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FX Impact Stripped Top Rail Threads

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Squirrelmageddon

Squirrelmageddon

Member
Sep 27, 2023
136
179
Houston, TX
I have two M3's and both of them have stripped one M3 thread in different locations along the top rail. The very first time I took apart my M3 and removed the top rail I immediately noticed how shallow those M3 top rail screws are. I make it a point to use my torque driver and only use 10 in lbs when threading those in. The top rail is 8mm thick with a 3mm counter sink. So the M3 x 8mm screws are only threading into the module under the rail with 3mm of M3 thread. That's not a lot considering the alignment of the entire gun is dependent on that top rail keeping all of those modules tight and straight. FX really could have gone another 4mm and used M3 x 12mm instead so that we can get some torque on those screws.

Anybody else run into this?
 
Yes, almost every airgun mechanic runs into these problem, having good tools will minimize the risk but will not eliminate.
I did not strip the threads but wore them down, the M3 screws were methodically removing the material especially if you don't pay attention to aluminum powder and shavings on the black screws.
When I started realizing it I started washing/brushing off the material from screws. But finally ended up re-threading all for helicoil inserts.
Also I have a digital torque wrench and torquing these M3 to 2.2 Nm, but now wet lubed with molybdenum grease (the very highest concentration of molybdenum I found for reasonable price in Honda Service Grease, not a product you can get over the counter)
 
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I used a tap to gain a tad more thread count and clean up the factory threads. I then installed a slightly longer screw then the factory. I have also always hand tightened them by feel and haven't had any issues since. I wouldn't recommend this for people who are inexperienced or lack mechanical ability though. As some know, I have dissassembled mine a ton in the past researching and chasing my own power dreams.
 
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You're putting steel threads that are larger in diameter into the aluminum on top of bolt won't wear the heli coil like it does to aluminum. NEVER used copper anti seize on aluminum treads as copper corrodes aluminum.

The Reaction of Aluminum to Copper in Electrolysis

The Reaction of Aluminum to Copper in Electrolysis. Electrolysis involves the manipulation of chemical reactions based on their electric potential. The reaction between the two elements in an electrolytic cell is a reduction-oxidation -- or redox -- reaction. The element that is reduced gains...
education.seattlepi.com education.seattlepi.com
 
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mubhaur --=--
"Does Heli coil makes the things more sturdy than before ?"
Using the standard FX screws seems to enhance the screw grip. However, if you wanted to do so, you could get larger diameter screws, matching the Heli coil, drill out the holes to match and enhance the strength even more....at least it should with the increased area of the screw diameter.
 
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Airgun-hobbyist said:
Yep it happened to me as well. I won't be torqueing them tiny metric screws to spec anymore because of it either. I got lucky and was able to drill the hole deeper and then chase the threads down with a tap. There's a longer cap screw in there now and holds like it should.
Click to expand...
I was going to do this last night and replace all the M3 x 8mm with M3 x 10mm. Turns out 10mm's went right in without a fuss. Out of the 12x top rail screws, 9x of them are M3 x 8mm. I got 7x of the M3 x 10mm to go right in like they were threaded for 10mm. 2x of them had slight resistance at the last MM. I went ahead and torqued those two screws down anyways, pulled em back out to check for debris, and when they went back in they went in smooth as the screw cut that last MM of thread itself, without a tap.

So far the most part, we can just pull out the 8mm's and put 10mm right in without any work.
 
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Usually the threaded lengths that engage and hold - 3mm in this our case - it is enough to engage 1.5 of the screw OD.
We must admit that we are just way too much of a mechanic...all of us that managed to wear out these small threads. Me myself for sure disassembled these screws at least 20-30 times, and I know that only ones not to pay full attentions and the damage is in its own way.
I don't regret what all I have done, it was a good learning curve, I am proud of it... also learned to damage control diy.
 
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If you want to stay with the same M3 fasteners which I highly recommend (explain in a sec), then you can get a kit like this that enlarges the original m3 threaded holes on the block, so it can accept m3 helicoil inserts, then you reuse or install new M3 fasteners-


This kit comes with 10 HC inserts. You can buy more of the inserts like a 50 pack, and you already have the tools from this kit.
I personally would stay with M3 fasteners on the impacts backbone(wether staying with the factory black tie in plate or upgrading to the AM backbone rail) for two reasons-
1. If you look closely at where FX drilled out the m3 holes on the block, they are really close to the edges of the block, so just redrilling and re tapping for these M3 inserts, one has to be very careful to not stray outwards with the drill bit. If you’re careful and take your time, there shouldn’t be any problems
2. If you upgrade to a larger m4 fastener, unless you plan on investing in parallel head fasteners, the type where the outer diameter of the socket head is closer to the diameter of the screws threads(meaning M4 threads but with the same diameter head as the M3), you’ll have to open up the drill outs for M3 heads on the AM backbone and factory plate.

I recently researched these types of fasteners, parallel heads and these types of socket head screws are pricey.

Of course if you are a machinist and have access to equipment you can turn the heads down on the m4 screws, but keep in mind reason #1 that I spelled out
 
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If you want to stay with the same M3 fasteners which I highly recommend (explain in a sec), then you can get a kit like this that enlarges the original m3 threaded holes on the block, so it can accept m3 helicoil inserts, then you reuse or install new M3 fasteners-


This kit comes with 10 HC inserts. You can buy more of the inserts like a 50 pack, and you already have the tools from this kit.
I personally would stay with M3 fasteners on the impacts backbone(wether staying with the factory black tie in plate or upgrading to the AM backbone rail) for two reasons-
1. If you look closely at where FX drilled out the m3 holes on the block, they are really close to the edges of the block, so just redrilling and re tapping for these M3 inserts, one has to be very careful to not stray outwards with the drill bit. If you’re careful and take your time, there shouldn’t be any problems
2. If you upgrade to a larger m4 fastener, unless you plan on investing in parallel head fasteners, the type where the outer diameter of the socket head is closer to the diameter of the screws threads(meaning M4 threads but with the same diameter head as the M3), you’ll have to open up the drill outs for M3 heads on the AM backbone and factory plate.

I recently researched these types of fasteners, parallel heads and these types of socket head screws are pricey.

Of course if you are a machinist and have access to equipment you can turn the heads down on the m4 screws, but keep in mind reason #1 that I spelled out
 
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