I recently purchased my first blaster jm m4a1 gen 9. Was running perfectly straight out out the box and pretty much started upgrading straight away. Started off with the basics first barrel spring and o ring, and now I have completely changed out the nylon gears, piston and motor. After putting my ■■■ back together everything sounds good no strange noises or gear grinding. I am using no name milkies in it and I have measured them reasonably consistent around 7.3 average. When shooting every so often the ■■■ will dry fire and no gel comes out or a gel just spits on 5 or so metres in front, also some gels are exploding. Also once I switch to full auto the gels accuracy goes out the window flying everywhere most top spinning to the ground. The spring in it is a 1.2m equal and I have test it with a 7.2m and a 7.4 barrel with similar results. I’m next to try the stock spring but I couldn’t imagine it’s the spring as most I see run similar setups with no problems. My only thought is due to my gen 9 being the newer version with the base plate of the grip having no motor height adjustment the pinion is touching the bevel gear incorrectly. When I installed my new motor I just measure using a vernia the base of the motor to the top of the pinion on the stock and adjusted the new metal one to match. Also i forgot to mention I have a rizer hop up which I adjust to suit for single fire and goes reasonably straight but once I go full auto it turns to shit. I’m lost on what else it could be
kind of sounds like tappet timing.
with all the upgrades, did you replace the tappet return spring?
you may have inadvertently misaligned the t piece somehow although i can’t really see how.
did you do the barrel?
on the pinion mesh, if that were messed up you’d hear it. motor and gearing is only responsible for box cycling (read: pulling the spring back)
what you describe is likely a compression issue.
as a side note…above the right hand shift key is the enter key…makes things a little easier to read. and of course if you’re on a phone…
Yea I replaced the spring with a heavier one so I don’t think it will be that.
I did the barrel myself on the stainless 7.2m but the alloy 7.4 was already done so I don’t think it could be that. The stainless one from what I can tell looks correct and I glued it and seal it really well.
Could the compression be in the piston? Before putting it in I tested the seal in the cylinder.
Hopefully that is easier to read
I should have asked about vacuum when the piston is being drawn back?
What motor did you put into it?
What voltage are you running it at?
I’m running Chihai 460 motor. I have a 11.1v and the stock 7.4v. With that kind of motor is it fine to run the 7.4 or should I be running the the 11.1.
What are you meaning about the vacuum for the piston?
It’s more about the overall speed of the motor inn relation to the tappet timing not is capability to handle the voltage
When the piston gets pulled back, if the holes in the head aren’t clear it will draw a vacuum
This messes with accuracy
There are heads out there that run find on 2s but not on 3s because the vacuum impact isn’t huge on 2s but really impactful on 3s
It’s an easy fix, opens the holes up or use an o’ring with a smaller cross section.
O rings can cause vacuum also if the are too fat (CS)
Always remember to use lube like grease and silicone oil. Problems can arise when things are too dry.
Are you referring to the head on the piston or cylinder? The cylinder and head is still stock where the piston is new. How do you mean open it up
This might be a silly question. What length barrel are you using. If you’ve kept it stock it shouldn’t be an issue but if you’ve made it a nice shorty your cylinder volume could be too high for the barrel. But you’re good on single so I doubt that’s the issue. That being said I did have a lot of issues with accuracy using my warinterest hopup. Once I got my hands on a dkj9 oh man did my situation improve
I run a gen 9 as well and I find with any upgrades it does get a little more inaccurate but a hop up fixed all those issues for me. I also run a 7.3 ID barrel. Seems the best size imo.
As to vacuum and tappet timing. I’d say those guys know more than me on that matter
My barrel length is 35 for the 7.2 and 33.5 for the 7.4 so I wouldn’t think that’s a problem for compression there.
I was always expecting accuracy loss with increase with of fps but just seems to be alot and even worse when in full auto. I might get a 7.3m soon and see how it goes.
I’ll pull it apart tomorrow and send in a photo of my piston head and you let me know what you think.
Is it worth upgrading the cylinder and head as well or does that not make a major difference unless your looking to port with a shorter barrel?
Thanks for the help as well guys
Depends on how good your seals are really. If the seals are good then there’s no real rush to doing them. But every stock one I’ve had has been a horrible seal so I replaced them with the 2 o ring head and nozzle. Every blaster is different to a point. You just gotta work out what you want out of it.