Marushin MP40 ... Loose Folding Stock Problem

I've seen a number of Marushin MP40s that have a common problem. The folding stock will not lock firmly under the foregrip when in the folded position.
All too often the stock drops 2-3 cms beneath where it should be.

I've one such example here and despite taking the pivot pin apart and reassembling I can't seem to cure this droop.

Has anyone any suggestions please

Thanks in advance

Hi Cerwyn,
It does seem to be a common MP40 problem.
I'm sure you've done all these checks, but just thought I list what I'd do in case it helps....
Flying by the "seat of my pants" my thoughts are as follows......''
As many of these are built from kit sets it may be due to an assembly problem; or if factory assembled, it looks like a manufacturing issue; or is it due to wear in the ratchet teeth???
Looking the the assembly instructions below:

a) I'd check for the release spring (part # 44) being installed the right way (as mentioned in the instruction sheet) either by the factory or by the kit set assembler?
and if it is in correctly, then
b) are the folding stock arms installed upside down? (a known Denix MP40 problem)
The only other thing I can suggest is:
(c) that the ratchet teeth in the housing may need some rotation alignment correction (due to wear??) Not sure if that's even possible? ''

Or is it just a design/production fault? '' ''
Well that's my "tuppence worth"! Hope I'm not "teaching my grandmother to suck eggs"! ''

Kiwigunner

Thanks very much KiwiG

I am grateful for your input and advice. I've something to work on now, two heads are definately worth better than one after all

The model I have here was built from kit and has done little more than sit in my gun cabinet on display from new. It shouldn't be a wear problem then, so I'll follow your advice and check the assembly.

Thanks again for your help:D

kiwigunner wrote:

(c) that the ratchet teeth in the housing may need some rotation alignment correction (due to wear??) Not sure if that's even possible? ''
Or is it just a design/production fault? '' ''

In my case it is too much tolerance between the teeth on receiver and on locking button.
There is enough play for the button to drop a bit. Over the length of the whole stock it is enough for a few cms that Cerwyn quoted.

Left: incorrect, gap seen BELOW middle tooth. This means button has rotated anti-clockwise, and stock drops (or droops, nice word play here!).
Right: correct position, but not sutained due to the gap above middle tooth. It could be corrected by glueing a thin metal sheet on top surface of the receiver tooth. Similar treatment could be done to prevent drooping of the stock when unfolded.

Some more data:
It would appear that early Mp40's (and possibly Mp38's) did not have teeth in the rotor mechanism for the folding stock. ''

This suggests that shimming the top and/or bottom for the rotor button might also solve the drooping problem.

At the risk of being labeled the "metal-putty man", '' applying a layer of this epoxy and filing to size might be easier than making a shim? ''


This site is worth viewing if members have not already seen it.
http://www.mp40.nl/index.php?page=mp-40


Kiwigunner

Hello putty-man ;-)

If putty can be filed, wouldn't it file/wear itself off during stock operation?

Once the metal epoxy I've used sets hard, it seems to be at least as hard as steel. And can be filed like steel! ''
So if the components are zinc, you'd need to putty both side of the action!
I've used the putty to make replacement nuts for bolts - after a couple of days of curing it's as strong as the original nut! ''

That's why I like using it ----- I'm nuts! ''

Kiwigunner

I see now why you like it so much :-)

kiwigunner wrote:

So if the components are zinc, you'd need to putty both side of the action!

Very good point, otherwise the harder putty surface would damage zinc, right?

Right, mate!

If you want it to look right when the stock is folded, squeeze the shoulder part of the stock in a vice so that it is a push fit over the forgrip when folded..

Mike

Metradio:
What a great idea! Have you found that it works in the long term?

Kiwigunner

kiwigunner wrote:

Metradio:
What a great idea! Have you found that it works in the long term?

Yes it does..

Mike

I read this thread with interest, as my Marushin ABS + Zinc MP40 has the 'stock droop'. Taking the button assembly apart, I noticed that my two 'teeth' were indeed the problem. Just for S&G, I turned the button 180º so that the opposite set of lugs would engage the button teeth. The stock now folds up nicely, but the button does not 'pop out' fully.

The stock now locks with an upward angle at full extension, a condition which I've noticed in online pics and wondered about...Now I know why.

I am somewhat loathe to epoxy or shim the button lugs...Or squeeze the arms in my vise...

It's too bad that Marushin didn't copy the one big tooth button instead of the two small ones...I could have put a tiny setscrew in the big lug and adjusted it as required...