ICS M4 Split Gear Box PolarStar Fusion Engine Conversion

The Polar Star Fusion Engine is designed to fit in most V2 gear box airsoft guns. The ICS M4, which utilizes a proprietary split-gearbox design, doesn’t seem at first to be a candidate for the Fusion Engine, but with a few simple modifications, the Fusion Engine can fit and the gun performs very well.


The ICS M4 powered by the Polar Star Fusion Engine

To put the Polar Star Fusion Engine (FE) in the ICS M4, the FE needs to be installed into the upper receiver first, then the lower receiver is mated to it. The upper receiver needs to have one side trimmed down to make room for the selector plate guide on the FE body. The pictures below show were the extra metal needs to be removed.



To insert the FE into the upper receiver, it needs to be slid in from the back of the receiver. The receiver pin tab can get in the way of the selector plate, so it will be necessary to gently pry it away from the plate as the FE is slid into place (when inserting and removing the FE)


A modification was needed to the safety level to make sure it engages when the selector is set to SAFE. The level was “squished” to make it longer so it will lift into place.

The lower receiver is then attached to the upper receiver. The Fusion Engine is held in place by the rear body pin, and by a new trigger pin that needs to be created.

The properly hold and align the FE within the ICS body, a trigger pin needs to be installed. The stock ICS body does not use a trigger pin, but there is a little “dimple” on the body showing where the pin should be. I used a drill bit (2.81 mm/0.11 inch bit) to drill out the pin holes on the body and then I sacrificed the drill bit to use as the body pin by cutting it down to the width of the lower receiver. I could use a 1/8″ bit, but you might need to carefully drill out the holes in the FE body to match.



The magazine release pin guide on the FE needs to be opened up a little to allow the mag release pin to align properly with the release button.

Also the hand grip needs to be trimmed down so it doesn’t press against the lower receiver, so it will fit properly.


The FCU wires run along the groove in the FE body to the hand grip.

The Fusion Engine works very nicely in an ICS M4 body. The only detriment over a standard M4 body is that you must remove the lower receiver, and back out the Fusion Engine to remove the inner barrel and hop-up unit, but once you have it dialed in, the gun is very solid and you can proceed to dominate the field!

– captainbingo