Disassembled Pics of The Gamo Big Cat Power Plant

[speedturtle]

From the last post that I've made regarding my Gamo Big Cat I told the forum that I find something quite unusual about my Piston Spring. Once the action is separated from the stock you can actually see that about 1/4 of the total spring length is somewhat fully compressed when uncocked. Also, I noticed that there are noticeable metal to metal fricion when I'm about to fully cock the spring. Well, my hunch was right. There was a problem with my piston spring... it was BROKEN! No wonder I somehow felt the impression that I'm actually losing power.

If you look at the pictures attached you would see the deformity that I am talking about. There was a doubling of spring near the spring guide on top even when there is no pressure exerted on the spring (the power plant is already disassembled from the receiver). When I took it off it was actually broken near the plastic spring guide. What surprises me though was that I was still able to use the Big Cat in spite the fact that the spring is already broken and I'm getting pretty good accuracy from her. I am almost at the point of making an idea that the Big Cat's design might get a lot more accuracy if they decided to lessen the total spring power to put the muzzle velocity to about 700 - 800FPS. Since my idea is that an airgun is a resonance element (or system) bringing the muzzle velocity below the rated 1000FPS (lead pellets) would make it resonate better with the lead pellets (in my case the CPHP's 7.9 grains pellet). Also since the barrel is actually lightweight (about half of the whole diameter is covered by the rifled barrel (a plastic material) that would mean that the actual barrel thickness is quite small. Well, that's just an idea. I am still studying the whole barrel cantilever design and I still have a lot of studying to do.

I also noticed that the spring might have scratched the metal piston guide heavily. Perhaps Gene or CDT or other airgunners who already had an experience disassembling their airguns can post their comment if the rear spring guide's condition is still normal or not. The way the my Big Cat was made was totally rough. If I had not read most of the GTA members precaution that the metal parts are actually very sharp (and they are sharp indeed) I would have probably have a hard time typing all this report right now due to finger cuts! LOL.

I hope Gene or other members can help me out on this one: "How can you safely take out the original piston seal from the piston?" Also, "can the James Maccari tarantula spring be used also as a replacement for a Crosman G-1 Extreme ?"

Hope others can give me some guide on these stuff. Thanks.

Speedturtle

[kiwi]

Quit kool how they put 2 springs in them....
i have been lucky never broke a spring yet..
"fingers crossed"

[Truman]

That is the spitting image of the insides of my Gamo Maxima!!! Apart from that rather nice piece of 'Gold' bling!

[speedturtle]

Is that a coincidence or what? Hehehe. Hey Truman, Did you notice something? Look at the location where the spring broke down, it is almost at the exact height where the top hat guide stops and we almost have the same break point at the rear spring guide. Must be a design flaw then? We never know.

Speedturtle

[Truman]

You're right you know!  I wonder why that is! Maybe there is some induced localised work hardening when they cut the spring off and it's the transition point between the normal temper of the spring and the locally induced!!

[Gene_SC]

Most all Gamo's share the same power plants.

[OHPLNKR]

This thread is great. Thanks for the great pictures being exchanged. I'm sure they are helpful to all of us novices that haven't had the opportunity or means to do a teardown and lube just yet. It really helps to be able to see the nomenclature up close and personal. Thanks to you all.

[rgt270]

.Great disassembly pix, Speed.  I'm wondering if you had any problem unscrewing the barrel pivot pin.  My Cat is down a lot of power and will soon be undergoing a home tune.

[speedturtle]

Hello rgt270, I did not disengage the barrel from the receiver since my concern is the piston spring and the power plant itself. I just want to find out if my hunch was right and I was - the piston spring is broken. If your Big Cat seem to give you the impression that it is losing power then try to disassemble the action and check your piston spring. Just a suggestion.

Speedturtle

[CharlieDaTuna]

Depending on how the spring is broken and where, many people can have a broken spring or bad seal and without a crony, would not know it.

It is not uncommon to see them broken at that point or at the front about the same distance. I've seen them broken on both ends on the same spring like that. It is also common for the broken section of the spring to thread/wind  itself down into the spring. Shooting light pellets can cause that as well as detonation and heavy pellets as well as bad wire. From what I can see on the seal, it does look like lube may have been getting past it as well as metal particles.

The Tarantula spring is a good spring to use providing that you have the machining equipment to make a fitted spring guide and tophat. If not, you shouldn't use it.

The "plastic spring guide" that you refer to is not a plastic spring guide but rather the spring block.  The spring block spring seat surface can easily be damaged by a broken spring. Just stick in a lathe chuck and resurface it.

[speedturtle]

CharlieDaTuna - 4/9/2009  7:45 PM

Depending on how the spring is broken and where, many people can have a broken spring or bad seal and without a crony, would not know it.

It is not uncommon to see them broken at that point or at the front about the same distance. I've seen them broken on both ends on the same spring like that. It is also common for the broken section of the spring to thread/wind  itself down into the spring. Shooting light pellets can cause that as well as detonation and heavy pellets as well as bad wire. From what I can see on the seal, it does look like lube may have been getting past it as well as metal particles.

The Tarantula spring is a good spring to use providing that you have the machining equipment to make a fitted spring guide and tophat. If not, you shouldn't use it.

The "plastic spring guide" that you refer to is not a plastic spring guide but rather the spring block.  The spring block spring seat surface can easily be damaged by a broken spring. Just stick in a lathe chuck and resurface it.

Thanks for the correction and knowledge Charlie.

I already bought the Tarantula Spring. Now, my question is this - Based on your statement, "would you say that the Tarantula Spring cannot just be just a drop-on spring on the Gamo Big Cat and therefore should have a new and "correctly fitted" top hat and spring guide? I can clearly follow your idea in here, it's just that I "thought" that we can "simply" use the tarantula spring as a "better" substitute compared to the factory spring. If that's the case to prevent "play" definitely I need a new top hat and a new spring guide. Is this the part where you are saying that based on the spring tension and the piston displacement that you compute the "proper" top hat weight to maximize the velocity and resonance of the whole powerplant?

Being the case, I guess this is not a part where a newbie can simply work around with but I'm willing to give it a try. I believe experience is still the best teacher and whether we are right or we are wrong we still have learned something from the experience. Or better yet, since you have already handled a lot of Gamo rifles would you be kind enough to quote how much would it cost to fabricate the top hat and the spring guide in relation to the James Maccari Tarantula Spring?

Thanks Charlie. I'm learning a lot! (and starting to spend more than I can support but that's the beauty of learning something). LOL!

Speedturtle

[CharlieDaTuna]

Ys, I have tuned several hundreds of  Gamos over the years and the Tarantula spring is certainly not a "drop in" spring. It does need to have a fitted spring guide and top hat machined to the  to the spring guide and the top hat to the  piston ID, as well as the cross pin block to be efficient.

Not sure where you are coming from with the resonance factors and really doesn't matter and I don't think that I have ever said that anywhere. I believe that because of the variables in springers, the resonance frequency or their harmonics and vibrations can be anywhere, not exactly constant and will change with where and how the gun is held, compression, combustion, pellet weight, caliber, or variation in velocity, and the variables in torque to name a few. Springer airguns (or any airguns) are far from being manufactured with precise and exact tolerances from gun to gun.

 What is important is to reduce and dampen the spring vibration or oscillation as much as possible and to keep the spring in line  as straight as possible (no cant) as it is being compressed and expanded during the cocking the firing cylce.

As far as the top hat weight goes in the Gamo, a good weight factor is between 47 and 52 grams  depending on the gun and caliber and acceptable for most applications.

There is no "Pro Tuner" or parts marketer that I know of that sells a high quality or precision tune kit. He can't. The JM kits that are available are as close as you can get without having it fitted  precisley to the gun on the bench in front to you. And his are pretty good I might add. There is one person out there, maybe two,  that sells a "chop it up" tune kit kit but it's far from high quality and often providing cheap springs and not what a pro tuner provides during their tuning process.

Hope this helps.

[speedturtle]

Thanks again Charlie.

I was the one who quoted myself on the resonance idea and it was my mistake if you had the impression that I quoted you on that. My mistake, Probably a wrong typo on my part.

For the past 5 days I am actually looking into some patent papers done by many inventors regarding barrel harmonics and shooting optimization systems and it was stated on some of these patents that the muzzle velocity and ammo weight affects the barrel deflection. It was from this info that I got the correlation that maybe since changing the top hat and the spring guide (plus the spring) that makes the whole piston assembly (with the piston itself) that the whole weight affects the muzzle velocity and thus arrive at a new velocity reading. But I know that there are more factors involve than these so I'm off to my computer again to read further.  Perhaps the resonance stuff is wrongly injected on the tuning part because clearly I think one major objective of the tuning process is to further reduce the spring deflection to increase the air rifles' accuracy. I do not wish to become a tuner but rather just an individual who is very much intrigued and fascinated by the whole air gun design and the reason why so many questions (and perhaps some are ridiculously inappropriate).

Probably I must have misinterpreted some posts regarding the James Maccari spring that I can just simply use it as a replacement for my broken Gamo Big Cat piston spring. For now I just have to save some money so I can afford a customized top hat and spring guide in case someone would be kind enough to make one for me. Hehehe.

Thanks again.

Speedturtle

[gamo2hammerli]

Don't know if the Gamos and Crosmans are identical to each other..... but from your exploded view the parts look the same. Maybe all springers innards look the same?

My Crosman Sierra Pro's spring broke a few months ago...I heard abit of grinding sounds but continued shooting until the piston wouldn't catch then I opened her up. This is what I saw. Lucky the ends of the broken pieces of the spring didn't scratch the inside of the chamber at all. Notice the two small parts.....they broke atalmost exactly the same spot as yours.

[speedturtle]

I think the cocking foot (the one that contacts the piston to cock the piston assembly) somehow touches the outer surface of the piston spring. Due to continuous cocking and firing it somehow scratches the same contact on the piston spring especially at the last 10% of the cocking process (the plastic part on the Rear Spring Guide is called the "spring block") and I believe this spring block is little bit long in its total length that is why the spring is fully compressed (totally touching each other winding). Perhaps it would be safer if the spring has some clearance from each winding by not fully compressing and the tradeoff would be to lose some velocity. (Don't quote me on this because this is just my wild idea). I also noticed that this spring guide has a play on it (it's not totally secured on the rear metal spring guide) meaning the spring blocks' I.D. is not that snugly fit on the O.D. of the Rear Metal Spring Guide. Maybe it is also this noticeable tolerance that pushes the piston spring to touch the rough edges of the cocking foot when it is fully compressed. Another idea - maybe the Rear Metal Spring Guide should have a tight O.D. tolerance so as not to let the piston spring wander around the chamber. Whenever the piston spring bulges (due to the severe compression pressure) the outer spring surface probably touches the rough surface of the cocking foot. The cocking foot is almost resting on that exact spot on the spring just right before the piston is locked by the seer. It would be nice if one airgunner can make a transparent fiberglass stock so we can see the action of the cocking. Hahaha. Just an idea.

Another airgunner also posted his broken piston spring and from his pic we found out that He also had the same break-up point on the rear spring guide. But what is more surprising in his case is that there is another break-up point at almost the exact distance where the top part of the top hat is located (the actual height of the top hat).

Probably it is really a big advantage to any springer user if he can open up his airgun after probably about 100 shots and start deburring and polishing and properly lubing the internals before he engages in totally breaking in his airgun to avoid this mechanical failure.

A lot of weird ideas from a newbie! Hahaha!