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DIY Tech Specific Tech How-To's for Customizing your Gun

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Old 05-15-2011, 05:16 PM   #1 (permalink)
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Crosman 3357 Accuracy, Consistency and Velocity (and Ball Detent Repair)

I’ve been trying to find ways to make the marker more accurate, consistent and get the velocity up to a decent level. There are a lot of areas that don’t seal very well, and a lot of gaps that allow gas to escape. (I also found a fix for those bad ball detents in your cylinders).

When I started with this marker, it chronoed at 197, got around 40 shots from a CO2, and seemed to shoot balls all over the place. When I was finished with all these mods, it chronoed at 278, gets around 32 shots from a CO2, and is noticeably more accurate and consistent. (as you’ll see later, the slightly reduced shot count is a result of hitting the valve harder/longer to get more gas out with each shot).

Ball detent – The rubber ring in the center of the cylinder, because of its age, gets hard, dried out, or turns to black goo. If you press a fingernail into it, and it leaves an indent that doesn’t bounce back, it’s time to replace.

The ball detent is a square shouldered gasket and not a round shouldered O-Ring. If you replace it with an O-Ring, you leave an open space in the side of the ball hole that will allow gas to escape.

After much searching, I found a rubber gasket that perfectly matches the O.D. and I.D. dimensions (O.D. 3/4”, I.D. 3/8”, Thickness 5/16”). Rockauto.com part number UW55 is a black rubber gasket that’s 5/8” thick, so if you cut it down the middle, it’s now perfect.








New Valve Assembly - Brand new complete valve body assembly = $15 from Crosman, the part # is 357-050 (includes the upper valve, air tube, lower piercing assembly, etc). Eliminates all those aged seals and gaskets. (this pic is the old valve assembly).





Cylinder to Barrel Gap – There is a relatively large gap between the cylinder and the barrel (1.2mm), that allows a lot of gas to escape out the sides, as the ball jumps the gap. I ground down the center metal part of the cylinder so the gap is now .80mm (any narrower gap and the cylinder detent would not seal in the back hole of the cylinder). There are actually two advantages to this, less gap between the cylinder and barrel, and the cylinder detent is at the very end of it’s travel, so it seals better inside the end of the cylinder plate.







Barrel Top Plate – The plate is held in by a small screw in the top of the barrel. This plate has a square hole where the latch hooks, and if it’s worn, will allow looseness in your barrel closing, which will affect the cylinder indexing and seal of the cylinder detent. The plate is no longer available, but you can adjust it some by loosening the screw and pushing the plate as far as it will go towards the front of the barrel. I do have a couple extra plates if you desperately need one.





New Cylinder Detent – The detent is pushed forward under spring pressure, and constantly rubs on the back of the cylinder as it rotates, so the rounded face of the detent can get flattened and worn down. The detent pops into each cylinder hole as it lines up, and it needs the rounded end to seal into the hole. Part # from Crosman is 357-036.





Valve to Cylinder Plate Teflon Seal – I noticed that the cylinder plate just press fits up against the front of the valve, no gasket or seal. This is an area where gas could escape, so I wrapped teflon tape around the end of the valve and pushed the cylinder plate on tight, to give it a better seal.






New Hammer Spring w/ Roller Bearing – In order to get more gas out of the valve, this mod forces the hammer to hit the valve harder, faster and for a slightly longer duration.

The hammer spring has probably weakened with age, so I purchased a new one from Crosman, part # 357C027.

I noticed that during use, the hammer spring slides up and down the back of the hammer, with direct metal to metal contact. I made a small roller bearing and added it to the upper part of the spring, which makes rolling contact with the hammer and also, because of the rollers thickness, puts even more force on the hammer. The roller bearing is made out of an old air tube (valve assembly left over from replacing with new valve assembly). The air tube is thicker in the middle, and has a small metal ring at each end that pushes on the gasket in the end of the valve. I flared the end of the tube and cut the other end off with a dremel, now the ring stays put on the cut off tube end, so I used epoxy to attach it to end of the spring (there is enough space between the inside of the tube and the spring end for some epoxy to fill the gap). I also had to dremel off a bit of the square edge of the frame piece, where the lower piercing valve assembly is mounted, for the roller bearing to clear when it rides down in the cocking position.









Barrel Funnel – (thanks to agentSmith for this idea) - So that the ball does not hit the sharp edge of the barrel opening, I cut a small tapered funnel into the end of the barrel. Just take down the end of the barrel opening a little, and make sure it’s sanded smooth. If for any reason, the ball does not enter the barrel end exactly lined up, it won’t hit the sharp edge of the opening.






Polish and Lube – I micro polished all surfaces that make contact / movement, and lubricated them all with silicon lube. This made the entire action much smoother and easier to operate.


Have fun and good luck with your modding. I've now taken apart and reassembled the 3357 so many times, I can almost do it with my eyes closed.
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Last edited by acrewofone; 06-17-2011 at 10:36 PM.
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Old 06-15-2011, 11:06 PM   #2 (permalink)
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ever consider selling this service to other 3357 owners? I'd be interested for sure.
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Old 06-20-2011, 01:48 AM   #3 (permalink)
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I am also interested in buying if u decide to sell
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Old 06-20-2011, 09:27 AM   #4 (permalink)
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Quote:
Originally Posted by melkson View Post
ever consider selling this service to other 3357 owners? I'd be interested for sure.
I would do the following:

frames stripped and repainted
barrels stripped and repainted
new complete valve assemblies
barrel opening coned and finished
new cylinder detent
new ball detent
new index finger
new hammer spring
new barrel latch rubber
valve to cylinder plate teflon seal
new style lever bushing (metal instead of plastic)
interior workings cleaned, polished and lubricated

for $75 Paypal (includes U.S. return shipping)

(would take about 2-1/2 weeks, due to parts orders from Crosman take 7-10 business days to get to me)
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Last edited by acrewofone; 07-31-2011 at 09:48 PM.
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Old 06-20-2011, 11:21 AM   #5 (permalink)
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I'll be getting back to you on this. Might have to wait until August, but i'm interested in maxing out my 3357's. Is there a discount on tweaking multiples? 3 for $150?
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Old 06-20-2011, 11:58 AM   #6 (permalink)
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Quote:
Originally Posted by melkson View Post
I'll be getting back to you on this. Might have to wait until August, but i'm interested in maxing out my 3357's. Is there a discount on tweaking multiples? 3 for $150?
Not much discount, due to the cost of parts. 3 in a box adds weight for more shipping cost, but maybe 3 for $200?
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Old 06-20-2011, 05:56 PM   #7 (permalink)
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I'll check with my bud to see if he's interested in having his 3357's done.
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Old 06-22-2011, 12:34 AM   #8 (permalink)
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Hey wait a sec. Your hammer spring is made of round wire. Mines made of square wire. Is that what crosman has stock now? Or is that an aftermarket one you found?
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Old 06-22-2011, 09:06 AM   #9 (permalink)
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Quote:
Originally Posted by Echo View Post
Hey wait a sec. Your hammer spring is made of round wire. Mines made of square wire. Is that what crosman has stock now? Or is that an aftermarket one you found?
New one straight from Crosman. Every hammer spring I've seen has been round wire, I wonder if your square wire is a really early model (like the early cylinders without the rubber ball detent and the early plastic air tubes).
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Old 06-22-2011, 09:44 AM   #10 (permalink)
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I'll see about pics tonight. They're brass air tubes and rubber ball detente though. Do you think that the round spring is any stronger?
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