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Post 1)

This is a short description on how to assemble the famous (infamous?) Miata "eBay Bilstein" struts. This post leans very heavily of posts from Miata.net and Miataturbo.net.
This post assumes you have the following:
- 1 set of Miata NB Bilstein struts (either MSM, "Hard S" or B8)
- 1 set of MACHINED eBay sleeves, typically for a Honda Civic or Acura, with springs
NOTE: The sleeves should not be used "as-is" when you get them from eBay. They need recesses machined on a lathe, or use will NOT be safe
- Miscellaneous hardware

This is what you need in addition to your stock struts That's the machined eBay sleeves, bumpstops (you can re-use the stock bumpstops and cut them up, but I'm not a fan) and bumpstop washers.

And this is what the result should look like First you have to prep the shock- remove the spring perch by means of a BIG hammer and a wooden support. This will expose a small tab that keeps the perch from rotating. This tab needs to be removed. You can try hitting it with a chisel (AKA big screwdriver), try bending it side-to-side repeatedly, or, if all else fails, grind it off.

The result should look like this: Note the missing locating tab: Next step is to wrap some electric tape around the shock body approximately 3" from the circlip that will support the sleeve. This is not strictly speaking necessary, but since the outer diameter of the shock is a little smaller than the inner diameter of the sleeve, it's a good idea to take up the slop. Then you slide the sleeve (see picture) over the shock body. Push it all the way down. Make sure the machined area of the sleeve fully encompasses the circlip. If it rides on top of the circlip, eventually the circlip will come off, the sleeve will drop all the way to the bottom and nothing will hold up your car anymore. Next we need to carve up the bumpstops. I like using Honda Civic bumpstops. They're firmer and smaller than the stock Miata bumpstops and are considerably cheaper than most aftermarket parts at only $8/piece

Bumpstop before carving: And after: This length seems to work well with stock NB tophats on an NB Miata. Your mileage might vary. If you have extended tophats, you need a longer bumpstop or your tire will hit the inner fender. Or something else, that is not a bumpstop, will limit your suspension travel in a much harsher manner.

Post 2)

Time to install the spring perch. It consists of two aluminum nuts and a plastic washer. One of the aluminum nuts has a lip. That is the actual spring perch. The spring will surround the lip. The other aluminum nut acts as a locknut. The plastic washer is supposed to reduce NVH, so why not use it. it's time to add the recently brutalized bumpstop and bumpstop washer. There are two different yet equivalent versions. One is a modified retainer from a swaybar endlink kit, the other one is a stock Honda Civic part. The silver one (Honda) has a flat side and an uneven side. Make sure the flat side points up (away from the shock body). The modified swaybar part has a dished (concave) and a convex side. The dished side should face up- meaning the convex side faces the shock body.

Now we slide the bumpstop over the shock rod and then add the bumpstop washer. On top of the washer goes a rubber bumper. This bumper has a lip that will sit inside the hole in the tophat, isolating the shock rod from the tophat. Unfortunately, I don't have a picture of that rubber bumper installed. You will have to imagine it.

Then it's time to add the tophat to the mix (also no picture- sorry!)

Post 3)

After you install the spring and the tophat, all that's left is to add the upper bumper and associated hardware. You can either use the black rubber part that came with your original strut, or you can use the part you cut off the Honda bumpstop. Supposedly this will make for a slightly smoother ride. Your call. Then we add the upper washer to keep it all nicely contained And lastly the two nuts secure the upper washer When you look at the finished assembly, you will notice the "rattle gap". Meaning the spring does not actually touch the tophat when the strut is completely extended. This is a byproduct of using much stiffer springs. If the spring would be raised all the way, so it touches the tophat, your car would ride higher than it does in stock configuration, since the stiffer springs don't compress as much as the stock springs. Or in other words, the shock allows for more droop-travel than needed at that spring rate.

The added droop travel, however, is actually helpful for softer landings after jumps etc. So you may want to use it. In order to take advantage of this and to eliminate occasional clunking caused by the spring unseating and re-seating, you can add a helper spring like this: This helper spring (black, right under the tophat) is much softer than the main spring. So when the car rests on the suspension, the helper spring is fully compressed. However, when the suspension unloads the helper spring extends the shock all the way, giving it more absorbing potential. This way you have created a progressive compound spring.

Post 4)

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