weird ICS M-4 Problem

[Edrahil]

So I have no clue whats wrong with my m-4.

I have a fully charged battery (tested with multiple, in fact), and hook it up to my m-4, pull the trigger and get a weird almost grinding sound. but the gun cycles and fires, a grand total of 20 feet or so, at a pitiful FPS.

I've taken the gearbox apart and saw no stripped gears or broken anything. My next step is to completely clean every gear and re-grease the works, but i dont want to go through all that if anyone else has an idea.

So I ask the peanut gallery for their input. ideas?

Daniel

[slickridley]

My first gut check says the motor isn't high enough,

[Star_folder]

How does the piston look?

[VoidSuicide]

Both the above ideas are good I'd say, but you might still want to regrease the gears before putting everything back. no sense in taking the gb apart 3 months from now to do something you could do now.

[Dominum]

The motor not being high enough could cause the grinding, but it would not cause the lack of FPS when it cycles. I am probably thinking along the lines of Starfolder, that the piston is worn in a manner that causes it to be pulled back, and then the teeth skip on eachother so that the piston is only halfway back or so when it is released. Bear in mind, in an ICS this could happen without any visible wear on the piston or sector gear due to the fact that their tolerances aren't always great and the upper GB shell and lower may be just far enough apart where the piston teeth and sector gear teeth have only a small amount of contacting surface area. This could mean that when it tries to fire, once the piston gets to the point where the pressure of the spring is too much for the small amount of tooth contact it slips. This would cause both issues, but may not show wear for a while if both the piston teeth and sector gear were of high quality metal.

[Edrahil]

I'll need to check again, but i do believe that the lower part of the gear box is making that sound, rather than the piston.

[VoidSuicide]

If the grinding is coming from the low end of the gearbox then maybe there's something not sealing properly that is causing the low fps.

I would definitely check the piston/piston gear first tho because I don't think a slightly worn o-ring would hurt fps that much.

[Dominum]

You could have multiple problems at once. Though it is less likely of course. This could mean your loss of compression could be something like a torn oring, cracked piston head, air nozzle, or cylinder head. The grinding would then have to be explained by something unrelated, like a lost tooth or improperly mounted motor.

[Skywalker]

My money is on the piston head being broken and a part of it made its way down into the gears. The 20 ft thing is the exact problem I was having when my silent piston head came apart. Make sure there isn't anything lodged in the cylinder head/air nozzle too.

[Dominum]

I should have though of this earlier...

Since it is an ICS, do the following: Remove the upper, and cycle the lower GB to see if it is grinding on it's own, etc. Then, remove the upper GB and use a flathead on the piston to pull it back and release it manually, with your thumb blocking the airnozzle. This will give you a good idea of the quality of compression. Let us know how these two tests go.

[Edrahil]

the lower gb is making the grinding noise, but i've found out the cause of all my troubles.

Somehow, and i dont know how, the spring guide broke about 1/4~1/2" up from the base, so the spring was low and getting caught on the gears in the lower, which was impeding the FPS. No damage to the gears or the spring, but the grinding in the lower gearbox is (i believe) from plastic shards that have gotten caught in and around the teeth. So i will need to clean them and regrease them.

[Dominum]

That makes perfect sense.