Now you remove the piston from the housing and dump out any remaining goo from the inside of the housing. Let them drain for a few minutes:
After they have drained a bit, use a file or a Dremel with a grinding bit to smooth off the top of the housing. It just looks better, and it will keep you from snagging the insert or the rubber sleeve on the jagged edge of the housing.
Next you drill a larger hole in the bottom of the housing. Koni says 14mm, which seems HUGE to me for an M12 bolt. I put the bolt in a drill bit gauge and decided that a ½” hole is more than large enough to accommodate the M12 bolt. If you were slightly off center with your pilot hole, that might not work for you. My ½” hole ended up being perfect for the bolt.
I stepped the holes up rather than jumping straight to the ½” bit by using a 3/8” but, then the ½” bit. I worked fairly slowly even though I had bits that are designed for metal. It makes the hole cleaner and does not risk the strut housing jumping out of the vice.
When you look at what all Koni sends to you, you see some metal rings that look like they should go inside or outside of the OEM housing. The directions say that you need them only for housings with an inside diameter of 48mm. If you have 45mm I.D. they are not needed.
We have 45mm:
After cleaning up the holes at the top and the bottom and slipping the rubber sleeve over the end of the housing (with the end with the lip facing up), insert the insert (duh) into the housing.
It is an interference fit, meaning that it will stop right here:
Koni says to use the bolt that they supply to “draw” the insert into the housing or to whack the top of the insert (not the piston- the body) with a deadblow hammer to “drive” the insert into place. This is where I encountered my first issue. I wrote about it a bit here, as I was looking for help:
I never came back to that thread to post my fix, but I will detail it here.
Koni ‘s supplied bolt is 1" long. The insert was resting 1 5/16" inside of the housing.
I was not keen on banging on the housing, so I decided to purchase longer bolts to draw the insert into place. Even if the 1” bolt had been long enough, I wanted to get 4-5 threads of engagement and there was no way that the Koni bolt would do that. Plus, I don’t really trust an allen head bolt for work like that.
After talking to Koni, I determined that the allen bolt that comes with the kit is an M12-1.5 x 25. For those who don't know how to read the specs, the size is an M12 with 1.5 threads per millimeter and a length of 25mm (about 1" for we Americans).
I decided that I will first try to draw the insert into the housing, but with the bolt being too short, that means that I need a longer bolt. I got excited when I realized that the bucket of a couple dozen BMW e30 lug bolts that I have from stripping parts cars during a track car build are the same M12-1.5 size/pitch, but then I found that they are only about 28-30mm, which is not much better than the Koni bolt.
I went to Fastenal and ordered 2 more bolts in M12-1.5 in 40mm and 45mm lengths, planning to use them to draw the insert into the housing and then replace them with the Koni bolt (complete with LocTite).
This worked like a charm. I placed the housing in the vice and used the 45mm bolt to get the process started. I put a flat washer around the bolt to keep it from marring the bottom of the housing (not a big deal, really) and drew the insert into the housing. Once the nubs were in the housing, it was very simple to just continue turning the socket wrench to draw the insert to the proper location. After the 45mm bolt bottomed out in the threaded end of the insert, I removed it and went to the 40mm bolt, pulling the insert in my 5mm more. I then used the 30mm BMW bolt to draw it in the rest of the way.
Lastly, I removed the BWM lug bolt and used the Koni bolt, including some red threadlocker and the Koni-supplied washers, then slid the sleeves up into the proper position.