Updated results for the Prometheus Hard Piston
In Part I of the Mega-Piston Review, the Prometheus Hard Piston turned in a mediocre performance. Here are the results of a new piston, retested using the same testing methodology.
Updated results for the prometheus hard piston
In our previous review of the Prometheus Hard Piston, the test results showed significant damage to the piston after the first 1000 round stress test cycle. This was a surprising result to many, including myself, considering the impeccable reputation Prometheus as a top of the line parts maker.
Updated results for the prometheus hard piston
The damage to the Prometheus Hard Piston was much more severe than any of the other pistons in the review, and did not seem to correlate to a weakness in the design of the piston itself. A possible source of the damage may have been the premature engagement of the sector gear first tooth and the piston second tooth. Several pistons in the review displayed slight interaction between the first sector gear tooth and the second piston tooth, but since none of the pistons were modified to correct for this shortcoming, the Prometheus piston was likewise left alone. Most of the pistons compensated "automatically" through slight deformation of the second tooth to allow the sector gear tooth to slide by, but the Prometheus piston may have been unable to do so due to its reinforced design. To verify these theories, a new piston was ordered for follow-up testing and the piston tooth engagement position photographed.Piston Fitment
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As can be seen in the piston fitment photos above, the second piston tooth is completely engaged by the sector gear, to a much more pronounced degree than the other pistons in the round up. This likely led to the piston "bottoming out" against the spring guide before the sector gear has gone through a full rotation, placing tremendous stress on the second piston tooth. Additionally, the torque generated by the Systema STU gearset in combination with a 9.6V battery was apparently enough to completely shear off the second and third teeth of the piston, causing severe alignment issues with the rest of the piston teeth and the resulting pattern of damage to the piston. It is obvious that the simplest remedy to this situation is to trim or remove the second piston tooth so as to preserve proper tooth engagement.
Updated results for the prometheus hard piston
After removal of the second piston tooth, the new modified Prometheus piston was reinstalled into our testing platform, and sent through 1000 cycles using our test M140 spring. Here are the results.Prometheus Hard Piston (Modified)
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With the slight modifications, the piston performed extremely well, easily handling the M140 spring without much visible wear. The small nick on the third tooth did not result from the test, but was due to a slip of the Dremel tool during removal of the second tooth. One thing of note here is that the second tooth is tricky to remove if the side reinforcement rails are to be preserved. A steady hand and a precise tip is definitely necessary.
Conclusion
It is pretty clear from the follow up test that proper installation of the Prometheus Hard Piston *may* require slight modification, depending on your specific combination of parts. Because of the piston's reinforced design and relatively hard plastic material, failure to properly modify the piston for full compatibility can likely result in rapid catastrophic failure as in our initial tests. With the proper modifications in place, the Prometheus Hard Piston performed admirably in our first round of tests. Stay tuned for the results of the next 1000 rounds.