SRC M4A1 problems

[RandyAB]

No super glue...

[Azathoth]

Originally Posted by RandyAB

So, I got the gearbox apart and found a few things.

1: The teeth on the bottom of the piston were stripped away spreading shavings all over the gearbox. Why would that happen and how can I prevent it from occuring in the future? Is there a good aftermarket upgrade that I should be looking at for replacing the piston?

2: The seal between the piston head and the aluminum cylinder no longer forms a seal. Is that likely the o-rings or is something out of spec?

3: My big worry when putting this puppy back together is making sure the shims are correct. Is there a good guide that somebody could point me to for this?

All the best
Randy

1. That occured because of either poor assembly/AOE from the factory, a lemon etc. Pistons should be the weakest link in the gearbox and that it failed is a good thing. Replace with any aftermarket that will fit your budget.

2. That air seal *could* be from a worn O-ring how long have you had the gun? Could also be poor assembly, lack of lubrication. Is their damage to the piston head?

3. I googled this on youtube YouTube- Deadman's gearbox shimming guide airsoft mechbox. I shim by "gut feeling" or with digital calipers

[RandyAB]

The gun was only used for a week but probably had about 5000 bb's through it. There was no apparent damage to the piston head. Any suggestions about good aftermarket upper assemblies (piston, cylinder etc)? Generally the budget is pretty open but I do appreciate value

Thanks for the link

Regards
Randy

[Azathoth]

At the top end I recommend prometheus Hard or system supercore piston,

At the good bang for buck modify, G&P

Their are china brand Element, JG pistons that are good but it's a real crapshoot to get the "right" piston from the production batch that is good (or sucks less). Unless you can read/write Chinese avoid them because you won't be able to figure out which are batches or specific runs are good.

Although I doubt it an Oring problem, you can get them at Home depot, parts source, Mcmaster. When selecting an Oring size is not the only consideration, make sure that the rubber is soft and supple so that it will expand during the forward motion of the piston.

Originally Posted by RiotSC

for standard bore cylinders, the piston head O-ring should have an OD of ~24mm. AS568 DASH number 116 O-rings made from Viton or BunaN (Nitrile) are perfect for the applicaton.