Monday, February 28, 2011

BMW Repair Tips - BMW Spark Plug Damage & Problems

Replace your spark plugs, before this happens to you!

Here is something that recently occurred in our service department on a vehicle that had been driven very few miles. The vehicle is a 1989 635csi with only 75k miles. Due to the low mileage, tune up service intervals were several years apart. The car ran exceptionally well, which almost made the owner postpone the service awhile longer. However knowing that rubber components like hoses and belts would dry rot over time we felt a full service was well overdue.
When removing the spark plugs, we met resistance on the number 2 plug and the plug broke off in the cylinder head. What had occurred is the threaded portion of the spark plug has not been coated with anti-seize and over a period of time fused the steel portion of the spark plug to the aluminum cylinder head. I have always been a little skeptical of BMW?s long-term service intervals just for this very reason. Having serviced these cars for over 30 years,
I know that there is many things under the hood of a BMW that cannot be detected by a diagnostic tool or the collection of dash warning lights. Rubber components like water and vacuum hoses and belts will dry rot in dryer climates. Remember if your wiper blades inserts are falling apart every 6 months, the same could be happening to the water hoses. Even tires will suffer sidewall cracks over time.
The situation on the spark plug breaking ended up working out. After the spark plugs' threaded lower portion sheared from the hex drive upper portion our technicians used a #EX5 Easyout to removed the piece without any damage to the threads or having any debris fall into the engine. (Easyout is a brand name for a bolt extraction tool) The size listed is required for all single cam engines, which use the 14mm spark plugs. If the threads on this vehicle would have been damaged it would have certainly required removing the cylinder head.
Don't take a chance: Replace your spark plugs once a year using a dab of anti-seize on the threads. Torque them to the recommended specs. On the box, or in your Bentley repair manual. This also give you a chance to inspect the electrodes and see how each cylinder is burning. A wet spark plug could mean a leaky fuel injector. An oil fowled plug would indicate potential internal problems. For an illustrations and descriptions of different types of spark plug failures, you can download this great PDF from Bosch's website.

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