I have been building AEG's for 14 years, regularly non stop. I have NEVER had a tappet plate be the reason an AEG does NOT feed. Other issues with tappets, sure, but never not feeding at all.
It is a bit of a story to explain how the tappet issue was discovered.
The AEG in question used to feed, but because I did not correctly install a Retro Arms carbon fiber barrel and the barrel/hop/receiver combo is just barely incompatible without some filing / adjustment.
Before that initial adjustment, and improper assembly of the barrel, the hop up was a little loosely fitting ( but had no compression issues from the mate. +/- 1FPS or so, but I knew my overall compression was bad. I was down ~70FPS for a build of this kind and I was troubleshooting this.
First is I fixed the barrel after I learned more about it. This firmly, and flush, sat the hop up against the gearbox like it should be and affixed everything in place like the barrel was designed to do. Genius really. Except this change cause my AEG to stop feeding entirely. Literally went from perfect to zero.
Based on the way the hop up is aligned and installed with the gearbox, even though the barrel adjustment was the latest change before the feeding issue, an experienced builder would know that this is not the reason why the AEG doesn't feed anymore. Something else is causing the issue, it just happens that the proper installation manifested the issue.
The compatibility parts in question:
- Retro Arms Gen.1 split - this has seen many AEG bodies and builds and has never been difficult to use.
- Retro Arms carbon fiber outer barrel
- Older Lonex Cylinder head, not the ones with the oval eyelets and rubber pads that actually cause feeding issues in some gearboxes. This one historically also worked fine.
- Retro Arms 21.4mm nozzle. Again, historically these are great.
- Retro Arms hop up RETRO-6388 ( no magazine o-ring )
- FPS 60 degree flat bucking
- FPS tappet plate ( this one specifically )
I changed the parts that were easy to test.
- Nozzle first. It has worked before, as mentioned earlier, and in my experience Retro nozzles are pretty tight to their tolerances so I had high expectations this would not be the fix. Adjusting from 21.4 to 21.2 resulted in "improvement" but no fix. 21.4mm nozzle put back.
- Bucking : I haven't used this one before, but it used to feed too. I tried various buckings from Prometheus to G&G Green to Maple Leaf. No improvement even with the green buckings which are famous for their reliability. Original FPS bucking put back for trial / error reasons.
The last thing I wanted to replace anyway, because I was having compression issues to begin with ( -70 FPS ) made me think my tappet timing was off. The tappet is being driven by a Siegetek sector gear with the large crescent tappet cam, so I had thought that perhaps my tappet open time was too long to begin with. So I replaced it with a Retro Arms DSG tappet that this gearbox originally had in it previously when it was a DSG.
Fixed!
No other parts were changed, it was all a 1x1 process so I know the tappet was responsible for the feeding problems. I do not know why, but I know the tappet was responsible. The tappet flag was only slightly trimmed from the factory, but that bottom section should not make or break whether or not the AEG feeds at all. As mentioned, there is a DSG cut tappet in this AEG now, so very little in the way of a flag anymore. If anything, I have would expect the short DSG flag to cause feeding issues, not fix it, leading me to think the initial geometry that FPS has in their tappet plates is incorrect.
But, this resulted in a 100% successful feed. Compression issues were still there but I was back to my original output of 1.1j. Ultimately changing the FPS red flat hopped bucking out to a Maple Leaf Macron brought my FPS back up, and that will be another review.
Unfortunately, so far every single FPS product I have used has been a bit of a miss...
But I like the innovations FPS is bringing. I think their overall concept of the tappet plate is good. I like the compatibility of heavily reinforced gearboxes like Lonex. I like the middle sections of the tappet had slots added to reduce friction. I'm sure that is negligible but improvements in efficiency are still improvements.
I'm also not so arrogant to say this tappet will not work in ANY build at all. I'm sure it will. But, so far, every single tappet plate I threw at this gearbox ranging from SHS to Lonex to Retro Arms once they released their CNC POM plates have all fed. Even stock ACM plates worked. This one, is the only one that does not work at all. It's a new issue to me.
So, buy at your own risk. But, in my opinion, just buy SHS. I have never had one fail. Not even in DSG's and I have had a SHS DSG tappet exceed 100k before the ECU died. For $4, half the price of FPS, and a forth the price of Retro Arms... Just buy SHS when you can.
