankfire unit onto the back plate by turning it at a slight angle to get the single shot trigger past the R.H. spade handle and making sure that the rocker arm is above the projecting portion of the new back plate trigger. Seat the buffer tube in the main housing clamp.
7. At this point it is easier to proceed if the back plate and unit are positioned upside down on the table.
8. Re install the clamp cap and the two 1/4-28 screws, leaving them loose enough to allow the unit to be moved into it's final position on the buffer tube. The front edges of the main housing should just butt up against the upper spade grip frame and the sides need to be parallel to the sides of the back plate. When it all looks nice and square with the back plate, carefully snug up the clamp bolts working evenly between them (tightening one side more than the other tends to cant the unit on the buffer tube.) Also pay close attention that the front edges of the main housing stays parallel to the back plate in the vertical plane. When you have the unit square and parallel with the back plate surfaces, tighten the clamp screws securely.
9. Turn the assembled unit and back plate upright and loosen the 7/16" jam nut on the rocker arm adjustment screw. Back the 1/4-20 adjusting screw out until it just touches the back plate trigger.
10. Reinstall the back plate assembly on the gun.
11. After making absolutely sure that the chamber is empty, charge the gun and rotate the crank enough to cause the cam to trip the rocker arm/back plate trigger. Listen for the sear to release the striker (It probably won't at this point.) Assuming that it doesn't, turn the rocker arm adjusting screw in (clockwise) a little and rotate the cam past the next lobe to see if it trips the sear. Repeat the process until the rocker arm reliably depresses the back plate trigger enough to achieve sear/striker release. You want the adjustment set just far enough in that the gun will fire reliably across all six lobes, but not appreciably more than this. Check the function of the single shot trigger at this point.
12. At this point it is time to remove the back plate/Crankfire unit as an assembly from the gun. Make sure that it can be removed and replaced with out any interference between the back plate trigger and the main trigger bar inside the gun. There is plenty of clearance on my TNW gun here, even with the rocker arm adjusted to put excess pre load on the back plate trigger.
However, on my gun it appears that the radius, for the interface between the main trigger bar and the back plate trigger, was probably generated on a belt grinder by hand. So I have no idea how much dimensional latitude may be present in other guns. I don't think it will be a problem, but please pay close attention here and let me know if you do have a problem.
13. Assuming all is well at this point, test firing the gun is in order. There are two methods of operation for the "Deadman" crank handle. You can engage the drive dogs by applying pressure against the spring-loaded handle to the "IN" position and then rotate the crank. Or you can leave the handle in the "OUT" position (freewheeling) rotate it to the desired speed and then move it over to the "IN" position to engage the drive pin on the shaft and fire the gun in short bursts. The single shot trigger is attached directly to the rocker arm weldment and will fire the gun any time it is depressed. I have found the best position for the crank handle, when using the single shot trigger, is to let it lay towards the rear of the gun on top of my hand when holding the spade handle. Also, I prefer using two fingers on the single shot trigger, may just be me, but it seems to afford better control than using just my index finger alone. I haven't had the opportunity to try "bump firing" with the single shot trigger, but I think it might work pretty well this way, if one was inclined to do so.
14. If you want to reverse the crank handle from one side to the other, the procedure is as follows. Remove the dust cover. Looking at the cam, you will see a 1/8" roll pin in the drive slots. Drive this pin completely out. There is an E clip on the end of the drive shaft next to the housing. Remove this clip. Withdraw the shaft/crank assembly; the spring load on the rocker arm will push the cam down a bit, so some pressure on the adjusting screw end of the rocker arm is in order. Remove the cam and reverse it so that the drive slots are on the same side you want the handle on. While holding the cam against the spring loaded rocker arm to align the holes, slip the shaft/crank assembly back in. Replace the E clip and the drive pin.
15. Clean and lubricate the Crankfire unit the same as your gun. Use a little grease on the cam pins and the rocker roller. Just make sure that everything in the unit can move as freely as possible, any drag or binding will serve to decrease the unit's performance.
16. SAFETY CONSIDERATIONS: The spring loaded "Deadman" crank provides only a small safety feature in that the crank is automatically disengaged from the cam when firing pressure is released. Please do not attempt to defeat this feature. A fixed crank hanging off a LIVE GUN is a matter of "when" not "if" it will get bumped! But, DO NOT rely on this feature to put the gun in a SAFE condition, it DOESN'T! The single shot trigger is always HOT, and will fire the gun if it's loaded. The only SAFE condition for the Browning guns is when the chamber is EMPTY; NO BELT in the gun and the top cover is OPEN!