LPE Airbrake piston heads

[Tinkerton]

I recently received two production samples from a batch of airbrake piston heads from LPE - Lees Precision Engineering.

 

Packaging: the packaging on the piston heads (I received both a metal and a plastic one) are perfect. They came in individual ziplock/resealable bags, which are just the right size for keeping fiddly things like tappet springs, bushings etc in! And in a jiffy bag. This is perfectly adequate protection for almost any internal gearbox part, so no qualms there.

 

Piston heads: These piston heads are CNC milled from 2014 T6 aicraft grade aluminium billet (for the metal ones) and acetal billet (for the plastic ones) both the piston heads come with an aluminium collar (again, 2014 T6 aircraft grade) which you insert through the back of the piston to centre the piston head, and A2 grade stainless steel screw, which is very nice as some pistonheads don't come with either! The including o-ring is also a fantastic fit, and very easy to get on and off for maintenance, however once on its very secure. This piston head IS ported.

 

Now, the main difference, and indeed the 'unique selling point' of these pistonheads is the airbrake 'protrusion', which is a bit ronseal, really, (for our overseas readers, 'does what it says on the tin') the protrusion extends from the piston head into the corresponding hole/tube/vent on the cylinder head, and as it does so, restricts airflow, creating a small pocket of pressurised air which the piston assembly uses as a buffer

(compressed/presurised air is actually a very good shock absorbsion medium, the higher pressure the less elasticity the air has, so the more it slows the item down, don't believe me? Try it for yourself! Get a spare cylinder, and piston with piston head, then while covering the hole that the tappet nozzle goes over with you finger, try to insert the piston with some speed/force. This is the airbrake principle/theory in practice.)

 

Anyway, enough phsyics, and back to the piston heads. The machining on the heads themselves is flawless, minimal tool marks, and a very smooth finish. These are well built piston heads indeed, even if they were 'flat faced'.

 

Another unique feature of the LPE airbrake piston heads is the double radiusing of the o-ring slot.

As owners of guns with V2 gearboxes will no doubt be aware, square, or angled corners don't transfer stress very well, which is why a popular mod to most v2 gearbox shells is to 'radius' - that is, to make circular - the corners of the apeture that the cylinder assembly fits in. This leads to better stress/load transferance through the rest of the gearbox shell, and eliminates (or at least, greatly reduces the risk of) the 'box shell snapping.

 

These piston heads work on the same principle. The flat face of the head has a radiused 'join' to the main body of the piston head, so any shock/stress/load created by the impact of the piston head is more easily transferred to the rest of the piston assembly. Think about it, what takes the most pounding in a gearbox? The pinion gear? Possibly. The secotr gear? Its likely. But the piston head impacts the cylinderhead with forces of the power of your main spring EVERY TIME THE GUN CYCLES. That's two flat peices of material hitting each other face on hundreds of thousands of times over the life of your gun, with up to and beyond 2 joules of energy each time.

 

 

Piston heads take a beating. That's why these ones are so wildly OVER engineered. The radiusing of the oring slot (including the back face, that keeps the oring on the piston) and the airbrake are all designed to impart as little stress as possible to your gearbox, and manage that stress in a sensible, non-damaging way.

 

Now, onto the collar. These piston heads are available with laser cut AOE shims. Yellow being 0.5mm, and red being 0.38mm. They are very very thin. However, some guns do need a lot of AOE adjustment, which is why the shaft of the piston head and the collar interact in such a way that you have a whopping 5 mm of AOE adjustment, while maintaining proper centering of the airbrake.

 

This again is supremely useful, as AOE adjustment is starting to become another 'standard' upgrade, like metal bushings and the 1j springs of yore.

 

Performance: I do not have a chrono, so can't give fps readings before/after the installation (into my kalash AKS-74, for those wondering) nor do I have a decent camcorder for a video, but it does make a noticeable difference to the noise coming out of the muzzle of an aeg. It is less twangy, like a spring, and more thunky, like... something that's not a spring.

 

There was no noticeable power or range decrease after installation.

 

Final Thoughts:

 

While a majority of aftermarket AEG gearbox upgrades affect something noticeable, like the power (main spring) or the rate of fire (gears, motor, wiring) or the strength of spring that can be pulled (motor, gears, wiring, mosfet). This is NOT one of those upgrades. While it does make a slight difference to the sound emitted from the AEG, the main selling point, and advantage of this upgrade (in my opinion) is the longevity it offers.

 

I have tried to crush the metal pistonhead o-ring channel with a small hobby vice. I cannot.

I have tried to flex the airbrake protrusion off centre using a vice and brute force. I cannot.

 

This piston head will no doubt last longer than the entire rest of your gun. Including the time that it takes to degrade.

 

While expensive, this is possibly one of the most worthwhile upgrades you can fit to your AEG.

 

Conclusion:

Appearance: 9/10 - nicely machined, nicely packed, nicely finished

Performance: 10/10 - nigh-on indestrucable. while no 'performance' increase per se, the sheer strength and reliability of these piston heads, combined with stress managing features like the double radius o-ring channel and air brake more than make up for it.

Value for money: 7/10 - while expensive (£20 rrp for a metal piston head with AOE shims) and much more expensive than other piston heads, its not that much more expensive than a prometheus piston head, and remember two things: this will last longer than you will, and its being designed, produced, and retailed by a fellow airsofter in the UK.

 

Overall: 8.5/10 - I would personally rate this as a vital upgrade to any high-performance AEG. High powered DMR AEGs? slap one in. Support weapon being used for long sustained bursts? slap one in. 'loaner' or back up AEG? slap one in. High ROF short stroked super speedy death hose of doom? dont slap one in. Put a plastic one in, with the airbrake taken off (very simple to do, sharp knife, and lots of patience).

 

The bottom line is this:

If you want a piston head that can take a beating and carry on going, through oblivion and back, and will actually look after other parts of your gearbox, this is it.

[bn_]

Very good read Tinkerbell.

 

Might actually get me one of these after reading.

 

Thanks!

[[NL]Infinity]

This looks like an interesting product!

 

Now, I'm not really familiar with the term AOE, but I assume it means "Angle of Engagement".

So with the shims you can change the angle, under which the sector gear grips the piston, am I right?

[Rob15]

Infinity' timestamp='1298108717' post='2426336']

Now, I'm not really familiar with the term AOE, but I assume it means "Angle of Engagement".

So with the shims you can change the angle, under which the sector gear grips the piston, am I right?

In short, yes, that is correct.

 

Over the years the tolerances and dimensions from the original TM gearboxes have gone all over the place with so many after market parts, one of the issues this creates is pistons sitting (or more specifically, the first pick-up tooth) too far forward so the first tooth of the sector gear only partially engages with the piston until it has been pulled back and the next teeth are engaged.

 

On high-speed set-ups this can result in the first tooth being snapped clean off the piston, in standard to mid rof it means the load is only spread over a small surface area of the teeth and can cause uneven wear. With that in mind these piston heads have been designed to allow for precise adjustment (far more so than using sorbothane or other foam padding which can also vary in thickness being a compressible material) from 0.38mm with a single red shim up to 5mm using a combination of shims while maintaining alignment on the piston itself.