MP5 SD mechbox parts recommendations
 

I bought a used and upgraded TM V2 mechbox and was putting together my frankenMP5 last night when I had a bad piston lock up. Nothing would release it. Battery was fully charged and worked fine previously. Couldn't press in the piston from the nozzle either. Ended up opening it up to free the spring to avoid having to get a new one.

So I find the following:
Deepfire polycarb piston, full teeth, but one tooth seems to be cut off or missing. No debris in the box.
Modify high torque modular gearset
Unknown cylinder
Unknown cylinder head
Unknown spring
Possibly stock nozzle or modify nozzle
Unknown tappet and selector plates, could be stock possibly

Now that the box is all apart, I'd like some suggestions on what to add or change. I plan to keep the Modify torque gear set but am unsure of what to get next.

This is going to be a CQB primary but I'll probably use it on occasion out doors. It will have an inner barrel no longer than 229mm since the suppressor I use is a tracer unit and would like it to remain functional.

So looking for suggestions on which piston, cylinder head, nozzle and maybe a new spring. Thinking about the sorbo head but also would the systema silent head work in this application?

Get Modify everything, polycarb piston (like the BEST quality piston I've come across yet), standard ported pistonhead, bearing spring guide and 90 spring (I get ~330-340fps out of my MP5A5). And get a Guarder clear hop up rubber as well. All can be had through Jugglez. I dont' see a lot of reason to change the cylinder or cylinder head, you can if you like but still. What does the cylinder look like?

Buy Element parts from my shop :D

I need to clean it all still. will post a pic of everything this weekend.

Chances are I'm going to be paying Jugglez a visit this weekend anyway. :D I'll just ignore his hand in my wallet as I stock up on parts.

unless you can offer me free shipping.... :rolleyes:

Alright. I had some time this morning to clean the parts and pull them all out of the mechbox. Here are some pictures.

Piston:


http://i282.photobucket.com/albums/k...C/IMG_2239.jpg

http://i282.photobucket.com/albums/k...C/IMG_2223.jpg

After cleaning it up, it looks more like someone tried to cut that tooth out. Is that a common mod for high torque? I thought that was done to high speed setups.

The following 3 images show other damage on the teeth:
http://i282.photobucket.com/albums/k...C/IMG_2238.jpg

http://i282.photobucket.com/albums/k...C/IMG_2237.jpg

http://i282.photobucket.com/albums/k...C/IMG_2224.jpg


Spring guide: Possibly Modify?

http://i282.photobucket.com/albums/k...C/IMG_2235.jpg


Spring. If the guide is Modify, I'll assume the spring is too:
http://i282.photobucket.com/albums/k...C/IMG_2236.jpg

Stock nozzle:
http://i282.photobucket.com/albums/k...C/IMG_2233.jpg

Cylinder/tappet:
http://i282.photobucket.com/albums/k...C/IMG_2230.jpg

Selector: stock? contacts need some cleaning
http://i282.photobucket.com/albums/k...C/IMG_2240.jpg
http://i282.photobucket.com/albums/k...C/IMG_2241.jpg

Empty box:
http://i282.photobucket.com/albums/k...C/IMG_2234.jpg

Modify High Torque Modular Gearset:
http://i282.photobucket.com/albums/k...C/IMG_2226.jpg


So I definitely want to replace that piston but now am unsure as to which one to get. I'll stick with Modify but need some direction as to what's better for me. Regular polycarb full teeth, ultra or ultra special? (or even the deepfire titanium?)

Jugglez seems to be out of stock of V2 modify pistons so I may just pick up the cylinder set unless someone can suggest getting the ultra or ultra - special piston. Then I'll change directions and get that with the systema silent head set and reuse the old cylinder

Avoid any Deep Fire parts, they suck. Even the titanium piston will develope cracks around the groove where the teeth fit in......... even within a few hundred cycles. Foudn that out with a CA M249 I have in my basement that I'd been working on, new piston, test cycling and such.............. cracked piston. Get whatever Modify piston you feel like, the standard version is awesome.

Oh, the tooth missing, that is what caused the piston to retract and jam, the sector gear mismeshed since it grabbed the second tooth and the spring compressed fully preventing the gear from releasing the piston. Keep the bearing spring guide, cylinder is stock something, likely TM, no reason to change it or the head.

Thank you sir! Very much appreciated information, direction and suggestions.

I'll probably decide when I'm perusing and ogling the mountains of goodies at Jugglez place tomorrow. Will be either the Modify set or the systema set and standard piston.

forgot the piston head.

http://i282.photobucket.com/albums/k...C/IMG_2228.jpg

sorbo pad was installed off center and has fallen off since this was taken. :(

Am I seeing things, or did the person install the sorbo pad on top of the existing rubber pad? One's suppose to remove the existing padding... I can't even imagine what the AoE would look like, though it does explain why he'd take the second teeth off.

I was thinking that too but wasn't 100% sure about the sorbo install. It didn't make sense at first why the pad was like that since it had moved and would likely fall off during a game of intense use. And it fell off with me trying to adjust it. :o

I'm actually glad that it seized up and I had to open it up. Gives me an opportunity to make it solid.

Still debating though:

Modify Cylinder Set + sorbo
or
Modify piston, nozzle + Systema silent head set

Price wise both are in the same ballpark but I'll have to reuse the cylinder with the 2nd option and have no sorbo options.



Are sorbo piston heads and sorbo cylinder pads meant to be used together? Or is only one or the other only necessary?


Old piston head:
notice the bits of sorbo pad lodged inside.

http://i282.photobucket.com/albums/k...C/IMG_2225.jpg

Just my thoughts...

1. Modify polycarbonate full tooth piston
2. I wish you took a pic of the piston head...if you don't want to sweat it, just get a modify vented polycarbonate bearing piston head.
3. Consider tossing that cylinder hear (the only thing I haven't had 100% sucess with Modify parts are their cylinder heads...a couple of times, they haven't fit mechboxes nicely).
4. Consider getting a new Modify airseal nozzle...they're not expensive and now's the only time you can swap it out
5. How's the tappet plate? Worn/gouged/no-cracks

Best of luck,

Tys

You are not required to use them concurrently. I've been just using the cylinder cushion.

I must have been updating while you were typing. :p

Tappet appears fine but I'll check again.

I've read that the systema silent isn't all that silent so I may just stick with the Modify cylinder set and get a new sorbo pad. Only reason to get the set is that Jugglez doesn't have a V2 cylinder head in stock.

thanks.

any benefit from using both over?

Personally...I swear by the systema silent head sets. They're not silent...but, personally, I feel that they do significantly "soften" the shock transmitted to the mechbox and they do "quiet" the noise a bit.

There's others that are supposed to be even quieter (i.e. angel silent head)...but I don't have any personal experience with them.

Best of luck with your upgrades!

Tys

Even more cushioning? I think that's the idea anyways. At the very least, the o-ring on the MASK piston head is silicon rather than rubber. Apparently that's suppose to be a good thing.

Thanks for the input. I do appreciate the help.

Decisions, decisions, decisions. Systema or Sorbo? Oh well, I'll sleep on it and decide when I have the parts in hand.

Why don't you do both. Cut the Sorbo to fit in the Systema, thats what I did and it works great

I am putting a lipo in my mp5 and I was told that this was needed cause of the speed to prevent damage. Now what is true or not.

I guess I could but I read a review that the systema didn't silence much and also resulted in a decrease in FPS. I'm aiming for 335-350fps.


I see some truth to doing that in your situation with high ROF. Something about allowing the sector gear to mesh properly. What spring are you using?

I have the Modify High Torque Modular gearset already. I'm not planning to go high speed for high ROF so using a lipo is not necessary.

The Sorbo helps with the sound too and I figure they work better together than apart.

I have a 100 spring in now and before the lipo batt I was getting ~330 fps so with the high ROF I think it will be more fps but I don't know how much yet.

Negatory on ROF affecting FPS

Picked up parts from Jugglez today.

Modify Cylinder set
Modify S100 (the one in there was shorter than the S90 spring)
Sorbo piston head and pad

Will see how it all goes together. :)

Update:

Installed everything and it's shooting well but seems underpowered. The spring was a significant upgrade so I don't see how it can't pierce the side of a coke can. Yeah, that's right, it won't penetrate even one side.

Could it be the Mask sorbo piston head in combination with the sorbo pad? How can I go about testing for leaks? There is still a fair amount of air coming out of the barrel. All the orings were oiled and appear to have a decent seal. I used a thin coat of 20wt shock oil on everything.

I was expecting the Modify S100 to be slightly overpowered in the end.

cost more, but you can never go wrong with Prometheus parts. They are the unnecessarily more pricy version of Modify.

doesn't help me all that much but thanks for the info. :rolleyes:

Have u checked your air seal? When your mechbox is open push the piston into the cylinder with your finger over the end of the cylinder head without the airnozzle. If you can push it down and theres resistance your airseal is good. If not you may need to check your piston Oring or your cylinder had Oring. Then put on the airnozzle and try it again, if air leaks out crazily you may also need a new air nozzle, I believe Modify has a double Oring one which is great.

yes, I did a basic compression test but didn't test to see if there was a leak between the cylinder head and nozzle. there was significant resistance when I tried to push the piston into the cylinder while covering the cylinder head opening. I guess I'll have to tear it down again and make sure there is a proper seal between the cylinder head and nozzle. will probably give all the orings another silly bath to swell them up a bit. I also did try to stretch out the one on the MASK piston head but it didn't stretch much. more than likely because it is silicone.

the nozzle that comes with the cylinder set is a POM nozzle and not the modify one so no oring.

You have a big airleak somewhere, don't always blame the spring, that 100 will blast through both sides of a can easily. Leak can be anywhere between the pistonhead O-ring to the hop up rubber. If you got a ported piston head, then I've had problems with those also not inflating properly every time and causing wildly varying fps readings, even over 100fps difference at times. Someone once mentioned to not use grease on the O-Ring, just use a wipe of silicon oil, I tried it and it worked great right away............... haven't tried recently though. But make sure your hop up rubber is good too, it'll affect the velocity. Avoid the blue rubber Madbull ones, I have yet to find a set that actually seals well without being distorted, and I actualy bought at leasta dozen sets of them last year to use in client's guns. Not worth the price paid at all, even if cheap.

Long over due update:

With talking about testing the MadBull .25 tracers at next weekends FR game, I finally decided to break the gun down and open the mechbox once again. I'm getting good at this!

Anyway, I think I discovered the leak or possible leaks. It is possible that the hopup rubber was not seated quite right. While checking the madbull TB length with my tracer unit sensor the inner barrel seemed to seat better and actually lock down with the retaining c-clip. (MB TB = 229mm but is about 15-20mm longer than the stock UTG inner) TB clears the tracer sensor so good on that front. Rubber is the stock CA one that comes with the newer metal unit. Will continue to use it since it's brand new.

Next possible leak is with the nozzle. I took the cylinder out and did another compression test and all was good. Pushing the piston in and pulling it out while covering the nozzle tip with my finger results in little to no movement of the piston. But I noticed when the nozzle is near the end of the cylinder head, just before the spring releases, I can hear air leaking between the cylinder head and nozzle.

Now is there any way in ensuring a better seal between them? Will teflon tape work and stay put? Would it not eventually get worn and moved by the moving nozzle?

I will probably just end up getting the modify one with the double orings to eliminate this air leak. More money in to this gun and I will eventually need to get a new lower receiver. Cracks are forming from slight fitment issues and JB Weld can only do so much. :P

Last question, is the tappet plate suppose to flex much during a cycle? mine seems to bend a whole lot when I try to advance the piston by turning the gears.

Okay, so I gave in and figured I'd just get a new Modify tappet and Modify nozzle (w/oring)

Hope this eliminates the air leak otherwise I'm lost as to what else it could be.

The tappet rides in two grooves, having one of the grooves off (because it's part of the upper mechbox shell) is why it's flexing when you manually turn the gears. And Tys (m######## whatever numbers he uses for his name) took apart two MP5s as parts guns a while back and sold me an A5 stock and lower receiver/grip since mine was cracked all to hell and eventually wasn't able to hold the motor plate in place. So hit him up to see if he has the other lower still as a spare.

You rang....? The Internets notified me that my name was typed...(poorly though:D)

Just a couple of thoughts on this one...(besides I hate working on MP5's ;))

As said, the tappet rides in a groove on either side of the mechbox shells and is sort of captured in place. It doesn't get nearly as bent out of shape as it appears when you open a mechbox (where it's kind of wang'ed and all bent out of position). Better to have a thin piece of plastic there that flexes...rather than a brittle one that breaks.

I think I have another lower....it's probably deep, deep in the spare parts bin.

If the mechbox compression checks out...and the barrel is nicely seated in the hopup rubber...and it's all seated nicely in the hopup unit....It's got to be the fit between the nozzle and the hopup rubber.

You could try swapping the hopup rubber to a different brand/hardness.

Take a good look at the pins/holes that hole the hopup unit into the body (not just the right half but also the left). If those holes are messed up...the body/front end won't hold the hopup in the right sport (which should be tight up against the mechbox).

Also, I figure since the inner barrel is clamped to the front end by the metal clip that attaches it to the gas tube....make sure that you're not inadvertantly pulling/moving the hopup/inner barrel out of position as you're assembling the SMG.

The're nothing in the upper body that really holds the mechbox in place in relation. The mechbox is held by the lower receiver and the lower receiver is indexed to the upper...mostly by the front body screw. If there's a lot of slop in that connection...your lower is moving around...moving your mechbox with it. The rear body screw also indexes the upper and lower together, but a tiny bit of movement there would not be as significant as movement up front.

Keep in mind that anything "just barely tight enough"...will probably shake itself loose with normal usage.

Best of luck,

Tys

LMFAO, yes you! Guess the spotlight works wonders.

Stalker/Tys, thanks for the info and help. Will get the stuff from Jugglez tomorrow and try to install it all this weekend. I gotta get both my MP5 and M4 back together for next weekend. :(

The FrankenMP5 will be making a brief appearance with tracer rounds at FR on the 28th. :D

Got the new bits and installed it. Seems to work fine. First shot does not penetrate a can still but the second one right after it does go through both sides. I'll chalk it up to being a new spring. Will have to put it up against a chrony to get a true idea what it's shoot but I'm happy with where it is being a primary CQB weapon. Solid, heavy and crispy.

Okay, another over due update. FrankenMP5 has been put on hold as my M4 was severely fubared and I don't have funds to fix both as well as recently acquired an AK and m500 for any CQB'ing. Plus I had to harvest the mechbox for the M4. :(

So anyway, I had chronied the current setup and was getting sub 200fps. not that great considering that the spring was suppose to be in the 360ish range.

Upon breaking it down, I discovered that everything was fine except that the silicon oring was torn. So that is where my air leak developed and caused a drastic drop in FPS. I don't know where or how it got pinched in the cylinder but it looks like it got caught, pulled and torn while cycling. Again, compression test before with the silicon oring was superb but I have a feeling that it was too loose though.

I have gone to a standard rubber oring in the M4 and will see if it this setup works. Compression test seems to pan out as identical. I'd love to have stuck with the silicon oring for durability and longer life but will have to confirm that the dimensions are actually the same.

Before I put more into the MP5, I need to find a TM or CA plastic lower receiver to deal with some fitment issues as well as get a new mechbox. Might just get a drop in when the right one comes around.

Hey Coachster, I read some of your Threads and saw that you bought the Sorbo Piston head. Was wondering after all your installments, how do you feel about it? I'm looking at getting the Sorbo Piston head and Mask pro cylinder head for my Mp5 as well. Any input would be great, thanks:)

well, if you read my posts, you'd know that I haven't had a stable platform to see anything significant in terms of testing. Sounds wise, it's different. You'd have also read that the silicon oring I had torn and caused and air leak so I can't report on how well it performs.

Currently they are both being installed (piston and cylinder heads) in my M4 to reduce any possibility of cracking the mechbox again. My previous M4 setup was rock solid but I was crazy enough to attempt running her in -8c weather and it was shooting 380-385fps. They will probably stay in the M4 since I need to use a stock TM shell to fit an old systema receiver I'll be getting shortly. A reinforced box would be nice but it simply won't fit. The fit is that tight already it apparently leaves a gap when other boxes are used.

I have a stock JG box in the mail so I'll eventually be purchasing a new set of internals to rebuild the MP5. But who knows, I might stick with a drop in for the MP5 and be done with it.

I've been in your shoes...and who hasn't? Upgrading can be a pain in the ass, and without starting off with a good gun...well, it bit me in the ass too. :( I have a system drop in mechbox for my MP5. The only thing I changed was the spring. Went with a Modify S100+. So far very pleased. I wanted my gun to be quieter, so I looked into the Sorbo pad, but the facts that I got seem to be kinda cloudy. Anyway, thanks for your input, best of luck for upgrading. I do recommend the drop in, but it does come with a price;)