Sharp Innova-tion 2
Pete Evans concludes his look at the Sharp Innova, and gets to cure its wind problem
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.
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!
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.