Shimming new gears issue - Is this normal?

[freshblake]

The shafts on the gears, depending how you're shimming them, could be sticking out past your bushings. Also I had an issue where my motor height screw on my grip was loosening from the shock of firing so I just used some blue loctite to set it where I want.

[ao_tenshi]

I've done some re-shimming and the issue is improving. Now the only issue remaining is when I test fire in semi-auto the gun will seize half the times (can be released if go into auto). However, in full-auto this issue does not occur.

This semi-auto gearbox seizure issue does not happen if I put back the stock gears that's factory shimmed. So Im guessing some of my shimming is still not right...

Any idea on shimming which gear would likely resolve this issue?

[ThunderCactus]

If it won't start back up in semi, but does in full, it means you're resting on the cutoff lever. The problem is usually that you're releasing the trigger too early in semi

[ao_tenshi]

Originally Posted by ThunderCactus

If it won't start back up in semi, but does in full, it means you're resting on the cutoff lever. The problem is usually that you're releasing the trigger too early in semi

I've been doing full trigger pulls. I've noticed that if the piston is the in back position, the semi will seize to move. But if the piston stop in the front position from auto, then switch to semi its less likely to cause a seizure.

[ao_tenshi]

Originally Posted by ao_tenshi

I've been doing full trigger pulls. I've noticed that if the piston is the in back position, the semi will seize to move. But if the piston stop in the front position from auto, then switch to semi its less likely to cause a seizure.

Been doing some research and wondering if short stroking would resolve the issue described?

[lurkingknight]

no because you would then need to put a stronger spring in to get fps back... and a g&p120 motor is already weak as shit, making it pull a stronger spring just loads it more, so if you are getting semi auto locking with a g&p 120 on 13:1s and m90, you are going to get far worse with that setup on a 120 or 130 spring if you shortstroke 3 or 4 teeth. You have too much mechanical load on the motor. It's not strong enough to pull through that load if it stops right on it. Faster ratio gears are more mechanical load. Higher spring ratings are more mechanical load. Heavier piston assemblies are more mechanical load. Bad shimming is more mechanical load.

you need more battery or more motor to reduce the area in the cycle where semi auto lock occurs.

Even with a massive motor and battery you can still semi auto lock a gun, it just happens a lot less.

[freshblake]

OP, read this

http://www.airsoftcanada.com/showthread.php?t=25310

[ThunderCactus]

You need battery with more amperage (you're using a NiMH arent you?)
or higher torque gears, or a high torque motor (high torque windings, not neo magnet) to continue using that battery.
amperage is torque and you don't have enough of it to move the spring in the rear position

[ao_tenshi]

I am using 7.4v Lipo @25C

So Im still stuck with semi seizing when the piston previously stopped at the backward position. This is not the same as the case where the semi-trigger pull was partial causing a seize. Similarly in another build, where I've done AOE and Sorbo, I had to use a shorter spring to correct a similar symptom.

For this current build, I've done the AOE and added a sorbo pad. Should I shorten (cut a few coils) the spring?

[Azathoth]

How many shims do you have in that gearbox.
list it like this

Bevel gear Right / left
Sector gear right/left
spur gear right/left

It sounds like overshimming

[ao_tenshi]

I've tried a number of different combinations. The last one I landed on was:

Bevel gear Right 6 / left 2
Sector gear right 2 /left 2
spur gear right 6 /left 3

Right being top and left being bottom if looking at the trigger switch side of gb.
the numbers are shims in 0.# MM

[ThunderCactus]

IF the gears spin freely when the mechbox is screwed shut, then the problem is 100% your motor simply can't provide enough torque to overcome the force of the tensioned spring.
Assemble the gearbox without the anti reversal latch, spring, piston, cylinder, tappet, etc, and see if they spin free.
Then assemble with everything and see if the air nozzle moves back and forth freely (that'll determine if it's rubbing on the sector)
You'll need a new motor, and I'm not surprised since the G&P M120s are just about the bottom of the barrel for motors.

[ao_tenshi]

Originally Posted by ThunderCactus

IF the gears spin freely when the mechbox is screwed shut, then the problem is 100% your motor simply can't provide enough torque to overcome the force of the tensioned spring.
Assemble the gearbox without the anti reversal latch, spring, piston, cylinder, tappet, etc, and see if they spin free.
Then assemble with everything and see if the air nozzle moves back and forth freely (that'll determine if it's rubbing on the sector)
You'll need a new motor, and I'm not surprised since the G&P M120s are just about the bottom of the barrel for motors.

I see, ok I've ordered a Lonex A2, will try it as soon as it arrives. Just surprised the motor cant pull a M90.

[lurkingknight]

it's not just the spring, the faster the gearset as in lower ratio the more load there is for the motor to overcome.

[Azathoth]

TO THE OP:L

With the gearbox open, put a 0.2 mm shim on the spur gear (middle one) such that is is on the gear face not on the axle. Use this 0.2mm shim to ensure that their is sufficient space between sector and bevel. 6 shims or 0.6mm is a huge amount.

If you have a pair of digital calipers use the mathematical method to shim the gearbox instead of the 'doing it be feel'.