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PostPosted: Tue Oct 06, 2015 9:15 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
Posts: 286
Location: Hill Spring, Alberta
Recently, after many thousands of pellets, the main spring in my 490 fps Surge broke.

I have my PAL now, so I replaced it with a 1200 fps spring.

After not more than about 2,000 pellets, the new spring broke in two places. It may of course have broken one place, and then
later on at the other. Three coils broke off the back, and two off the front.

The gun was still shooting about 775 fps, but began to make a strange "whap" noise so I decided to do a full lube tune including
honing the cylinder, after doing the "two screw mod" on the trigger. I had no idea the spring had broken until I disassembled it.

I have the Macarri heavy tar to coat the spring this time, the clear tar for other moving parts I guess, and the super moly for the
piston and cylinder.

I believe the spring is a Umarex part since it came from R&R which is a Umarex warranty/repair place, so does anyone have
any idea why it would have broken?

There wasn't any mis-use, dry firing etc., but my first shot with it dieseled and Chronied at 1195 fps (Loud bang) and when I installed the spring I just used light grease on it. Would one dieseled shot or the light grease do it? It never did after that first shot, get anywhere near 1200 fps.
(The dieseling came from the oil I used too much of on the breech seal.)

Peter :D


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PostPosted: Wed Oct 07, 2015 12:29 am 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
I'd imagine that with the spring tar your problems will be over, but no guarantees. I wouldn't use clear tar on anything period because I believe it's silicone. You could try a better quality spring, like Vortek. The oem Umarex (Chinese) springs are not as good but they'll be safer with the tar. You can also make a plastic liner for the piston to help dampen vibration, which is how I do it because tar is so messy and costs power. I do it to reduce noise which I'm sure you'll find is a nice bonus.
Since you've broken two so far and your velocity seems low I'd check the gun for leaks, meaning the main and breech seal. Leakage causes excessive piston impact which transmits to the spring, but leaks also break scopes and upset accuracy. What pellet weight was that 775?
Dieseling isn't good for the spring but I don't think it's all that bad either, but maybe if the wire had a defect it was enough to push it over the edge? My guess is defect + many shots with a leak but who knows.
Check the pix I just posted: topic69801-15.html of the blue Diana main seal. This damage is typical and leaks, many seals are much worse. So I'd pull it out and check it, replace if needed. If your breech is leaking I'd replace and/or shim it so it doesn't. The main seal should be the same as a Diana 34 or 350. An O-ring from a hardware store should fit the breech, my guess would be an AS568-109, but I'd take the old one with for comparo.


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PostPosted: Wed Oct 07, 2015 9:55 am 
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Joined: Sun Nov 30, 2014 8:22 pm
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Location: Hill Spring, Alberta
Thanks Chevota.

Does that plastic liner go between the piston and the tube the spring fits in, or between the spring and that tube?

The pellet weight is 8.33 grains (JSB Exact 4.53.)

I've looked at the thread with the pictures of the before and after seal. I have two, both in near the same condition as the "before", so
I'll sand one and see how I make out. What grade of sandpaper did you use? I have everything up to 2000 grit.

The breech seal seems ok, and I already have a shim in it and some spare seals if I need them.

Thanks

Peter :D


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PostPosted: Wed Oct 07, 2015 4:11 pm 
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Location: United States
Seals can be very tough so I use 150-180 to get them close, then 320 for a final finish so the sealing lip is nice and sharp.
It can be a workout too. I tape a full sheet of sandpaper to a perfectly flat surface like a table, then put the seal face down. With one finger on the seal so pressure is even I rub the seal around in circles. Rotate the seal say 1/4 turn every few circles to help sand it evenly, and you'll probably want to alternate fingers since it's tiring. I also use a caliper to ensure the thickness is even as I go.
And remember, you don't want to go so far that the OD of the seal is too small or thickness too short. That blue Diana seal I sanded in the pix ended up .005" larger OD than the tubes ID which I think is pushing it but it works. The seal should extend past the center dovetail by at least .010" but that's cutting it close and since each gun is different it may be too much. .015" is safer. The trick is you want it so when fired the seal compresses down as far as possible but no metal to metal contact. So really the only way to know that is once you get close you sand .001-.002" at a time and test fire it until it makes contact, then either sand another seal so it's a little thicker or sand the dovetail down a bit. The seal may compress a bit over time as well so I'd check it now and then or add a few more thou for insurance. Dry firing causes the piston to hit much harder so having minimal seal as a bumper means it'll probably hit so be super careful you never do that. Different pellets cause it to hit differently as well so if you set it up using a 10.5gr Barracuda then it'll probably hit when using a 7gr.
Make sense? And the way you know if it's hitting is you sand the dovetail so it either has nice fine sanding marks or till it's shiny, then if it makes contact it'll leave a print on it. The last gun I did it made contact at .008", so .010" works but will need to be checked now and then. .012 would be safer, .015 more so but less bennies. The oem gap varies from gun to gun but probably more like .030 +- .010 so in most all cases you get something out of it.
The liner goes inside the piston so it's a more snug fit on the spring and being plastic it dampens vibration.


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PostPosted: Wed Oct 07, 2015 5:04 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
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Location: Hill Spring, Alberta
Thanks for the information on sanding the seal. I began using 150 grit and using my palm sander which made the seal rotate all by itself as long as I held the centre stationary with my forefinger and used my thumb and middle finger to hold it down.

It worked ok (next time I would put something hard and flat between the sander and the sandpaper), but I quickly realized that taking it down
even 0.030" wouldn't get past the damage. (I kept measuring with a micrometer and when I reinstalled it (using a heat gun and large screwdriver it popped right on) it looked to me perilously close to being too low although it probably had still about 0.020" clearance.

So I've ordered a new seal to come with my spring from R&R in Manitoba.

Its a good thing I love to tinker because I broke another spring today. I'll put it under a different thread for the information of those with Quest 1000's. This time I know why it broke.

Peter :D


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PostPosted: Wed Oct 07, 2015 5:26 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
My only concern with a palm sander is the cushioning under it may make the seals face convex, but using the old seal is a great way to get a feel for the work. To measure the depth of the dove vs the seal I put a straight edge across the seal and use a feeler gauge.
So you broke yet another spring??? Wth? Where is that post you mentioned?


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