Short Stroking... Two Birds, One Stone?

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Hangtight

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Before I go blindly cutting teeth off gears I thought it might be a good idea to throw this out here and pick the collective mind of the forum.

The situation is that I have a nice little CQB M4, M110 spring, 170mm barrel and the appropriate cylinder, 20rps, but it has a couple of issues. First, it's running too close to the field limit for comfort. What's OK on my chrono could well be over on a site chrono. Second, it has a nasty habit of jamming the piston at the rearmost point of travel. Loosen the buffer tube screw and there'll be a little 'thunk' and it'll cycle again. What seems to happen is the spring isn't completely centred by the guide and at the point it is fully compressed it will bind in the back of the piston.

So the idea is that if the piston can't travel right back there won't be quite as much stored energy in the spring, and it won't bind.

And if I'm only taking a single tooth off the sector, is there any point taking the corresponding tooth off the piston rack?

 
If the piston has more than one metal teeth, go for it. You don't need to remove the piston's last tooth.

 
7 Tooth piston so no issue there. I'll post some numbers once it's done. Thanks.

 
As long as the last/release tooth on sector is same as the other 15 teeth on sector

then there is no real need to remove just one tooth from piston's rack

no point what so ever removing rack or part metal rack to grind off one or two teeth

(we have to grind the bare rack when AoE/SS or risk heating/melting the piston if modding in situ of the piston)

But no need to remove teeth from piston for just one or two teeth

the weight is really f*ck all anyway

The piston issue as I understand is perhaps the replacement piston may be slightly different to the original one

in these cases some pistons & the way the teeth are cut can sometimes "bottom out"on full 16 tooth retraction

So yes SS a tooth will be worth considering on shorter barrel guns

If the spring is binding inside the piston or on the guide - eg tightness then this needs looking into

the spring should move freely on both blah blah blah..........

As for FPS - the spring could be changed or an irregular spring fitted differently could alter fps by about 10fps

other options that alter the FPS will be bearing/spacer inside the piston and bearing spring guide

these will compress the spring more/less - a bearing is about 4,5mm or 1.5 teeth compression

The teeth pitch is 3mm and any extra or less compression will equate to about 15fps per tooth

THIS IS ONLY A ROUGH AS F*CK GUIDE THOUGH

So if you remove a tooth then you can expect say...

352fps - bit warmish now n then remove a tooth

-15fps or maths crap multiply the figure by 0.95 to reduce it down

will bring you down to say 335fps

The tooth you remove from sector gear SHOULD be the first tooth - pick up tooth

you could remove just one of the release but this can effect tappet plate timing of release

so really avoid removing teeth from release side of the sector

Remove a tooth from the pick up side or first tooth that engages the piston

(I screwed up following a bad guide - f*ck me what are the odds of picking a nob's guide to follow)

No need to remove the piston's teeth off rack - as long as you have a metal release tooth still

(at least 3 metal teeth or 7 metal teeth or full metal rack)

plastic release tooth won't last long in use

Most of this you probably - well yeah I'm positive you knew all this anyway - so just confirming

soz for wall of text - yup just hack off a tooth on sector pick up side and it should work I feel

 
A few shots through the chrono before taking things apart, and the spring has settled down. Seems like a couple of days sat in the corner to contemplate its actions last Sunday has done the trick. But on taking it apart (again) I found the spring guide tube had unwound from the base plate, leaving a gap the last coil of the spring could fall into. Hence the piston binding. I knew it wasn't the piston bottoming out as this is one of my checks when I build. I've put a nice chamfer around the id of the piston anyway. It looks like the only damage is a couple of tiny slivers taken off the plastic piston teeth.

Another step along the learning curve, and another spot to remember to Loctite...

 
The HC05 bearing spring guide came adrift when I ripped it open after less than 50 rnds

it was a push fit type - right w@nky G&G stuff

due to that I then began checking stuff more

another guide with a cross/philips head screw was out of bag loose - jeez

yeah mild/blue loctite - just a drop comes in handy

(I put way too much blue on a motor height screw and f*ck me ended up regretting OD it when I was mullering it adjusting the motor height later - way too much and didn't think it was THAT strong - works but even with a think flat head I managed to muller it so much just getting it out - aging it about 5 years in 50 seconds. Ergh should of just chucked it hot soapy water or something but instead carried on mullering it. Yup more lessons learnt - easy on the loctite even the mild stuff) 

Has anybody noticed how we now spend more time now than just slapping stuff together like our first attempts

But the builds are gradually getting more and more precise & higher quality - well usually

 
Samurai said:
Was it an SHS piston guide?
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The one I had I think was cheapy TWG Big Dragon - one with round locating pins:

(yeah I know the pic below is a v3 but wanted to find a pic with screw showing)

http://www.taiwangun.com/en/spring-guides/spring-guide-w-bearing-v-2?from=listing&campaign-id=19

if you look closely there is a screw right inside that was a bit too loose for my liking:

spring_guide_v3.jpg


I think SHS used to have a screw at the end maybe on some like TM ones with no lugs

but think now they don't have a screw at the end and are pressed or threaded on without a screw head

my SHS v2 guides are now like these:

s-l300.jpg


 
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I've always been careful about putting stuff together, but it's a constant learning process about where that care needs to be directed.

But then you see stuff like...

swiss-4.jpg


and you wonder why you bother.

 
Hangtight said:
Guarder  bearing one.
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Yeah sounds like that Big Dragon type that the recessed screw comes undone

Hangtight said:
I've always been careful about putting stuff together, but it's a constant learning process about where that care needs to be directed.

But then you see stuff like...

swiss-4.jpg


and you wonder why you bother.
Click to expand...
Click to shrink...




Yeah that is just f*cking bollox & asking for trouble imho

I mean yes the spring won't quite pop out coz the "arc" of say 2 o'clock to 10 o'clock will keep it in ?

But under max pressure/strain the spring will want to burst out so the spring imho will not be held in true alignment when it uncoils under pressure - f*cking lazy carftmanship imho plus swiss-ing below the runners have to be careful not to lose strength on plastic piston holding the rack in under pressure - mind you the little holes have hardly made much difference to the weight

Seen some way too stupid swiss-ing imho to lose weight but then they put in a bearing or an ultra heavy piston head

I'm no expert and sure we all do stuff differently - I'm still altering stuff as & when I learn from my continuous mistakes I make

I'll just go with my swiss-ing on top can lose about 15% maybe 20% with large holes but that is plenty for me so far

 
Hangtight said:
For a bit of context on that last pic...

http://www.patrolbase.co.uk/blog/short-stroking-swiss-cheesing-part-1/
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Yeah saw that a while back when researching Short Stroking

read a number of posts and some looked a bit roughly done - my OCD & fussiness kicks in

BUT ffs how I picked up a BAD guide and used a WRONG guide to follow/check which teeth to remove

PatrolBase is correct in taking off the first/pick up side

I took off 2 teeth on the release side and had to cut the tappet fin to release the tappet earlier

then a further 2 teeth on the pick up side which is what I should of done and yes it works

BUT now 4 teeth off in a longer 360mm Raider is perhaps a bit light on stroke/volume

so that needs to swap around the box say for a FireHawk or short Raider - another to look at

Thing is though there is a lot of info out there & there is still some bad or very wrong guides still

I had a repair kit pile of $hit that I started to shim following the guide which was wrong

nothing about shimming to bevel/pinion just plop it in and fat washers not shims supplied

no wonder it worked out crap - nothing to do with my total $hit experience

but the guide & its pictures - the classic was it had fitted a 3/4 port cylinder around the wrong way !!!

the port was about 20mm from the front of the cylinder head ar$e about face

No $hit - look very carefully at the port on the cylinder....

53ieNT2.jpg


NO F*CKING WONDER I HAD A NIGHTMARE !!!

(following a well written guide by muppets who refit the cylinder ar$e about face)

I didn't fit the cylinder as per guide - truth was it was a full cylinder in my box anyway

but jeeez these instructions on the back was perhaps written by w@nkers for w@nkers  

well I was a w@nker anyway - still am but I'm a little bit more wiser now

 
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I'm constantly surprised the relationship players have with the internals of their guns. When mine jammed on Sunday, I stripped it down at lunch. I didn't take the gearbox apart, but people still look at you like you've grown a second head or something!

 
I am no expert in fixing stuff

BUT

I have a wealth of experience in breaking stuff - f*ck yeah

I have obtained a fair amount of wisdom in wrecking stuff - oh yes...

now need to ensure I don't keep making those same stupid mistakes

(sort of what life is all about I guess)

 
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