A tree fell on my tractor...

Dear Car Talk

Dear Car Talk | Aug 01, 1990

Dear Tom and Ray:

I have a 1976 International Harvester tractor that I use for general farm purposes. About eighteen months ago I made a miscalculation in felling a tree which landed across the middle of the tractor's hood. The only damage I could see was a big dent in the hood which I straightened out. However, ever since then, the tractor has run terribly. The number four cylinder doesn't seem to fire, and gas seems to be mixing with the oil. I have replaced the spark plugs, wires, condenser, coil, and points, but none of that has helped. Is it something serious? Do you have any suggestions?

TOM: Well, Ned, it could be something serious. But before you go ahead and rebuild the engine, check the simple things. For example, you don't say that you've changed the distributor cap. If the fallen tree cracked the cap, that could prevent the fourth cylinder from firing.

RAY: When the rotor spins around inside the distributor cap, it spins past each of the spark plug wires. As it passes each wire, it sends electricity through that wire to a spark plug.

TOM: But if the cap is cracked, grease and moisture build up around the crack, and create a conductor that "steals" the electricity intended for the spark plug. When that happens, the cylinder doesn't fire, the engine runs lousy, and at least some of the raw, unburned gas left in that cylinder seeps past the rings and down into the oil.

RAY: A massive vacuum leak near the fourth cylinder could cause the same symptoms. So you might check to make sure a vacuum hose wasn't knocked off when the tree fell. It may be something that simple, Ned.

TOM: We're confident that you'll fix the tractor, Ned. What worries us is your forestry skills. We'd feel better if you signed up for one of the Click and Clack seven-day advanced tree-felling seminars. If the seminar is too expensive, then at least take the one day Click and Clack mini-course in strategic tractor parking.

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