.22 Mk I Sharp Innova, A Restoration Project. Restoring The Exhaust Valve, A Detailed Guide.

This blog entry is going to be in as much detail as I can manage, as I want it to be the sort of thing that I would have found really helpful the first time I worked on the Sharp Innova. I have already stripped and inspected this air rifle in a previous blog entry HERE , so today I will repair the exhaust valve using the T.R Robb Sharp Innova seal repair kit and test the power output.

The T.R Robb exhaust valve repair kit, which consists of a stainless firing pin, exhaust valve spring, a red inlet packing seal, an inlet ball seal, two big O rings for the valve guide seal and chamber seal, and two small O ring seals for the transfer port and inlet valve seal. Also a blob of silicone grease for the seals and a small bottle of silicone oil for the pump rod seal.

It is important to have a clear working space so you can keep track of all parts that have been removed, I keep small parts in a tin as it's a real bugger if they get lost. I am lucky in being able to do my work on the dining table, however the dog thinks that the table is also his bed.

The dog whines a lot if I move him from his bed.

So here is the guide in all it's tedious, mind numbing, gut wrenching detail.

Remove the action from the stock. Then remove the circlip from the pin that connects the pump arm to the front of the cylinder. Drift out the pin with a suitable sized punch. The pump arm can now be removed through the pump slot in the cylinder - it may need to be wiggled a bit.

Pin and circlip already tapped out.

Next, drift out the smaller roll pin in front that secures the sight unit to the cylinder; this can be a bit stiffer but it will move more easier using the correct sized pin punch. 

Correct sized pin punch for the roll pin is important.

Grasp the sight unit and pull it from the cylinder, outer barrel and inner barrel. This may need a lot of wiggling if it's not been removed for a long time.


Pull the pump rod down to the front of the cylinder using the pump arm linkage and line up the pivot pin with the hole for the pump arm linkage and cylinder. Twist the brass pump arm pivot base a little so the pivot pin lines up with a hole on one side; only half of the pivot pin will be visible in the hole on the other side so tap it out from this side with a smaller pin punch. 

Old dart head makes an excellent small pin punch.

Remove the pump arm linkage from the pump rod and remove the pump rod through the front of the cylinder, push it out with a screwdriver at first, then pull it out the rest of the way.

Pump rod shouldn't be this greasy.

To remove the cylinder from the breech block, first remove the brass collar screw on the underside of the breech ...

Only finger tight , the stock screw locks the collar screw in place.

... then using a flat head screwdriver, remove the stud screw under this.

This stud screw appears to hold the whole rifle together.

Remove the spacer that sits between the bottom of the cylinder and breech block; use a thin blade to lever it out at first, then it should slide out by hand.

A little tab on the spacer is good for leverage.

Remove the cylinder with the exhaust valve inside from the breech block, this should drop into the breech hole and pull out easily, revealing the transfer port O ring on top of the cylinder.

Transfer port O ring seal is pretty swollen.

Unscrew the exhaust valve back guide from the cylinder end, this should move by thumb pressure alone.

If the exhaust valve back guide is ever too tight a tool can be made up to fit the two small holes.

Then remove the spacer with the bumper inside it, the exhaust valve spring, and bumper plate - these should tip out into your hand. Using a piece of dowl from the front of the cylinder, push the valve out of the back, then remove the firing pin from the exhaust valve.

Valve with firing pin, bumper plate, spacer with bumper inside, and exhaust valve back guide.

The exhaust valve unit consists of the longer air chamber and the shorter exhaust valve guide. Unscrew them; you might have to use mole grips at first as they can be tight.

Remove the valve spring and inlet valve ball from the air chamber ...

Split the valve parts to get to the air inlet valve parts.

... and the exhaust brass valve stopper and exhaust valve seal from the exhaust valve guide.

valve guide, seal, and stopper.

inside the air chamber, the inlet valve packing is held in place by the inlet packing stopper. Unscrew the stopper using a wide fat blade, and the packing should fall out.

Inlet packing washer well and truly stuck in there.

(In this case, the packing was wedged in tight and I couldn't even prise it out, I had to very, very carefully mill it out using a mini drill and small drill bit so as not to damage the air chamber.)

Note inlet packing washer dust around the air chamber.

Milling into one side of the packing then the other, it eventually came out, spinning up the drill bit, leaving me with a grubby air chamber.

Needs a bloody good clean.

Clean the area where the packing washer sits in the air chamber with white spirits to remove any crap that might hinder a good seal.

Kitchen towel wrapped around a pick really shifts that crud.

Prise off the exhaust guide seal from the exhaust valve guide and the chamber seal off of the air chamber.
  

Oh so handy pick in action.

Then, with kitchen towel and white spirits, clean the air chamber (inside and out), the valve guide, packing stopper and valve stopper thoroughly.

Decanting a bit of white spirits into the lid keeps the rest of the bottle clean.

I lightly ran the outside of the air chamber and valve guide over a file to smooth out any scratches caused by the mole grips

Wet and dry or sandpaper will do also.

All the parts being replaced were put to one side; they consisted of the firing pin, the remains of the packing washer, inlet valve ball, exhaust valve spring, exhaust valve seal, exhaust guide seal and the chamber seal. 

Old worn parts, look at the state of that old packing washer.

Place the clean and replacement parts in order ready for rebuilding, along with a small blob of silicone grease for the O ring seals.

Lining up the parts for reassembly makes the whole proccess a lot easier.

Take the air chamber, insert the new packing washer and prod it into place.

That pick came in handy for prodding the packing washer into place.

Then the inlet packing stopper, guide it into place with your little finger.

Inlet packing stopper screwed in finger tight.

Then tighten it down using a wide flat blade.

Even tighter, though a chisel blade would be better than using the spacer.

Drop the inlet valve ball inside the inlet packing stopper to rest on the packing washer.

Inlet valve ball just drops in.

Place the valve spring on top of the inlet ball and put the air chamber to one side.

And so does the valve spring.

Take the new guide seal, thumb it over the screw thread of the valve guide and roll it into its recessed groove.

This is the smaller of the two large O rings.

Smear a dab of silicone grease over the new O ring seal.

The O ring spins around in it's groove easily.

Smear the new exhaust valve seal in silicone grease and pop it into the valve guide.

This is the smallest of the two small O rings.

On top of this goes the small brass valve seal stopper.

Seal stopper just pops in.

Align the air chamber with the exhaust valve guide so the valve spring sits on top of the valve seal stopper. Screw them together as tight as can be done by hand compressing the new valve guide seal.

Screw all the way un till there is no gap squashing the O ring for a good seal.

Thumb the new chamber seal into place, smear it with silicone grease and put the whole valve to one side.

The larger of the two big O rings is a tight fit

In order to get the best seal for the pump head and chamber seal, the inside of the cylinder needs a good clean. A few balls of kitchen towel soaked in white spirits pushed down the cylinder with a piece of dowel will loosen any crap ...

There was a lot of crap all in all.

... then ram a few dry balls of kitchen towel through until the inside of the cylinder is clean and shiny.

Ooooh, oh so shiny.

Pop the shorter end of the new firing pin into the valve guide end of the exhaust valve and align it with the back end of the cylinder, making sure the transfer port is aligned with the transfer port hole in the cylinder, and the same with the the stud hole.

Lined up correctly and ready for insertion.

Push it in until the stud hole appears in the bottom hole of the cylinder ...

That pick came in handy again for centering stud hole.

... it should be nice and tight with the new chamber seal fitted.

the longer end of the firing pin reaches the end of the cylinder.

Place the bumper plate over the firing pin and let it slide down to rest at the stop in the firing pin.
 

I must stop biting my nails.

Making sure the bumper is inside the spacer ...

This bumper only came out of the spacer if it was pushed out, some can be loose.

... insert it into the end of the cylinder to rest against the exhaust valve.

It really doesn't matter what order they are put in, as long as they're in the right order.

Place the exhaust valve sping inside the bumper to rest against the bumper plate, making sure the wider end of the spring is facing to the rear to rest against the exhaust valve back guide.

The valve spring must go in this way round.

Place the exhaust valve back guide on the spring, push into place and screw in by thumb.

Really needed that new exhaust valve spring, the old one barely pushed the back guide past the end of the cylinder.

Now the cylinder and valve can be returned into the breech, so with the old transfer port O ring seal out of the way, put a dab of silicone grease on the new O ring seal and press it in place around the transfer port.

The silicone grease helps the transfer port O ring stay in place.

When inserting the cylinder back into the breech, the cylinder is best pushed in along the bottom of the breech hole to stop the transfer port seal from moving out of place. The cylinder will stop short of the back of the breech hole, so pull the trigger and slide it back further until the stud holes in the breech and cylinder line up.

The hole in front of the stud screw is for a stud screw that pushes the spacer against the cylinder on most Innova's, not this one though.

Screw the stud screw back in lightly and slide the spacer into place so the forks of the spacer sit either side of the stud, then tighten the stud screw fully and screw the brass collar back onto the stud screw.

Only needs to be finger tight.

Fitting the pump rod, pump arm and linkage and front end sight unit is simply a reversal of the disassembly process.



I changed adaptors on my Deben Whisper silencer and fitted it to the action  so as not to piss off the neighbours, then it was off to the shed for a test of the muzzle velocity over the chronoscope.

The Deben Whisper comes with four adaptors, and I still can't use it on most of my air rifles.

Really must sort my shed out.

Two pumps gave me 257 FPS with 14.5 grain RWS Superdomes, which equates to 2.13 ft/lb.

Three pumps gave 392 FPS with Superdomes, which is 4.95 ft/lb.

Four pumps gave 463 FPS, which is 6.9 ft/lb.

Five pumps gave 501 FPS, which is 8.08 ft/lb.

Six pumps 550 FPS, which is 9.74 ft/lb

Soon after that the blow off valve cut in, but I was getting around 560 FPS by that time. This took the rifle up to just over 10 ft/lb.

Fitting new O ring seals to the loading bolt should up the muzzle velocity, given the state of all the other O ring seals they are most likely failing at the moment. Then if the muzzle velocity still needs to go up, I can adjust the blow off valve higher.

TTFN

All the best, Wing Commander Sir Nigel Tetlington-Smythe.