My TM M4 Is Having a Hard Time Cranking
 

I recently bought a used M4 so I could learn how to work on it. I just put in an M120 spring and Guarder metal bushings. I also reshimmed it using systema shims.

Basically what is happening is that it seems like it needs a lot of juice to get the gun firing. If my battery is a little low it will just draw the piston back but wont bring it back far enough to let it go foward. If I fire it fully auto it will be fine unless I keep firing it fully auto in bursts. When I do this it sounds like the battery is about to die. I can hear it have a hard time trying to spin again but once it gets going it sounds fine. I'm using a 9.6v battery and it is working fine on my commando that has an M120 as well.

What do you think could be causing this problem. I am just about to crack this thing open again but wanted to see what you guys thought might be the problem first. Thanks!

Could be that the motor is situated too "high" up. Try lowering it via the adjustment screw.

Put in a lighter spring, or get a big-ass battery. Seriously. I just bought a Non-working Marui MP5 SD5 with this same problem. Even my largest battery would not crank that sucker over. When I opened it up the spring was the strongest I've ever seen, and I've seen %200 PDI springs. I put in an SP110 and it worked like a charm.

It could also be a bit over shimmed or underlubed. (or horribly over)

Take that into consideration too... A big ass battery in a crane stock is always a great idea though.

I never touched the adjustment screw for the motor. I don't want to mess with it if I really dont need to. Do you really think its this?

I was thinking that it might be over shimmed as well. But when I closed up the mech box and turned the gears, they would turn with little effort. Does this change when everything is put back together?

Should I have a tiny bit of play in the axels of the gears when I reshim? Right now I have pretty much no play in any of the gears except the bevel gear has a tiny bit.

The M120 is a strong spring. If you still use the mini 600mah battery, dont be surprised.

When you re-shim, it will adjust the height of the bevel gear, and as a result, the motor must be readjusted.

Did you close it up with the screws as well? It does make a difference.

Yes, you should. There should be about 0.2-0.3mm of wiggle in the axles. If there's no play in the gears, that adds various problems from very loud gearboxes to cranking difficulties.

Huh, thats good to know... damn too bad I already took apart my gun because I got bored last night :smack:

I closed it up and put all the screws in as my last check. When I reopend it last night I did the same thing. The gears turn with minimal effort so it doesnt seem like the motor would get hung up on them.

hmm in the guides I read, i thought they said that I wanted the spur gear and sector gear to be tight and the Bevel gear could have a little play. So that's wrong? It could be, I know not everything on the internet is accurate, just want confirm. Thanks for your help!

The battery is a 9.6v 1100mah nunchuk. I figure this should be enough since this is what I'm using to power an M120 in my M733.

Then you have other setup problems. Re-check your mechbox entirely, or find a local expert.

I know but thats why I'm here trying to figure it. Any more suggestions?

This stuff has to be looked-at directly, discussing it online will only create a repeated list of anything that can go wrong, and even then... you have to see the thing.

So again, find a local expert. Canada is not local to you.