TM MP5A4/A5 Gear Replacement Help Needed!

[GODSPEED|seven]

Hi, I have this old TM MP5A4/A5 that was working like a charm, until earlier today; as I was firing it, all of a sudden the sound went from clear crisp pops (shooting) to high pitch whine (not shooting).

When I got home, I tried adjusting the motor height by +/- 1mm with no effect. So I decided to take the gun apart and open up the gearbox..

It's pretty much all stock TM parts. I noticed that the top-most gear (the one that engages the piston) has 3-4 teeth (on the lower part of that gear, not the part that actually engages the piston) that are completely eaten away. I guess it was old (I have the TM EG560 Motor.. or is it 650.. I forget). But I also noticed the piston had the 2nd, 3rd & 4th teeth quite alot shorter than the rest (like half eaten away). The 1st big 'tooth' is fine.

While It was my first time having to open a gearbox, I'm not scared to have to play inside of it. I closed it all back up and everything fit nice and well...

BUT, my issue is this:

• What type of gears do I need?

• Should I replace the Piston?

I was looking at the following parts:

Modify V2/V3/V6 Top Speed Gearset
http://www.airsoftparts.ca/store2/in...oducts_id=1568

to go with this:

Modify High Speed Ultra Piston - New Version
http://www.airsoftparts.ca/store2/in...oducts_id=1369

or

StormTech MAX Impact Polycarbonate Piston
http://www.airsoftparts.ca/store2/in...oducts_id=1495


The gun is all stock TM, while I'm not currently looking to upgrade anything, I want to keep the option open for putting in a M100 Spring.

I want to keep the 750-850 Rounds/min ROF (using a Ni-MH 8.4v 2500mAh Large type). The sound on it with the stock parts was just beautiful; no whining at all, just nice clear and crisp "pops".

I understand there are various different metals for gears, as well as high speed, ultra high speed and the torque ones.. Since my gun is shooting a M90 Spring I believe, I must stick with the speed ones (which I like).

The gearbox does not appear to have bearings, but just nylon inserts (which is also better for lower powered quick firing guns.. from what I understand).

I would like to buy parts from Canadian Retailers.. to avoid a 2-3 week shipping time. And would really like to keep the cost below 100$.

All help/tips/links is greatly appreciated!

[Boyso]

You can use a High Torque gearset anyway, but the High Speed is perfectly fine with a S90.

I use the Modify piston myself, perfectly fine, comes with the second tooth already removed. For the Stormtech, I'm not a fan of transparant plastic stuff, I can't trust their durability (Like those old N64 purple controllers, always the first to break :P)

One thing I had to do with the Modify piston was to file the rails a bit since I was using a clone gearbox shell. Since your's a TM, you shouldn't have any problems.

I'm still recommend metal bushings, simply for durability, but I haven't read anything about nylon ones in high speed setup so I'll let someone else chime in. I have nylon bushings in my M1A1 and it's perfectly fine for now, altough not many BBs went thru it.

EDIT : Oh and order from AirsoftParts. Jugglez is awesome. But my wallet hates him as I order too often !

[Kos-Mos]

I like to use a set of high torque over high speed. Though Modify's gears set are a bit misleading... their "high speed" is close to a standard set, while "super speed" is higher and "high torque" is slower.

If you use a decent battery, you get about the same ROF with soft (sub 350fps) springs, but you can also crank harder ones with very little difference.

I also don't like laser guns... takes away some of the realism.

I would go with a Modify high speed set:

http://www.airsoftparts.ca/store2/in...oducts_id=1016

Add a modify Ultra piston, the difference between high speed and reg is the second tooth that is removed. It is good for both high speed and high torque:

http://www.airsoftparts.ca/store2/in...oducts_id=1369

You should as well change the bushings, since you will have to redo the shim job anyways:

http://www.airsoftparts.ca/store2/in...roducts_id=880
http://www.airsoftparts.ca/store2/in...roducts_id=676

People say that the double oil channel eats away at the gear's shaft... I ran over 50 000 BBs in a single summer on a set and the finish of the shafts is not even attacked yet... Just use some decent lithium/ceramic grease to fill them with assembling, and do a yearly maintenance on your gun (you should do that anyways).

[GODSPEED|seven]

Well you guys certainly helped me out alot here! I'll be ordering those parts sometime during the week.. I may very well have pictures to go with my work.. I hate this, but it's kind of exciting at the same time, because it'll be my first time doing this. I like playing with mechanical stuff.

As for shims, I get the idea; I guess i have to assemble it, try it out and if it doesn't sound right, try and adjust shims again? right?

[Boyso]

Go one by one. Add a shim to the spur, and go on. Make sure it's just one shim away from touching. Don't make it too tight. Put the screws in and spin the gears while moving the gearbox left and right. Take your time, you'll "feel" it

[Kos-Mos]

Originally Posted by GODSPEED|seven

Well you guys certainly helped me out alot here! I'll be ordering those parts sometime during the week.. I may very well have pictures to go with my work.. I hate this, but it's kind of exciting at the same time, because it'll be my first time doing this. I like playing with mechanical stuff.

As for shims, I get the idea; I guess i have to assemble it, try it out and if it doesn't sound right, try and adjust shims again? right?

To do the shim job, you should remove everything from the mechbox, install the spur gear (with it's bearings) and shim it centered. You will need to screw at least 3 screws around the gear to make sure it is closed tight (no mater how strong you are, it does not work if you hold it with your hand). Shims usually come in 4 sizes, and combining them will let you increase/decrease by about 100mil (0.1"). You need to first fit each gear separately to perfection, then use the shims you already have to fit each gear vs each other. Leave a tiny gap between each gear or you will break them and scrap a 50$ gear set.

[HKGhost]

And one most important thing that most people forget to do is do and Angle of engagement mod. It will align your piston to your gears so you don't strip out your piston again. Add shims to your piston head till the piston teeth engage the gears teeth perfectly.

[GODSPEED|seven]

Thanks alot for the valuable tips guys, it's all very helpful. I'll keep posted with info if I encounter any issues or get it done right.

[Kos-Mos]

Originally Posted by HKGhost

And one most important thing that most people forget to do is do and Angle of engagement mod. It will align your piston to your gears so you don't strip out your piston again. Add shims to your piston head till the piston teeth engage the gears teeth perfectly.

Depends...

So far almost all the guns I worked with that where not cheap clones where perfect with just the parts in there (either stock or upgraded cylinder sets)...

It is a lot more important to double check if you install a custom sorbo pad over an existing cylinder head (ie. mod a TM cylinder head).

[GODSPEED|seven]

I noticed they sell a special tool for Bushing installation (modify bushing kit thing-a-majig); do I NEED it to install bushings? or will they come out/go in pretty easy?

[Boyso]

You don't "Need" it. Just take the end of a soft screwdriver to "push" them into place. Don't hammer them in, you'll deform them.

[GODSPEED|seven]

I got the following parts:

- Modify High Speed Ultra Piston [New Version]
- Modify 6mm Stainless Steel Bushings [Double Oil Channel]
- Modify Stainless Steel Shims
- Modify V2/V3/V6 High Speed Gearset
- ARS Sticky-G Molybdenum Gear

Will probably get the stuff monday.. anxious to get started!

[Boyso]

Oh and get yourself a glass of whiskey and some smokes, it will help if you run into troubles! :P

[GODSPEED|seven]

Forgot to update the status of my gear replacements..
hehe... everything worked like a charm. The gun feels brand new now. Fires with a very distinct 'clank'.. For a first time changing gears, I'm more than satisfied. Shimming took a while, but I figure thats normal.

Thanks for everyones help and tips, they were greatly appreciated and followed.

I'm lovin' it (no.. not McDonald's.. my MP5 dummy!) :P

[THe_Silencer]

Glad to see you figured out your first gearbox. You Sir have become a man!