An engine in a sticky situation: Dealing with a stuck spark plug
- Article by: PAUL BRAND
- July 22, 2011 - 3:51 PM
Q I recently took my '02 Chrysler minivan in for 100,000-mile service and was told that one of the spark plugs would not come out of the cylinder head. The shop tried, but it would only come out so far. Rather than force the plug out, they just screwed it back in place and replaced the other five spark plugs. The van is running fine but what happens if the old spark plug goes bad? Is it OK to do nothing, or should I pursue having it replaced?
A Welcome to the world of steel-bodied spark plugs and aluminum cylinder heads. It's not uncommon for high mileage spark plugs to stick in alloy cylinder heads. The dissimilar metals screwed tightly together create an environment prone to corrosion. That's why I always remove spark plugs at about 30,000 miles, apply an anti-seize compound to the threads and reinstall them. This assures they'll come out cleanly for replacement at 100,000 miles.
At this point, you have two choices. First, leave well enough alone -- at least until the stuck plug begins to create driveability problems and misfires. Or have a shop remove the stuck plug, then clean and repair the threads in the cylinder head. Several tools and parts are designed for specifically this purpose. If the threads in the head are not pulled out or completely destroyed, a thread "chaser" may restore the threads by "rolling" them back into shape adequately enough to accept a new spark plug. The chaser does not cut any metal, so there's less chance of debris falling into the cylinder.
If the threads are significantly damaged and unsalvageable, a threaded insert like a Heli-Coil can be installed in the spark plug hole. Terry Frost, owner of Block Head Engine Machining in Crystal, recommends removing the cylinder head to prevent metallic debris from failing inside the engine when re-taping the spark plug hole for the insert. Frost says that this procedure can be done with the cylinder head in place, although there is some risk of debris falling into the cylinder. But he tells me the risk can be minimized by blowing any debris out of the spark plug well before removing the old plug, and greasing the insert tap before cutting new threads. The grease will catch and hold most of the debris.
By the way, Frost also suggests a trick that may remove the old spark plug without damage. Apply a good penetrant like Deep Creep and run the engine up to full temperature before trying to unscrew the plug. The aluminum cylinder head will expand more than the steel body of the spark plug. If you're lucky, the plug may come out without significant damage to the threads in the cylinder head.
Q I recently had my low-mileage 2006 Buick Lucerne serviced. On the inspection report, the comment was "right front outer tie rod loose." I suspect that it may have been the result of potholes. Should I forget it or get it repaired?
A Have it checked by a second shop. Or check it yourself. With a floor jack lifting the RF suspension and the wheel/tire off the ground -- and a jack stand securing the chassis -- grab the tire at the 9 and 3 positions (like on a clock) with both gloved hands and try to push and pull the tire in and out. If you feel movement, try placing a gloved hand around the outer steering tie rod end and use the other hand -- or a helper -- to push or pull the tire. If the tie rod end is significantly worn, you'll feel a differential movement in your hand between the tie rod end and the steering arm.
If there is identifiable play in the tie rod end, have it replaced and the wheels aligned. And by the way, this is a wear-and-tear component, not something specifically worn or damaged by potholes.
© 2015 Star Tribune