Monday, 19 November 2012

Slowly but surely

Holiday, other commitments and a short spell off due to injury means it been a while since there was any reportable progress on the Cobra, but I have still managed to keep some things ticking along.

I have progressed the intake manifold design where the major elements are at least in place in the CAD model. There is still some detailing to be done, but I believe there is enough in the scheme to suggest that the basic layout will work. 

One area of concern I identified was around the thermostat housing neck as on the model, it looked a little too close to the alternator tensioner. Since it would be a while before the lower intake manifold (to which the water neck is bolted) is manufactured and to gain some confidence in that the elements of the CAD model bore some semblance to reality, I decided to manufacture a mock-up plate. 

This is bolted to the cylinder head but provides the opening that the manifold would, including the fixing positions and sure enough, there was a clash. 

At least I know this bit of the CAD model is reasonable! I have since found an alternative water neck and all seems well now.

Other, more tangible progress has involved the assembly of the rear axle. I completed the hub assembly by fitting the drive shafts and these are a simple matter of bolting up the to the inboard brake discs. With these in place, I can start to look at rear wheel geometry (camber and toe). An initial assessment indicates that I will have to modify the shim arrangement already in place, but from other blogs, there is a knack it does not seem to be too onerous a task.

 I also collected the steering rack and mounts from the kit manufacturer and mocked these up at the front of the chassis. The arms on the rack are too long so will have to be ‘adjusted’ (read set about with a hack saw) to allow the proper toe adjustment. I am also not too keen on the provided mounting straps so I will probably end up making replacement billet versions. I also collected the radiator (bespoke for this car) in the same trip to allow me to add the proper inlet and outlet positions to the CAD model for routing the cooling pipes as well as consider methods for mounting the fan.

Once the steering rack has been modified, I can look to carry out the initial wheel alignment - camber, castor and toe at the front along with camber and toe at the rear. I say initial as the full weight of the car on the wheels will tweak the settings, but it should get me quite close.

Tuesday, 28 August 2012

Let the games begin

A bumper update this week thanks to the long weekend. Since receiving the chassis and borrowing a spare bonnet from the kit manufacturer, I have been working away at creating a CAD model. This was finished up to the necessary level ahead of the weekend so I could break out the tools and start building!

The build manual recommends assembling the rear axle off the chassis, then lowering the framework around it. This seemed like a sensible approach, so I made it the first task as manoeuvring a bare chassis sounded easier than moving a partially assembled one. The rear axle is straight out of the donor Jaguar with the lower wishbones pivoted off the differential. This means that the pivot mounting brackets determine the toe and thrust of the rear wheels and have to be carefully aligned with shims. The brackets that hold the assembly into the chassis are drilled to provide the correct alignment (in theory), so I set about mocking up the pivots to determine the correct shims. I will still have to measure the alignment when the axle is complete to finally check the toe and thrust measurements, but this should give me a good start. 

With the shims established, I could fix the lower pivot brackets and make my first attempt at lockwiring the bolt heads, which proved easier than anticipated (when you wrap the wire the correct way around the bolt head!).

 The rest of the rear axle assembly continued as per the Haynes (Chilton) manual including shimming of the rear brake discs (rotors) to centralise them in the callipers and assembly of the rear brake callipers. The assembly of the inner pivot tubes proved to be fun thanks to the multitude of spacers, thrust washers and seal retainers, but the liberal application of grease held everything together long enough to assemble the pivot shaft without a pile of bits on the floor!

At this stage, the driveshafts and rear uprights would be fitted, but as I am still waiting on parts to complete their assembly, I moved on to fitting what I had to the chassis. This was simply a case of lowering the rear of the frame over the assembly and fitting 8 bolts.

With the rear assembly as complete as I could make it, I moved onto preparation for engine installation. This involved fitting the two fuel lines (feed and return for the injection system) along with the brake pipes. The fuel lines were installed using brackets I designed and a work colleague machined for me (thanks Colin), held in with rivnuts. 

The brake lines use a series of push-in clips and these (along with the fuel line clamps) have to be spaced to provide sufficient support as this is inspected at the Individual Vehicle Approval (IVA) test. Most of the fitting was relatively straightforward, however the front brake pipe proved more challenging due to the tortuous route under the engine mounting bracket. Two sore thumbs later and I was ready to fit the engine and gearbox assembly.

The chassis design allows for excellent access for this job and the only hindrance was a lack of manoeuvring space for the engine crane. It turned out to be easier to lift the engine up and slide the chassis under it before rolling the crane (and engine) into place. The engine mounts were bolted into place and the powertrain was in its new home. The gearbox tail housing is currently sat on a piece of wood until I can fabricate the rear mounting bracket.

With the engine installed, I was able to turn my attention to the front suspension. As per the rear axle, this is lifted straight from the Jaguar donor and bolts up to the chassis in the same way. The only real deviation is the bespoke steering arm to suit the new rack as well at the omission of the various shields. This concluded my weekend of construction – not bad for a few days work!

There is still some work to complete the front suspension assembly – making up a new pair of rigid brake pipes from the calliper to the flexible hose as well as setting up the front angles – camber, castor and toe. The geometry will be much easier to work on when I have the steering rack so this will have to wait for suitable funds! At least I can amuse myself with designing the intake system in the mean time.

Monday, 6 August 2012

Here's Chassis!

Big news – the chassis has finally arrived! Some last minute issues with the powder coating meant that is had to be stripped and re-applied twice and readiness for this Saturday’s collection was looking doubtful, but the sub contractor managed to finish it just in time.

I arrived at Gardner Douglas just as Andy was fitting the last of the rivnuts so timing was impeccable in the end. Andy was also good enough to lend me some donor Jaguar wheels to get me rolling in advance of the proper Halibrand replicas being purchased. I was also able to borrow a spare bonnet (‘hood’ to subscribers across the pond) for digitising into the computer to help with the induction system design. Not much else to say really – I am itching to start assembling the donor parts onto the chassis, but first job is to create a reasonably accurate CAD model of it to allow (in the first instance) the exhaust design to be carried out.

Monday, 30 July 2012

Donor Rebuild Part 3

Chassis collection is now less than a week away, so I have been concentrating on the donor component rebuild in preparation. The lower rear wishbone has two pairs of needle roller bearings for the inner pivot and these are a light press-fit into the respective bores. The gap between each pair is to allow for a grease fitting on the outside to be used during servicing and a sleeve is used to provide the running surface.

The final job on the rear uprights is the installation of the wheel bearings. As per other parts of the original car, the bearing clearance is controlled with spacers. In this case, the bearing has to be pressed into place with a known thickness spacer and the clearance measured. The target clearance can then be achieved by selecting a slightly thinner spacer of the correct thickness. The final bearing clearance is achieved by installing the driveshaft through the middle with the correct spacer in place and fully tightening the hub nut. Before this can be carried out though, the inner seal needs to be pressed in place.

Monday, 16 July 2012

Donor Rebuild Part 2 - pivots

The big new is that I finally have a completion date of the chassis which will be ready by the end of this month. The donor brakes and differential are back from reconditioning and I am progressing the rebuild of the suspension components. To this end, I have been working on the lower front wishbones and fitted the replacement bushes

In addition, I have assembled the lower pivots on the rear uprights. This is a particularly involved process as there are two taper roller bearings which must be shimmed to achieve the required endfloat. This involves a dry build with a known thickness of shim pack in place and then the float of the bearings measured. Shims can then be removed to achieve the required clearance on the bearings. It then has to be dismantled to allow final assembly with the bearings packed with grease and the outer seals to be fitted. These are very ‘old school’ where a ring of felt material is used – this has to be soaked in engine oil for at least 24 hours to ‘load’ it with lubrication before a very messy installation. Still, this is now completed and it is all held together with a temporary retainer because the lower pivot shaft does the job in the final assembly, but this can only be fitted on the car.

One last job remains on the rear uprights with setting the bearing clearances for the output flange. This has required a specific bit of tooling to be manufactured, but fortunately, I have access to a lathe to allow this. There is still some assembly, checking and shimming required on the differential which centres the brake discs in the callipers and sets the rear suspension geometry (camber and toe) however, this is more easily carried out as the parts are assembled to the chassis. Bring on the end of the month!

Monday, 28 May 2012

Donor Rebuild Part 1

With the chassis on order as well as the differential and brakes out for reconditioning, I have turned my attention to the suspension components. I cleaned and painted these some time ago before putting them into storage and now was the time to dust them off and start reassembly. Every serviceable part (bearings, bushes seals etc.) is being replaced so after wading through various Jaguar parts catalogues, I have procured the vast majority of required components. No doubt shortfalls will be found as I progress, but I have at least been able to make a start:

First up are the drive shafts (which also double as the upper rear 'wishbones'). These are each a 3-piece affair with universal joints connecting each section

Next up, the front uprights. When I originally disassembled these, the stub shafts were quite badly worn at the wheel bearing locations, so new ones were purchased

The front hubs get new bearings and seals along with replacement dust shields for good measure

Finally, for this update, the front upper wishbones. I have chosen to go with polyurethane bushes to replace the original rubber items from Jaguar. There is some contention on the use of these on the Cobra Club forum, but the majority of people use them, so I figure its a good starting point and it is not too onerous to replace them after the vehicle is up and running (if that ever happens!)

Tuesday, 8 May 2012

Stoneleigh 2012

Taking a break from the build (not that I have a lot from which to take a break!) I took a trip to one of the biggest kit car shows of the year. It gave me a good opportunity to look around a large number of other people's Cobras to get a better feel for some of the detail options and overall look that can be achieved starting with substantially the same shape.

There were also a few other vehicles that caught my eye. Maybe one day...