I was attempting to change my plugs today. I started with the driver front and it will not budge. I was afraid of stripping it out. I know these cars have aluminum heads. Should I try again and use extreme force, or should I let the shop do it? They said they would change them for $20. (labor). Plugs cost me $20, so I would have $40 in this task if I get them to change.

I think the plugs are original. It is ludicrus.

For $20, let them get dirty!!!

__________________
1988 W126 420 SE

beware of fundamentalists!

LOL. Yeah, but the negative is that he cannot do it until Friday and knowing them, they will have it until Monday. They have done me like that in the past. I will take something in on Friday morning, then they get to working on other cars, then mine sets there all weekend, as does everyone elses. Since this is a "quick" repair, I guess they may get it done fast.

I feel like a fool, because they are ridiculously easy to get to, yet I still cannot change them myself. I do not know why there are in there so tightly. I may try again tomorrow and hope I do not damage the heads.

Try to remove them with the engine hot.

I prefer changing plugs with the engine cold. If room temperature plugs are installed and torqued to spec on a hot engine the aluminum head will shrink as the engine cools and the plug heats up and expands, which will combine to increase the head's grip on the plug, especially with taper seat plugs.

If you can get them out, let the engine cool to near room temperature. Then install the new plugs and torque them to the minimum spec using a torquewrench and the published spec range. It may be in your owner's manual. The spec is in my owner's manual - 10-20 NM (7-15 lb-ft) for the M103 taper seat plugs. Look in the index under "spark plugs".

For stuck plugs it's best to use a T-handle and apply equal force to each side, so you don't place a bending moment on the plug, which can break off the insulator. If you use a conventional breaker bar, support the pivot point with your free hand to mininmize the bending load that you place on the plug.

Also, use a large 1/2" drive T-handle or breaker bar and put a shock load on it - like an impact wrench. A shock load is more likely to break the plug loose than a steadily increasing pull.

Duke

Thanks. Well, the engine was rather warm, but not "hot" when I tried to remove it. I did not even attempt the others after the first one failed to turn. I used a 1/4 inch ratchet, so perhaps I should use a larger 1/2 inch ratchet? Unfortunately, I do not have a "breaker bar" nor a torque wrench. I have changed plugs in a lot of cars and I have always just got the plugs finger tight, then used the socket/wrench to snug them in- never had any problems doing that.

Thanks for that tip. I am off again tomorrow, so I may give it a whirl again if the weather co-operates. It was 66* today, but 41* forecasted tomorrow, so it may have to wait. Back in the 50s and 60s after tomorrow, then I am not off again until Tuesday. Go figure.

I learned a long time ago that buying the right tools saved way more than their value in damage I created by using the wrong tool, especially when dealing with aluminum engine components. I would never attempt to change spark plugs with 1/4" drive socket components, and I always torque spark plugs to the proper specification. Taper seat plugs, in particular, need to be properly torqued. Many overtorque them which is why they are sometimes tough to remove or take the aluminum head threads with them.

Look up Harbor Freight on the Web and buy some tools including torque wrenches. A lot of their goods are made in China and pros may look down on them from their Snap-On tool boxes, but for the amateur/occasional mechanic you can't beat their value.

Duke

Hello:
I had a simular problem with my 1992 300-E The spark plugs expand with head and cool and will tighten especially if the dealer cranks them down. first always change spark plugs on a cold engine. I used a little Wurth Penitrating oil spray to help loosed the seat the plugs are in. Make sure you you have the right socket for your plugs and use a firm slow preasure keeping the socket and rachet and socket stright not cocked.

I put a little anti seize on the plugs and a dap of dielectric silcone in side the plug boot so they will come off much easy next time.

Take you time :

Happy New Year
Bob Geco

take another week and start soaking with PB Blaster [available at most auto parts stores] Apply 3 or 4 times daily, hot and cold. Will come out easily.