PolarStar Fusion Engine Tips and Tricks, Nozzle Alignment, Safety Lever and Barrel Extensions

When adjusting nozzle alignment issues with a V2 PolarStar Fusion Engine, the most difficult alignment issue to solve is having the nozzle sit too high in the hopup. This isn’t a common problem, it often occurs when an upper receiver and lower receiver aren’t matched (from different manufacturers). One way to bring the nozzle down so it’s centered in the hopup is to add a small set screw to the back of the Fusion Engine. You can then adjust this screw as needed to bring the nozzle down. The set screw, when pushed out from the back of the Fusion Engine, presses up against the back of the lower receiver, forcing the nose of the Fusion Engine down. Without the set screw, in this case, the buffer tube screw will pull the Fusion Engine back, raising the nose of the Engine. The set screw prevents that from happening. Note that using a rear set screw as shown may cause misalignment in the pin hole above the trigger. In this cause simply leave the trigger body pin out. The Fusion Engine will be held in place by the grip screws and the rear buffer tube screw and the pin isn’t needed. You can see in the last picture the downward rake of the Fusion Engine and the missing trigger body pin. This was needed to get the nozzle centered since the upper receiver did not match the lower properly.

For the V2 PolarStar Fusion Engine, if you need to adjust the nozzle up in the hopup, you can help center the nozzle by adding a shim under the front cylinder, or, if possible, you can tighten the rear buffer tube screw (assuming the screw goes into the back of the Engine). Note that tightening the rear buffer tube screws puts pressure on the trigger body pin and the rear body pin, so have the pins installed before tightening the buffer tube screw, and loosen the buffer tube screw before removing them. For shimming, I use simple washers from the hardware store, but sometimes thinner shims are needed. Just about any material can be used a shim, even cut up business cards. If you would like different thickness washers, official P* shims are available from P* retailers.


Sometimes the placement of the V2 PolarStar Fusion Engine within a receiver causes the semi auto trigger pull to have a “bump” feel to it. This is due to the safety lever being partially engaged and when you pull the trigger; it hits the safety lever then pushes it out of the way. One way to fix this problem is to grind down the selector plate by about 1mm. This allows the selector plate to site a little further forward without engaging the safety lever. See the picture below to show the small cut in the selector plate. An alternative is to cut down the “D” part of the “P” safety lever to allow the selector plate to move forward more.

IMG_2237 P1060983_annotated

A small tip when having problems with shot accuracy and consistency. Always remove your barrel extension or flash hider when trying to solve shot consistency problems. You want to eliminate anything past the inner barrel as the potential cause for the problems. Check the extension or flash hider for any white marks, which would indicate the BBs are hitting it on the way out. The pictures below show where the BBs were hitting the end cap on this extension. There wasn’t any play with the inner barrel, so the end cap was drilled out to make the hole bigger so the BBs wouldn’t hit it.


PolarStar Fusion Engine Parts Identified

Here are some pictures that identify the various parts of the PolarStar gen3 V2 Fusion Engine. I hope this is helpful in creating a common “vocabulary” when discussing various parts of the Fusion Engine.

Happy Airsofting!

– Rudy

How To Update The PolarStar Fusion Engine Firmware

I offer a service to upgrade the PolarStar Fusion Engine Firmware, but for those that would like to upgrade the FCU firmware themselves, here are the instructions on how to do it. Please note that PolarStar Airsoft nor Bingo Airsoftworks can be held liable if you damage or destroy your FCU by attempting to update the firmware. Please proceed at your own risk.

To update the FCU firmware, you’ll need the following:

  1. IMG_2215Purchase/acquire the AVRISP mkII programmer and download and install the Atmel Studio 6 software
  2. Plug the programmer into a USB port on your computer. The light on the programmer should be red.
  3. IMG_2213Carefully remove the heat shrink covering from the FCU. It’s easiest to cut on the edge of the circuit board with a razor blade.
  4. Insert the 6 pin connection header into the connector on the programmer.
  5. IMG_2216Attach the programmer to the FCU and hold in place using a clip or rubber bands. Make sure the red line on the data cable lines up with pin 1 on the FCU circuit board programming jumper pad (pin 1 has square solder trace)
  6. IMG_2217Attach a fresh battery to the FCU. The light on the programmer should turn green.
  7. fcu_firmware1Launch the Atmel Studio 6 software and access the Tools | Device Programming menu.
  8. Make sure the Tool drop down reads “AVRISP mkII”. Make sure the Device drop down reads “ATmega169A”. The Interface field should be “ISP”. Then click Apply.
  9. Click on Device Signature Read button, and a device signature and Target Voltage should be displayed.
  10. fcu_firmware2Click on Memories option in the left column.
  11. Backup the existing firmware by clicking on the “Read…” button. Enter a file name and accept. The programmer will read the current firmware and save as the file specified.
  12. In the Flash (16KB) field, enter or navigate to the path of the new firmware .hex file from PolarStar Airsoft.
  13. Make sure “Erase device before programming” and “Verify Flash after programming” are checked.
  14. Click on the Program button to program the FCU. The light on the AVRISP mkII programmer should turn orange while programming.
  15. Disconnect the battery from the FCU, disconnect the FCU from the programmer.
  16. Important: Reset the FCU (hold the settings button down while plugging in the battery) and then verify that the firmware revision is correct (most current is re22)
  17. IMG_2211Reapply heat shrink to FCU. Punch a hole in the heat shrink for the select switch before heating and shrinking.

Happy Airsofting!

– Rudy

PolarStar Fusion Engine FCU Firmware Upgrade Service

FCU with re22 FirmwareI’m now offering a service to upgrade your rev2 FCU firmware to the latest revision (re22). The new FCU firmware adds anti-stiction mode with automatic varying poppet dwell. This feature will automatically add a few extra ms to the poppet dwell if the gun has been idle for a period of time to help eliminate “dead-shots”, where the poppet fails to open on the initial trigger pull due to o-ring static cohesion.

I charge $18 to upgrade your FCU firmware to the latest version re22 (covers return shipping for US locations, international is +$8). The upgrade includes removing the existing heat shrink, uploading new firmware, and reapplying new heat shrink covering. Note that updating the firmware will also reset the FCU shot counter to zero. Only available for rev2 FCUs (gen2 and gen3 V2; V3; M249 and M240B Fusion Engines).

You would send out your FCU, and it will be sent back within 2 business days. I guarantee that your FCU will will be sent back in good working order, and you will not have to worry about your FCU being damaged or “bricked” due to the firmware upgrade.

Maintaining the MP7 Fusion Engine Conversion

Additional updates have been made to the MP7 Fusion Engine conversion. The enhanced design allows the Fusion Engine to be extracted from the MP7 without requiring the gun to be taken apart.

The upper solenoid cradle has been redesigned to allow the fire select switch to be mounted on the cradle, and the trigger switch implementation has been changed so it now uses the standard trigger/battery contacts on the top of the switch assembly. Additionally the solenoid air supply fittings have been changed so the stock Fusion Engine fittings can be used, which allows more air to flow to the solenoids, especially the poppet solenoid, so the poppet triggering can be more reliable.

My friends at Amped Airsoft were nice enough to make a video showing how to extract the Fusion Engine from the MP7. Check it out below.

Happy Airsofting!

– Rudy

Updated video on maintaining the Fusion Engine MP7

Lubricating PolarStar Fusion Engine Nozzle and Poppet

When swapping the nozzle on the PolarStar Fusion Engine, or doing periodic maintenance on the Fusion Engine (every 25K-30K rounds), it’s important to lubricate the nozzle with high quality grease. I strongly recommend using the TechT Gun Sav grease.

Here are the locations where you need to apply lubrication:

P1070027The poppet should also be lubricated periodically. Here are the locations the where the poppet should be lubricated:

3-IMG_9035b 3-IMG_9035

Happy Airsofting!

– Rudy