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MY NEW THEOBEN EVOS

Discussion in 'Anything Airgun Related' started by valboskie, Aug 23, 2014.

  1. valboskie

    valboskie Busy Member

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    Hi there I missed out on the evo on the other thread but
    I have managed to pick up a very nice one.
    its very under powered
    Its doing 4.1fpe with superdomes in .22 its in great condition i tried to pump it up but i never had the pump adapter in tight enough and i lost all the air from the ram
    i have pumped it up again tonight there is no gauge and it was to dark to chrono when i finished
    so im not sure what power i have yet.

    I also picked up another one a few days later from the same guy.
    It has some slight pitting to the action and some dings and scrapes to the stock.

    it has issues
    the cocking shoe is broken well that's what he thinks you break the barrel and it just flops there is no resistance at all .
    i emptied the ram of air and re filled it ..its holding air again but i dont know know at what power its at
    i will empty the ram again till i get the new cocking shoe

    the Allen plug at the back is missing that allows access to the valve.
    does anyone know where I can purchase one of these .
    are they a specialist part or will other allen bolts fit.
    also does any one know the size ect for the oring

    Could anyone please advice me on what's wrong and where to check going by the information I have written above.
    I have found a cocking shoe I just need the valve cover bolt and o ring.


    The pump does not have a gauge does anyone know how much pressure each stroke of the pump produces its a brocock slim jim pump
    I don't want to over fill it.
    and help and advice would be greatly appreciated

    some pics of the rough one first

    View attachment 102426 View attachment 102425 View attachment 102424 View attachment 102423 View attachment 102422
    atb
    david
     
  2. valboskie

    valboskie Busy Member

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  3. cloverleaf

    cloverleaf Honorary Member

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    May . have mercy on your soul...
     
  4. valboskie

    valboskie Busy Member

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  5. valboskie

    valboskie Busy Member

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    i was a bit nervous buying a theoben rammer but now i have two to play with and try and sort out.
    wish me luck lol.
    i take it you don't like theoben rammers then.
    have you had a bad experience with them
    atb
    David
     
  6. engraver

    engraver Keyboard Hero

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    Ha ha, it doesn't look good on the old Theoben Evolution this does it,:D

    Had very much the same with the last brand new .20 walnut carbine I bought from drapers in Nottingham, about 10 yrs ago, was enough to put me right off them.

    I just cant get that first fenman I had out of my head though, it was the best self contained gun I ever had by a fair bit, and it did put some serious quarry away in the ten years trouble free shooting it gave me.
     
  7. cloverleaf

    cloverleaf Honorary Member

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    Indeed, I've owned a Fenman (from new) as well as a couple of HW90s in the past.

    To its credit the Fenman had a lot of character and handled well enough.. however it had persistant issues with leaking and a pretty nasty trigger. In addition I could never get it to group that well and the recoil seemed somewhat harsh. Flogged it after it was returned for the second time for a leak that reduced the output to around 9ftlb. Theoben's customer service and attitude left a lot to be desired too - however at least that's one thing you'll no longer have to worry about :p

    I found the '90s to be broadly similar in their behaviour - better trigger (but not as good as the Rekord) and perhaps less displacement under recoil, however it was still very sharp - especially for a rifle of such mass. I also did some tests and found the '90 to be pretty inconsistant (maybe 20ft/s extreme spread) and very inefficient at around 20%; compared to typical figures of 30-35% for a decent break barrel and 35-40% for a decent underlever. IIRC I also found the shot development time to be somewhat unsplendid; which isn't surprising given it's enormous piston and massive stroke.

    I've not had change to test the efficiency and shot development time of some proper Theoben rammers (IIRC Jim Tyler's found the development time to be pretty quick) nut would certainly be interested to do so.

    Anyway, good luck ;)
     
  8. thisisdonald

    thisisdonald Engaging Member

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    Cloverleaf... how does one go about calculating the efficiency %?
     
  9. 177

    177 Donator

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    I can't work it out - you said you were concerned about taking on a rammer and missed out on a great opportunity at a very attractive price as a result, and now you've gone and bought two :rolleyes:

    Check the piston crowns on both guns before you mess bout with anything else - if they are in good shape you have something you can work with. If they aren't, replace them BEFORE you monkey on with anything else...


    That's me.

    I owned a .22 Fenman from new and got rid of it just before it was 15 years old. With a 4x40 Gold Crown scope on top I can't even begin to tell you how much game that rig took over the years, and how fond of it I was.

    I don't know whether I am looking back through nostalgia tinted glasses or whether it really was that good but it needed precisely nothing done to it in all those years and thousands of shots, and it was a real tack driver. Still pushed over 11 FPE when I sold it...
     
  10. cloverleaf

    cloverleaf Honorary Member

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    There's a guide with respect to spring guns here ;)

    For a gas ram rifle you obviously don't need to worry about spring rate etc; but do need the force acting on the piston in both cocked and uncocked states. This can be calculated from the internal ram pressure (uncocked), piston dimensions (effective area) and stroke. If you need more info I don't mind updating the other post with some info on calculating gas ram efficiency; providing I have the time to do so :)
     
  11. engraver

    engraver Keyboard Hero

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    Had a chuckle to myself as maybe we owned the same gun as mine also had a 4x40 gold crown scope lol maybe it was just the scope that was good or we both owned the only good fenman around:D:D

    No seriously mate, no rose tinted specs needed here, my dad was alive at that point and took his last keepering job and needed a quiet gun for rabbits around the estate gardens, So I lent him the fenman even though he didn't rate airguns.

    After a few weeks I went to the cottage to visit him and he said the gun was brilliant, and had shot the most of the rabbits around the gardens at night, he told me how he rested it on the gate post and connected with little rabbits right out to max ranges, that is something I said you shouldn't do dad! but he said "well I do and it did" I put it down to the short barrel and quick lock time.

    And if you look at secondhand ones now its rare you don't see one with the forend scratched or marked from others doing the same,

    Try doing that with an Eliminator and watching where the pellet ends up!:D

    Yes I have big regrets about getting rid of my fenman and it was mint, as I treat them all with kitten gloves even though I hunt in all conditions, the bluing on those 1990s theobens is the best bluing Ive seen on an airgun apart from venoms and V mach guns.
     
    Last edited: Aug 24, 2014
  12. tomsteebs

    tomsteebs Donator

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    My gasram slr98 is nice to shoot and accurate. My hadrid is the trigger (same as the evo), although it's not that bad once you adjust it. I am planning a v-mach trigger of some description. Mines consistent, accurate, beautiful, short, multishot, self contained, zero twang and yet to have any leaking issues. I have someone who will pay £750 for it, but I've said I will keep it.

    Cloverleaf probably thinks I'm mad!

    I quite like this gasram, almost my perfect rifle in all honesty.

    If you like the rifle, then that's what matters.
     
  13. engraver

    engraver Keyboard Hero

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    Your SLR Tom is a bit special, I would hang on to that one, because when you find a good one, you may have to kiss a fair few ugly frogs to find another.

    I had a mate who owned a SLR88 before even the Rapids came on the scene, and although he got a rapid (one of the first) he still wishes he had kept that old SLR and back then the theoben engineering was top drawer, in fact I think theoben stopped making the SLR88 because it wasn't cost effective, it was so well engineered.

    It wasn't until they got machinery to cheapen the process and cut cost that a full decade past until the 98 was re introduced.

    Those old 88s didn't suffer half of the ram problems the newer ones do, same with the old Siroccos and hw90tb euro custom.
     
  14. valboskie

    valboskie Busy Member

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    i got the low power one all pumped up today its shooting at 10.7fpe .
    i put 350 pellets through it and it was a joy to shoot .
    accuracy wise i need more practice .
    at first when i zeroed my hawke eclipse at 25 yards i was hitting the 15 and 20mm knock down no problem
    i went out side and hit various targets out to 55 yards .
    then the accuracy went after about 220 shots or so i carried on shooting till i got fed up so went to the indoor 25 yard range the zero had shifted 4 inches left.
    it could just be the scope
    im still very happy with the evos first outing.

    i really need a dust cover screw for the other evo to hide the valve ,
    if anyone has any info on the allen bolt i would be very grateful
    atb
    David
     
  15. valboskie

    valboskie Busy Member

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    When i bought the first one i was told it was shooting sweet at 11.8fpe with no problems.
    i never went to buy one that needed anything doing .
    i phoned the seller who lives quite a bit away from me and he offered me a refund ,
    he then contacted me about a second evo he had that needed a cocking shoe and an allen bolt to cover the valve
    so he did me a deal on the second evo i could fix it or use it for the parts i needed then sell the rest
    i also bought a slim jim pump and the attachments needed to pump the ram.

    i really like the look of the evo it just feels right when i shoulder it ,
    hopefully i can get both shooting sweet as rammers if not i will look into converting the rough one to a springer
    atb
    David
     
    Last edited by a moderator: Aug 26, 2014
  16. tomsteebs

    tomsteebs Donator

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    Little bit of gasram info from a Ben Taylor interview which I thought was interesting-


    To find out more about this technology, I spoke interviewed Ben Taylor, who invented gas ram technology, by telephone in England. In 1976, he and his business partner Dave Theobald were unhappy with the state of the art in spring-piston powerplants. They had made and sold eight spring rifles, and they all suffered from not keeping the energy that Taylor wanted. So he had a thought: what if you used compressed gas in a cylinder with a piston instead of a spring?

    So he built one, using a brake seal for cars from Lockheed, and it worked! At first, he pressurized the gas ram with 150 psi air from the shop and got only about eight or nine foot-pounds of energy. “Then we tried 300 psi nitrogen from a bottle and got 1,000 fps in .177. I shot that same gun for five years with the same charge in it,” Taylor says.

    In 1981, Taylor and his partner applied for a patent and tried to interest various airgun manufacturers in licensing the technology. A couple of times they came close, but ultimately no deals were consummated. “So we decided to manufacture it ourselves. It took 10,000 pounds to get set up. We sold 490 the first year, 1,000 by the third year,” he says.

    Gas rams offer a number of advantages, Taylor says. “They are totally tireless. You can leave them cocked for as long as you like. Nothing wears out. The seals don’t wear. Recently I serviced gun number 25 from 1982, and it was the first time it had been serviced since it had been manufactured. You have to remember to shoot, or cock-and-decock, a gas ram every few months, otherwise the seal can get bonded to the bore, and that will cause failure.”

    He adds, “We found that if a gas ram is going to fail, it will do so within the first week. Otherwise, it will last for years. Right now, there are more of our guns out there that have never been serviced than those that have been serviced.”

    There are a few disadvantages to gas rams. Unlike a spring powerplant, which often will keep operating at reduced velocity even if the spring gets broken or bent, if a gas ram fails, it won’t work at all.

    The biggest problem, Taylor says, is that, because Theoben gas ram powerplants had a valve where people could increase or reduce the pressure of the gas inside the powerplant, people, in a quest for more power, tend to overfill them.

    “There is a sweet spot on the pressure vs. velocity curve,” Taylor says. “If you go beyond that, you increase the pressure, but you don’t get any benefit. The gun becomes hard to control and won’t shoot straight. In addition, there is the danger of burning the piston seal. We actually had to design our high powered guns so that over-pressurizing them wouldn’t create reliability problems.”

    Taylor told of an interesting experience at the test range one day. “We had two 30 foot-pound guns of the same caliber shooting the same pellets. One was a gas ram and the other was a precharged pneumatic. We had chronographs set up at the muzzle, halfway down the range, and at the target. We found the gas ram was retaining energy much better at the target. When we recovered the pellets, they looked like they had come from two different manufactures. The pressure from the gas ram had flared the skirt of the pellet flat to the bore, so that it looked like a cylindrical pellet, and the gun was shooting flat like a laser!”
     
  17. andy001

    andy001 Engaging Member

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    I've a fenman, and i've had no problems with it.

    However, as with the OP i bought a second one to fix up. It had been over pressurised, which in turn elongated the hole stop pin in the rear of the cylinder to hold the piston etc inside. Yep, cylinder was kaput.
    Also, the ram had sealed itself inside the piston and the strut had broken away from the piston!!! The valve at the back of the cylinder was kaput also, so I couldn't release the pressure on the piston! It was almost impossible to get the rear retaining pin out of the cylinder due to the pressure on everything. I had to carefully drill certain critical areas to release the pressure.
    It taught me a valuable lesson...!
     
  18. engraver

    engraver Keyboard Hero

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    Thanks for sharing that Tom I enjoyed reading the history of how the ram was invented.

    3 out the 5 I owned fell into the category of fail in the first week lol, two went forever maybe still going.

    Like Ive always said you either get a good un or a really bad one, if you get a good one that shoots nice never tampered with hold onto it!
     

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