O-rings - need some serious advice

[abdelnour]

hi

im replacing the handle on my cressi Comanche and I hit a major challenge

while trying to insert the handle into the barrel the O-rings get stuck inside the holes on the sides of the barrel (the ones used for the screw that holds the handle)

as I pushed harder the holes in the aluminium barrel tore the O-rings and just destroyed them

I managed to get new O-rings


any advice on how I can insert the handle with the new O-rings without butchering them like the older ones?



thanks

 

[abdelnour]

anyone?!???

 

[Diving Gecko]

I don't know what this is called in English but I am wondering if the holes for the screws have been sanded or whether there are metal "chips" (burrs?) sticking out on the inside which could cut the o-ring? If so, sand them off.
Also, remember to lightly grease the o-rings.
Perhaps what happens is that as the o-ring is getting pushed by the two holes it expands a bit into the hole and gets cut on the inside of the hole. So, try to also sand the inside of the holes, so they aren't too sharp. Alternatively, or additional, find out a way to try to avoid the ring going into the hole. Perhaps you can find two pieces of rod, the same diameter as the screws, and push them slightly into the holes (so the tip of the rod is flush with the inside of the barrel) so that as the ring approaches it wont be able to expand into the holes. Or perhaps tape the holes from the inside? But make sure the tape doesn't sit in a location where the o-ring will be sealing once the handle is pushed all the way in.

Hope you figure it out.
David

 

[abdelnour]

Hi David

Appreciate the detailed response

I did check for chipping or jagged edges but there weren't any

I am considereing the sanding option indeed

I did try taping the holes with the brown scotchtape (the one used for cartons) but then I pierced it to insert the pin but I couldn't see clearly to aligh the holes with the handle hole (there were pieces of tape I couldn't get out)

Its funny we actually thought about the same solution...but yes ur diagnostic is right, as the o-rings are pushed against the wall of the barrel inside, once they hit the holes they expand outside creating a problem

I don't have any screws I can block the holes with

I've been using cooking oil so far to lubricate the process so far so I went out and bought a proper o-ring grease so I'm thinking of greasing the hell out of everyth and hoping for the best!

 

[Diving Gecko]

I think the tape option is still very viable. There is no problem having the tape sit in the barrel afterwards. Just as long as the o-ring is not trying to seal on top of it. To help with aligning and being able to punch through the tape and into the holes perhaps start by inserting the handle without the o-ring and align it and then draw a line from the barrel onto the handle where they meet. Then tape, grease o-ring and insert the handle again. When the line you just drew lines up, you know the hole is just under the tape and you should be able to punch through.
Excessive greasing can be potentially bad as well as you can get more stuff stuck in it, but don't think that would be a big issue in a speargun barrel - once it is sealed it wont be opened again (like eg. underwater housings for cameras). Just make sure you don't use WD-40 as that is supposedly corrosive to the o-rings.

Good luck,
David

 

[abdelnour]

I think the tape option is still very viable. There is no problem having the tape sit in the barrel afterwards. Just as long as the o-ring is not trying to seal on top of it. To help with aligning and being able to punch through the tape and into the holes perhaps start by inserting the handle without the o-ring and align it and then draw a line from the barrel onto the handle where they meet. Then tape, grease o-ring and insert the handle again. When the line you just drew lines up, you know the hole is just under the tape and you should be able to punch through.
Excessive greasing can be potentially bad as well as you can get more stuff stuck in it, but don't think that would be a big issue in a speargun barrel - once it is sealed it wont be opened again (like eg. underwater housings for cameras). Just make sure you don't use WD-40 as that is supposedly corrosive to the o-rings.

Good luck,
David

I managed to do the tape idea on the handle end of the gun but I am suspecting that there is a bit of tape between the o-ring and the barrel because I tested it by blowing air with my mouth through the muzzle end into a bathtub and it leaked

my biggest problem now is trying to take the handle apart again because everything is super stuck is if it were welded or glued

this assembly project turned out to be much more complicated than I thought

 

[abdelnour]

I finally pulled it off

I managed to smoothen the holes' edges by a thin "needle" file

then I applied silicone grease (called O-ring Grease, brand is Molykott) all over and everything slid through easily without damage (hopefully)



thank u diving gecko for ur help and feedback


cheers

abdelnour

 

[Diving Gecko]

Hi Abdelnour,
That's great news. Weird that it was such an operation, eh?
I suspect, they don't care at the factory - or that they have some sort of jig they mount the gun in during inserting of the handle. One that holds the barrel while inserting two small rods into the screw holes to prevent the o-ring from expanding into the holes and getting cut...?

But great that you sorted it out.
Happy hunting,
D.

 

[abdelnour]

im pretty sure it involves two poor workers, one plugging the holes on the sides and the other shoving the parts in lol!

ive done a bit of research these makers buy most of their parts pre-made from china and they assemble it at their factories

anyways, thanks again man

happy hunting to you as well

cheers

abdelnour

 

[Diving Gecko]

ive done a bit of research these makers buy most of their parts pre-made from china and they assemble it at their factories

abdelnour

Very true - I actually ran into a Taiwanese company at a dive show in Shanghai. They told me that they produce one of the highest priced guns of one of the most renowned European speargun companies. (I know which model and company). I have no reason to doubt them and living in China and knowing a bit about production there I don't resort to thinking, as too many people still do, that all Chinese-manufactured stuff is crap. Eg. most of the high-end electronics in this world is from the Chinese mainland. And some of the worst crap is as well. (And then of course, Taiwan on a lot of levels should not be considered as part of the mainland, but that's another discussion altogether, that I am not about to open;-)).