Bambo : First Mod

M249 in earth and sand

13mm slimline hop up
38cm aluminum barrel (7.5mm ID)
Nylon T piece
Alloy nozzle and cylinder Head
Stainless steel cylinder (100%)
Alloy piston head & shs piston
1.25mm spring
Metal spring retainer
18:1 shimmed SHS gears
460 short Chihai red motor
Easyfet V2
Magazine modded for higher capacity.

Waiting for some glue to dry before I chrono it :wink:


Seems to be all over the place. Using mystery gels that look like milkies…


Check your gel consistency. Particularly size.

I’d be checking nozzle seal into t piece too

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Yeah, dodgy sized gels are one thing…but air seals are the #1 to get 100% right before any type of proper testing with gels, barrels, cylinders, porting etc. etc. can be properly evaluated.

Yeah, I was looking at two gels that fell out on the table , thought WTF? and grabbed the callipers… 6.64 and 7.86 mm . Grew 20g of AKA tenacity hard weight for 3.5 hours and got 8.16 mm but they were consistent. I’ll see how they go and try a shorter grow. Also thinking of winding back to a 1.2 or 1.18 spring, will check the nozzle and throw in a green o-ring in it. On a steep learning curve :wink:

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Well, there’s your problem … :face_with_raised_eyebrow:

Well I grabbed a new gearbox, and I won’t tell you all my misadventures, but after getting it working it ran like a one legged dog 70-100 fps, lots of jams. After going over and over the build trying to find the air leak I decided to throw in the old T-piece and plastic barrel. Instant increase to 200 FPS, and pretty consistant. I broke the old T piece off the aluminum barrel, looks like I’ll pick up a new one and use a bit of silicone to seal it until I figure out how I stuffed up… :roll_eyes:

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Holy hell how did that happen?

Maybe it’s just the pics, but they look like the wrong size bearings?
Do they take some force to push into the seats @Echo3319 or just drop in?
None of them look to be centred in the gearbox casings?

A lack of shimming can cause the gears to shift sideways under load and pop out of the housing also :thinking:

I can answer both those questions, The bearings were the right size, 6mm but after the piston head came loose from the piston, things kinda went sideways… :upside_down_face: and yeah I’m still finding my feet at shimming, for awhile I was going too tight… I’ll have to have another go though, I noticed my bevel gear has a bit too much play at the moment. Practise makes perfect, I hope… :thinking:

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Yup…from every rebuild comes knowledge :+1:
Anything unknown or questions that need answering are only but one post away on this forum :ok_hand::sunglasses:

I’ve always gone with no ‘play’ but not ‘tight’ with nylon boxes, as they will flex :thinking:
Such is the nature of angle cut gears😅


That’s certainly the issues that I had back in my Frankenstein Gen8 days.

Beveled gears naturally want to walk over the top of each other under load.

My poor suffering 480-490 FPS Nylon boxes needed plenty of additional extra threaded bolts throughout the sides of the gearbox halves! :open_mouth:

Even when shimmed “tight” under no load, I still experienced this same issue of flex allowing gears/bearings to depart the locating pockets. :stuck_out_tongue_winking_eye:

I even resorted to adding “packing” between the gaps between the gearboxes and receiver housings to try and hold everything together!

It always came down to spring rates at the end of the day. I was trialling F100 Truck springs to achieve 480-500 FPS out of a nylon Gen8 box! :roll_eyes:

All good fun at the time…but I’m sure that @Echo3319 ‘s problems are from other issues than M190+ spring rates :joy::+1:

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Keep talking, I’m soaking it up :wink: One of the greatest tips I got was down at Xforce at North Lakes. I’m now using araldite like loctite… No more wandering piston heads :rofl:

Do you often find your piston heads down the road or in the neighbour’s yard?

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Naw, Sideways in the cylinder, with the bearings and the retainer jammed up between the piston body and the spring retainer, and it only happened twice… Not as if I’ve made the entire gearbox explode showering my neighbors with parts… so far… give me a week or two…

the ONLY time i didn’t bother…not forgot, chose not to…

ran fine for weeks
i chrono’d on field one day
then pop (fuse)

it had come loose, the retaining bolt for the head was in the gears and i was never so lazy again.

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Photographic evidence of how bad this can get :slight_smile:


Wow, looks like I got off lightly. What do you guys reckon? Loctite or araldite ?

A non setting thread locker is ideal.
Hard setting glues can fracture under stress impacts and still come undone, whereas a soft setting locker might come loose, but will not completely wind itself apart unless kept unchecked for a long period of use.

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