loose spark plug tops

[martauto]

This could apply to most cars so here we go.
Each time I change or replace the plugs on my 325 (e46 325 cab) the screw on piece on the top on four plugs were loose !!!!
I know for a FACT that I did tighten them up really good each time so can you offer a reason why this should happen please ??

Cheers Mart.

[Tzantushka]

Heat & vibration?

Does strange things to threads...

[ah]

I hope I’ve not made a big mistake every time I’ve serviced my 320i because I’ve always taken the tops off,as the cap won’t push on the plug with the top on.

[boiliebasher]

I hope I’ve not made a big mistake every time I’ve serviced my 320i because I’ve always taken the tops off,as the cap won’t push on the plug with the top on.

Assume you are talking about an E30 320i engine, if so Ive always done the same thing with my m20b25. So don't worry, that makes at least two of us!!!

I believe O.P is referring to an E46 so I think that's an m54 engine? Different setup i.e coil over plug so entirely different ignition system compared to traditional rotor arm, dizzy and HT leads setup seen on the older engines like our m20's

[flybynite]

It is just different plug lead designs, some grip the thread, some grip the screw on cover.

Wouldn't be the first time I put plugs in and then had to unscrew the top because I forgot and couldn't be bothered to take the plugs out and re-torque them. (mainly because I never liked changing plugs in alloy heads)

[martauto]

It`s the M54B25 engine and at least four from six were very loose, strange how this is not the first time this has happened.

Mart.

[Speedtouch]

Yes, they often work loose, though with the high voltage of HT electronic ignition, it won't usually cause any loss of spark at the plug tip. You could try using Loctite or similar to secure them...