I have a max roofing nailer that the nail feeder turns and jams. What causes that? It can't feed nails

Broken or dirt or kinked scroll spring or the wrong nails or loose nail rail that not slide smooth nails or the impact pin self is turned wrongside to the nails because of an service cleaning or , ? but on much nailers there is important a little bevel on that bevel must have the right direction against the flow of the nails in to the back of the nailer there must a little space between the nails because it will have a problem with the second nail also when the pinion is shorted by use it will have the same nail jam trouble. the top of the nailer must also be clean the right air about max 7 bar pressure the piston must be good pushed back high enough after release the trigger thats the first thing to control and the valve must be clean and working smooth push it in by hand its should not hanging

Some causes, in order of probability:
Roofing nailers get a lot of tar build up on them, especially around the nose safety and nail feed pawl area. Cleaning off this buildup will usually take care of most problems with roofing nailers.
On the side of the gun away from the side you load the nails on there is a small cylinder with a piston inside that attaches to the feeder pawl. If air isn't getting to the piston or the piston's o-ring or spring is damaged, it won't cycle properly to advance the nails.
If the driver doesn't retract fully, the next nail won't be able to advance properly for the next shot. This can be caused by o-rings in the head that are worn or out of their proper place.

I have noticed that some if not all brands are now using metal wire instead of copper to make coils. Metal wire is stiffer and does not bent down out of the path of the driver. If you are using coils welded together with metal wire (some wire looks copper collored, however when tested with magnet is found to be metal), and after firing a few nails, open side door and check if the leading wire is not bending down. Leading wire will not allow the nail the fully move into the path of the driver. Stiff wire will also cause the next nail in line to pull down slightly. When nail is pulled down slightly, it will be out of the path of the driver. The driver will hit the edge of the nail and cause it to flip. The nails can also flip if the feeder is not pushing the nails fully forward due to low pressure or weak spring or springs (some nailers have a spring pushing feed piston others use air). Finally, the feed piston or the body of the nailer where the feed piston is housed could be worn. With feed piston in forward position (normal) and the feeder claw removed, apply outword pressure to feeder with thumb checking for loose fit. The feeder shaft should not be loose nor move from side to side with thumb pressure. If shaft is loose then most likey lower body of gun worn with no repair. Good luck with you nailer.

Nailers that use strips of nails (one nail directly behind the other) will sometimes drive two nails at once and is caused by damage to the driver. The nails are so close together that the driver will hit the first and part of the second nail head. Coil nailers, as your an451, use nails seperated by welded wire making it very difficult the the driver to hit the second nail. Usually when a coil nailer shoots two nails, it is acutally the trigger valve that acutates twice (two very rapid fires). Two very rapid fires is caused by faulty trigger valve. I have seen a roofing coil nailer fire one nail and a second nail drops out of the gun. Caused by weak / malfunction of nail feeder or wire used to weld nails together is too thick.

Hitachi coil roofing nailer will skip nails if the piston oring is worn, the feed spring is weak or lower bumper is cracked. Easy to check. Remove nails and air supply. With side door open point nose of gun up then down again. If the piston moves up and down in the cylinder, replace the piston oring. If piston does not move and is in the up position, check the feed spring for tension. With air supply removed and door open, slide feeder back and press on feeder from door side to check tension. It should spring back to position against rails.If is feels loose, replace spring and retainer pin if the pin is worn. If piston oring is good, and the feeder has good spring tension, suspect lower bumper and the plastic part below the bumper called the "sheet". Remove head and pull the cylinder to examine lower bumper. Parts are available at www.toolpartsdirect.com. Good luck with your repair

Make sure that orings are in good shape, lower bumper not cracked, (no leaks and the driver/piston stays at the top position, if piston drops a little or all the way down with no nails in gun, replace piston oring). Also check spring tension for feeder and two check paws in the door (feeder tension should be firm ). Adjust the timing screw up or down one or two turns and test (timing screw at the top of safety foot, head of screw pushes on the firing valve ). Test for lower bumper cracked. Remove nails and leave side door open. Hold the nose of the gun against coiled air hose or thick rubber and press and hold the trigger. The piston will stay down against the bumper until you release the trigger. No air should leak out the driver path. If air leaks past driver suspect bad bumper. Test action of feeder piston. Remove side cover to feed piston and clean debris. With air disconnected, move the feed piston back and forward. There should be a little resistance, if it moves very easy, suspect orings worn. As soon as you connect the air line. the feed piston should move forward with force, note the position of the feeder. Now with air disconnected, place nails on the feeder. The first nail should be well within the path of the driver. If not fully under driver path suspect worn feeder / feeder retainer pin, or debris inside feed piston chamber preventing piston from full forward travel (debris from inside of the gun will enter the feed piston chamber usually broken bits of lower bumper). Replace parts as needed. Good luck with your repair.

This is a fantastic nailer, very powerfull. Information about your nailer can be found below.

http://www.bostitch.com/default.asp?CATEGORY=BOS_FRAM_NAILER&TYPE=PRODUCT&PARTNUMBER=F21PL&SDesc=21%26%23176%3B+Industrial+Framing+Nailer+System

You should not need to lube the rails for the nails to feed. Your nailer uses plastic collated nails and should travel very easily inside the rails. I would remove all the nails and check for broken pieces of plastic from nail strips. Feeder should feel snug within rails and not wobble and spring should pull tight. When you install the nails do not release feeder against the nails with force as this could break the plastic strips and cause jam. Nail not feeding is usually caused by wrong nails, weak pusher spring or pusher guides broken /missing. Simple test for proper nails.
Place a strip of nails on the outside of the rails aligned with the edge of the rails and see if the first nail is perfectly aligned with the path of the driver. If the head of the first nail is angled back slightly from the path of the driver, the nails will not feed properly. Good luck.

You should be able to open the load cover and be able to remove the nail. Sometimes the nail wire is located in the wrong spot which will cause the feed pawls to get jammed, and also cause the nail to get hung up. After you get the nail dislodged make sure that your canister is set to the correct level for your size nails. Then lay the nails down to load it. Check the placing of the wire on the nails in relation to the feed pawl. If the wire is on the feed pawls you need to find another roll of nails and do the same thing. Sometimes the wire is misplaced during production and affects certain nailers. If you have any questions please post again.

if u are right nails for gun,then make sure when u put coil in and feed in front of firing pin the nails are straight with pin and connecting wires are not bent causing nails to fall out of alingnment.

Max nailers are very good quality and parts are not expensive. Parts and parts list at www.toolpartsdirect.com. Check the following to repair not feeding problem.
Check paw in the door should have a light spring action. Feed paw should have a medium spring action. You may have to pull the feed piston back and hold to check feed paw spring action. Feed piston should have heavy spring action. If springs seem ok then remove feed piston and replace two orings. If the feed piston spring is broken replace with correct part. Make sure that the ports that direct air to feed piston are not blocked with bits of rubber or dirt. Sometimes parts of the bumper will break off and spread thru-out the gun. Good Luck and enjoy. (parts not expensive)