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Sourcing a 13mm Piston

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Crispin

Spearfisherman ;=- --->
Sep 14, 2001
261
31
118
Hey chaps,

Now that I live in NZ getting parts for these guns is pretty difficult.

I'm after a source to get a Mares 13mm piston for my Cressi SL (I dont want the Cressi ones because they corrode)

I could get a 13mm piston from Pelengas but im not sure of the brand, and I know the Mares ones work.

Can anyone recommend a source to get a decent piston.

Thanks.
 
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yeah ive had cressi's since the late 90s Pete, I've modified it a lot, and it's my favourite gun by far, however, the foremost metal ring on the piston does corrode, and I find the corrosion flakes into the plastic on the piston, which im not keen on, so im trying to improve it. I can easily get a cressi replacement, but I would like a Mares one, or I might try a Pelengas to see how it fares.
 
Well my Cressi-Sub "SL" has an all metal piston and how you stop corrosion is once your gun has dried off, after being washed, you squirt some oil into the muzzle relief ports and keep the gun muzzle upwards for about 5 minutes to allow the oil to flow down over the piston. You can use WD40 to do the same job, but not with a plastic composite piston as WD40 can weaken the plastic if it is that white stuff seemingly used only inside pneumatic guns (may be acetyl). The black plastics used in pneumatic guns are like the white plastics also swimming in oil, but WD40 does not seem to affect them. I have used WD40 for years on all my metal piston guns, but never on the plastic piston guns. The other reason is a Mares spearfishing representative told me that WD40 should not be used on those later guns and he seemed to know what he was talking about.
 
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yeah ive had cressi's since the late 90s Pete, I've modified it a lot, and it's my favourite gun by far, however, the foremost metal ring on the piston does corrode, and I find the corrosion flakes into the plastic on the piston, which im not keen on, so im trying to improve it. I can easily get a cressi replacement, but I would like a Mares one, or I might try a Pelengas to see how it fares.
Just be aware that the mushroom head on some pistons has a rear "bump" to aid in sear lever relatching in that you don't push the piston too far back as it acts as a stop. That rear bump will not always fit on guns with different shape sear levers, so you need to check before doing any piston swaps.
 
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Just be aware that the mushroom head on some pistons has a rear "bump" to aid in sear lever relatching in that you don't push the piston too far back as it acts as a stop. That rear bump will not always fit on guns with different shape sear levers, so you need to check before doing any piston swaps.

Thanks, yes I was pondering about anything that might stop this working, and that came up on my list, others have mentioned that the Mares and Cressi pistons are interchangeable though, so I've taken a punt on the pelengas ones. But yes, i'll be measuring and comparing the ends and running some tests when I make the swap to make sure it's safe, There's always a part of me that worries whenever I have a loaded pneumatic in the water anyway - regardless of parts, especially my sporasub one air, I don't really 100% trust it if that makes sense, I'm always (even more than the cressi's ) super cautious to make sure it never points at anything I don't want it to. I'm still pondering trading it for a beuchat revo concept, but for a 100cm gun at 30bar, it packs a hell of a punch - especially for the pelagics down here in NZ. Thanks for the advice Pete - much appreciated.
 
Yes, it is good practice to be wary of a cocked pneumatic speargun, or any cocked speargun for that matter, as there is always that one in a million chance that something has unexpectedly failed, jammed or come adrift and you don't want to be the gun's next victim, or anyone else! I always hesitate for a second when I hear the mechanism click over the mushroom tail before I remove hand pressure from the loading bar just to make sure that the piston has really locked and then I rapidly remove my hand from that end of the gun. With valve operated guns this approach pays off as the spear rebounds slightly after you release hand pressure on the loader as the firing valve engages and the tiny amount of air left behind the piston equalizes with ambient pressure. Hydropneumatic guns are the same, always that slight rebound action of the spear if they are valve operated triggers.
 
Pelengas pistons arrived last Friday - picked them up today, thats pretty decent turnaround time from the Ukraine to NZ.

The finish looks to be good, with zero metal exposed to the seawater, i'll get the vernier's on them tonight, but it looks like the only contacting surface is the o-ring at the rear, which is different to the Cressi piston in that it has the guiding skirt at the rear and an additional o-ring. Anyway - i'll give it a go tonight to make sure it fits then strip the gun completely for a full service, i'll try and video the process if I can.
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You want to make sure that the piston nose matches the anvil or shock absorber face as the more surface area to impact on then the less stress on these parts, plus the piston does not want to be pushed sideways as it hits the anvil or it can crack the piston. In the Pelengas gun the anvil is a polyurethane bush, in fact there are two or three of them depending on the gun model.https://forums.deeperblue.com/threads/pelengas-pneumovacuum-speargun.100126/
 
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