DIY: Lower Airbox Thread Inserts

[drrust]

Like many, I had some of the plastic in the lower airbox strip resulting in loose screws for the air box cover. Several solutions are proposed in various threads on the subject. The simplest is to insert sections of zip ties in the stripped holes. Others suggested epoxy in the holes.

In the thread below inserts pressed into the holes was suggested.

https://www.m3post.com/forums/showthread.php?t=1310681

Some research found these inserts of various sizes:

https://www.ezlok.com/assets/documen..._240Series.pdf

A screw for the airbox lid was measured 5.11 mm at the outer edge of the threads and 3.5 mm on the shaft. The screws are 25.5 mm long or 1 inch. The M4 insert seemed to be a good fit for those dimensions.

I was able to order the following from Fastenal:

https://www.fastenal.com/product?query=0185932&fsi=1

To install one needs a drill with a 7/32 bit, flat bottom punch, hammer and a hard surface (vise). With the lower air box out of the car, drill out the holes. Resting the edge of the box on the surface of choice, drive the insert in the hole with the hammer and punch. Push them in until flush. Should look like the picture below.

In terms of screws, I also ordered some M4 screws. I thought stainless screws would look better over time, but one can't use a magnetic bit to hold them. I also could only find Torx screws in stainless. Today I would stick with carbon steel or plated screws even if they weren't Torx head.

For those interested in inserts in plastic here's additional info.

https://www.ptonline.com/articles/fo...s-for-plastics

I hope this helps others who are dealing with this issue. The M5 insert may also work but some of the plastic maybe thin, so take care.

Update: after several uses and a few trips to the shop, some of the inserts pulled out. I think this was from mechanics using a driver vs. hand tightening. Likely the same reason the plastic gets damaged to begin with.

I replaced with inserts that get pulled in from the back. These have a small flange to prevent pull through. I bought them from McMasterCarr.

https://www.mcmaster.com/#94510A320

Install requires drilling a through hole then pressing in on the bottom side of the box. A. couple locations have very little space against the box so I filed the flange so the insert would fit better. The first time I pressed in the inserts and installed the box, put on the lid and screwed in the fasteners. One insert had popped out while trying to get the thread started. So it's better to put the lid on and initially pull the inserts in with the box out. This set up needed a longer screw. I initially used 35 mm but those extend a bit far, so I replaced with 30 mm long screws.

After having been in for some time and having a couple jobs done by mechanics. Most inserts stayed in place. One had dropped out and I reinstalled with some 5 minute epoxy. Some of the other locations had cracking, but seem to to be holding up.

[pbonsalb]

Looks good. I have a couple of stripped holes. One remedy I am considering is installing a centrifugal supercharger, but the threaded inserts would be cheaper.

[drrust]

Originally Posted by pbonsalb

Looks good. I have a couple of stripped holes. One remedy I am considering is installing a centrifugal supercharger, but the threaded inserts would be cheaper.

I like your thought process! A true enthusiast! I'm sure you can also justify a new tool for the job too.😉

[shimmy23]

Thanks! I have several that are stripped

[roastbeef]

great, another project i have to do now.

thanks!

[roastbeef]

op, i'm going to be doing this soon. how is it holding up? do they seem anchored in there pretty good?
i was also thinking about using a soldering iron and inserting the tip into the center of the anchor and sort of melt it into the box.

[drrust]

Originally Posted by roastbeef

op, i'm going to be doing this soon. how is it holding up? do they seem anchored in there pretty good?
i was also thinking about using a soldering iron and inserting the tip into the center of the anchor and sort of melt it into the box.

They are holding up pretty well. None of them came loose at least for now. The first time you tighten a screw in them, it seems too tight, you may also see some metal particles. After that the first few times the threads seem like a normal thread.

Not sure if heating will help or not. They are in there pretty tight. There are other insert designs for ultrasonic heating. Googling plastic thread inserts will show those variations.

[roastbeef]

just ordered titanium hardware and the inserts you suggested. i'll post the results. thank you for the idea sir.

[drrust]

Originally Posted by roastbeef

just ordered titanium hardware and the inserts you suggested. i'll post the results. thank you for the idea sir.

You should use some steel screws to seat the inserts initially. Then use the Ti. They should look good.

[VictorH]

Can you still use the stock Torx airbox screws or do you need to switch to different ones? If you have to swap out, what do you order?
Thx

[drrust]

Originally Posted by VictorH

Can you still use the stock Torx airbox screws or do you need to switch to different ones? If you have to swap out, what do you order?
Thx

For the M4 inserts one needs to get some M4 x 0.7 machine screws. Length of 15 to 20 mm. Get the type of head you would like. I had some Phillips head screws initially, but then bought some Torx head screws (I could only find them in stainless). The stainless looks good, but you have to be careful when you take them out, because they aren't magnetic.

[drrust]

This is how the M4 stainless screws look installed.

[drrust]

Found some zinc coated screws which look similar to the OEM heads.

https://www.belmetric.com/4mm-zinc-t...ok5mqdb8tlkvm3

[Helmsman]

Realize I'm far from sophisticated; simply replaced the original sqrew with a larger one (maybe drilled up the cover, cant remember). Had it off for filter changes etc numerous times since, rock solid...😉

[roastbeef]

They eye candy has arrived. Just waiting on the inserts and I'm hoping to get it done this week.

[Johal E32]

^ Do you have a link for the hardware you purchased?

Thanks

[roastbeef]

It's from ti64.com, but I don't have it fitted yet, so I can't say it works well yet. Just search "m4" on their site and they should come up. The washers are m5 size, but they'll do.

[drrust]

You may have been able to go with a slightly shorter screw. The threadless section near the head maybe in the depth of the insert.

[roastbeef]

Originally Posted by drrust

You may have been able to go with a slightly shorter screw. The threadless section near the head maybe in the depth of the insert.

yea, i wasn't sure. i remember the oem screws being about 1" so thats what i got. if i need to order shorter bolts, i can order some, but these are the longest they have. im also going to play with the height of the lower airbox with my karbonius. they provided shorter mounts and that might affect how the neck area of the lower box is fitting.
right now there is a slight gap, and i can't even get an oem screw to grab, but it might just be a little blown out as well.

[pbonsalb]

That titanium should hold the plastic lid to the plastic box more securely.

[roastbeef]

Originally Posted by pbonsalb

That titanium should hold the plastic lid to the plastic box more securely.

Lol and look cooler doin it.

[pbonsalb]

And save 2 farts of weight.