Scubapro G250 can't be serviced??

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The only real "flaw" in the G250/V/156 you are at the mercy of getting within range of just the right specs/tolerances on all parts or you can have trouble.
 
So, I switched balance chambers to see what the difference in minimum cracking effort was (knob fully out position). The difference in base height as measured by @Open Ocean Diver was 0.024"/0.6mm. That's less than a half turn on the knob. I started with the old style, shorter base chamber and a cracking effort of 1.05". Sure enough, when I put the taller base balance chamber in my G250, the min cracking effort went from 1.05" to 1.12" measured with the precision cracking effort pump. It all makes sense, if not really significant. On the other hand, I'd rather be able to get 1" min on my G250 than 1.1", so there's that.

As for which balance chamber clears the wiper o-ring, here's a picture:
View attachment 651929
As you can see, in my reg, there's 79.5mm clearance from the knife edge of the orifice to the locking pin hole in the barrel.
When the pieces are set out at that distance with the old balance chamber, the wiper o-ring is just inside the crown, and thus performing its function. More surprising is the amount of compression on that poppet spring. It's fully 1/3 compressed in its least compressed position.

My conclusion? For the G250 at least, it doesn't matter which balance chamber you use, unless you want below spec cracking effort (which I do :D).
One of these days I'll take a look at the G260...
Would you say your uncompressed spring is approximately 26mm in length?
 
That might explain that low cracking effort...
It did help a bit, Installed longer spring 24.44 cracks .9” Spring inconsistency seems to be the key variance I’m always seeing. Your shim idea is the perfect solution.

What do you think is best... install the shim on the BC side or poppet side of the spring?
 
What do you think is best... install the shim on the BC side or poppet side of the spring?
I'd put it on the BC side. There's a little more room to have the spring stay centered.
Screenshot_20210407-114154_Chrome.jpg

Not much room here...
 
https://www.shearwater.com/products/teric/

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