Diycoilovers

(editors note: Disclaimer: If you can not competently complete this project and/or if you can not produce a strut that is safe, DO NOT ATTEMPT THIS PROJECT. If you have any doubt, DO NOT ATTEMPT THIS PROJECT. You take sole responsibility for the quality of your product. )

Greetings all. I thought I would document the creation of the strut insert type coilovers I am working on, in case anyone wants to duplicate it. The total costs look like this:

DOM 2 inch OD diameter tube - 4 ft: $26.86 (plus shipping - figure $50 after shipping)

VW Rabbit KYB Strut Inserts - Front: $179.80 (free shipping)

R1 Racing Mitsubishi Eclipse Coil-Over Sleeve Kit: $70 (shipping included, source eBay)

2 10-inch long 2.5 inch ID coilover springs - you choose the lbs/in: $80 (100 after shipping)

1 foot of Drill Rod, some .250 mild steel plate: $10 (local pipe & steel place)

Some fittings to avoid cutting threads: $32.35 (shipping included) Part numbers 46685K268 and 4513K328

Total cost: right around $440

Now, I don't want anybody to think this was a simple project, or that $440 isn't a bit of pocket change. But if you go shopping for prebuilt coilovers that fit our cars, $440 and a bunch of work starts to look pretty good. (editors note: $260 if you are comparing to the strut-less strut tube/coilovers that are available, $180 was the cost of the struts.)

Anyhow, on to the build!

The first part I made was the mild steel tabs that form the lower mounting points. I started with some 6 inch wide quarter-inch steel plate, which I rough-cut with the plasma cutter:

Then I marked it out into 1.5 x 3 inch rectangles:

And cut them out on the band saw:

Then a little grinding on their edges to make a 45 deg chamfer so they can be welded to the main tube, and here they are:

Next I created some rings that would slip over the main tube, that would support the threaded aluminum sleeve. I made these out of drill rod, which is the most common pipe at any steel yard. It is pretty rough stuff, but was around the right size dimensionally. It is about 2 inch ID, about 2.375 OD. It is generally some tough stuff, I think it's used in the oil industry and that's why it's called drill rod. Anyhow, I cut out a 3 inch chunk to start with. It was a bit small to fit over the main tube, which is nominally 2 inches, but actually measured out to 2.002 or so. So I put it on the milling machine and mounted up the boring bar, and took it out to about 2.008 so it would slip over the main tube:

Next, since it was some rusty, rough stuff, I set it up in the lathe:

And took a few clean-up cuts on the outside of the stuff.

Finally I put them in the band saw and cut them into about 3/8 inch rings. The finished product can be seen here:

These rings will be welded to the main tube and will support the threaded sleeve the spring sits on. Here is a shot of the rough mock-up:

OK, now on to the main tubes. I wasn't sure exactly how long the main tube would need to be, so I started with about a foot of the A513 type 5 (DOM) 2 inch OD tube. In the end, the final length was right at 10.5 inches. I started with the bottom end. It would need to have some type of end-piece that held the bottom of the strut, but had a drain hole for the water that would no doubt get in there. I was just going to cut a 2 inch diameter piece of steel plate, and put a hole in the bottom of it. This would support the little cup that came with the VW strut insert, which the strut insert end is supposed to sit on. But then I discovered that the little piece that came with the strut insert would fit almost perfectly into the ID of the tube, which was around 1.76 inches.

Here it is tacked in and ready for final welding:

Then I TIG welded it in fully:

Yeah I know, my TIG welding skills are OK at best. I'm working on it though...

Anyhow, here is a shot of what I had so far, vs the stock part:

The VW strut is really pretty close to the X1/9 unit, it extends a bit longer (seems to have about 6 inches of travel), and has a slightly larger diameter rod on top. The units I used were KYB GR2s, which offered A LOT more resistance to plunging than the ones on my Scorpion (oops, there I said it, I'm building these for a Scorpion, not an X1/9, but I'm also going to build a set for my X1/9 race car. My Scorpions the guinea pig now tho. Maybe they'll share...)

Here is a shot of the top of the VW strut, vs the Fiat:

Anyhow, the next step was the threaded aluminum sleeve. I don't know what kind of crack I was smoking when I started this project, but my original intention was to do ALL the machining myself, including cutting the threads in the aluminum sleeve, and creating nuts out of 3.5 inch 6061 aluminum round. Whole lotta work there.... so I started. The aluminum tube I started with was 2 inch ID (nominal) with .250 wall thickness. So it had to be bored out a touch to make it fit over the 2 inch OD main tube. Then I set it up on the lathe and made the initial thread cutting pass, just to check to make sure I had set the gears on the lathe right. I'd never cut threads before. Here is a shot of the sleeve after this was done:

The thread pattern is 12 TPI. Then I put it back on the lathe and started cutting the threads:

After a few more passes I came to realize that my little Harbor Freight mini-lathe was probably inadequate for this job. A 2 inch tube presented a torque load that was on the hairy edge of its capacity, and I could only cut about a thousandth off with each pass.... hmmm... how deep are threads supposed to be, anyway? I might be here all year.... After uncountable passes, I finally got to this point:

Contemplating cutting the internal threads correctly and to the right size had me seriously wondering if my (very) modest machining skills were up to it. Maybe there was a better way. eBay to the rescue! I started looking at what was out there, and it turns out the "tunerz" market is full of these things, for all different cars. Prices were pretty cheap, most around $70. Some vendors were doing stuff like selling the kit for $0.99 and charging $65 for shipping. I worried that the stuff might be junk, but it said that it was 6061 aluminum and included the sleeves, the nuts, the springs, the wrenches and so on. I took a chance and ordered up a kit for a Mitsubishi Eclipse. It turned out to be well worth the money, and probably saved the project. It was not exactly a bolt-on, but here is what came in it:

Don't worry, it came with 4 of everything, some of the stuff is already out of the box. Anyhow, the short sleeves that were apparently for the rears were almost exactly the right ID. They were about a millimeter larger than the main tubes. They are about 4.5 inches long, with about 4 actual inches of adjustment. The longer tubes and springs I assume are for the front (the kit did not come with any instructions at all). They are a bit thicker, and therefore have a smaller ID, which is about .018 too small to fit over the 2.002 inch main tubes, so they will have to be bored out a little.

I did some testing to try to determine the spring rate, by taking a front and rear wheel off one side of the Scorpion, and then setting up the springs so that the cars weight would settle on them, one corner at a time. I found that the long springs compressed about 1.25 inches with the weight of the front corner of the car on them, so I'm guessing they are about 350 lbs/inch. I will use those in the front. The short springs I will discard, and will order up 450 lb/inch springs from Summit for the rears.

The free height of the long springs is about 8.25 inches, so I welded the lower mounting tabs all the way at the bottom of the tube, instead of a couple inches up, to make up for the height deficit. I know I gave up a bit of suspension travel in doing this, but I want the suspension to be much stiffer than stock, and judging from the tests I've done so far, the amount of suspension travel I lost, I won't need anyway.

OK, so now I still had the top of the strut tube to deal with. The VW strut insert came with a new top cap, but of course it was for a strut tube I did not have. As I said in the last post, I had planned on cutting all the threads myself, so I was going to cut the internal threads in the top of the strut tube and then fabricate a cap for it.

But after the trouble I had just cutting threads in the aluminum sleeves, I decided to try to find something different. I checked out McMaster Carr, who basically have one of everything, and selected a threaded sleeve and a plug to go in it. They had some drawings of these things (it's a great website for shopping online), so I kind of knew what I was getting but didn't know exactly what I would have to do to make it work.

My plan was to weld a threaded sleeve to the top of the strut tube, to avoid having to cut threads, then drill a hole in the top of the plug for the strut rod to come through. Well, I don't know what I was thinking, I assumed the plug would be mostly hollowed out and the material at the top would only be a quarter inch thick or so. I didn't notice the 6000 psi capacity of the plug... that might have been a clue that it was a bit heftier than I thought it would be.

The threaded sleeve looked about right though (150 psi capacity). It had an OD of 2.2 inches, which was a bit big. The plug only threaded into it about a half inch, and it was 2 inches long, so I cut them in half, so one of these pieces could be used for 2 strut tubes. I also turned them down to 2.1 inches, so they would more closely match the main strut tube diameter. Here is a shot of the finished product, next to the raw starting point:

The drill rod rings would support the aluminum sleeve from the bottom, and this thing would be on top of that, so once everything was welded in place, the aluminum sleeve would be permanently captured. I thought about turning this piece down to 2.0 inches, so that the sleeve could slide off the top, but it looked like that might compromise the integrity of the part so I elected not to. The next set I build, I might try the next size smaller coupling and plug to see if they would work better.

Anyhow, that plug needed some serious machining. I plunge milled a 3/4 inch hole down the center of it, all the way thru, as a starting point. Then I turned it upside down and started boring it out with the boring bar. When I had removed all the meat that needed to come out of it, I hacked off half the 2 inch hex portion at the top, since it was about a half inch thick, to bring the weight down. I then chucked it in the lathe and faced it so it was pretty.

Here are some shots of the finished plug, one that has been plunge milled, and one that is stock. The part on the right is the stock VW part, just for comparison:

Another angle:

I'm pretty pleased with the way it came out. As one last step, I might machine the bottom of the plug so that it has a "pent roof". That would help center the strut more than the flat roof it currently has. This would involve mounting the piece on a tilted rotary table on the mill. That's for another day.

Then I turned my attention to the strut top. Surprisingly little work had to be done up there. Since the VW strut rod was bigger than the Fiat one, I had to enlarge the hole at the top of the little cup. There is also a washer that sits down in there. I could not find an exact match, so I had to go with a washer that had the right size hole, and grind it down a bit to fit down in the cup. Here is the finished product, with the stock Fiat parts for comparison:

The pieces below that did not need any modification. Here they are in order of assembly:

Finally, the upper spring perch had to be considered. Turns out the stock part can be modified fairly easily. First I removed that rubber part, then cut off the cup that holds it. This left the lower part with an OD of about 2.375 inches, near perfect for a 2.5 inch ID spring. As for the spring perch, the stock part is really 2 pieces of metal spot welded together. The upper part is the actual spring perch, and the lower part is a shelf about 3 inches in diameter, which is good for "perching" a 2.5 inch spring. I used the band saw to cut it off in about 8 passes, leaving an octagon shaped piece, which I smoothed to round with the grinder.

The stock piece is on the left, the modified piece on the right:

I measured and bored the holes in the lower mounting tabs. The upper holes are about .020 inches more "outboard" than the lower, so I took this into account so as not to hose up my camber too much (editors note: Front and Rear are different, measure before drilling). As a sidebar, I considered boring the holes large on purpose, say to 5/8 or so, then creating indexes (5/8 inch OD "plugs" with the holes offset by various amounts) to allow for camber changes. I may still do this to rough-set the camber, then fine-tune it with the camber plates I intend to create. That's a whole other series though.

Anyhow, here is what things looked like after the mounting tabs and the threaded cap were all in place:

And here is what the mostly finished product looks like:

Note that I am holding it in a slightly compressed condition. The spring was not long enough to be under tension at the outer limit of the strut rods travel (remember, the VW strut rod extends further than the Fiat rod, and the spring I am using is shorter than the stock spring, but stiffer). So when it is at rest, the spring is a little loose. Here is what that looks like:

I can't think of why it would make any difference, once the weight of the car is on it. I suppose if I got the car airborne, something may pop out of position, but I find that pretty unlikely.

So far I've only got this one strut done, but the first one is the hardest, right? I started modifying the long aluminum sleeves for the rears. I am going with a 6 inch sleeve back there, with about 5.5 usable inches of adjustment. Here is a cut-down sleeve compared to the unmolested stock one:

My plan is to finish up the machine work on all four, then powder-coat them machine grey. I will powder-coat the new springs from Summit blue so they match the other ones. I'll send out pics when they are all done, but that will probably be at least a month from now.

If anyone out there decides to duplicate this, keep us posted. There are no doubt some easier methods than what I have used. But I'm pleased with what I have so far.

-Pete Whitstone