Distributor Cover Crack Can Cause Engine Misfiring. (I&T's Maintenance & Repair).

Q We have several regular customers who do their own minor maintenance and minor repairs, but call on us for more major maintenance items or repairs -- or when they can't determine the cause of their current problem. We have one such situation in which a late model gasoline-engine tractor (that we sold new) sporadically misfires, and at other times operates normally. We have made all the usual checks related to the three basic requirements of compression, fuel and ignition, all without locating the cause of the problem. Any thoughts on this?

A Based on the more-detailed information included in your Email letter, it sounds as though there may be a fine, hairline crack in the distributor over. Such a crack can eventually fill with debris which, when it absorbs just enough atmospheric moisture, can short out the high-voltage side of the ignition system. Then when the debris dries, it permits the system to resume normal operation. If upon inspection, this appears to be the problem, installation of a new cover should restore normal engine performance.

Melvin Long's career included new-product development for John Deere and hands-on management of a family farm. Now retired, he continues to tackle technically-oriented projects, including publication of a book on hydraulic system diagnostics.