The car was running a bit rough at idle, so I pulled the plugs to inspect them and was greeted with this disaster in cylinder 2 (contrast with a good plug). The HT cap descending into the cylinder head was covered in soot and the plug was loose in its hole. Hopefully this indicates whoever changed them last didn’t torque this plug up properly, as opposed to the thread in the head being ruined. New plugs and leads are on order! In the mean time, I’ve refitted one of the old plugs that the previous owner supplied with the car.
Since the last update, I’ve been busy with a whole host of smallish jobs on the car:
- Turret oil
- Central locking
- New tyres
- Wheel alignment
- CAS oil seal replacement
Since picking the car up, I’d noticed a horrible rattle coming from somewhere inside the cabin when accelerating hard. Initially I thought it was a fixing that’d worked loose deep inside the dash, but then I noticed it went away if my hand was resting on the gear lever. Hoping it would be a simple fix, I replaced the knackered old gear knob with a slightly less knackered leather one that’d come spare with the car. This helped for approximately 24 hours, before the noise returned and worse than before. I blamed the gear knob again, as it wasn’t in great condition. Using it as an excuse to order the solid brushed aluminium knob I’d been after, I expectantly replaced the knob again but the noise persisted.
After reading around a bit, I suspected that the oil level in the turret (area of the gearbox where the stick links to the rest of the transmission) was a bit low and so pulled off the gear knob, centre console, top shift boot and the gear stick itself to access it. Turns out, it was only slightly below the correct level. I replaced it anyway, with some 75w-90 gear oil. Removing the old oil was a bit of a faff, I used a turkey baster to suck it out. Luckily the rattling culprit was found - the gear stick itself! It’s a two-part stick, with the top part of gear stick screwing onto a stub attached to the turret. A dab of thread lock and putting everything back together was enough to banish the noise entirely. I ended up driving across town (to buy the thread lock) with no shift boot between the transmission tunnel and the cabin - it was somewhat unpleasant with exhaust-pipe heated air blasting into the car, not to mention the noise of the road.
Next up was remote central locking. I used a forum discount code to get 20% off and saved another £6 on delivery (the business was based 2 minutes’ walk from home!) for a grand total of £30 which got a kit with two pop-up keys and enough solenoids for both doors and the boot. A quick trip to Maplin for some relays for the boot solenoid and hazard flashers and I was ready to go.
The key even had a space for the immobiliser tag, making my keyring even lighter.
The installation was fairly straightforward, but the notorious rubber tubes between the doors and the car body caused no end of trouble. After much cursing and poking and prodding I managed to get the wires through, and then drilled and riveted the solenoids in place in the doors. Spent an infuriating half an hour trying to work out which cable I’d sliced or fuse I’d blown that caused the electric windows to stop working, before realising the window killswitch on the dash had been pushed. Why the frig does a 2-seater need a window killswitch?!
Being upside-down in the footwell wasn’t exactly comfortable or flattering but it was the only way to get the job done.
For the boot release, I used the spare slave solenoid wired up to a relay, and mounted the whole assembly behind the carpet next to the boot catch. Luckily there’s a 12V feed just next to the battery (fuse socket for the electric aerial, which I don’t use) so I wired a 10A fuse in line and connected it up to the relay.
New Tyres/Wheel Alignment
When I got the car the steering was very wandery and difficult to keep in a straight line, especially on the motorway. While I initially thought the problem was incorrect pressure in the front tyres (it was at 34PSI! Correct pressure is 27/28), it was still a bit unsettled on the road even at the correct pressure. In addition to this, the outside edge of the nearside front was wearing at an alarming rate compared to the rest of the tread. Ordered up a couple of Uniroyal RainSport 2s from Black Circles as they have legendary grip in both wet and dry conditions. The rear tyres are cheap Nexens, and while I would prefer to be running the RainSports front and rear, they were fitted by the previous owner in February and thus are in perfect condition. Hopefully the fact that they’re terrible means I’ll get some easy oversteer practice and can replace them sooner rather than later.
After getting the new tyres fitted I took a trip to Avia Autos in Bridgend who did a 4-wheel alignment check. The tracking and camber at the rear was perfect but the front was out by a mile, hence the uncertain steering and uneven tyre wear. After 45 minutes and a quick trip back to get the steering centred, the car felt much more sure of itself on the road. A good blast with the top down around some local B-roads made sure of that.
CAS Oil Seal
The car was slowly losing oil, and it’s not uncommon for the cam angle sensor (CAS) O-ring to fail on MX-5s. The other common failure point is the cam cover gasket. I had a good look and feel around the top of the engine and it felt like the CAS sensor was leaking, but I ordered a new gasket along with the O-ring just in case.
Replacing the O-ring was a 20-minute job. First I undid a couple of bolts and unclipped the CAS wire connector to gain access to the unit, then marked the cam cover and the CAS itself so the ignition timing wasn’t wrong when I put it back. There was an existing blob of Tipp-Ex across the join, but the halves were offset because the engine has previously had the ignition timing advanced to 14°. This is supposed to help with low-end torque, but apparently shows less of an improvement on the 1.8 compared to the 1.6. The engine pulls like a train even from 30MPH in 5th gear, so something is obviously set correctly.
Once I’d made my own marks with a marker, I poked a 12mm spanner carefully down between the brake lines and the aircon pipe and slotted it onto the CAS bolt. It needed a good yank to release it, but it came out easily and I was careful to not drop it down the back of the engine. When the CAS was free to spin on its axis, I made sure it was in the correct position and then slid it straight backwards away from the cylinder head. Doing this instead of rotating it as I pulled allowed me to see the orientation of the lugs that slot into the exhaust camshaft - useful for when I was refitting it. The CAS unit itself needed a bit of encouragement to fit through the narrow between the engine and bulkhead, but once it was free it was a simple task of pulling off the hardened and flat old O-ring and fitting the springy new one.
The gap seemed a lot narrower on the way back in, and I had to remove the dipstick to make room. Once it was in position ready to reinsert into the cylinder head, I realigned the lugs and jiggled the unit back into place. This took a few attempts because there was very little resistance when rotating the CAS lugs so if it wasn’t right first time, it would get worse with every movement. Eventually it snapped home with a satisfying clunk. Then it was just a matter of refitting the bolt and nipping it up just tight enough that I could rotate the CAS to the correct position to align the markings and then tighten the bolt fully. Refitting the previously removed bolts and reconnecting the sensor cable finished the job, and I then topped the oil level to the F mark on the dipstick, where it has since remained. Hopefully this fixes the oil leak, as it was definitely a lot simpler than replacing the cam cover gasket.
The engine was sounding a bit noisy after a drive the other day so I checked the fluids and to my horror found that the oil level was almost off the end of the dipstick. I had some Castrol GTX 10W-40 spare from the Subaru’s last oil change so stuck 1.5L of that in as an interim measure.
Cue a quick Google to find the recommended engine oil grade - only to discover that this appears to be a matter of religious importance amongst MX-5 owners. Some stick with the original Mazda recommendation of 10W-40 from the owner’s manual; some use the updated recommendation of 5W-30, yet others swear by fully synthetic 0W-40. The latter divides opinion further, with some owners claiming it’s a bad idea because it might end up dislodging deposits from the engine which then move and block other parts of the oil passage ways and others saying it is excellent for cold-start protection. In the end I went for Mobil Super 2000 10W-40 semi-synthetic. £24.99 from Halfords, job done. Ordered a genuine Mazda filter and sump plug washer from mx5parts.co.uk, which turned up a day or so later, and I was ready to go.
The oil change itself was fairly straightforward - jack up the front of the car, crack the sump plug (no sign of the old washer anywhere, somebody was lazy…) and let the oil drain, remove the old filter and pre-charge and fit the new one, put the sump plug+washer back in, drop the car, fill with oil, party.
The only slightly niggly part of the job was trying to get the old filter off and fit the new one without making a horrendous mess everywhere. The filter is fitted on the side of the block, directly beneath the inlet manifold. Makes sense because there’s lots of space there, but actually reaching it and getting a good angle to undo it is really fiddly. Luckily it wasn’t on too tight so it came off without much of a fight, although it did drip oil down the side of the engine. A couple of handily-placed rags soaked up most of the spill though.
When fitting the new oil filter, it’s a good idea to pre-soak it with oil so the engine is fully lubricated as soon as possible after the initial start-up. On the Impreza this was a matter of brimming the filter, letting it soak and then brimming it again, as the thing screwed straight into the bottom of the block meaning no inversion and no spilling. However the MX-5’s filter is mounted vertically so a saturated filter will happily dribble oil everywhere at the first opportunity. I poured fresh oil into it a little bit at a time, until the fabric seemed to be saturated but there was no excess oil swimming around inside the filter body. This meant I could turn it on its side without much mess - perfect as getting the filter back through the narrow gap between the strut brace and the inlet manifold was a bit tricky. Before fitting the filter, I ran a bead of oil around the seal so it mated nicely with the engine block.
Anyway, once that was done it was a matter of adding 3L of fresh oil through the filler cap on the rocker cover and then brimming it to the F mark on the dipstick a bit at a time.
Once this was done the engine sounded much, much happier. My fuel economy even went up by a couple of MPG but I suspect that’s unrelated.
The one slightly concerning thing is that the car seems to be going through oil fairly quickly - I suspect there’s a leak somewhere. Chances are it’s the rocker cover gasket or the CAS (cam angle sensor) seal - both are at the top of the engine and there’s some evidence of oily wetness around there.
Something to investigate and fix soon, I think. Not today though, Portal 2’s just been released.