Good way to know if the Piston seal fit is good?

[byhsu]

i put my piston with the seal on and it goes down by gravity.  It seems too lose for me.  But then I cover the little hole on the outside of the receiver with my finger and turned the receiver up, the piston stayed in place and didn't fall out.  Does that mean the Pistol seal fit is good?

[Stinger177]

Which gun, and which seal (Brand - ARH, Vortek, Weihrauch, etc.) does this pertain to?

Also, what lube did you use on the seal and piston?

 

[byhsu]

Which gun, and which seal (Brand - ARH, Vortek, Weihrauch, etc.) does this pertain to?

Also, what lube did you use on the seal and piston?

 

The HW35E, original seal.  I have not put any lube yet, just working on the internals first.  Honda M77 Paste will be the lubricant.  Thanks

[Stinger177]

In my experience, it usually requires a finger push to get the piston to slide down, not just gravity. That being said, the ultimate test is a chrony reading.

If your testing the fit without lube, then yeah, it may just fall on its own, but I've never done it that way. I always just go ahead and lube it first.

More experienced people will certainly chime in, I'm sure.

 

[Bayman]

Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.

[byhsu]

Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.

Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then?  It is the original seal.  I took the gun apart, the seal seems fine. 

[Stinger177]

That seal looks well....ok....to me. I don't see any scars on the edges or the typical circumferential split or crack inside the outer lip.

What Ron was describing is that the "parachute' design creates a tight seal upon compression of the stroke, so there is nothing wrong with that design. Some other (non-parachute design) seals do not expand outward, and so need to be sized to fit tight without the power compression of the spring. Sizing a seal for proper fit is a rather difficult thing to do.

Personally, whenever I have a Weihrauch apart, I replace the OE seal with either a JM, or more recently, the Vortek Vac-Seal. Pretty much every Weihrauch that I taken a part had some flaw in the seal, be it a clip or cut in the lip, or that circumferential split.

What ever you do, be sure to de-burr the inside of the cocking slot with a half-round jewelers file. I buy mine from the hobby shop and you can get a whole set of sizes and shapes of files for about ten bucks. I use the one that is half-round on one face and flat on the other.

And then be very careful about re-fitting the new seal when re-inserting. It really doesn't take much to nick the lip of the seal.

 

[Bayman]

Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.

Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then?  It is the original seal.  I took the gun apart, the seal seems fine.

from the pictures the seal looks fine. Tighter isn't always better. There's different designs and they all have there points. That seal maybe loose because of the seal or the bore. If it was making good power beforehand, reuse it. Just don't go nuts with the lube, you'll regret it. Here's the results of somebody's idea of a "lube tune". They smothered the thing with grease and moly to lubricate and dampen the spring noise. It eventually got in front of the piston and detonated until it burned a hole in the piston seal and collapsed the spring.

[Mark 611]

Piston seals need about 2lbs of pressure to push in the tube! seals that fall under their own weight of the piston are way to lose IMO, and will cause damage to the rifle, I've had a few new out of the box HW rifles with seals that were to lose or under sized, on 1 of my rifles it actually cracked the stock after 30 shots test firing it! If use a seal that needs to be sized I leave it a tic tight because they will break in on their own! JMO

[airgunbuff]

Lots of great info here learned the hard way ! pay attention and learn from others and you should be GTG
kindly
ron

[Toxylon]

I've had a few new out of the box HW rifles with seals that were to lose or under sized, on 1 of my rifles it actually cracked the stock after 30 shots test firing it!

Gotta wonder if an undersized factory seal was the reason my HW95L's stock cracked in two places within the first 100 break-in shots, using mid-weight quality pellets and proper cocking / shooting technique. They replaced the stock free of charge, once I presented the evidence with some mighty heavy words, but things were a bit tense for awhile, having invested over 400 euros into my first high-quality airgun ever. Since then, I've learned how even 400 doesn't give you a problem-free pellet shooter. Gotta go for the 600-euro LGV for that.

[HectorMedina]

Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.

Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then?  It is the original seal.  I took the gun apart, the seal seems fine.

Something no one has mentioned:
Question: Are those two "dark dimples" a "footprint" of the TP?
If so, that gun is clearly oversprung for that design of gun/seal.

JMHO





HM

[Bayman]

Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.

Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then?  It is the original seal.  I took the gun apart, the seal seems fine.

Something no one has mentioned:
Question: Are those two "dark dimples" a "footprint" of the TP?
If so, that gun is clearly oversprung for that design of gun/seal.

JMHO





HM

The two dark dimples next to each other on the same radius is a print of the transfer port. The smaller dark dimple opposite of those on a different radius is remnants of the molding process. Pour stub. All these traits are common on most Weihrauchs. Especially higher output guns that have been dieseling. Which I suspect by the looks and the loose rotation of the seal on the piston.

[Airnut]

Could this also be a byproduct of shooting to light a pellet??

[Yogi]

When you cover the transfer Port with your finger AND press the piston down, is there much resistance?  It should fight you the whole way, IE not move.

-Y

[byhsu]

The two dark dimples next to each other on the same radius is a print of the transfer port. The smaller dark dimple opposite of those on a different radius is remnants of the molding process. Pour stub. All these traits are common on most Weihrauchs. Especially higher output guns that have been dieseling. Which I suspect by the looks and the loose rotation of the seal on the piston.

Yes, the dark dimples are the transfer port, opposite one could be from the molding, as it is a little above the rest of the seal.

Now the reason I opened her up was because I was getting some shots about 2 inches either high or low, don't know now which is the actual zero of the gun, as is sometimes high and sometimes low, I have not really been able to tell which point of impact corresponds to the zero.

I do not have that problem with my other rifles HW97k .22, R1 .22, HW30s .177, HW50s .177.

Could the loose fitting seal be the cause of the problem? maybe too much recoil slamming on the receiver tube that is causing my shots to go high or Low? 

before I took the HW35 apart it was shooting the Crosman Premier HP 7.9gr .177 at about 800fps, JSB RS 7.33gr at 860fps, JSB exact 8.44gr at 790fps and the H&N FTT at 784fps.

I don't mind slower velocity as long as the rifle is accurate, but so far it is not.

[byhsu]

When you cover the transfer Port with your finger AND press the piston down, is there much resistance?  It should fight you the whole way, IE not move.

-Y

when i cover the transfer port with finger, and push down there is some resistance, but still goes down and if i flip the receiver upside down it won't fall down due to gravity.

[Bayman]

Replace the seal. If you can push it down, even slowly with your finger over the port its no good. Shifting POI can be a seal problem. Replace the seal. Definitely. I wasn't aware of these two conditions.

[Bayman]

I thought you were just doing a tune and all was well before hand.

[Mark 611]

Pushing a piston with a lose seal by hand that has pressure and holds at the TP is not the same as a spring that has several hundred PSI of pressure when moving the piston
 forward!