Contractors have to replace the o-rings in their staplers and nail guns periodically because damaged o-rings can lead to air leaks. If you find that your nailer or stapler isn’t performing at its peak, its o-rings might be in need of replacement.

Here’s how to replace the o-rings in a Bostitch MIIIFS. (If you know that o-rings are not the cause of your troubles, here’s our guide to troubleshooting common nailer problems.)

Step 1: Make sure you have all of the necessary tools and equipment.

The Bostitch MIIIFS and MIIIFN each come with a special kit for replacing the tool’s o-rings, as well as a repair kit. These kits contain all of the tools you need to perform this repair. Need a new o-ring kit for your Botitch MIII? Click here to buy one online. 

With most other nailers and staplers, you can use standard tools for the o-ring replacement process.

Step 2: Disassemble the entire nailer/stapler from the top down.

To remove the top cap, take out the four allen head screws. Take out the three screws on the poppet actuator to remove the actuator. Then remove the shoe base to access the bumper.

Step 3: Remove the poppet from the piston stem mechanism.

If you’re working on a Bostitch MIIIFS or MIIIFN, use the special wrenches included in the tool’s kit to perform this step.

Step 4: Remove the external and internal o-rings located on each part, and thoroughly clean all of the parts.

You want to clean all of the parts using tool oil in order to remove any grease, dirt, and debris that has built up over time. You should also take this opportunity to inspect each individual part for damage, because leaving a damaged part in your tool can really harm your equipment.

Step 5: Add new o-rings to the nailer/stapler.

Before installing the new o-rings, apply a slight film of o-ring grease to each one. You should also apply some more tool oil to the moving parts to facilitate reassembly. Be sure to use the appropriate grease rated for the o-rings used in your application.

Step 6: Reassemble the piston mechanism, poppet head, and driver assembly using the wrenches in the tool’s repair kit.

Step 7: Tighten the assembly so the plunger is flush with the top of the poppet.

Step 8: Test out the tool to make sure that it’s functioning properly and  the problem has been fixed.

If you find that your tool still isn’t functioning correctly, the source of your problems is probably something other than o-rings. Check out our blog post about common nailer problems.

You can prevent your newly installed o-rings from wearing down quickly and becoming damaged by adding enough tool oil to your nailer or stapler—typically, it needs two to three drops of oil a day to maintain its peak performance.

For more information on Bostitch products or replacing the o-rings in your tools, call us at (800) 787-1786 or email info@cityfloorsupply.com to speak with a hardwood flooring professional from our in-house equipment repair shop.