Tuning Repairing a 1998 Air Arms Pro Elite

[Bill_S]

Back in 1998, I purchased an Air Arms Pro Elite in .22 from Jim Maccari. I used it a lot during the first few years, then my interests shifted to other things. About 5 years ago, I took it out for a cleaning and it didn't fire correctly. It suffered the common (for Pro Elites) seal detachment. I set it aside thinking that I'll send it off for repair someday. Paul Watts was doing Pro Elite tunes back then, and planned on using him. Fast forward to today, and Paul isn't taking any new guns for tuning right now.

When I bought the gun from Jim Maccari, I purchased two extra Maccari-made seals for the Pro Elite, a pair of piston rings, and a Maccari-made compression spring to have just in case.

This thread will be about my repair efforts, and possibly to seek answers to questions from people who know more about this gun than I do.

I'll illustrate this thread as much as I can. This is my first post here, so there will be a bit of a learning curve for me about how the forum works.

Here goes. Taking off the trigger guard on this beautiful rifle, always my favorite.

The action mounted in the spring compressor that I built about 20 years ago.

There was a lot of spring preload. I'm guessing 2". This is the point where the spring finally relaxed...

More in the next post.

 

[Bill_S]

Removing the spring guide and spring, slathered with Jim's Black Tar. That stuff really damped spring noises.

Here's the piston showing residual glue on it. The glue, when combined with a machined dovetail, held the seal in place. Just not very well.

Here you can see the dovetail seal mounting feature. It's not a 45-degree dovetail, but more like 30-degrees. That's not a lot of mechanical grip for the seal when/if the glue fails. Note the machined space for the piston ring just under the dovetail area.

I tried different solvents to remove the old glue, but then resorted to a 1/2-hour soak in paint remover - the dangerous kind. I poured a thin layer into a stainless steel can, then just dunked that part of the piston in it. I had already removed the plastic piston ring just under the seal area to prevent it from being destroyed by the paint remover. You can still see the piston ring at the rear of the piston that's sticking out of the can. After the soak, the old glue came off with a wipe from paper towels.

More in the next post.

 

[Bill_S]

Here's a comparison photo showing the Maccari seal purchased about 20-years ago and the old Air Arms seal removed from the compression tube. The Maccari seal is a dark gray, hard rubber type of material. It does not have a parachute feature and is taller.

Its diameter is larger than the original seal, and as-is won't enter the compression tube. If I use it, I'll have to remove some material somehow. I have some ideas that I'll float later in this thread.

Here's a shot of the piston side of each seal.

Here is my first question. Should I work with the Maccari seal (I have two of them) or should I look around for an original replacement Pro Elite seal? I've seen them for sale on U.K. websites and wonder if anyone has had any experience ordering from overseas?

 

[Bill_S]

Along the way, I've been measuring critical components in case I need to modify them for one reason or another.

I've been doing scale drawings of some of the components, like the piston.

The original spring and Maccari's spring are different in a couple areas. The Maccari spring is made of thicker wire (~0.156 dia) compared to the ~0.148" wire of the original.

Overall, original spring shown on top with guides...

Unfortunately, the Maccari spring has one spring end that's not squared well. It's about 10 to 15 degrees from square. I don't know how much that will affect things.

A spring calculator showed that the Maccari spring is about 60 pounds/inch compared to 51 pounds/inch of the original. I don't need more power and always preferred a smooth shooting cycle over fps.

 

[Bill_S]

I had to make a couple tools to remove parts along the way. The E-ring that holds the cocking link to the barrel is in a tight place. I took a piece of thin wood, drilled a hole through it near one end, then took a bandsaw to cut across the hole to produce a semicircle. Being wood, it wouldn't scratch the surrounding metal like a screwdriver that is pressed into service.

To remove the barrel from the compression tube, there was a screw that used a locking nut.

The locking nut required a spanner to loosen, so I created one from some scrap 1/16" steel sheet that I had laying around. I drilled a hole near one end first (see below) then ground the end to open the hole on one end.

I dressed and shaped with hand files, then bent the tangs over in a vice. Now I have the correct tool for this task. The photo below shows the screw and locking nut removed from the gun for clarity.

 

[Bill_S]

I was pleased to see bearings inserted into the flats on the sides of the breech. It's not like other airguns that use a brass shim between breech and tube at the pivot. There a a lot of little details that I admire on this gun.

 

[Bill_S]

Time for another question - does anyone know what adhesive or glue that Air Arms used for their seals? I can guess with the best of them, but if someone knows for sure, I'd love to hear it.

The adhesive had a tremendous grip on the almost polished steel dovetail area of the piston. I was thinking that I could mask off the rest of the piston and sandblast to roughen the dovetail, but because the original glue was so strong, there may be no need to do that. I WILL apply the glue a little more thoroughly than the little dab they used earlier in the thread.

 

[Bill_S]

One more question if I use the Maccari seal - because it is too large for the tube as-is, the diameter needs to be reduced. The front of it is a conical section, so if I shorten it from the front, that will also reduce the diameter. I have a drill press, so I was looking to chuck up the piston by the rear shaft and spin the seal against some sandpaper or a file to shorten it.

Because it's cone shaped, at some point the diameter would approach the compression tube ID. I'd test often for fit.

Has anyone done this? With the hard durometer seal, would a file be better than sandpaper? Should I mill a little flat on the seal where it contacts the tube, or just shorten the seal to produce the correct diameter and keep the sharp sealing edge?

 

[Bill_S]

Oops! Double post deleted.

 

[Bravo1956]

You probably have one with the dreaded "tapered chamber". My in 22 burnt the seal pretty fast, PW tuned it to about 14 ft lb and it is very peaceful. He has since found a way the ream the chamber and remove the taper, did not know if he is still tuning.

 

[Bill_S]

I have heard about irregular tube IDs on some Pro Elites. Mine is an early one. I don't know if that makes any difference. When I first got it, I ran thousands of rounds through it, averaging low 800s to high 700s with Crosman Premiers for 20-21 ft-lb. It was the smoothest shooting, most accurate springer airgun I have owned. The seal detached around year 15 of my ownership.

Paul was on my short list of tuners to work on it when the seal failed. His Sunnen hone could take care of tube ID issues nicely. Unfortunately it doesn't look like he's taking new work at the time.

I'd check for a tapered tube myself if I had some round object at the right size. The piston is a fairly loose fit, relying on the give of the piston seals to take up the space. I couldn't tell anything using the piston alone. It just slipped in and out without any resistance. Once I have a proper sized seal on it, then I can check.

 

[Bill_S]

To get an idea if I have a tapered chamber, I found my old telescoping bore gauge set and carefully performed some measurements. These aren't ideal measuring tools for a deep bore, but should give me an indication if something is wrong. It may not be accurate enough to conclude that there is no taper though. For one, they are not long enough to reach completely to the end. I cannot determine is the chamber is out-of-round by the limitations of fishing the measuring tool into the cocking slot for measurements. I can measure only across the chamber, not vertically, because of the tool's angle.

Because I can't reach straight into the bore, I had to pay very close attention to their orientation when coming in through the cocking slot.

However, I did get measurements ranging from 30.01 mm to 30.04 mm at four different depths in the chamber. That's a spread of a little over 0.001", so that's encouraging.

I do wish that I could reach to the transfer port to judge that last important inch or so.

There is one deviation that I could measure - the diameter of the tube at the cocking slot is a bit smaller than the compression diameter. I suspect that punching the cocking slot and trigger cutouts in manufacturing caused this area to be deformed and out of round. That could make a tight spot when inserting a new seal and piston before it is in its working position.

I'm tempted to just glue on the Maccari seal, trim it to fit, then give it a try. If it doesn't work well, then I could go to Plan B.

 

[Bill_S]

 I did some measurements of the vintage Maccari seal for the Pro Elite. It's made of a very firm elastic material. It appears to be a turned part, possibly made on a lathe. It's oversized, so will need to be fitted to the compression chamber.

I did a little looking around for various adhesives with a strong bond between plastic and steel. I'll probably use JB Weld Original because of some evidence of impact resistance over competitors, even those said to be especially formulated for plastics.

 

[Bill_S]

Plan B will be to order parts (OEM seals, etc.) from the UK after the COVID confusion wanes. I'd probably have to put the project on hold until later summer before I could order from overseas and expect reliable delivery. I don't believe much is available in the USA. If someone does sell Pro Elite parts domestically, I'd love to hear about it.

I've been musing about a Plan C too, where I use a 30mm Vortek seal adapter meant to replace old leather seals on R1/HW80 with modern seals. There might be a way to machine my Pro Elite piston to accept the adapter.

I don't know the measurements of the adapter, so I've punted for now and did a rough first-cut concept of how this might fit on my existing piston.

In this scenario, I'd machine away the dovetail, but leave some important metal around the trigger latching shaft to keep stability. I'd then machine the Vortek seal adapter to fit over that. If that could be done, I might be able to use standard HW80-sized seals. That would really ease parts availability.

There are some issues that I'd have to work out with this concept, but it's a distant Plan C for now.

 

[Bill_S]

Because this isn't a common gun, I found a PDF that has an exploded parts diagram. It was a bit difficult to track this down, so here it is for any PE owners who want one. The link is at the bottom of this post.

Because the owner's manual came from the UK, I'm not sure if powerplant components are different or not. I am not able to find my own paper copy for comparison.

BTW, my USA-spec piston with rings weighs exactly 400 grams.

View attachment PRO-ELITE-manual.1617982967.pdf

 

[Michigander]

Very interesting. I would buy a couple original seals from airgun spares if they are still available. Just in case. You will have no problem ordering from them.

If the Maccari seal OD at the base is really only 0.006" smaller than the bore, and there is 0.037" interference on the dovetail, I don't see how the seal can squeeze past the dovetail. But they glued them for a reason. Once you know the material used, go to the Loctite website for their recommendation for the proper instant adhesive, perhaps 406. Be sure to clean the metal surface with acetone, and use the Loctite primer on the plastic. The adhesive needs to be somewhat flexible. I think they typically use some type of urethane as a modifier in their plastic and rubber adhesives. Follow their instructions on cure temperature and time.

Seals are fitted by sanding the OD. Glue sandpaper to a block of wood to avoid rounding over the tip of the seal. Spin the piston with the seal mounted to sand. Best fit is supposed to be such that the piston will drop down the bore of its own weight. I would stop just short of that.

If you know how to use a spring calculator, you can determine the spring dimensions to give the power output you are looking for. Preload distance times rate gives the load uncocked. Preload plus stroke distance times rate gives the load cocked. Average load times stroke in feet gives stored energy during cocking. 35% of the stored energy will be transferred to the pellet on average.

A type of short stroke adapter might be used to convert to another style 30mm seal. The kind typically used on the TX is not practical because the Elite dovetail is so large in diameter. But maybe the design could still work if the dovetail portion were machined to be closer to the TX.

If you want to improve bore consistency, you can make a lap from brass. Machine to a diameter that just fits along the entire length of the bore. Drill and tap one end 1/8 NPT, then split that end with two saw cuts. Charge with lapping compound and work up and down the bore. Use a hex socket plug to adjust the fit until you get the same drag the length of the bore.

 

[Bill_S]

Thanks for all the information. Airgun Spares in the U.K is one source that I identified early on. It's good to know that they are reliable. It looks like they will re-open on April 13th. After putting this repair off for about 5 years, I can wait a few more days.

I'll check into Loctite products. It sounds like you might have good experience with their products.

For now, I'll probably stick with original spring. It looks like I can get some spares for the future from Airgun Spares. I'll lay in a supply of repair parts for the future.

BTW, I did find the original shipping box for the Pro Elite, and a factory label on it states that it was packed 3/12/1997. Hard to believe that it's that old already.

 

[Michigander]

For those who might be reading this thread and aren't familiar with laps and lapping, they can be purchased in various sizes then machined to fit. We always just made them as I described above for finishing bores to exact size. Soft brass is best as it allows the abrasive particles to embed in the lap.

https://www.travers.com/brass-barrel-blind-hole-laps/p/112470/

 

[Michigander]

Here is a link to the Loctite compatiblity chart for their instant adhesives. I have used them with very good success in industrial applications. The only trick is to select the right adhesive and follow the instructions to the letter. For this application I would be interested in their toughened products for shock resistance. And pay attention to the gap requirements. The inside surface of the seal will need to be in contact with the top of the piston. Sanding of the bottom of the seal may be required.

http://dm.henkel-dam.com/is/content/henkel/8745_CA_Brochure_Pgs4-5_Interactive_v3_Finalpdf

 

[Bill_S]

Getting the mating surface of the seal flat and smooth might be an issue. It looks like two cutters were used to shape the cavity that fits over the dovetail, and there's a definite step between the two. I'm guessing that it's about .010" from the feel of it. It's visible in the photo below.

Unfortunately, the step is in a very awkward location near the edge of the dovetail. Not apparent in the photo is a small burr in the center of the cavity, but that can be dealt with easier. I don't have access to a lathe anymore, so I'm limited.

I'll check to see if any of those adhesives are good at gap filling. Thanks for the link. It's a lot more thorough than the consumer list that I encountered yesterday on the Loctite site.

Great info on the split brass laps too. I haven't used one before. I'd probably have to jerry-rig a longer mandrel to reach deep enough into the bore, but that seems straightforward.