MP5 SD mechbox parts recommendations

[CDN_Stalker]

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.

[m102404]

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

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

[CDN_Stalker]

Originally Posted by m102404

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

Tys

LMFAO, yes you! Guess the spotlight works wonders.

[coach]

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.

[coach]

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

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.

[coach]

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.

[hebet]

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

[coach]

Originally Posted by hebet

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.

[hebet]

Originally Posted by coachster

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