Picking up bad vibrations?

Aircraft crews have reported their M230 machine guns are vibrating too much when the gun is moved or fired. The vibration can cause M230 gun and cradle components to wear out fast, leading to expensive repairs.

Investigation has revealed the main culprit is Rev-C recoil clamps. Some of the recoil clamps were manufactured incorrectly. Other recoil clamps were installed wrong. Excessive wear on the shoulder pins and piston rod on the recoil mechanism can also cause vibration.

The torque on the recoil clamps was increased from 50 to 85 lb-in. This can make it difficult to remove the barrel without first loosening the clamps.

If an M230 is vibrating, a repairman should measure the gap where the recoil clamps meet. If the gap exceeds .01 inch, replace the recoil clamps, NSN 1005-01-182-4045, and file a quality deficiency report.

If vibration still occurs, verify that the shoulder pins are installed correctly and seated securely. If they're not, send the recoil mechanism to AVIM for disassembly and inspection of the recoil mechanism shoulder pins and piston rod.

The shoulder pins should measure a minimum of .39 inches, measuring from one flat surface to the parallel flat surface, excluding comers. The end diameters should measure a minimum of .311 inches. If the pins aren't within tolerance, they should be replaced.

The maximum width of the square hole on the piston rod where the shoulder pin sits is .417 inch. It it's more than that, replace the piston rod.

This information can be found in TACOM maintenance advisory message 06-017. The MAM contains changes to TM 9-1090-208-23-1-1, TM 9-1090-208-23-1-2, TM 9-1090-208-23-2, and IETM 1-1520-Longbow/Apache that will help pinpoint the causes of excessive M230 vibration. See your TACOM logistics assistance representative for the MAM or get a copy of it:

https://aeps2.ria.army.mil/commodity/mam/tacom_wn/06/mam06-017.html