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Discussion Starter · #1 ·
Base gun is a KWA TK.45C SE I bought on release. Converted to a DSG in November of 2019 with these parts:

Siegetek 14:1 9-tooth dsg set
ASG 22TPA motor (moved to 28TPA in June of 2020)
SHS 14.5T lightened piston (with extra teeth removed)
Lonex POM piston head (w/o bearings)
- Important note: On first assembly, I used a 3mm flat washer for AOE correct. I replaced the piston & piston head in I think April last year with the same washer.
Lonex cylinder & cylinder head
SHS 21.4mm nozzle
KWA RM4 tappet (This is used instead of the stock one so I can use aftermarket nozzles. Along with a brass spring spacer to return the tappet faster.)
Gate Titan Expert (Came with the gun)
Guarder SP160 spring (Also have a SP150 and SP170)

Maple Leaf 70 degree macaron (Now an 80 degree)
Prommy 208mm barrel
Stock propriety hopup chamber.

When first assembled, it worked pretty well. Was getting 390 +/- 2 fps on 0.20g. 40~ rps on an 11.1v, no feeding issues. Worked surprisingly well for my first DSG. Kept it clean and maintained. Replaced the piston, piston head, cylinder, and cylinder head (was only in stock as a complete kit) in April last year as some of the piston rack came off and scratched the cylinder walls. Worked fine after those were replaced.

About a month ago during a game, it started feeding inconsistently. Figured it was the tappet plate as it had about 50k rounds on it by now. Disassembled it and I was correct, ordered a couple new ones. I also noticed that when I last replaced the piston head, I didn't tighten the screw enough and it had shifted on the piston. Since it was red loctited on, I just ordered a replacement and drilled the center off the old one. I also decided to order a 70D polyurethane airpad and use that instead of the flat washer to correct AOE. It all arrived and put it in.

Now the problems: fps had dropped to about 315 on 0.25g and was very inconsistent at about +/- 12 fps deviations. I noticed I can push the hopup against the gearbox and it pushes the nozzle back slightly instead of going farther into the bucking so I replaced the tappet spring. (Still have this issues, not sure if it was there from the very beginning.) I then decided to take a high speed video of the gearbox firing and see if the nozzle was being pushed all the way forward or fast enough. When viewing the video, it looks like the nozzle is coming back too early and air is still being pushed out.

Video:
https://photos.app.goo.gl/cJy3aGVhFvpdA7AL7
Full Auto video:
https://photos.app.goo.gl/iicG79nhDSccqNse7

So I then trimmed the start of the tappet (to the point that it was more than the broken one. Though it still feeds.) to try and delay the sector from pre-engaging it. Even tried setting the AB higher on the Titan to 80%. I maybe gained 10 fps but it was still very inconsistent. I then googled some and ended up getting rid of the airpad to see if thats the issue. This brought me back up to about 330 fps on 0.25g but, still inconsistent. Then I found an airleak with my bucking to barrel so I tefloned it and that brought it up to 360 fps on 0.25g. And yep, inconsistent still. I then threw in a SP170 I had tried before and it went up to about 380 fps on 0.28g (What I normally use.)

I was tempted to leave it there but decided against it. I was readjusting my hopup for the new spring and figured out it would settle at around 375 after one mag but drop to 360-355 after 3-4 of semi spamming.

I found a way to remove the mag well and put in a different pin to hold the upper to the lower and tried the paper test on the hopup. Blew it away every time. So I figured I had finally found the issue after about 5 days. I threw in a MAXX adjustable nozzle and it would still blow it out no matter what I set it to.

At this point I'm pretty certain its still tappet pre-engagement but no Idea how to fix it. I've googled about everything possible at this point so here I am. Any advice or ideas are appreciated. Sorry for the long post but I felt I had to explain my whole process.
 

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i think id probably try reworking tappet, nozzle, and tappet spring. Hard to follow but whats your most recent shot to shot on chrono? if its between 355 and 360, Id probably leave it. Looks like thats what you were at last

If its going from 375 to 355 there’s probably something going on.
 

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Discussion Starter · #3 ·
i think id probably try reworking tappet, nozzle, and tappet spring. Hard to follow but whats your most recent shot to shot on chrono? if its between 355 and 360, Id probably leave it. Looks like thats what you were at last

If its going from 375 to 355 there's probably something going on.
Would start at 385 on first mag, drop to 375 on the second, then down to 355 by the fourth. FPS would vary about +/- 5 per mag but degrade over time.
 

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Sounds like a seal is heating up and getting loose. I would look at the piston head o-ring.
 

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Discussion Starter · #7 ·

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A 7fps +- difference like that isn't much to worry about. Seems like your gun is perfectly fine. However, since this is with the Hopup dialed to 0, we would need to see what it clocks in at for it dialed in correctly. That's when we will start seeing what is really going on.
 

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Discussion Starter · #9 ·
A 7fps +- difference like that isn't much to worry about. Seems like your gun is perfectly fine. However, since this is with the Hopup dialed to 0, we would need to see what it clocks in at for it dialed in correctly. That's when we will start seeing what is really going on.
Possibly, I'll have to wait until tomorrow with daylight to readjust it and redo the test. Though I'm still certain there is an air leak through the pickup tube thats connected to the tappet pre-engagement and no idea how to solve it.
 

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Im not sure if its worth pursuing the possible air leak at the expense of tappet plates. Considering youre at 367ish with a .28 I’d say make sure youre using a good grease on components and be done.

I haven’t worked with the RM4 style tappet but that spring seems like it could be a problem but thats mainly because it’s different. Maybe try a longer and shorter nozzle and see if it seals better. Just one of those things youd have to try to see if it helps esp if worried abou engagement if you dont think its sealing in the chamber
 

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I haven't worked with the RM4 style tappet but that spring seems like it could be a problem but thats mainly because it's different.
Tappet spring design is superior in my opinion, measured against TM v2 spec it provides more tension. OP even added a spacer to preload it further.

Unfortunately the tappet plate itself is rather soft plastic with a thin fin.

OP - it's great to see another TK45c user, especially one who DSG'd theirs a month or so before mine. I haven't had gearbox sealing issues after replacing the piston head O-ring with an X-ring (I believe 17.12x2.62mm NBR with Superlube) but to be honest I don't have nearly the round count you do so I cannot comment on longevity. My FPS issues stemmed mainly from the nozzle-packing seal since I found my hop unit had allowed my inner barrel assembly to move internally.

If you're interested in my build thread I have it here https://www.digitalcomplex.org/index.php?showtopic=2284
 
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