Replaced seal gamo 440

[Crock Pot]

After not being able to get a gunsmith in my area  about a month ago I built a spring compressor and followed some instructions on a tune for the Gamo 440 after my spring broke.  I ordered the appropriate spring ,seal, Molly paste ,heavy tar and went about installing it.  HOWEVER I did not pay enough attention to the inside of the punched out cocking slot and holes etc with my sandpaper and the edges were still a bit sharp.  All went like clockwork but when I installed the piston it was very tight ( I used a bit of silicon spray as I did not have any grease) and when I pushed it a bit hard it all of a sudden went in but very small bits of the seal were shaved off (and also small bit of my thumb).  When I had the thing together it was like a different gun a lot quieter and no vibration and more accurate but it was a bit down on power.  I thought this must be because I damaged the seal. It also dieseled a few times when I shot some tighter pellets (Big Bill said could be lube leaking past a damaged seal).  I ordered two more seals and decided to replace my seal when they arrive.

BUT - now that I have shot about 750 shots through it (while im waiting for the new seal to arrive) the dieseling has stopped and the power has risen to the point that it penetrates a phone book slightly further than my wife's Shadow 1000 witch has had about 1000 rounds through it and it is more powerful than before the spring broke.  I do not have a Chrony yet so the phone book comparison is my only test against a new gun that has almost been broken in. My wife's gun always had a bit more thump than my 440 before my spring broke.
I am not sure now if I should go ahead and replace the seal or not.  Any thoughts or advise would be greatly appreciated.
Rob

[Big_Bill]

Well Rob,

From what you are saying, it looks as if the seal seated itself, the dieseling must not have been very bad. All springers diesel a small amount, enough that you can smell the oil when shooting in the basement. If your rifle was dieseling very strongly, it could have damaged your spring and seal before 700 rounds.

I would get dielectric grease to lube the sides of the seal, as I don't know how long the silicone spray will hold up ?

I'm glad you built a spring compressor ! and that you are enjoying your Gamo 440 Hunter..:-)

[Crock Pot]

Thanks Bill,
I went to a auto shop on the weekend but they did not have any dielectric grease.  I will keep looking. it dieseled about 5 times here and there where I could hear a loud crack but nothing for about 250 shots, now every so often I only get that oil smell you described and accuracy is consistent..  I am really enjoying this gun because I am not afraid to work on it. It all started when I found out how easy it was to put in the GRIII myself.  Next time I have it apart I will sand all the inside of the slots smooth. How will I know if the silicon spray does not hold up? will it squeak?  Also I am in the process of organising a Chrony so any ideas what would be a MV I could expect from this gun using Beeman FTS(waiting for those JSB exacts to come). I might have been a bit heavy on the TAR too..  
Rob

[CharlieDaTuna]

Hey Rob... the Silicone spray will not get the job done or hold up. In this kind of application, it has very little lubing benefit if any. You should get some 100% Silicone grease available at most automotive stores. They use it for spark plug boots among other things. A small tube of it will last forever.

[Crock Pot]

Hey Thanks Bob,
I suppose I will redo the seal when it arrives. and sand those slots properly.  the instructions on your site I could follow easily, I just should have paid more attention to the inside of the punched out holes.  I will definitely use the silicon grease this time.  At least I know I can do it and it is fun.
thanks,
Rob.

P.S I quite enjoy this forum. thanks for putting me on to it.

[Big_Bill]

Well Rob,

You have the word of the Man himself, I ask for dielectric grease, but it is dielectric silicone grease, sorry.

I would hold off shooting it until you get the silicone grease, when the silicone spray gives out,friction will destroy your seal, I can't say how many shots will destroy it, but it will.

Bill

[Crock Pot]

Thanks Bill,
I will get that grease! I suppose I will have to pull the 440 appart to get the grease in anyway so if I have damaged the seal I will wack a new one in as I ordered two.
Thanks again,
Rob

[Crock Pot]

Having trouble finding that silicon grease.  I contacted the local service station workshops and asked about 100% dielectric silicone grease used for spark plug boots. He did not know what I was talking about but after ringing a Bloke in Darwin he got me in a small 3 ml sachet which only said - 3ml sachet - silicone compound - silmore Taiwan. I am not sure if it is 100% silicone though.
 The other stuff I found was -
 Dow Corning 4 electrical insulating compound. Which had written on the tube -
- Designed to meet MIL - s -8660
- provides moisture barrier 70F to 400F
- flammability -1
Does anybody know if I could use either of these things when I replace the seal?

[johncedarhill]

Would Divers Silicone work? Being in Australia you might have access to that. I use it to lube fittings on HPA tanks.

what he said, although dive shops usually charge a lot for a thimble full

or your local electrical wholesale (trade supplier) will probably be able to get equipment from one or both of the following

http://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0556446

http://au.farnell.com/jsp/search/browse.jsp;jsessionid=NWQDTLSVMBVPECWNBBS1Y4Q?N=0&Ntk=gensearch_001&Ntt=silicone+grease&Ntx=&_requestid=15093

fin

[Big_Bill]

Sorry Rob,

I did not think you were from Australia, or that they would call it something else, down under. lol

Any 100% silicone grease will work, as Bob said.

Bill

[Crock Pot]

Thanks All,
I will keep looking for it and let you know how I go.  I am sure I will find it sooner or later and this time I will take my time and do it properly.  The time her is 12:30 pm so if I don't answer straight away thats why.  Thanks again,
Rob

[Crock Pot]

Hey Nearair,
I just checked it with the Dow Corning silicone compound I have at home and it is the same as the Dow Corning tube on the link you sent me. Only an older tube - still looks ok.  I will give it a go.  Thanks Heaps,
Rob

no bother, i was in the same boat years ago, no one in bearing suppliers etc knew what the hell silicone grease was, everyone i asked had it in within a few weeks though, good luck in your quest  

fin