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Offline teknix

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HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« on: September 19, 2008, 01:54:25 PM »
The gen4 is a great marker but there are some manufacturing flaws that lead to the marker not working properly. I?m going to try and discuss these here and various ways to fix them and get your gen4 working flawlessly.

Low Velocity Issue or Maker Not Recocking and ?Farting?

To fix a low velocity problem with the gen4 could be a number of things, but first make sure you have a full tank of air or CO2 and your marker is well oiled.

1.)   Small nub between ball detents: The most common reason for low velocity with the gen4 is the bolt sticking and not cycling smoothly. The first cause of this is a small notch inside the front of the gun on the top between the detents. This notch is from the hole for the front screw that holds the top rail on. If you have this nub of metal there just sand it off carefully until it is smooth and the bolt can move smoothly through the tube in the front of the gun without catching.



If the bolt still doesn?t move smoothly you may have to sand the notches on the side of the bolt a little deeper to help the bolt pass the ball detents easier. (Note: I used a dremmel tool to do this)

2.)   Bolt sticking inside the barrel: Also to cause the bolt to not cycle smoothly is the bolt on the gen 4 travels into the barrel a little ways. Usually aftermarket barrels are a little smaller bore so the bolt will stick inside of it and jam. You could fix this one of the following ways:

a.)   Sand the start of the inside of the barrel wider so that the bolt can pass into the barrel smoothly. After you sand the small section of the inside of the barrel I would suggest polishing it with some metal polish to make it smooth. (Note: I used a dremmel tool to do this)



b.)   Place a couple o-rings on the end of the threads of the barrel so that it will space it farther from the gun so that the bolt will not travel into the barrel. (Note: this will cause a gap between the barrel and the breach which could cause ball chops or inaccuracy.)

c.)   You could also sand the outer diameter of the front of the bolt so that it will fit into smaller barrel bores if you did not want to sand the barrel itself as mentioned in section a. However, I would not suggest doing this to the bolt since it could cause air to escape behind the bolt and could cause the more friction for bolt operation.

3.) Check Hammer and Bolt O-rings: A common cause for ?jackhammering? or ?farting? is one of the o-rings on the bolt or hammer are damaged or broken. Check all the o-rings the gun for tears and replace them with new o-rings. If the o-ring on the hammer has a tear or is damaged air pressure will leak behind it and not recock the gun.

4.) Get a Harder Drive Spring: Install a harder drive spring and/or stack the drive spring with anther smaller spring. You can buy a spring kit from RAP4 or use other spyder spring kits. Use a heavier spring than the stock one and/or stack the spring with another spring towards the back on the white spring guide. You can cut the stock spring to almost the size of the spring guide and then add to the front of it a hard drive spring and this should jump your velocity up. This causes the hammer to press and hold the valve open longer and harder to allow more airflow.



5.) Get a lighter Valve Spring: You can also make the valve easier to hold open and allow more air flow if you replace the stock valve spring in the front section of the gun with a lighter spring. You can get these springs in a spring kit, the same kits that have the drive spring have valve springs as well, they are the shorter cone shaped springs.

6.)   Drill the bolts air hole wider: If you?ve done the above steps and you still have low velocity you could widen the hole in the side of the bolt bigger to allow more airflow. Just make sure you stay between the 2 o-rings on the bolt.



7.) Drill more holes in the valve: If you still have problems with velocity after steps 1-6 then you could take a more extreme route and drill a few extra holes in the valve. The stock valve has 2 holes currently in the middle section. You can add 2 more holes on either side of the valve to allow more airflow. Drill these holes inside of the valve in-between the o-rings as the picture shows.




8.)   Sand down the valve pin: This goes along with drilling more holes in the valve and is suggested against if you are mechanically challenged or not very steady handed. You can also increase airflow my sanding down the valve pin so that the diameter of the pin is smaller than the stock one. Just sand down the middle of the pin NOT the plastic part or the tick end. Be careful not to damage the plastic part on the end of the pin because this is what seals the valve and if it is damaged your gun will leak air.



Offline teknix

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #1 on: September 19, 2008, 01:55:41 PM »
Ball Chops Frequent or Balls not Feeding Properly

Ball chops are usually a feeding issue from the magazine but can also be cause by the bolt. Below are the possible causes of feeding problems or ball chops.

1.)   Get the new bolt from RAP4: Some of the earlier guns came with a bolt that was too short and left a large gap in the breach. This gap allowed for the balls to sometimes get pushed back into the breach and then a second ball would load half way into the breach and when the gun fired it would chop the ball. This is fixed by emailing RAP4 for a new bolt that is longer and fills this gap in the breach and only allows one ball to be loaded in the breach at a time.



Thanks to LeopoldStotch for images

2.)   Magazine ratchet lever not fully depressed: Sometimes the little switch on the magazines that release the ratchet will not get fully depressed and thus not feed the balls into the gun. To fix this I used some epoxy putty to build up the area in the gun where the lever hits to depress is more. Epoxy putty is usually sold in the hardware section of most stores and is specifically in the plumbing section. It is used to fix pipes. It is kneaded into a clay and can be molded and then hardens like steel in a few minutes. After you build up the area where the lever hits in the gun you can sand down the epoxy to the desired level. Make sure the magazine still fits in the magwell straight and isn?t tilted from the epoxy holding it up. This also helps with wobbly magazines in the magwell.



3.)   Sand the ratchet release lever notch on the mag: Sometimes the ratchet in the magazine will not hold right and it will be loose easily and want to push the balls out when you don?t want it to. The ratchet lever will not catch because it is being depressed buy the plastic in front of the slot where it sticks out of the magazine. To fix this just sand the front of the slot to allow the lever to move further forward to catch the ratchet.



4.)   Ball detents in the magazine feedneck work too well: If you have the miIsig magazines they have ?better? ball detents in the magazine feednecks which hold larger sized paintballs in a little too well. The ball bearings in these feednecks are larger and hold much better but sometimes they will not feed large balls at all or some of the time causing it to chop. To fix this just remove 2 of the 3 ball bearings from the feedneck by unscrewing it. 1 of these bearings is good enough to hold the larger paintballs in the mag, smaller sized paintballs might roll out easier though.



5.)   Pin in ratchet comes loose and magazine will not work: If the small pin inside the ratchet in the magazine comes loose the ratchet will not wind up and the magazine will not work. To fix this open up the magazine and squeeze the pin back in place and bend the metal so that it will not pop out of place again.



Other Modifications

Here are some other modifications you can try with your gen4 but aren?t necessary.

1.)   Easy internals strip mod:  To make it easier to clean your bolt and inside of your gun without completely disassembling it you can cut the slit the rest of the way on the back of the charging handle to allow the bolt to slide out the back of the gun without having to take off the top rail with the charging handle or foregrip to be able to remove the rail. Now all you have to do to take the bolt and hammer out of the gun is remove the stock and unscrew the 2 back plugs and then take a long rod and push it down the barrel to push the bolt out the rear of the gun.




2.)   Faster magazine winding tool: Here is a tool I made to wind the magazines up for the T68's, milsigs, ect... without hurting your fingers and it is 10 times faster than by hand. I just took a small dowel rod and cut a slit in it the size of the mag winder and then wrap the end with electrical tape to make it fatter and softer for an easier grip.

Now all you do is put it on the mag winder in the slit of the tool and turn the stick with your hand and it goes a lot faster. I made this thing after trying to wind up a bunch of mags and my fingers were hurting like heck...well no more!




« Last Edit: September 19, 2008, 02:02:14 PM by teknix »

Offline Orpackrat

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #2 on: September 19, 2008, 07:02:03 PM »
Excellent post.

Offline skwid

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #3 on: March 02, 2009, 12:26:36 PM »
Thanks for this.   

Offline pirahna590

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #4 on: March 04, 2009, 08:04:03 PM »

6.)   Drill the bolts air hole wider: If you?ve done the above steps and you still have low velocity you could widen the hole in the side of the bolt bigger to allow more airflow. Just make sure you stay between the 2 o-rings on the bolt.



7.) Drill more holes in the valve: If you still have problems with velocity after steps 1-6 then you could take a more extreme route and drill a few extra holes in the valve. The stock valve has 2 holes currently in the middle section. You can add 2 more holes on either side of the valve to allow more airflow. Drill these holes inside of the valve in-between the o-rings as the picture shows.






 Wondering if these procedures can be done to the gen6 as well ... Anything to increase velocity is a good thing I would think :D If we CAN do this to the gen6, what sized drill bits do you recommend for the for drilling out the bolt and valves? Im not set on doing this just yet, but considering it ;)
« Last Edit: March 04, 2009, 08:08:01 PM by pirahna590 »

Offline teknix

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #5 on: March 04, 2009, 08:32:41 PM »
Yeah it is possible. You will loose gas efficiency though since you are allowing more air to fire per shot. For my T68 I just ended up getting a high flow aftermarket valve. I think it was "New Designz Spyder High Performance Valve"

It seems to work well but the drilling is a cheaper solution.

Offline pirahna590

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #6 on: March 04, 2009, 09:56:32 PM »
hmmmm ... might be something to consider over modifying the components of the T68, an still have the t68 components as a back up for IF the aftermarket part fails or what have you ... what kind of performance gains did u see with this mod? Were you able to shoot a lil more accurately, farther ect? By any chance were you able to chronograph the marker before an after? Not so important, but curious as to the differences so I can judge for myself if its worth doing or not. Thanks for the info :D

Offline skwid

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #7 on: March 05, 2009, 12:00:04 PM »
I too am interested in what performance gains you achieved.

I am thinking about getting the new designz valve, but what springs did you use with it? 
« Last Edit: March 05, 2009, 12:15:40 PM by skwid »

Offline teknix

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #8 on: March 05, 2009, 01:22:31 PM »
It will increase your velocity if you are having problems there. It could help you run on a lower pressure if that is what you want to achieve. I was using the hardest spring for the main drive spring in a spring kit with the old valve but with the new one I can get the same velocities off of the lightest spring in the kit.

Offline pirahna590

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #9 on: April 09, 2009, 05:56:25 PM »
that messed up somehow ... but Im askin this ;)

 Anyone ever think about " boring " out the inner diameter of the main bolt, down to this opening here? I mean, if you can increase the whole here, for more airflow an get somewhat of a performance gain, then you should be able to bore out the inside of the bolt as well an gain a lil more there right? Granted, your probably not going to get to do too much forwith out compromising  structural integrity ... but still SOME ;)

« Last Edit: April 09, 2009, 05:58:10 PM by pirahna590 »

Offline Orpackrat

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #10 on: April 09, 2009, 06:39:24 PM »
that messed up somehow ... but Im askin this ;)

 Anyone ever think about " boring " out the inner diameter of the main bolt, down to this opening here? I mean, if you can increase the whole here, for more airflow an get somewhat of a performance gain, then you should be able to bore out the inside of the bolt as well an gain a lil more there right? Granted, your probably not going to get to do too much forwith out compromising  structural integrity ... but still SOME ;)




That was actually listed as one of the ways to increase the velocity of the Gen4.

Offline jackal

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #11 on: April 12, 2009, 11:46:51 PM »
Great post first off. 
  I'm having a rough go with my RAP.  I bought the GEN6 conversion kit and have used it four times on the field.  I've hand a horrendous time with it.  I have multiple ball chops every mag.  My mags seem fine based off of what is posted here and everything else seems in order except for the the bolt does allow the ball to fall back and leave a gap.  It's not as big of a gap as pictured but I think it's enough to double feed. I just thought that since it's the newer conversion kit it should have the new, longer bolt.
  What are some other reasons why the balls are chopping and their possible remedies?  I tried different brands of paint, some do worse than others but I have multiple breaks no matter what.  I can't play with it at this point.  Any suggestions?   

Offline teknix

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #12 on: April 13, 2009, 09:35:22 AM »
You should have the new bolt with a gen6. It might be your ball detents. Try removing them and taking off the oring on them and screw them back in tight to avoid double feeds. Also if it chops the last round of the magazine the mag might not seat as far up into the breach as it should and not load the last round fully into the gun.

Offline jackal

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #13 on: April 16, 2009, 10:57:32 AM »
Thanks.  I'll give that a try and see if that works. 

Offline DRSUPPRESSION

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Re: HOW TO FIX YOUR T68 GEN4 (velocity, choping, ect...)
« Reply #14 on: July 31, 2009, 04:00:30 PM »
try the new powder ball pb balls in 68 they work really well are hard enough they dont barrel break