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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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Dear Tom and Ray: 

Can one have too hot an ignition spark? There are several aftermarket ignition systems available for older car engines, most claiming to produce more voltage than stock systems. But can you overdo it? Will too hot a spark wear out the spark plugs faster or cause any other problems? — Clyde 

RAY: It will wear out your spark plugs faster, Clyde. It'll also wear out the other parts of the secondary ignition system faster – the plug wires, rotor, distributor, etc. So you'll be buying new ignition parts more often, but it won't do any permanent damage to your engine. 

TOM: The idea is that a higher-voltage (or “hotter”) spark will do a better job of burning all of the fuel in the cylinders. And technically, that's true. But in reality, it only really helps if you suffer from excessive turbulence in your combustion chambers. 

RAY: My brother suffers from that, and we've been trying antacids ... with no luck so far. 

TOM: Turbulence inside the cylinders increases as the engine speed increases. And if your spark is not hot enough, the swirling gasoline-and-air mixture can blow out a weak spark, causing an occasional "miss" or "stutter" at high speeds. 

RAY: But if you're not experiencing that problem, you probably won't notice the difference a hotter spark makes. 

TOM: Of course, you're welcome to install a hotter ignition system anyway, Clyde. You won't do any harm. But let us know in advance so we can invest in some auto-parts stocks.  

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