Rusty Spark Plugs

[wetandwindy2]

so am down to the last few jobs on my mk2 2.8 ghia auto,engine has a small misfire so decided to change the spark plugs but they are well rusted in how do i get them out without breaking ,i thought soak them for a day in wd40( is there a better penetrating oil ) and then take it up to temp and try and slowly try to crack them open or has anybody got a better idea.I had the the car at a mechanic friend and he didnt want to touch for fear of breaking them

 

cheers Iain

[insanitybeard]

I think it's unlikely that the plugs are rusted in because they seat in an aluminium cylinder head, more likely a combination of heat and differential corrosion has caused them to become very tight. Are the exposed parts of the spark plugs you can see rusty? As you say your best bet is going to be to soak 'em in penetrating oil for a bit and then warm up the engine, probably a few times if necessary to allow the oil to soak in fully. You could even try some freeze spray and alternate between warming them and cooling them, hopefully with persistence they will eventually loosen up.

[seatkid]

i thought soak them for a day in wd40( is there a better penetrating oil ) and then take it up to temp and try and slowly try to crack them open or has anybody got a better idea

 

 

Wd40 is very very poor, not at all much of a penetrating oil. My favourite is toolstation's tectane MOS2 penetrating oil

 

http://www.toolstation.com/shop/Automotive/Lubricants%20&%20Sprays/Penetrating%20Oil/d60/sd2795/p62311

 

Although I've never used it, people are always recommending PlusGas as the ultimate penetrating oil.

 

Your plugs have probably been overtightened. I doubt penetrating oil will reach the threads. I would use a good fitting plug socket and give a couple of knocks with my hands via a suitable long bar/handle in the unscrewing direction, to try and initially crack them.

Edited February 19, 2014 by seatkid

[BigDog]

Get some proper penetrating oil ideally containing graphite (e.g.Plus Gas as Seatkid says). But I would want to try and blow out any crap with compressed air (especially grit) that is sitting around the plug first. That way the crap doesn't end up inside your cyclinders when it washes down with penetrating oil.

When a plug first moves, stop and tighten it a little then loosen/tighten/ loosen in little steps. There will probably be some hard carbon deposits on the first threads and these need to be gently broken up otherwise if you just carry on loosening in one go then there is a likelyhood of the plug becoming difficult to turn again and damaging the thread in the head on the way out. Be sure to use a good quality plug socket and breaker bar, and two hands so the socket stays straight.

Remember the plugs make a high pressure gas-tight seal to the cylinder head. There is no chance of penetrating oil getting down into the threads until the seal lifts a little. I would be inclined to:

 

1) Use an air line to blow the crap away from each plug

 

2) Apply penetrating oil around each plug

 

3) "Crack" each plug (meaning get it to JUST moves) and work it in tiny little steps of a few degrees until you have loosened 1/4 turn or so.

 

4) Leave the penetrating oil to do its job a few hours, longer if you can.

 

5) Apply more penetrating oil and carry on loosening and tightening in little steps.

 

6) If a plug becomes harder to loosen, then stop and tighten it again, apply more oil and try loosening / tightening again in steps.

 

If a thread is damaged then it may be possible to get it fitted with a Helicoil insert rather then a new head.

Don't get your HT leads confused - number then with Tippex or similar.

I used to use copper grease on spark plug threads to try and prevent this problem from recurring but I think winding the plugs in and out every 5000 miles is the best way.

Matt

Edited February 19, 2014 by BigDog

[wetandwindy2]

thanks for the advice guys will try them once am fit and healthy again