Tuning My Impact Story

Jump to latest Follow Reply
cahil_2

cahil_2

Member
Apr 16, 2015
1,216
463
Whitehall MI, United States
I have two impacts; a mk 1 and a mk 2. I set the mk2 up to shoot slugs. I have never messed with my mk 1 and it has been flawless. So last spring I decide that I am going to put a power plenum on my mk 2. I figured it can’t be that hard and it wasn’t. I couldn’t achieve the power that I figured it should have and I tried different tunes but could only achieve around 900 fps. So I decided to put the original hammer spring back in it and now I am getting the power I wanted for pesting pigeons. After some time I started to notice a loss of power so I bumped the reg up a little. Well this power loss and reg increases kept happening and I couldn’t fathom what was causing it. I headed out squirrel hunting about a month ago and when I got to my spot I decided to shoot a shot and it just went click. I figured I would tear it apart and see what I could find. I figured the valve rod broke but it ended up being the C1 came unscrewed from the valve rod. Screw it on and a little more locktite and I’m good to go but I have to lower the reg, but she is shooting great. Then I decide to put a slug power kit on it, but now I’m using air up like crazy and to top that off I have a slow leak which I don’t understand because I didn’t open up anything sealed. Took me a while but I finally locate the leak as coming out the barrel. Well to me that could only be the valve, so I call FX and they agree and will warranty me some parts. I am impressed with FX for their willingness to help and supportive attitude. But I want to use this gun so this morning I put the original plenum back in it and no leaking and plenty of power as well as shot count is better too. Right now I am leaning on not even putting the power plenum back in after I get the parts. I couldn’t see any obvious problems on the valve except that the seat looked worn. Thought you guys would enjoy reading my story and distract from other things going on right now. 
 
I learned pretty early on with my first Impact that just the act of degassing the gun can cause problems with the o-rings not sealing properly after you air it back up. These guns and the o-rings just prefer to have pressure in them and on them all the time.

As soon as you mentioned the gradual decrease in power, I was thinking the valve rod was unscrewing itself, causing it to get longer, hence, less power. When it came off, broken gun. At least it was an easy fix.

I also agree, air coming out the barrel is a valve leak. Sometimes those leaks will just fix themselves if you take it out and shoot it a bunch of times in quick succession, not always, but sometimes. Can you tell I had a “lemon” of a first Impact? I had all these things happen at one time or another. LOL

I agree with your decision to leave the power plenum out of the gun if it’s shooting nicely. If you have a problem in the future or decide to tear it apart for maintenance, then put it back in. I have the external, aftermarket plenum and it’s always worked great on my MKII so I haven’t installed the power plenum either. My external plenum is large, so I currently have the capability to generate more maximum FPE than the power plenum could give me. Maybe one of these days. I just hate to mess with a gun that’s shooting great. I did just have a valve rod break, fixed it and my gun has been shooting more accurately and consistently than it ever has. That’s reason enough not to mess with the gun. 

Do you use the dual transfer port and pin probe or modified stock probe? Did you install all of the parts that came with the slug kit? They are supposed to be used with the power plenum only, well, I guess it depends on the one you have. The spring, spacers and rubber ball are for the power plenum Impact, that’s what I was told after I bought mine anyway. I tried the pin probe by itself but I already had my gun heavily modified, so I didn’t see any gains. I took it right out and it’s been sitting since.

My gun is plenty powerful and I’ve been shooting more and more pellets lately after getting tired of testing slugs constantly for almost 2 years. I was able to turn my reg. down to 120BAR, my HS preload is about 1/2 way, the valve adjuster is 3.25 lines, power wheel on max. and I’m getting 930fps with the 33.95gr. MKII’s. That’s perfect for every day use. Even with the valve rod problems with this gun and a plethora of problems with my first Impact, I don’t think there is a gun out there that can compare for my shooting needs and wants. 

I shot this group after retuning my gun for pellets(MKII’s) after my valve rod broke. Probably the best 5 shot group I will ever shoot, so I love to share. 5 shots at 75yds. I liked your story, I needed to read something and then write something myself to keep my mind off of all the madness going on right now. Have a great day!

Stoti

7924E412-96E1-424A-B0E4-D02FE608DB39.1604526866.jpeg
B9A7AE81-5332-4B7A-8533-4961C9E99B5B.1604526866.jpeg



 
Upvote 0
It's great to hear that both of you are doing well with your troubleshooting and mods. Nice group it is for sure stoti.

I had the same thing happen to me with my gen1 Impact. I noticed a velocity drop one day, after about 5000 rounds on my Impact, so increased the reg pressure and shortly thereafter, while I was out at the range, I pulled the trigger and click but nothing more happened. In my teardown troubleshooting, when I got home, I found that the hammer seat had unthreaded itself from the valve rod. An uncommon but not unheard of problem with the Impacts, I used a tap to clean up the threads in the hammer seat and then wire bushed the valve rod threads and put it together with a drop of blue Locktight I have another 5000 more rounds on it and no problems as yet.

Some months later I decided to install a power plenum but got the polish one so I did not have to change out the valve as I figured it may give me problems with the new valve seat, machined into to the valve body, not mating to my old worn valve pin seal. After a two month wait I got the plenum and installation was a breeze with no leaks after. I was able to lower my reg fifteen to twenty bar to 135bar and still shoot my 36.2 NSA slugs at over 1000fps.

Then for some unknown reason I thought that the Slug Power Kit with the pin style probe would be a good Idea. I had to drill the valve adjustment knob out for the new valve spring that replaced the internal one. I saw on one of Ernest’s videos where he put a piece of an o-ring down the hammer seat, to help keep things from coming loose, before he put it together. So, I did the same then added a drop of locktight to the threads and screwed it back together. But a few rounds after installation, my new pin probe, somehow managed to shove a slug down the barrel port. Had quite the time getting the barrel off with a pellet stuck down the port but I finally managed and put the modified stock probe back on. Left the new valve spring in as I had drilled the valve adjustment so I could install it. After the install I had to back off the trigger spring adjustment Allen screw significantly to get any adjustment out of the power wheel. But after I did things turned out very well and there is plenty of adjustment now. The Impact was shooting the NSA 36.2 slugs at near 960fps with < MOA accuracy

So I naturally had to modify something else, since that was done but the addiction was not, so I werqed out a way to put some tension on the barrel. Have not got out to the range yet to see how my two new mods have done but I expect things may be a bit more consistent now so maybe it will shoot a little better than < MOA. ;^)

These guns are great for easy tuning, repairs and modifying.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu