piston short stroking at iba pa

Piston short stroking, a well-known technique for helping increase ROF, was implemented on the Yarik Kalsador since this PMC AK is designed as an urban warrior weapon.

The logic is simple: decrease piston cycling time by removing teeth from the piston and the sector gear. Advantage? Less stress on the gears, the motor, and the battery. Gain? One sixteenth rps per every tooth removed. Loss? 15-20fps per tooth removed.

All pics courtesy of Soulman of ACM dot Com.

First, the piston.

After removing the metal bar with the metal tooth, remove as many teeth as you want. Three teeth, the minimum accepted number, was removed for the Yarik Kalsador piston.



Then cut out the center part of the piston underside to make way for the metal insert.



Next, cut out a channel along the sides of the cut-out middle so that you can move the metal insert to butt against the intact tooth.



Next, cut off the retaining right angle in the metal insert



Last for the piston part is making a metal extension to cover the gap exposed by moving back the metal piston insert.



You can use any flat metal bit for this extension. An aluminum bit from a U channel was used in the case of the JG piston of the Kalsador

Be sure to super glue the metal insert and extension to the plastic channels.

Now for the sector gear.

All pics for this post still courtesy of Soulman

Remove the corresponding sector gear teeth with a rotary tool or something suitable.



Smoothen the curve with a file and some sandpaper.



And you're done!



Be sure to check piston and gear teeth engagement.



Note that Soulman removed the second to the last tooth and part of the third tooth of the piston to prevent premature engagement. Since the Yarik Kalsador is intended to have only 13-15rps (and thus mimic the RS), only part of the second tooth and a smaller part of the third tooth was removed from its piston.

Btw. incorrect teeth engagement resulting from using piston, piston heads, and sector gear of different brands can be remedied by piston head shimming. This technique requires putting appropriate spacer/s of appropriate number/thickness between the piston head and the piston itself.

The stock piston of the Yarik Kalsador was also lightened by cutting holes in the piston.



This technique makes the piston easier to push for spring, thus decreasing cycle time and, more importantly (as Kom Bangus has pointed out), helps prevent premature piston teeth engagement.

The piston rails were left relatively intact by drilling small holes along its middle.

Futher lightening insurance was made by replacing the bearings in the CA piston head with a plastic insert from a bb loading tool.




The lightening done to this piston is, admittedly, relatively conservative. Other people have done much more radical removals and one has observed strong vibrations in a lightened piston/strong spring combo.

You can use a small drill bit to start the holes and enlarge them with either files, cutting edges, or a hot soldering tip. I choose to be safe by smoothing the hole edges with a rotary tool and by dragging the edge of a stripping knife along the edges.

As additional measures, the internal rails of the mek and the cylinder were polished, the piston lip beveled, bearing bushings used on all three gears, and the mekbox shell painted.



A chaoli motor was used since the intent was to see just how far stock ACM components can go.

As it stands now:

• good rof, unsatisfactory fps with a stock 035 spring, a bearing spring guide, 9.6v 1400maH Intellect stick battery
• satisfactory ROF, satisfactory fps with a PDI 190, bearing spring guide, and 9.6v 1400maH Intellect stick battery

Problem: battery lasts for only half a hicap mag with the PDI 190 and bearing spring guide.

Next:

• try the SP120 spring/bearing spring guide combo with a 9.6v stick battery
• try the sp120 spring/bearing spring guide combo with a 10.8v stick battery
• as a last resort, try the 11.1v li ion stick

After those issues are solved, all the Yarik Kalsador will need to complete itself is a trigger-activated, full-auto only, magazine motor switch. he he he . . .

Galing nyo komrad!!

tx for the compliment, kom hans, but that is a long way from the truth. i'm just messing around trying to learn things. maybe someday i'll know half as much as the AK mastahs like you, kom TuK$, and mastah Rambo.

Komrad,

I'm still learning malayo pa to be called mastah.. but hope someday be rank among them..

kaya type na type kita, eh, kom hans