A little while back I was using my Great Stuff Pro14 foam dispensing gun to do a bit of exterior sealing on the house. While using it I noticed that it slowly started to clog up to the point where the foam was barely coming out of the gun. I didn’t think too much of it since I was getting close to an empty can. However, it just wouldn’t quite stop coming out while the trigger was pulled. This led me to think that the gun was getting clogged internally. I quickly decided to tear the gun apart to see if I could get it cleaned out before it was completely clogged up.
Before we get started, I’ll mention I took all these pictures upon reassembly of the foam gun. I’ll be covering both disassembly and reassembly in the same pictures since there are a lot of pictures. Also, it helps to have a tub of acetone to put parts into during disassembly to stop any uncured foam from curing inside the gun. So, lets get started.
First, remove the foam can from the gun if necessary. Next, remove the screw from the adjustment knob on the back of the gun.
Under the adjustment knob is a plate that is held in with two screws. Remove the screws and the plate.
Unscrew the brass adjustment screw. There will be a steel ball and spring (which is under pressure) behind it.
Behind the spring is another brass part. Notice that it fits into a slot on the trigger for reassembly.
Remove the brass part and the rod. The rod may be stuck in there pretty good. A pliers on the shaft may help to free it, but be careful not to mar the surface of the rod. It must seal against o-rings in front of the trigger when you reassemble things.
With the rod removed, clean it up as well as you can. Make sure not to mar it up and pay special attention to the tip that seals the gun.
Next, remove the foam can mounting piece. It has a hex base so you can use a wrench to remove it.
On the bottom of the mounting piece, there is a brass piece with a slot in it. Use a flat bladed screw driver to remove this piece. Behind it is a spring and a white plastic ball. You might need to remove foam to get to it. I just used a small flat bladed screw driver to scrape it out. Some acetone may help too. Try not to poke too far into the gun. The white piece is a plastic ball that seals things. If it gets scratched up it may not seal.
After things are disassembled, clean the foam off of everything you can. Just be careful not to mar up the sealing surfaces where the plastic ball seats.
Next, remove the tip from the gun. It has a hex section to get a wrench on it to unscrew it. Once it is removed, scrape the foam out of the inside of it. The rod’s tip seals around the hole in the end, so try not to mar that surface.
When you go to reassemble things, I used some teflon tape to help seal things up. I used three wraps and I think a few more would have been a bit better, but mine did not leak.
The tube is the next piece to remove. Again it has a hex section for a wrench. However, I couldn’t remove it with just that. I had to use a channel locks or vise grip type tool to get a good grip on it.
Once it is removed, scrape the foam out of the inside of the tube. You probably aren’t going to be able to clean it perfectly. This is what mine looked like when I reassembled it.
Now, remove the trigger. It has an e-clip on one side. Remove that and the pin slides right out and the trigger can be removed.
Remove the brass piece in front of the trigger. It has two o-rings in front of it, so make sure to remove those as well. If they are damaged at all be sure to replace them.
When reassembling this piece, first just screw it in a little bit. Once the rod is reinstalled, you can tighten it down so it seals properly.
Next up is to clean the handle section of the gun. Its a bit more tricky, but you can work at it from both ends. Clean it out as best you can.
Once everything is cleaned up to your satisfaction, you can reassemble the gun in the reverse sequence.
After this fix, my gun has been working very well ever since. Good luck with your own.