X-308; Spark plug gap 3.2 litre VIN: ..849979

Hi guys!

I had to pull the spark plugs on this engine yesterday, because I suddenly lost compression - I assume due to cylinder lining ‘wash-down’ - and wanted to squirt some oil into the cylinders to regain compression.

Noticing the plug gap was varying between ca 0.9mm and over 1mm, I started to investigate what the gap should be and found a table showing 1.2 to 1.3mm for my engine (albeit ROW, whereas ‘leaded’ was 1 to 1.1mm).

I set the gap to 1.2mm, and after I had put it all together again, it failed to start… (Compression was back, but it didn’t fire up.)

Does anyone have any insight to share on this, please?

Kind regards,

For the “Inch-heads” among us, that would be: 0.047 and 0.051 respectively for my AJ26 engine.

I had to do the oil in the cylinders trick more than once on my Nikasil 4.0 AJ27. Just to say, after pouring the oil in, it still won’t start on the button in fact my experience was it was still really hard to get it to fire and involved several cranks with the foot hard onto the floor before it lurched into life. Once it had run for a minute (and blown clouds of black smoke out) it was back to business as usual. As for plug gaps - I bought ‘pre-gapped’ plugs and was shocked at how wide the gaps were. Wider than you’d think…

On this engine, I have done this twice now, plus a few times on other engines. I’m surprised you refer to your AJ27 as a nikasil engine; thought that was one of the upgrades between AJ26 and AJ27. I have a Technical Guide introducing the new engine, but it doesn’t say specifically… Will investigate.

Anyway, I got the plugs out again and reset the gaps to 1.0mm and squirted yet a couple of hits of oil from my specially adapted oil can into the cylinders. I also adjusted the Throttle Position Sensor to sharpen the throttle response - disconnecting the battery as appropriate whilst doing so - and when I started the engine (started right up), it revved up really high as it should after the TPS has been “tampered with”, I literally couldn’t see my house for the white(!) smoke! Neighbours looking on terrified! It took a ten minute spirited drive to clear the system of the oil… I was all smiles though, knowing it was alright and the car had started again!


You’re right - white smoke, not black. I have a very poor memory… Actually the first few AJ27 engines were Nikasil and my 99MY car had one. Fortunately it had done almost no miles in its first year of life and after 2000 petrol was low-sulphur so it escaped those problems.

Really glad to hear you’re up and running again.