BXProject

I got a call from Lana this morning, about half an hour after she'd set off for work. Telling me she thought there were serious engine problems as it was really loud, rattling/knocking, down on power and the engine management light had come on. My first thought was that she had cracked her sump on the track, lost the oil without noticing the light, and the engine had thrown a rod. But no.

While I was on the way with a tow rope, I gave her a ring and asked her to check the spark plugs. Sure enough, one of them was rattling around in its tube, held loosely in place with the HT lead moulding. I've only known that happen once before, in a mate's Astra (and he was on the way to a scrapyard for a starter motor at the time, so he had to bump start it solo afterwards, down a dual carriageway slip-road )

Screwed the plug back in place, and all was well, apart from the engine light which may well just be flagging a stored fault. Question is, why? I changed them 22k miles and 13 months ago, so if I'd forgotten to tighten them up, surely it would have become apparent before now! And I tighten them all up by hand, then work along in sequence to nip them up more. So if I'd forgotten to tighten them they'd all be loose - I'd hardly miss out just one of the middle plugs. But I just can't see a logical explanation Must admit I didn't use a torque wrench, just nipped them up half a turn to compress the washer. But no different to the many plugs I've changed previously (although I suppose I've never put in long life plugs before and they'd never be in longer than 12k miles or so...)

BMW and ignition systems are like opposites. Most people with 3 series Bimmers at work have to have regular (pencil) coil replacements because there so useless.

I guess it could just be a sloppy thread, remembering the pressure under the plug will perpetually increase and decrease, not to dissimilar to tapping on the bottom with a hammer. Add differing rates of expansion and i suspect the plug might un turn by 100th of a turn on every cold start, 13 months downt he line and the bugger has unscrewed it self! Could try a tiny bit of thread lock i suppose? The high temp one.

Are the plugs washer grips or the smaller thread taper seat?
Funny you mentioned Astra I ran OHC Victors for a few years with taper seat ones. If you fitted Lodge plugs the taper was a midges dick out and they would work loose about every 800 miles

They're the usual crush washers I think (I was certain but now I'm doubting myself!)...am now wondering whether the thread may have been slightly damaged on that one cylinder, so locked up before it was fully tight? Although I'd have expected blow by the threads if that was the case. Either way, they're supposed to last something like 60k miles as they are platinum or iridium tipped so it's unlikely she'll keep the car long enough to require another change. I did copper grease them though just in case!