GTA
Airguns by Make and Model => Gamo Airguns => Topic started by: dwood5 on February 04, 2012, 11:13:41 PM
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I recently tried to remove the hinge bolt on my Hunter 440. Couldn't unscrew it using all methods available to me in my machine shop. Finally put it in my mill and carefully drilled out part of it, then punched-out the body and screw head.
Comments from others on this forum indicated that my experience with the pivot bolt was not unusual.
When I received the new pivot bolt from GAMO, it became instantly obvious WHY it was so tight.
The 'head' of the screw is tapered. It is short, but is a 'self-locking taper' just like a Morse taper [and many others]. The "ear" [or yoke] on the receiver has the corresponding female taper. Those that have experience with Morse taper drill bits will understand what I mean. They don't "release" without being forced out by some means.
My original pivot bolt had a straight screwdriver slot. The new one has a Torx T-25 head.
DON
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same problem here but vis- versa, had torqs and changed to flathead slot, was a nightmare though, had to resort to cutting the slot in the screw while on the gun with a dremel cut-off wheel, quite frankly i think that gamo needs to use a higher quality metel screw i had to do the same with other screws holding stocks on , and i never have problems with torqs head anywhere else
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Riffmeister,
I'm having the same issue with my Big cat. I wanted to do a thorough tune and lube everything with a quality moly grease. Well, same as you. I felt the metal corners of the Torx T-25 give way. I don't have access to a lathe or mill, but i'm "dang" good with a dremel and drill press. Could you please elaborate on how you were able to extract the hinge bolt and where you purchased another one. I really don't have to remove it, but it is mangled and looks like *(&^. Part of my tune job is to replace that terrible trigger with a Charlie da Tuna #4.
The squirrels are getting braver!
Ron
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Oh, great! I'm new here and already replying to my own post! ::) After reading for a few hours, once I started using the proper terminology and the search engine, I've answered most of my own questions. Gamo uses a liquid similar to Ultra Loktite. It must be heated to release the chemical bond. Unless your very lucky. Usually I am, but not today.......... So I'll just clean up the torx head and be done with it. Thanks for letting me ramble...... not a good way to join a forum....sorry.
Ron
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Thanks for following up with your solution and welcome to the forum.
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My original post as to why the Gamo hinge bolts are so hard to remove has been discredited several times in this forum. I contend that it is the tapered head of the bolt that locks it into the yoke. When I removed mine I found no evidence of any chemical bond. In fact, the remaining threaded portion was easily removed with my fingers.
Keep in mind that my experience is with a single 9-year-old Gamo rifle: my Hunter 440.
The attached pictures show what I discovered. I actually removed the second 'good' bolt just so I could take these pictures. I had to use my milling machine again and destroy the bolt as I was unable to remove it with a torx driver. New bolts are available from Gamo for $5.95, but they only sell to an FFL.
I don't know in what order the pictures will appear. One picture shows the original bolt which is now in two pieces. I used the mill to drill into the threaded end a hole that was substantially smaller than the root diameter of the 6 mm thread. I did not want to damage the threads in the gun.
I went deep enough that I was well into the body of the bolt. Then I took a punch, placed it in the hole and gave it a solid whack with a hammer. This caused the bolt to fracture at the junction of the body and the threaded portion. The body of the bolt went sailing, the threaded portion remained in the yoke.
The short threaded piece seen in the picture was easily removed by hand from the yoke. There is no way it was ever held with any chemical bond.
One pic shows a new factory bolt in the jaws of my dial calipers. If you look closely, you'll notice that the top of the bolt is held in the jaws while the bottom of the bolt head has some clearance. This is the shallow taper. I'm not referring to the chamfer at the bottom of the head. The chamfer never touches anything when the bolt is installed. It is the larger part of the head that has the slight taper.
Several other pictures show the hole in the yoke where the head of the bolt goes. You'll notice that there is no "bottom" to the hole. It is not counter-bored like you would see for many cap-screw applications. It just has a slight taper. If it wasn't for the tapered hole and the tapered bolt head, the bolt would just drop though.
This bolt is not your ordinary socket-head cap screw!
For those that question the "holding ability" of a taper, consider this: it is a taper that holds the drill chuck in your drill press. It is a taper that holds the drill in the tailstock of your lathe. In both cases the taper easily withstands the torque of drilling.
I believe it is the "wedging" of the tapered head in the tapered yoke that that makes the removal of the pivot bolt such a PITA!
DON
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they just dont want us working on them . and i have had lots of experince with morse taper. have you ever dealt with taper button locks? they work on the same princapal. looks easy to remove but when you get the button pry bar in place and smack the rim with a good hammer blow ,the bar slips and messes up the end of the lock , then its torch time
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DWood,
I certainly meant no offense to you or your findings. I was passing along information which I had gathered from this and other websites from experienced airgunners. Mostly Mr. Tuna himself. It is obvious that the bolt is tapered, I don't think your conclusions were ever in question. Is it possible that BOTH circumstances are in play? Maybe. Dunno, I was never able to remove my hinge bolt.
It was above and beyond a measure of courtesy for you to dissect your rifle once again simply for a photo-shoot. (pun intended) Thank you for taking the time and pictures which obviously reveals a tapered bolt.
As far as Gamo goes, I don't see why they have to ship parts to a FFL only. These (parts) are not regulated. CYA perhaps? Or just to be a pain?
Thanks again for all your troubles and showing us how to remove the hinge bolt.
Q: If they can be removed when heat is applied to the bolt, as others have done, wouldn't that cause the bolt to increase in size making removal even more difficult? Not being argumentative just curious.
Ron