"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.

"Let's start at the very beginning...

"... a very good place to start. When you read you begin with A-B-C, when you sing [build a kit car] you begin with D'oh!-F**k-Me". I know it doesn't scan very well, but I'm sure Julie Andrews could make it work, should she decide to quit being a nun and become a mechanic instead.

I really didn't know where to start, so I thought that before I actually tackled anything build-wise, I should clean up as much of the donor parts as possible. The engine looked like it had some bits I could comfortably remove, so the project began with the removal of the alternator, that's simple enough, right? Not when the hinge bolt snaps, with half of it still in the bracket on the engine block. Grrr. The easiest way to remove it, I thought, would be to disassemble the outer cover of the alternator, splitting it in half and allowing it to be removed from the engine. This worked, only after snapping two of the rusted bolts that hold the alternator together. Grrr. All these broken bolts have proved impossible to remove completely, so the alternator cover has been scrapped and I'll decide what to do when I next need the alternator.

Further stripping of the engine allowed me to start tarting up the gearbox, which now looks very pretty:

Along with the gearbox, I've been modifying the differential to fit (after a fair amount of head scratching, wondering why it wasn't going to fit - thank you the internet), cleaning it up, trial fitting it, painting it and inserting new seals. All I now need to do is create some spacers to go between the diff' and the chassis and I can permanently install it. One bit of potential good news that I discovered whilst reading up on MX-5 specs is that the "S" variant of the mk2, of which my donor was, originally came fitted with a limited-slip differential, so I'm hoping this is what I have. I need to find a way of confirming this without dismantling the whole thing.

I've also been slowly dismantling all the other donor parts:

I've got a bit stuck stuck on a couple of bits, such as the brake caliper pistons and the main nut holding the front hubs together, but once my new compressor arrives I can tackle them again with manly power attachments!. One thing I have discovered though, is that the brake master cylinder doesn't fit. It would seem that the chassis is primarily designed around a mk1 and my mk2 cylinder is too big for the hole:

I can either try and grind down the cylinder (as I have had to do slightly on the clutch master), open the hole in the chassis further or source a mk1 cylinder from a breakers yard. I don't think I could cut it down enough without compromising it and I don't really want to wreak the powder-coating on the chassis too much, so I think I'll just buy another and hopefully sell the original on eBay.

Collection!

Well, the time has arrived. 16 weeks after placing my order with GBS, the kit was (mostly) ready for collection! One hire van (which was not really as "long-wheelbased" as I had hoped) and a 3+ hour drive later, we arrived at the factory and got straight on with having a cup of tea. You can't rush these things.

A large part of the Zero was sitting, waiting for me.

Whilst we waited for the busy guys from GBS, I wandered around, took some photos and had a look at the sad looking carcass of my donor car. Poor thing, you could almost see the tears pooling in the empty sockets of it's once bright eyes headlights.

Checking off the parts and loading the van took a good few hours (this is an area I think GBS could do with improving), but we were finally loaded. I didn't have everything though. Whilst walking round the factory I noticed that some built Zeros had excellent-looking louvres in their bonnets, which I didn't know was even an option (another area GBS could improve on), so I left mine behind to have them stamped out. I am also missing a few items such as the propshaft and driveshafts (being modified), the ECU, dials, seatbelts, shock absorbers, the steering column stalks and a few smaller bits such as a couple of wiring looms, seat runners and a hand brake cable. Even without these bits, I have plenty to be getting on with.

When we finally got home, it was too dark to unload, so we left it overnight and started again in the morning. The next day we started emptying the van and filling the garage, which took a while as we had to go and borrow a hoist (cheers Nigel/ Steve) to get the engine and gearbox out, but once done, sorting could begin.

And there I was, standing in my garage, looking at my life savings laid out before me and one thing was patently clear: I have absolutely no idea what I am doing.

Money, money, money

Well, the last couple of days have been expensive! Firstly, I've been playing the head gasket lottery with the venerable Polo for a while now, so I decided to upgrade as soon as something better presented itself, which it did a couple of days ago. I've spared no expense and upgraded to... a Golf, and a T-reg Golf at that, luxury. Remote locking, cassette radio, all mod cons. The same day, I had a call from GBS, to discuss how much I wanted to spend on my donor car, which was something I hadn't really thought about in great detail until now. It turns out MX-5s are pretty excellent value, so I pushed the amount up a bit from "it runs" to "not a complete dog". I've never bought two cars in one day before!

The next day I got another call from the factory to discuss all the other cool bits I want to bolt on. I ended up ordering:

• ATR coilover suspension (awesome, nothing but the best!)
• Team Dynamics gloss black wheels (and tyres, might need those)
• Full weather kit (roof, doors etc)
• A windscreen and mirrors (quite useful)
• Smith dials (with a stainless steel surround)
• Roadster seats (with orange seatbelts)
• Quick release steering boss

The ATR suspension might be a little excessive, but hey, it's orange! Also, the seats I've chosen are not available with orange piping which is why I thought the orange seatbelts might look good. There are a few other items yet to choose, like the front grill, but that can be done closer to the collection date.

Whilst I now sit at the end of my drive, day after day, waiting for the car fairies to deliver me boxes of goodness I need something to read, so I printed out the IVA manual.

That's quite a tome!