Is it possible to blow a main seal while changing a timing belt?

Dear Car Talk

Dear Car Talk | Jul 01, 2001

Dear Tom and Ray:

Is my mechanic a crook? I had the timing belt replaced on my 1990 Mitsubishi Eclipse. The morning after I drove it home from the mechanic, I noticed oil pouring out of the car. It turns out that the rear main seal was blown. Is it possible that my mechanic did this while replacing the timing belt, or is it just a coincidence? He says he was working on the opposite side of the engine, and there was no way he could have done this. But I've heard that if you tap too hard on the front, you can blow the rear seal. What's your opinion? -- Jennifer

TOM: It sounds like just an unhappy coincidence, Jennifer. There's really no way he could have blown your rear main seal by changing the timing belt.

RAY: He's right that they're on opposite sides of the engine. The only thing that links the two is the crankshaft, and it's not supposed to move longitudinally more than a fraction of a millimeter. If it does, and tapping it in front pushes out the rear main seal, then your engine was in terrible shape to begin with (not an impossibility on an 11-year-old car).

TOM: So you really can't blame this guy, Jennifer. It's like going to the doctor for a hemorrhoid treatment and complaining later that the doctor gave you a headache. Wait -- that's a bad analogy. That actually happened to my brother once.

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