Sharp In­nova-tion 2

Pete Evans con­cludes his look at the Sharp In­nova, and gets to cure its wind prob­lem

Airgun World - - Contents -

Pete Evans de­scribes how to change the seals on a Sharp In­nova

Last time we took a look at the Sharp In­nova, a pop­u­lar multi-pump pneu­matic from the heady days of the 1980s. Thank­fully, there are still a lot of these around with ser­vice parts read­ily avail­able from a few sources. Any pneu­matic-type ri­fle must be able to hold a charge of air to be of any use, and over time this ne­ces­sity might be lost by nat­u­ral degra­da­tion of the seals, which means re­place­ment.

A lot of peo­ple are scared of work­ing with high pres­sure air, and rightly so be­cause per­ma­nent dam­age to health can oc­cur if ba­sic safety rules are not heeded. The most im­por­tant rule when deal­ing with these systems is to en­sure that no air charge re­mains in the ri­fle prior to work. That sounds like com­mon sense, but sadly there are times when com­mon sense is not as com­mon as you would hope. If you are care­ful and me­thod­i­cal, there is no rea­son why you can’t work on a Sharp, and have the joy of know­ing how your gun works, with the bonus of know­ing a job has been well done. So if you are still keen, let’s move on and see what’s in­volved in re­new­ing the seals deep within the belly of the In­nova.

WIND PROB­LEM

The Sharp can man­i­fest prob­lems by the in­abil­ity to store or take a charge. My own gun had a stor­age prob­lem that meant that a charge wouldn’t hold over a pe­riod of time, but a well-sealed gun should be able to hold a charge for long pe­ri­ods of time – a lot of peo­ple store their guns with one pump of pres­sure be­cause this is thought to pro­long seal life.

There are sev­eral ‘O’ ring seals in­volved in the stor­age process, and I would rec­om­mend that all the seals are changed be­cause iden­ti­fy­ing in­di­vid­ual seal in­tegrity is nigh on im­pos­si­ble, and the seals are not par­tic­u­larly ex­pen­sive.

Be­fore com­menc­ing the job, I con­sulted TW Cham­bers’ web­site for their in­for­ma­tive parts di­a­gram, matched the numbers for the seals – some come in a set which makes things eas­ier – and then a few clicks of the key­board, a lightly dented credit card, and 48 hours later, I was blessed with the nec­es­sary parts.

LETS THE WORKS COM­MENCE

At risk of re­peat­ing my­self, be ab­so­lutely sure that the gun is empty of any resid­ual air, for the rea­sons al­ready stated. There are a few fid­dly bits in­volved, so I would ad­vise read­ing through a few times to en­sure that you are happy to go through with the job.

First thing is to get the rear stock off; one cross-head screw holds this in place, and the stock comes away with the trig­ger guard and safety catch.

With the stock off and the gun up­side down, you will be pre­sented with a knurled nut into which the stock screw was se­cured. This needs to come out and is usu­ally only fin­ger tight.

Two screws will be ex­posed; the one from which the nut was re­moved, and a smaller, re­cessed one at the side. Both of these can be re­moved and stored safely. Re­moval is nec­es­sary to part the breech block and bar­rel from the com­pres­sion tube and pump arm.

Once the screws have been re­moved, give the tube a lit­tle wig­gle and the whole lot will move for­ward, leav­ing the gun in two halves. You will no­tice that there is small curved sec­tion of steel with a ‘V’ cut in one end; this is the cylin­der spacer, be care­ful not to lose it!

COM­PRES­SION TUBE

Put the bar­rel/breech block to one side and turn your at­ten­tion to the com­pres­sion tube. You will no­tice the trans­fer post ‘O’ ring seal on the top side, and on the end will be the ex­haust valve re­tainer, which will have two holes in it. The trans­fer port ‘O’ ring can be re­moved with a sharp seal pick, or den­tal probe, be­fore re­mov­ing the valve re­tainer.

There are a few tools you can use to un­screw

“Just one more seal to go; there is a sneaky one hid­ing in the out­let side un­der a brass col­lar”

the re­tainer; some use cir­clip pli­ers - which may not be in ev­ery­one’s tool­box, but I opted for a pair of thin, long-nosed pli­ers that ex­e­cuted the job well by in­sert­ing the tips into the holes and ap­ply­ing torque to undo the re­tainer. These re­tain­ers are not usu­ally very tight.

With the re­tainer out, you will be able to re­move the con­i­cal shaped valve spring, the ex­haust valve and then the cir­cu­lar bush in­side the end of the tube.

The pic­ture shows the or­der in which they sit in­side the cylin­der; note that the valve is of un­even length. Some mod­els have a bumper disc be­hind the valve – this one didn’t.

GET­TING TO THE HEART OF THE MAT­TER

With the valve out, the brass air cylin­der can be re­moved. The eas­i­est way is to move the pump arm slowly for­ward and back, and the air pres­sure will move the cylin­der out of the back of the com­pres­sion tube. Be care­ful that the cylin­der doesn’t shoot out of the tube – a slow, easy stroke is needed.

With the cylin­der out, you will no­tice an­other ‘O’ ring to change, around its in­let face. The cylin­der needs to be opened to fa­cil­i­tate chang­ing the in­ter­nal seals.

Start by hold­ing the cylin­der in padded, non-mar­ring vice jaws, and then screw a long M6 bolt or screw into the side. By us­ing the screw as lever­age, it will now be pos­si­ble to un­screw the two halves of the cylin­der, ex­pos­ing the in­ter­nal mech­a­nism. Are you get­ting ex­cited?

In­side, you will find a spring and ball bear­ing, which act against a seal at the in­let side to en­sure that the air doesn’t leak out. There is also a seal on the threads be­tween the two halves of the cylin­der.

To get at the in­let seal, you will need a wide-blade screw­driver to re­move the re­tain­ing tube. The seal might need to be en­cour­aged out, and this can be achieved by push­ing it out with your seal pick from the small hole in the op­po­site end.

Just one more seal to go; there is a sneaky one hid­ing in the out­let side un­der a brass col­lar – this one seals the ex­haust valve. To get the col­lar out, turn it up­side down and bang it down flat onto a piece of wood. The jar­ring ac­tion will move the small col­lar out, to re­veal the ‘O’ ring be­neath.

KEEP IT CLEAN

The air cylin­der is now fully stripped and it’s time to get things spot­lessly clean – we are talk­ing Howard Hughes’ bath­room clean. High-pres­sure air systems don’t like oil or dirt. Oil can com­bust un­der pres­sure, and dirt de­grades seals, lead­ing to leaks that would be bad news for your newly sealed gun. Clean ev­ery­thing with pa­per tow­els and de­greaser, al­low­ing all the cleaner to evap­o­rate. When you’re sure all is well, the seals and ‘O’ rings can be re­placed and the cylin­der screwed back to­gether in the re­verse or­der of dis­as­sem­bly.

A leak­ing pneu­matic ri­fle is about as much use as a leaky bucket.

Ex­haust valve, spring and bush. Note the un­equal length of valve.

The loose in­ter­nal com­po­nents in­side the air cylin­der.

The in­ter­nal air cylin­der can be coaxed out of the com­pres­sion tube.

With the screws out, the two halves sep­a­rate. Keep an eye on the cylin­der spacer.

Long-nose pli­ers make a use­ful tool to turn, and re­move the re­tainer.

Get the cylin­der held firmly – the screw helps with lever­age.

One cross-head screw holds the rear stock in po­si­tion.

Re­move these two screws, and re­mem­ber to keep them safe.

Re­move this nut, it should only be fin­ger-tight.

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