More Rally Cars - Goodwood 2011

Rally Cars - Goodwood 2011

A few rally cars from Goodwood Festival of Speed 2011

String Box

I thought I should post the method I used for setting up the suspension. At the rolling chassis stage I posted some stuff on setting the toe using laser alignment made from a steel ruler, a builders laser level and an assortment of straight metal edges but now the car is complete that is a bit redundant. There was another post here: Correct Ride Height where I just simply state "we string boxed the car" but didn't explain it, so here is how I did it - and continue to use it to make small adjustments.

I first learned this method at university where we had a Formula Student car. We had some fancy corner weight scales and also set the alignment using the string box method. By alignment I mean toe - how much each wheel is pointing "in" (towards the centre of the car) or "out" (away from the centre of the car) compared to the direction of travel, and the relation between each wheel.

All you need is a long bit of string, fishing wire or I use brightly coloured sewing thread, 4 axles stands and a steel rule. This guide will focus on taking the measurements rather than how to adjust it - as that will be specific to this car (although I will write that up too).

1. Camber

Before I get stuck in to measuring the alignment, with a bit of string and a ruler its unbelievably easy to measure the camber. I tied a small washer to the end of the string and taped it to the wing so it falls down the centre line of one of the wheels. This method assumes the body work covers the wheels when viewed from above. Make sure the car is settled. If I've just had it jacked up I sit on the corners then roll it back then forwards to a stop and wedge a wheel with a block of wood. Make sure the steering is centred as even a small amount of steering could pile on camber depending on the geometry.

It's pretty easy really - you take three measurements. Firstly measure the diameter of the wheel rim which in my case is 498mm. Note that the diameter of the edge of the rim will not be the diameter quoted for your wheels (i.e. 18" in this case). 498mm is 19.6 inches. 

Measure the distance from the string to the wheel rim at the top and bottom of the rim. For this wheel in the example this was 12mm at the top and 8mm at the bottom. If the top of the wheel is further away from the string than the bottom of the wheel, then this means that the wheel is leaning (cambered) inwards i.e. negative camber.

With an easy bit of trig you can then say the camber angle = inverse tan(8/498) = -0.46°. Note that the result of the calculation was positive but the top of the wheel tips in towards the centre of the car so this is negative camber. Luckily I have a digital inclinometer to check and this read -0.5°. I did this for all 4 wheels and got the following results:

FL = -0.46°         FR = -0.58°

RL = -0.23°        RR = -0.3°

For the Dax De Dion, the manual says the rear should be zero and the front should be -0.25°. The rear is set by shims which is easy to adjust and when you're done, that's it really. When I first set this up before the first drive to the IVA test, I spent a long time trying to get it perfect but the adjustment required was less than the thickness of a shim , so -0.23° and -0.3° on a target of 0° was about as close as I was going to get. Interestingly I have just referred back to some old posts at the rolling chassis stage here: Alignment and the camber was -0.1° and -0.2° rear left and rear right respectively. It seems that as everything has bedded in and a few spanner checks progressively tightening everything up has increased the camber slightly.

The front is a little harder to set up precisely on the Dax and is more like most road cars. The top of the upright is secured by two bolts in a long slot. To adjust the camber, you loosen the bolts, give the upright a tap so it slides in the slot then tighten up the bolts again. Needless to say, this is a little hit-and-miss and took ABSOLUTELY CHUFFIN AGES to get right and it seems  by the results above that over the last year and 2500 miles this has wandered out a little bit. Looking at my notes I had this at -0.3° front left and -0.35° front right but in normal driving a normal person can't possibly tell the difference between -0.3° and -0.5° camber so I probably wont bother adjusting it right now.

Next - toe measurement.

Intake Manifold Replacement

I admit to being a wuss and booking a garage to refit the intake manifold in order to fix the oil leak under the dizzy, I was quoted 5 hours = couple of hundred quid. I thought this isn't too bad really, already have the parts so I said ok. The bloke at the garage asked who built the car and was surprised when I said self-build and I wanted something as straightforward as a manifold gasket replacing.

That got me thinking and I later rang the garage back to cancel, having decided to do it myself. Armed with knowledge from all corners of the internet I got to work. First job, get some supplies from the kitchen, this could be a 4 cuppa job:

Then jack up the car ready to drain the coolant - its too low to get a bucket under otherwise.

I forgot how much I bloody hate draining the coolant, I always get it everywhere as the only way I can do it is to pull off the bottom rad hose as I my radiator doesn't have a drain plug. Anyway, that done, on with the job - disconnect coolant hoses from the inlet manifold, namely the thermostat and heater connection.

Next, all the connections from the carb. Fuel line, vacuum line, throttle return spring bracket, throttle cable.

Labels on all ignition leads

Note position of rotor

Position of distributor housing, complete with marks from previous distributor removal just to confuse things.

I removed the intake bolts and checked that they are all the same length so didn't have to note where they all came from.

Now remove the intake, the lovely sound of sealant coming unstuck. I had to get a long screwdriver in the front end and gently pry it apart but once the seal started breaking I could lever it up just by getting my hand in the carb inlet hole in the top. Quick look in the engine to see if anything has dropped into the valley, looks ok (paper towels stuffed everywhere immediately after taking this picture)

Here's the manfold with the old gasket stuck on. Its a rubber/metal type with lots of rtv all over. The end with the round hole (dizzy end) is where the leak was. There was no obvious break in the seal (assembled with RTV on the front and rear walls) but the sealant peeled off very easily and was saturated with oil on both sides so clearly the seal had been broken at some stage and once the oil has a small path through then its game over. 

To get to this stage had probably taken about 2 hours but that includes jacking the car up which takes a good 20 mins or so as I've only got one hydraulic jack and one scissor jack to get it on axle stands. I had also stopped for 2 cups of tea. The next stage is probably the most time consuming - cleaning everything.

I started off by going straight in with a stanley blade and most of the rubber gasket came off easily. The RTV bits at each end peeled off in one go but left a very thin film behind that even a blade couldn't remove and I didn't want to get any deep scratches in the machined surface of the manifold. I gave everything a good soaking in brake cleaner and found some fine wet & dry, 360 grit and 1200 grit. I went at it with the 360 and finished with the 1200 and it came up looking nice. One final wipe with brake cleaner on a cloth and half an hour or so later had nice clean gasket surfaces. I stuffed paper towels in all the runners to stop debris getting in then got a hoover with brush attachment to pick up the little flecks of silicone that were stuck to the casting.

The heads on the engine cleaned up nicely just with brake cleaner and a blade, no RTV had been used on the cylinder head side of the old gaskets so it was very easy to clean it up. The china walls front and back of the block did need a bit of 1200 paper just to get the thin film of sealant off. Again paper towels were stuffed everywhere and anywhere to stop dirt and debris spreading.

Got a nice picture of one of the inlet valves, I'd never seen any SBC valves before. I knew they were big but good heavens they are about the same diameter as my cup of tea!

Clean and tidy ready for reassembly.

The replacement gasket I bought was an Edelbrock 7201 which comes with exhaust crossover restrictors (not needed) and a replacement distributor gasket. The instructions recommend gasgacinch on the cylinder head side only, RTV around the water ports (extreme left and right holes on above picture) and RTV on the front and rear block china walls. So that's what I did. I ignored lots of the internet where people have done it differently "for years with no problems" and followed the instructions to the letter.

I painted gasgacinch on the gasket (cylinder head side only - the side without the black silicone bead embedded in the gasket) and on the cylinder head. Gasgacinch only holds the gasket in place for fitting, it doesn't do any sealing so there's no need to ladle it all over like gravy on your sunday roast. Just a thin smear then leave for 5 minutes before mating the gasket to the head.

Top tip here: loosen or even remove the rocker covers. Luckily I dry-fitted the gaskets to make sure everything lined up and the rocker cover gaskets stopped me getting the inlet gaskets in exactly the right place.

The RTV needs to cure for 15 minutes until you can touch it without it sticking to your fingers. Just enough time for a cup of tea and some biscuits.

Then confidently place the manifold down flat and level and don't move it too much once its down. Bolts in and torque tighten to 25lb.ft (34Nm) in two stages starting with the central bolts, then front, then rear. The centre ones are a pig to get to with my torque wrench even with a universal joint on my 1/4 drive.

All that remains is to refit everything that was taken off before.

Tada!

Oh and refill the coolant. I know my cooling system takes exactly 9 litres to halfway up the header tank. On my Dax I have found the best way is to unbolt the header tank and balance it on top of the carb, nice and high to get some rho*g*h going on, then just fill, fill fill, occasionally squeezing the bottom hose (lowest point), you can hear the system burping air. I don't know if this is the same for other cobras as some are plumbed differently. There are no other bleed points in my system apart from the small take-off just after the thermostat housing, which is the highest point of the system.

Filling went ok on this occasion, previously I have started the car with the header cap off if I suspected some air was still inside and let it burp the air locks out that way. Another good way I've found is to pull the heater return hose off which gives a good route for escaping air.

When I eventually found the car keys I started it up, it was a bit reluctant but of course the fuel bowls were completely empty and the inlet tract dry as a bone so after two or three pumps on the throttle then hold the throttle halfway while cranking it finally caught. Through all the escapades with this car I've learned not to worry when smoke billows out the engine bay, this was just a bit of oil on the headers that I dripped on when removing the dizzy, and spilled some coolant too which got burned off. As soon as it idled on its own (no choke of course) which pleasingly was about 15 seconds holding it at 1500rpm, I hopped out and got a torch and had a good look at the front and rear block wall seal. I had cleaned it all up to make it easy to spot new leaks. I've seen a trick with flour to show up leaks but makes a mess so I just relied on my 550 lumen bike light. A careful inspection showed nothing so I went for a drive, 30 miles or so. Got it nice and hot, got the revs up and inspected again with the torch when I got back. No obvious leaks so it looks like its good! I'll keep an eye on it of course but the next job now is to clean up the sump and bellhousing which are covered in oil. I didn't see any point cleaning them until I knew the leak was gone.

Total time from opening the garage door with tools in hand to starting the car and rolling out = 6 hours. If I was to do it again I reckon 4 hours is just about possible.

Longest Drive Ever! (so far)

At the weekend we decided to embark on a 320 mile round trip over two days, 2 1/2 hours and 140 miles each way (plus some extra local mileage at our destination) which is by far the longest journey we've done in the cobra so far. It took about half an hour to settle down and stop tensing up and desperately trying to work out what every small sound was - e.g. driving over a dry twig which snapped so loudly we could hear it over the exhaust made me nearly poo myself that something had fallen off!


We waited and waited for it to stop raining and eventually set off with very wet road. Naomi was brave and drove the first bit, flooring it on a slip road to join traffic was interesting - "slip" road is definitely the right term! The fuel gauge had me worried too, It's never been completely full apart from the IVA and I had forgotten that it doesn't drop in a linear fashion. Full to 1/2 is only about 20 litres so that was gobbled up in the first 70 miles and I was getting quite worried but then the needle barely moved for the next 50 miles. Range on a full tank I reckon is about 240 miles but that's pushing it a bit unless you know exactly where the petrol stations are!

Got into the swing of things but 2 hours on the motorway at 70mph must be reaching anyone's limit of fun in a cobra. We were togged up with ear plugs, hats gloves etc. We swapped drivers halfway but I was definitely ready to jump out and have a cup of tea by the end. Sunday morning was fun though, visited a number of friends and family and gave them all a go in it. I was especially pleased to go for a drive with my grandad who was an AA man for about 40 years and has been in the motor trade all his life. For him to say "not bad" was practically the highlight of my life so far. He nodded in approval as we thumped through the villages in 5th gear 30mph, 900rpm, then did the classic muscle car trick of 0 to a nice round number entirely in top gear.Rest of the journey home was ok. Slow traffic on the A1 southbound in the evening and we were crawling at walking pace for about half an hour, car was fine, fan working well and was actually quite pleasant with the heat wafting up from the footwells to combat the cold as it got dark. MPG for whole weekend was about 17, I reckon I can get a little more out, maybe 18 or 19 but not that bad really considering almost 40 miles or so were "demonstration" miles. The whole journey used about 150-200ml of oil but I know I've got a small leak from just behind the dizzy which is on my winter list to sort out so wasn't really concerned by that, everything is nicely rust proofed by oil now!
Just got to clean it all up and do a few cursory checks: header bolts need snugging down again as I could hear it chattering towards the end of the trip and I suspect the tracking is slightly off after catching a massive pothole.