Heli-Coil repair job was only tip of the iceberg

Dear Tom and Ray: I have a 2004 Chevrolet Suburban with a six-litre, V-8 engine. It blew out the No. 5 spark plug. I took the car to a Chevy dealer, who put in a Heli-Coil as a repair. Within 1,000 miles (1,600 kilometres) of driving, it blew out both the plug and the Heli-Coil. What are we doing wrong?

— Ken

Tom: You’re not doing anything wrong, Ken. But don’t be surprised if your next fortune cookie says “Time for a new cylinder head.”

Ray: When the threads in your cylinder head get stripped and a spark plug blows out, a Heli-Coil sometimes can save the day.

Tom: The Heli-Coil is basically an insert. It’s bigger than the original spark plug; so you screw the Heli-Coil into the cylinder head, and then the spark plug screws into the Heli-Coil. Got it?

Ray: But it doesn’t always work. Sometimes the hole is badly damaged to begin with, or sometimes, because of the design of the engine, it’s difficult to get good access to the affected cylinder. Or sometimes the mechanic screws it up. It’s a tricky job.

Tom: What the dealer did wrong was that he neglected to warn you that the repair might fail.

Ray: Now that it has, you probably need to have your cylinder head sent out and repaired, if possible. If it can’t be repaired, you’ll need a new cylinder head, which probably will cost you a good $1,500.

Tom: Before you drop that much on this vehicle, have the rest of the truck thoroughly checked out first. Make sure you’re not about to need a ring job or a new transmission, too, before you invest in a cylinder head.

Ray: But if the Suburban is otherwise in good shape, and you want to keep it for some more years, you should start cylinder-head shopping. Or get used to the sound of a V-7 engine. Sorry for the gloomy news, Ken.