68 special bolt drive spring

[Drcemento]

anyone know where to get one - picked up a special for a song and the main spring was broke with part of it stuck in the bolt handle.
PB sports does not have them listed.

I see someone posted same Question it the tippmann section with no answer so moving it here

[Carp]

Pretty sure an A5 main spring will do the trick for ya.... I'm 98% positive, I've seen that said before. 🤔

[Drcemento]

i've wondered about that... but looking at tippmann parts that A-5 spring is 4 3/8" long I measure my specials at 6 1/2"

[infamoussmiley]

Pretty sure an A5 main spring will do the trick for ya.... I'm 98% positive, I've seen that said before. 🤔

Sorry to be a nay-sayer, but it does not have the tension needed to get the marker to cycle properly and hit the right velocity. Prolite Springs are what you are looking for.

All the best,

Smiley

[Carp]

Dang it... ninja'd again. ..😆

[Carp]

It's a pro-lite spring 7" long and just need to trim it down a little. 😉

[Drcemento]

Nards! prolite spring no longer available on tippmann parts. com

[Drcemento]

wrote a PM to brettg in the hopes he's got a pile of them laying around from his HPA conversions

[Drcemento]

looking at McMaster they actually list some spring stock that is a perfect match dimensionally for the bolt spring I have.
will order it and report back. any low rent methods for undestanding/measuring spring tension? the spec for this is 4.3 lb max load and a spring rate of .85lb

[Drcemento]

reporting back...
the macmaster spring is crazy close. there is a slight bit more spacing on the original spring. I cut mine 1" longer to 7 1/2" and put it in. gun cycled fine, and crono'd at 250-260 after i pointed the gun down and fired a few times to get liquid in it. with just gas was only seeing 200-220

would cutting it even longer increase velocity? waiting on a couple siphon tanks graciously donated to the cause by Sethzilla to get a better reading on velocity. these things need the liquid!

also getting a little leak down barrel at times hoping its not the cup seals - they look good. used buna instead of urethane to replace valve seals hoping thats the issue.

[uglyduckling]

Did you ever make any more progress with these springs? I was looking on mmc as well and wasn't able to find what you did, I'm not experienced in spring specifications though. Are their any stronger ones available that would fit?

[Myrkul]

So there are a couple things you can do to bump the velocity. I run weak (black warrior kit) and trimmed down spyder valve springs in all my tippmanns. Obviously a siphon tank for liquid is a must have, but you can also flute the cup seals. That's a huge part of how brettg gets all of his smg68's working on HPA. The other parts include a SHP reg, and the valves that take 1/8" Npt fittings for an external gas line. There is enough volume in those fittings to make them work.

For the leaky cup seals, let them sit overnight in some air tool oil, and inspect the face of the side of the valve that is removable. There might be some scratches that need to be buffed out.

[uglyduckling]

I put the spring out of my prolite on a scale and compressed it one inch. That gave me 5-6lbs. .85 seems too low, unless I am not understanding how to measure spring tension