PolarStar Installation Shim Kit, Fusion Engine

Set of 4 precision brass shims to aid with proper nozzle alignment. We have included the most commonly used sizes but shims can also be sanded down for precise fitment.

Set includes; 1pc 0.020", 1pc 0.025", 1pc 0.032", 1pc 0.045"

While our V2 Fusion Engine is designed to original TM spec, not all manufacturers designed their rifle models to the exact same specifications. Therefore some models may require some minor modification to fit perfectly depending on the design of that particular model. The most common modification requirements we see being needed is shimming the engine in the receiver so that the nozzle is centered in the barrel when everything is installed.

Sometimes with rifles where the bolt securing the buffer tube screws directly into the back of the engine, we see that it pulls back on the engine and lifts the nozzle up or occasionally pushes it down. You can visually inspect the nozzle by peering down the muzzle with flashlight (first making sure the rifle is unloaded and air is disconnected) and seeing if the gap visible around the nozzle is equal on all sides.

If the nozzle is high, you can install a spacer in-between the rear of the engine and the receiver to push the engine forward when the buffer tube is tightened down. A good trick to help keep the shim in place while installing the engine is to smear a bit of grease on the back of the cylinder which will allow the shim to stick in place.



If the nozzle is low, you can install a spacer in-between the cylinder and the solid side plate (lower frame) of the engine to lift it up. This is done by removing the 3/32" button head screw from under the front cylinder and pivoting the cylinder assembly away from the side plates.  The screw can then pass through the center of the shim to keep it in place when the screw is tightened.