Sandblasting

Obviously, when you tear external parts from a 15-year old car they are not going to look like new but realistically the brakes and hubs from my MX-5 were not in a bad state and could have been used as-is. But where is the "fun" in that? I had originally planned to either buy myself a small sandblasting cabinet (more expense) or nip down to a friend's workshop and us his, however, the discovery of a hand-held sandblasting gun and a huge compressor at work unleashed the inner cheapskate in me. A few things I have learned:

• Sandblasting without a cabinet is not pleasant
• Doing it after work, in winter, in the dark, is worse
• No matter what you try to keep it out, sand will get into your eyes, ears and nose...
• ...and down your back, and in your shoes, and your hair
• You can quite easily turn the area directly outside a fire exit into a small beach

Front caliper piston removal

Before anything can be sandblasted though, it must be stripped down to its constituent parts. The brake calipers were fairly simple, the fronts just needing some compressed air to get the pistons out and a screwdriver to prise out the seals. The rears were a bit more complicated, with the pistons needing to be unscrewed from the handbrake adjustment mechanism, but once done blasting could commence. Considering they are relatively small, these parts take a while to blast as they are a very complicated shape with a deceptively large surface area. They also start to rust immediately afterwards, so they need painting or powder-coating pretty quickly. I painted mine and am very happy with the results. I used a brush-on caliper paint, which is very thin and tends to run easily, but with patience and multiple coats, the finish is very nice.

Before, after and painted

The rear hubs were a little more work. I wanted to replace the bearings, so the wheel hubs had to be removed from the main uprights. This was a simple case of placing an appropriately sized impact socket on each hub shaft from the rear and hitting them repeatedly with an FBH (... Big Hammer). The hubs came out, but unfortunately with the inner races of the bearings still attached to them.

Impact socket from behind

Now, I was prepared for this, having done plenty of research (well, watching a couple of YouTube videos and reading some forum posts) and the wisdom of the internet surmised that you could remove this half of the bearing with a hammer and a flat bolster of some kind to get in the join between the two parts and prise them apart. Well, I think I need to correct the internet on this point, because two ruined bolsters and a lot of swearing proves you can't. A little lateral thinking is actually required: A wheel bearing is made of hardened steel and whilst very strong, it's also relatively brittle, so a score line with a grinder and then a single whack with a hammer and bolster splits it like butter. The outer races still in the main uprights were then removed in much the same way as the hubs, just with a slightly bigger impact socket.

This does not work

This does though

At this point I also cut off the old dust guards as they spoilt the look of the hubs. The only other parts to remove were the old wishbone bearings, which was simply accomplished by bodging a 51mm hole saw and G-clamp together to push them out.

Bush removal - simples

Old bush and it's replacement

Once sandblasted, I used an etch primer to get a good bind to the metal and then a gloss black finish to match the wishbones. Reassembly was straightforward; luckily for me a colleague at work owns a hydraulic press, so he inserted the new bearings for me and I fitted some nice new strongflex poly bushes to the top mounts. The only other modification required was the addition of a length of tube to reduce the size of the bolt holes on the bottom of each upright as the GBS wishbone system is based on 10mm bolts whereas the original Mazda was 14mm.

Before, after and painted

I think the finished result is rather good.

A Bit of Panelling

Progress hasn't been as fast as it could have been recently (damn these small children and their ridiculous need for Birthday parties!), but I have made a start on some panel work. The most sensible panel to start with seemed to be the large piece that sits behind the seats which, along with keeping the water out, provides a fair amount of strength to the torsional rigidity of the rear of the Zero.

Panel ready for drilling

To get it right, the panel work is slow and a bit tedious. Each panel is cut-to-fit, but doesn't quite, as most seem to foul on a weld or overlap the edges of a support by a few millimetres, so each has to be carefully sized up, marked, filed down a bit, re-fitted, marked, filed down a bit, and so on. Once the correct shape, it can be clamped in place and all the beams and cross-members can be marked out, ready for drilling. It's then removed again and all the hole positions measured out and drilled (I've been using 1/8" rivets, so a 3.5mm drill bit works well) and then de-burred afterwards. The panel can then be clamped back in place again and the holes used as a template for drilling the chassis. Some people seem to only want to drill the square section tubing and not the round tube diagonals for fear of drilling off-centre, but I didn't seem to have any issues with it.

Because the chassis is mostly constructed of box-section steel and the car cannot be made entirely of right-angles, the panel wouldn't sit flush against the top and bottom rails. In these cases I either bent the panel slightly on the workbench whilst it was clamped between two straight edges or I just used a soft mallet to form it around the chassis itself. The finish is relatively neat but as this particular panel is going to be covered in carpet, it doesn't really matter too much.

Cleco pins in place

To be sure of drilling the chassis holes in exactly the right place, and to assist with fitting the panel later on, I purchased a set of "Cleco pins" and their respective tool. I had not heard of these little marvels before starting this project, but they are used extensively in metalwork and the aviation industries. They are basically a temporary rivet that is insert and removed with a special set of pliars, with each size of pin a different colour for ease of identification (1/8" is copper, 5/32" is black, 3/16" is brass etc). After each hole was drilled, I inserted a Cleco, therefore making the panel rigid very quickly. I should also point out here that a right-angled drill attachment is very useful, if not invaluable, for getting into some of the tighter corners of the chassis.

Riveting finished

At this point I may have gone a little over-the-top, but I decided to paint the insides of the holes in the chassis with a bit of Hammerite, to help protect against future rusting. Whether this makes any difference or not, I doubt I will ever know. The final stage in the panel preparation is the removal of the protective film, which is a pain. Where the film has been burnt by the laser cutter it's edges are melted and stuck to the aluminium, so it takes rather a long time to pick it off. Again, as this panel will be covered in carpet, the final finish is not too important, so I experimented with a few things such as wire wool, a knife, solvents and sand paper. Nothing really worked as well as my thumbnail, although I may try a hot-air gun or some IPA next time.

Along with being held in place with rivets, each panel is bonded with the notorious (in these circles anyway) GBS-supplied "Black Stuff", otherwise known as polyurethane sealant. This stuff is very tough and I would strongly suggest you apply it wearing gloves, as if you get it on your skin, it won't come off for weeks unless you bathe in white spirit. Before applying the glue, I cleaned both the panel and all the chassis parts with a degreasant to make sure the bond took well, then it was just a case of applying a bead of glue over every chassis part, making sure to cover every rivet hole, and re-fitting the panel, hopefully for the last time. Now, you could be quick with the rivet gun and hope for the best, but the easiest solution is to use the Cleco pins again. Once the pins are in you can have a cup of tea and replace each one with a permanent rivet at your own pace. After all the rivets were in, I applied a bead of Black Stuff along all the chassis rails in an attempt to make the panel water-tight. It's just like using silicon sealant on your bath, except you need to dip your finger in white spirit rather than soapy water!

Dynamat installed

I had also recently been thinking about some sound-deadening within the car, to try and make the finished product feel a bit more well-built and a little less tin-canny and after experimenting with different types of foam my mind wandered back to my in-car hi-fi days and the wonder that is "Dynamat". It's basically a squidgy, sticky rubber bonded to an aluminium skin and is designed to dampen the ringing of large metal panels and therefore tighten up the bass frequencies within a car when you install a ridiculous great sub-woofer. It's quite expensive and relatively heavy, but you don't need to use much and a few extra kilos doesn't really bother me. It's very easy to apply, you just cut it to shape with a knife (careful, the edges can be sharp) stick it to the panel and then for maximum effect squeeze all the air out with a wallpaper seam roller. Once finished, the result is really quite impressive, with a loud clang being replaced by a dull thud, just the result I was looking for.

First panel finished, bring on the rest...

Trialling - Part 2

After my last post about trials cars, Richard Lincoln (see his blog in the links on the right) sent me a link to a good little video which explains the Lotus 7's place in the history of trialling. Thanks Richard!

"Trialling"

I've been reading a lot of kit car magazines recently, all of which contain the occasional article about a random, from-scratch, one-off build or the racing progress of certain regular builders or owners.  After reading one such feature, my mind started wandering back to my childhood and, potentially, the source for my current interest in a self-build.

When I were nowt but a slip of a lad, my family used to holiday in north Cornwall, staying on a dairy farm owned by Roland, a childhood friend of my father, along with his brother and their families. Ro, like any good farmer should be, was (is) very mechanically minded and channeled his skills into his hobby... Sporting Trials Cars.

Courtesy of 750 MC Sporting Trials

Trialling is a particularly different form of motorsport to what I had previously experienced. It isn't a race as such, more a combination of slightly odd-looking vehicles, big hills and a scoring system akin to golf. Each trial comprises of a slalom-type course, marked out by poles, upon an often unfeasably steep or undulating slope, which each competitor and their passenger hurl themselves up. The objective is to get to the top/ end of the course, without touching the poles, stalling or going backwards. If the top isn't reached, each car is scored based on which gate they get their front wheels through, with the gate values decreasing the further along the course they are. The car with the lowest overall score at the end of the event is the winner.

The cars themselves are built to a very specific set of rules, which cover all aspects including dimensions, engine types, wheel sizes and safety devices. Locked or limited-slip differentials are not allowed, but independent rear "fiddle" brakes are used to control wheel spin, along with a highly mobile passenger (or "bouncer"), who is usually throwing themselves around trying the get as much weight as possible over whichever of the large rear wheels has most chance at grip. The smaller front wheels look comparatively like they've been stolen from a bicycle, when compared to the rear, and can turn virtually 90 degrees each way, meaning each car has the turning circle of a fork-lift. Allied to this some long travel suspension and you have a vehicle that is capable of some very impressive hill climbing. The fact that a modern trials car bears some visual similarity to a Sevenesque roadster is no coincidence, as the Lotus Mk I, II, IV and VI were all used successfully in trialling.

Ro, my sister and me in "Kernow 2"

Not only did Roland partake in the sport (and still does) but he built his own car. In fact, he built two. Each car was powered by the guts out of a classic Hillman Imp and I can still remember the fleet of discarded Imp bodies lying around the farm, having been surgically picked apart for useful bits over time. Whenever I visited, I always tried to get a trip out in one of the trials cars, and I think this is possibly where my interest began. Whilst not built for speed, they certainly felt fast to me at that age. They were light, uncomfortable and without any form of windscreen. They had a clunky gearbox with fantastic transmission whine and you could get from the bottom of a vertical (to my eyes at least) slope to the top in seconds. Brilliant. The fact that they (and their trailers) had been built in a farm shed was also rather amazing.

As far as I am aware, at least one of these home-built marvels is still running, as there are photos of Ro's son, Ben, driving it on the trialling websites, although Ro now uses a more-modern pre-built car for competition (built by Crosslé in Northern Ireland). If my Zero turns out to be anywhere near as much fun to own as one of these, I will be very happy indeed.

Suspension Bushes

I have recently been tackling a job that is both time-consuming and repetitive, but is ultimately rewarding and, for me at least, strangely calming; suspension bushes. Now, there are many discussions online about the correct way that these should or should not be fitted, so the method I ended up using is based on a bit of research and my own judgement and, so far at least, things have gone well.

As this build diary is potentially a future reference to others, I thought I would start with a basic guide to bushes and the type of bushes used on the zero, as researching this was very useful for me in the first place.

A suspension bush, fundamentally, allows a wishbone to pivot around a given point, in this case a bolt through the chassis, and therefore move freely up and down in the way suspension should (it's basically a hinge, see diagram below). They also provide a certain amount of isolation from vibration that would be transferred into the chassis from the road, the amount of which is defined by the material used in their construction.

Wishbone

GBS Supplied Bush

The bushes supplied by GBS are of a nylon type, harder than the polyurethane (poly) bushes many people upgrade their sporty road cars to and much, much harder than the metalastic (rubber) bushes used on standard road cars. The major benefit of these is, due to their stiffness, there is little to no movement in any plane other than the one intended (i.e. up and down), which is exactly what is required in a precision fast road/ race car. Another benefit is that nylon doesn't add any "rate" to the suspension, unlike rubber and some poly bushes which deform under load and act like little springs of their own. This make suspension set-up more accurate and predictable. The downsides are an increase in noise and driver discomfort, as vibrations will pass more readily from the suspension arms, through the bush and into the chassis.

Nylon Bush Diagram

The construction of this type of bush is very simple. Two nylon "top hats" are inserted into the wishbone's end, one each side, and a steel crush tube is inserted into the hole through them. Whilst in place, the crush tube remains stationary, held tight by the wishbone mounting bracket, and the nylon insert rotates around it, itself held tight to the inside of the wishbone end by friction. The ends of the nylon bush are in light contact with the mounting bracket, but only with enough pressure to prevent any lateral movement as any more would cause "stiction", which can lead to differing suspension rates on each corner, the amount of which being dependent on how much each bush was being retarded.

My method began by prepping the wishbones. Before the bushes could be inserted, each end needed to be nice and smooth internally. Unfortunately, each one contained a weld line that needed to be ground down and because I have had the chassis powder-coated, the residue from this process also needed to be removed. I happened to have the perfect size grinding stone attachment which took care of the weld and I bought a drum sanding attachment to sort out the powder coating. I also used the sanding drum to make a slight chamfer on the inner edges of the wishbone's end, just to make sure the bush didn't catch on anything.

Tools Used

Sanding Down

The bushes themselves needed a little work before they could be inserted. As they had come straight out of the mold they all had rough edges to one extent or another, with most of them fouling the crush tubes. A little time with a sharp knife or a round file sorted that out. Actually inserting them in the wishbones ended up being much easier than I thought; each bush was lubricated with copper grease, placed in position, and then both sides were slowly wound in with a nut and bolt and some large washers to spread the load. Even if they started slightly wonky, they pulled themselves true as they were tightened up. I don't know if it helped that the wishbones were still warm from the sanding, but I made sure I didn't let them cool too much first.

Inserting Bushes

Nylon In

At this point, I couldn't just stick the crush tubes in and be done with it, as each finished bush was a slightly different width to all the others and the tubes needed to be a spot-on fit. The best advise I found was for each tube to protrude out of the nylon by between 0.1mm and 0.2mm each end, enough for the tube to be clamped by the bracket, but not too much to allow side-to-side movement. My ruler was clearly not up to this level of precision, so I bought a set of Vernier callipers from eBay and got measuring. Santa was also very kind this year and bought me a bench grinder with a sanding belt attachment, which was perfect for slowly grinding down the tubes with a nice flat end. Once prepared, each tube was covered in copper grease and inserted into the bush (I basically ending up covering every mating surface with grease), which was then mounted to the chassis. Each joint requires large washers between the nylon and the bracket, with a couple of them requiring 2 on one side, as the brackets didn't seem to line up quite right (a bit of persuasion with a ratchet strap helped with that). All the bolts (which were also covered in copper grease, notice a pattern?) were the correct length, with none of them touching any other part of the chassis (which would be an IVA fail) and with at least 2 threads showing through the nyloc bolt (also an IVA requirement).

Careful Measurement

All Done

It's also worth noting that the bolts here, and indeed throughout the whole car, have to be high tensile. A metric high tensile bolt is stamped with a steel rating on its end, with 8.8 being the lowest grade considered high tensile, increasing in strength to 9.8, 10.9, 12.9 and beyond. The first digit is its minimum tensile strength divided by 100, so 800 MPa for an 8.8 bolt. The second number signifies that the bolt will begin to yield at, in the case of the 8.8 bolt again, 80% of the ultimate tensile strength, i.e. at least 640MPa. Imperial and stainless bolts are marked with a different system and, again, there are minimum grades of strength that are classed as high tensile.

That wasn't so hard was it? 1 down, 25 to go (if you include the pedals)!

The above diagrams were borrowed from an excellent post on the Westfield Sports Car Club forum, I'm hoping Frosty doesn't mind my use of them.

Ow

"Daddy hurt himself, but I've fixed it for him now." I clearly don't know my own strength!

Differential In & New Parts!

I reached a milestone today with the permanent installation of the first part, the differential. Due to the fact that the MX-5 diff' was never designed to have it's mounting arms hacked off by some muppet in a garage and then forced into a completely different type of chassis, some fabrication was necessary. The diff' is mounted with 3 bolts along the top and 3 more underneath at the front, unfortunately the top is not flat and cannot therefore just be bolted directly to the straight beam it needs to be suspended from. I've seen some solutions to this online; some people have built up the required height with washers (although this looks a bit temporary and is now frowned upon by the IVA testers) and some have mentioned that you can grind the top down enough to sit flat, but I've also heard mention that different models of MX-5 have different differentials which have a different shape to their support bar, some having a more pronounced curve than others. I decided to manufacture some solid spacers and paint them to match the chassis. To meet IVA regs, any spacer must be the same internal diameter as the bolt that is supposed to go through it, so I found some 10mm internal/ 16mm external bar online and used that. Cutting the spacers to match the shape of the diff' required some fettling (alright, a lot of fettling), but I think the results are worth it.

One of the bolt holes on the front of the diff' has a shroud that is mounted right through the body of the unit (this actually stuck out the top originally and needed some "persuading" to sit flush) and the other doesn't, so I used some more spacer bar, sprayed silver, to make another, just so it matched. I think the result looks decent enough.

Some more good news came in the form of the last of the parts I was waiting on from GBS, which included the modified prop shaft and drive shafts, steering wheel and boss, handbrake cable, some wiring looms, seatbelts, the ECU, the shock absorbers and a few other small items.

I've spent the remainder of my time recently inserting suspension bushes into wishbones, which is time consuming (there are 24 of them in the suspension and 3 in the pedals) but satisfying. I'll post something about them when I start assembling the suspension.