HELP! Diana 350 piston rod is loose and a whole bunch of other things

[Ike the GSD]

I took my 350 apart this morning because once again it has lost power. I pulled the spring and piston out of the compression tube and I noticed the piston seal had metal imbedded into the front just like the one I replaced. There are wear marks/galling on the cocking arm like its shucking side to side during the cocking cycle and the piston rod is loose. In fact the entire piston is loose to the point that it wiggles roughly .040 side to side up and down in the compression tube, it must have been like this since I've owned the rifle and I'm wondering if it may be the cause for all of the other issues?  I have done no modifications to this rifle, all I have done is replace the mainspring and piston seal. I'm worried the rifle isn't fixable!!!! If any of you guys wanna call me about this my # is 269-207-5094 Thanks guys👍
Wes

[Toxylon]

My 350 Mag (and D54) had a loose latch rod as well - they are not uncommon. The latch rod is connected to the piston head, so if one is loose, the other is, as well.

Now, does this affect the gun or its characteristics, is an open question I have no answer to. I know some people have shimmed the piston head to get rid of the play. I also attempted this a couple years ago with my 350 Mag. The shims (ultra-thin slivers of steel) didn't stay put, but the looseness still disappeared, from the bits of glue pushed in there. I can't tell a difference in the gun.

A rear bearingless piston's body inside the receiver must have some looseness to it, or the friction would kill most piston velocity. It's the seal that needs to fit properly tight.

Metal imbedded into the piston seal is a serious issue that needs to be dealt with ASAP.

A picture of the location, type and severity of the wear marks in the cocking arm would be really helpful. The cocking foot / cocking slot interface has to have some lubrication. Dry steel on dry steel in moving parts never ends well.

[Ike the GSD]

My 350 Mag (and D54) had a loose latch rod as well - they are not uncommon. The latch rod is connected to the piston head, so if one is loose, the other is, as well.

Now, does this affect the gun or its characteristics, is an open question I have no answer to. I know some people have shimmed the piston head to get rid of the play. I also attempted this a couple years ago with my 350 Mag. The shims (ultra-thin slivers of steel) didn't stay put, but the looseness still disappeared, from the bits of glue pushed in there. I can't tell a difference in the gun.

A rear bearingless piston's body inside the receiver must have some looseness to it, or the friction would kill most piston velocity. It's the seal that needs to fit properly tight.

Metal imbedded into the piston seal is a serious issue that needs to be dealt with ASAP.

A picture of the location, type and severity of the wear marks in the cocking arm would be really helpful. The cocking foot / cocking slot interface has to have some lubrication. Dry steel on dry steel in moving parts never ends well.

Here's apic of the cocking foot, my phone camera stinks but there's wear on the bottom and sides

[Ike the GSD]

My 350 Mag (and D54) had a loose latch rod as well - they are not uncommon. The latch rod is connected to the piston head, so if one is loose, the other is, as well.

Now, does this affect the gun or its characteristics, is an open question I have no answer to. I know some people have shimmed the piston head to get rid of the play. I also attempted this a couple years ago with my 350 Mag. The shims (ultra-thin slivers of steel) didn't stay put, but the looseness still disappeared, from the bits of glue pushed in there. I can't tell a difference in the gun.

A rear bearingless piston's body inside the receiver must have some looseness to it, or the friction would kill most piston velocity. It's the seal that needs to fit properly tight.

Metal imbedded into the piston seal is a serious issue that needs to be dealt with ASAP.

A picture of the location, type and severity of the wear marks in the cocking arm would be really helpful. The cocking foot / cocking slot interface has to have some lubrication. Dry steel on dry steel in moving parts never ends well.

How do I fix this?

[Ike the GSD]

Here is a pic of the piston seal with the metal imbedded

[happymecanic]

Hi Wes,

I had a very similar issue with my Ruger BlackHawk, which is a clone of the Diana 34. The rod was loose in the head, and the head was loose in the piston body. I solved this by nickel/silver soldering the rod and head in the piston body. I used a bushing to center the rod in the piston while soldering, and now all is good. Brass would probably do an equally good job. HTH.

[Ike the GSD]

Hi Wes,

I had a very similar issue with my Ruger BlackHawk, which is a clone of the Diana 34. The rod was loose in the head, and the head was loose in the piston body. I solved this by nickel/silver soldering the rod and head in the piston body. I used a bushing to center the rod in the piston while soldering, and now all is good. Brass would probably do an equally good job. HTH.

Thanks happy, do you think it will solve the rifle eating piston seals and galling the cocking arm foot? The whole piston seems to be fishtailing down the compression tube LOL! Where exactly on the piston did you apply the silver solder on that little ring/space between the crimps and the head area where the seal is attached? Pics would be great👍

[Roadworthy]

Interesting conundrum.  You seem to have multiple mysteries there, Wes.  You have shrapnel embedded in the face of the piston seal.  How did it get there?  The seal never goes as far back as the cocking slot when cocking the gun so it could have come from the cocking slot when the seal was last installed or the piston could be slamming against the end of the compression tube breaking off bits of metal.  I've never seen a 350 so I have no idea about typical wear on the cocking shoe.  A proper fix for the latching rod would probably be a new piston so by all means try other approaches first.  Good luck!!

[Ike the GSD]

Interesting conundrum.  You seem to have multiple mysteries there, Wes.  You have shrapnel embedded in the face of the piston seal.  How did it get there?  The seal never goes as far back as the cocking slot when cocking the gun so it could have come from the cocking slot when the seal was last installed or the piston could be slamming against the end of the compression tube breaking off bits of metal.  I've never seen a 350 so I have no idea about typical wear on the cocking shoe.  A proper fix for the latching rod would probably be a new piston so by all means try other approaches first.  Good luck!!

The metal is getting in front of the piston seal because the piston is shucking side to side up and down and every which way. The fix happy suggested seems like the best option right now because nobody has a piston in stock and frankly even if they did I don't think I should have to pay for this😬 This is a prime example of poor workmanship, apparently this is what we can expect from Dianas from now on and I'm done with this company. They farm most of their parts out to other countries anyway so when they say "Made in Germany" what they really should say is "Assembled in Germany" out of crappy inferior materials.

[Ike the GSD]

I called Diana USA today and the lady on the phone gave me the email address to the warranty repair department and she said I needed to give them the serial # which serial # do they need the one on the barrel or the one on the compression tube? They aren't the same??

[Roadworthy]

The airgun serial number is probably the one on the compression tube as that's where the date code is located.  You asked about my spring compressor.  I'll attach the info.

[happymecanic]

Thanks happy, do you think it will solve the rifle eating piston seals and galling the cocking arm foot?

I believe so. The rod being much more stable, the cocking foot glides smoothly in its slot. Of course I carefully de-burred and polished the cocking arm foot and slot, and applied tungsten paste to contact surfaces. Also I'd check the state of the compression tube walls in your gun, sometimes the finish is quite ''oh-hum'', even in German-made rifles. I had a Diana 240 that ate a seal in about 15-20 shots . I gently honed the cylinder using 400 and 600 grit wet/dry sandpaper wrapped around a plastic drum I made. I like to use light cutting oil when I do that, it leaves a much smoother finish.

Where exactly on the piston did you apply the silver solder on that little ring/space between the crimps and the head area where the seal is attached? Pics would be great👍

Unfortunately I didn't take much pictures when I did it, but here's one of the best. The piston head is the most massive part, so I heated it first to the point it was red hot. The heat climbed in the rod and piston body, and it was then easy to apply solder and have it ''wick'' in-between the parts. I then applied solder to the outer head/body without letting the piston cool down. Afterward I chucked the pistons in my lathe and machined off the excess solder - that could easily bo done with a bench grinder. Since that, both rifles (I forgot to mention I also did my AirHawk) cock and shoot very nicely.

I did all that in relation to seal replacement, as the original ones were cut from the factory install. Here's a link to my thread regarding this: https://www.gatewaytoairguns.org/GTA/index.php?topic=210684.0

[mpbby]

I had the problem with the piston being loose and bought a new one to replace it.

I would try

https://twchambers.co.uk/

https://www.versandhaus-schneider.de/index.php/cPath/40

[Ike the GSD]

I had the problem with the piston being loose and bought a new one to replace it.

I would try

https://twchambers.co.uk/

https://www.versandhaus-schneider.de/index.php/cPath/40

Thanks Marcos, I've tried everywhere and nobody has any in stock😕

[mpbby]

Not for that piston, but I already made a backorder at Chambers and everything went well

You just wait and they ask from Diana

[Ike the GSD]

Not for that piston, but I already made a backorder at Chambers and everything went well

You just wait and they ask from Diana

Ok, I'll keep that in mind, I'm going to try to fix this one first. The silver solder fix happy suggested should work fabulous, I'm crossing my fingers🤞 LOL! Thanks for your suggestions Marcos👍

[Ike the GSD]

Diana emailed me today and they're sending me a new piston free of charge👍

[happymecanic]

Good news! But keep the old piston as a spare, just in case...

[Ike the GSD]

Good news! But keep the old piston as a spare, just in case...

Oh I sure will, thanks again for your repair tip👍

[Ike the GSD]

The new piston arrived for the 350 today, now I just need to find a mainspring👍