issues with my high speed build.

[Hectic]

so im working on a "high speed" build.
I use the " " as its not much of a crazy build.
I started with a cyma mp5sd6 i pulled it apart (i gotta say wtf? They must have slimer from ghostbusters working there using his green slime to lube there boxes lol)
Anywho back on track. I out super shooter/shs 13:1 gears a lonex red piston and a modify m90 (or however they lable em its a 90 anyhow) spring and a sorbo pad (from a vsr10 but its pretymuch a perfect fit)
I spent alot of time shimming it as the bushings are a lil funky (they stick up far from the box) and it seems to be shimmed well.
I corrected aoe (had to shave an additional tooth off the piston)
And i removed the clear flimsy tappet plate and put in a stiffer white one (from a JG box i think)
Anyhow everything fits nice and i threw it together.
Once i test fired it it jammed up to the rear of the box (like as if the sector engaged early)
So i opened it and found that the spring had slipped over the bearing of the guide causing the piston to stick onto the guide.
I tweaked the spring a lil (squished the last coil a lil so it cant slip over the bearing)
So now i find it still seems to stick to the rear. If i screw with it a bit (keep pullin the trigger randomly) itll eventually compleate the cycle but only after the wires get hot.
Im using a 9.6 1600 mah battery and i figured it should work fine on such a weak spring. Am i missing something. Could it just be bsdly shimmed and im not beinng picky enough? Should i swap the bushings for bearings maybe so itll spin more freely.
The battery is as bit as i can fit in the gun so thats not really an option.
Im i being unrealistic, is a 330ish fps spring and 13:1 gears too much for a 9.6v 1600mah?
Guess i just need to know what to look at next. Ima try shimming it a lil looser and see if that helps but otherwise im at a loss.

Pardon my ranting just tryin to get this up for friday.

[lurkingknight]

I think I might have had the piston jam from a badly shimmed sector before... though there were a number of things that went wrong that led to that, so I can't say for certain it was the shimming alone.

What happened was it compression jammed and the tappet fin skipped out from where it was supposed to be and jammed into the gap between the tappet post and the side of the gearbox, it also wedged itself between 2 shims... was pretty gnarly.

I don't think asking a 90 spring and 13:1s out of a nimh of that size is out of the question.

Check to see if the lonex red is binding on the cylinder, they seem to do that some times.

One thing to watch out for is the weight of the lonex red... on a 90 spring and 13:1s you may run into pre-engagement. Most people who use them in higher end builds will swiss cheese it.

Check to see if it's sliding in the guide rails freely with the gearbox screwed together minus the spring.

[Hectic]

Yeah it moves freely in the guides and in the cylender. im thinking its most likely the gears are a lil too tight.
And perhaps the battery is a lil low compounding the issue.
Ima pic up some bearing bushings that hopefully sit flatter in the box and reshim and see how that goes.
I dont think the piston itself is too heavy but the way the stock head was attached was via a big ass block of metal as a nut and that adds some huge weight on it. May find a suitable nut n bolt or jut grab a whole head as itll coke with the nut bolt and washer to attach the head with.
I think on a 9.6 pre engagement wont be an issue. Maybe an 11.1 but the times it did cycle it wasnt all that much faster then a normal aeg (kinda dissaoointed really.)

[Hectic]

Also anyone know what size bushings this thing has. The 8mm ones i have dont fit. Are theh 7 or 6?

[ThunderCactus]

well are they 1mm bigger or 2mm bigger? lol
What kind of motor are you using?
and did you try moving the piston through the rails with the cylinder and sector gear out of the mechbox?

[wind_comm]

sounds like textbook poor shimming.

did you start with the bevel and pinion?

[Hectic]

No i started with the spur gear then the bevel then the sector. i agree tho its likely shimmed a lil too tightly

[ThunderCactus]

What's most important is that the gears spin 100% as freely as possible. It's okay to be off that .05mm since only marui ever made a .05mm shim lol
It's better to be a tiny bit loose than a tiny bit too tight!

Also, if the shimming was off on the bevel, you wouldn't be able to get the motor height set properly, if you've done enough motor height adjustments you'll easily be able to hear if you can't get the height set right. The advantage to shimming the pinion/bevel first is guaranteeing you can adjust into the right spot on the bevel. But I've only ever had to go back into 2 mechboxes of the hundred or so I've shimmed to re-adjust the bevel height. really narrow gearsets in really wide mechboxes lol

[Hectic]

I pulled the box out this morn befor i left for work and by pressing on the axels with them facing downwards i can see/feel that there is no movement in the spur and almost none in the sector so its definately a lil too tight.
Useually what i do with the bevel is hardly shim it off the spur the put a 1.5 or 2 mm shim on top leaving about 0.5-1.5 (idealy 0.5mm) of upward play thus the motor shims it off of the spur.
Ie when its setting without a motor it has barely the 0.5mm clearence off thesur and then the motor provides a lil more spacing between them once its in place.

[ThunderCactus]

I think you might want change the numbers or change your method, .5mm is huge lol
Shim everything to within .1mm at the most. The clearance between the bevel/spur and spur/sector should be as minimal as possible to ensure the most reliability, if you can get it within .1mm-.3mm that's perfect.
There are times you can get the shimming perfect, the gear spins freely and there's no axial play, so just go by how freely they spin.

[Hectic]

Yes brain is baking in the sun. My shims are 0.1 0.15 0.3 0.5 i mean with 0.05 play lol or even 0.1 ill be okay time for a smoothie i thinks lol

And yes i found with the lonex gearbox with 8mm bearing bushings i was able to shim it just snug snd it would spin freely when all tightened down. (would go round 4 or 5 times on its own with one nice pull of a finger across the sector.
I guess without bearings they gotta have that minor play as there isnt anything to help em spin. (tho the sector and spur gear on this gearset had bearings in the axel holes)
Wish i had a caliper to measure the bushings id grab bearing ones. Guess ill pull one out and compare em befor i buy. Prety sure they look like 7 comparing em to the 8's i have.

[lurkingknight]

I start from the bevel checking the motor height and setting the bevel to start... usually as few shims as possible on the flat side of the bevel. then I check for play on just the bevel and how well it free spins.

Then I do the spur... always a minimum of the narrowest shim to start to give it better spin to start.. then maximize the tooth engagement while not being too close (as in resting on/come in contact with) to the actual gear faces. I check play again and see if either of the faces will make contact. Then repeat for the sector. The sector is sometimes tricky though, too many shims will fuck up the cutoff lever on one side... but too many shims on the other side I've had the tappet slip between the tappet cam and the gearbox shell during a compression jam that wasn't pretty.

When I spin the gears I will spin several times forwards and backwards with the gearbox oriented the way it will sit in the gun. Then I will spin again while the gearbox is on either side and check the play and interaction at rest when the gearbox is resting on either side and adjust accordingly. Sometimes maximum tooth contact doesn't give the best friction free roll so it's a balancing act. Just be sure to test the spinning with the shell screwed together... don't forget to hold the cutoff lever out of the way lol.

I've not had a gearset blow up on me yet.... bearing fly apart and spur plow into the gearbox shell yes... but no critical gear failure, and both my guns use SHS gears with questionable bevels.

[Hectic]

The one issue im having with the spur is due to how the bushings sit in the box (they stick out a bit more then im used to) even without a shim the spur sits high. Like 0.5 of a mm maybe more off the bottom/left side of the box. Even without a shim i gotta shim the crap outta the sector (like 0.6 or so just so it doesnt rub the face of the large portion of the spur. Maybe ill try moving the bushings around and see if one sits better then the other to bring the sour a lil lowwer to the box so i only (hopefully) gotta use 0.15 or 0.25mm of shimming on the sector. I fear any more then the 0.6 or so i had in there ill have cutoff problems. And even with that it was running really close to the face of the spur. Ill try putting the high sitting bushing on the bevel and take more time shimming tonight and see if i can get it spinning more freely if its still a pain in the arse ima just grab a lonex shell. The last one i did went together so nicely and everything stayed put when closing the shell it was a joy to work on lol.

[pestobanana]

When you shim, are you putting all the screws in and tightening them to really see how much play there is when the box is together?

[lurkingknight]

you can probably take some sandpaper to the bushing to narrow it then unless there's not enough flange to work with. Just make sure you've got the paper backed on a flat surface and you an apply even pressure to the bushing.