Spark Plugs Stuck, Corroded Dissimilar Metals
06-27-2017, 02:40 PM
#1
Junior Member
Thread Starter
Spark Plugs Stuck, Corroded Dissimilar Metals
Hey friends,
Recently I was trying to change the spark plugs on my 2005 S55 AMG. I had planned on doing it myself but had a gut feeling I was going to screw something up horribly while removing the coil packs so aborted mission. I sent it to my mechanic to change them for me instead. Today he informed me that the plugs were stuck in the cylinder heads, he had managed to get 3 of them out but it had taken twice the specified amount of torque to do so (I think he said 25 either ft/lbs or nm is specification, and he was using 50-55 to get them out). He didn't want to continue removing them as he felt that he was going to snap a plug or strip the threads.
He told me that most likely since the plugs had been in the car for 100k miles that it was common the steel housing of the plugs had micro-welded itself to the aluminum cylinder heads via corrosion of dissimilar metals. I looked this up and verified that yes, this is an actual problem.
The only solution I found other than removing the cylinder heads was:
1) Warm the engine and spray the plugs with a CO2 based fire extinguisher through an inverted funnel basically freezing the plug like you would a lock you wanted to break. The idea is the aluminum expands faster and more than steel when heated and thus you will be able to get the plugs out when this process creates a size difference. Apparently this is a standard procedure that Lycoming, an aviation engine manufacturer, uses.
2) Spray the plugs with a penetrating catalyst like PB Blaster and let it soak on them for a few nights and hope this soaks down into the threads and loosens them up.
The car is currently just under 110k miles so those plugs really need changed, though my mechanic described the ones he managed to remove as "looking good" for whatever that's worth.
Does anyone have any experience with this problem or suggestions for fixing it? Thanks for any help you can provide.
Recently I was trying to change the spark plugs on my 2005 S55 AMG. I had planned on doing it myself but had a gut feeling I was going to screw something up horribly while removing the coil packs so aborted mission. I sent it to my mechanic to change them for me instead. Today he informed me that the plugs were stuck in the cylinder heads, he had managed to get 3 of them out but it had taken twice the specified amount of torque to do so (I think he said 25 either ft/lbs or nm is specification, and he was using 50-55 to get them out). He didn't want to continue removing them as he felt that he was going to snap a plug or strip the threads.
He told me that most likely since the plugs had been in the car for 100k miles that it was common the steel housing of the plugs had micro-welded itself to the aluminum cylinder heads via corrosion of dissimilar metals. I looked this up and verified that yes, this is an actual problem.
The only solution I found other than removing the cylinder heads was:
1) Warm the engine and spray the plugs with a CO2 based fire extinguisher through an inverted funnel basically freezing the plug like you would a lock you wanted to break. The idea is the aluminum expands faster and more than steel when heated and thus you will be able to get the plugs out when this process creates a size difference. Apparently this is a standard procedure that Lycoming, an aviation engine manufacturer, uses.
2) Spray the plugs with a penetrating catalyst like PB Blaster and let it soak on them for a few nights and hope this soaks down into the threads and loosens them up.
The car is currently just under 110k miles so those plugs really need changed, though my mechanic described the ones he managed to remove as "looking good" for whatever that's worth.
Does anyone have any experience with this problem or suggestions for fixing it? Thanks for any help you can provide.
06-27-2017, 03:20 PM
#2
Senior Member
Try a little Kroil in the plug wells overnight then just torque them out. When I had to change my plugs during a coil pack replacement, several people said not to use anti-seize in the M275 V12 engine because it wasn't called for in WIS. But your story above is the perfect example why I believe any dissimilar metals in high temp areas such as spark plugs and cylinder heads would benefit from a light coating of anti-seize.
