I saw a search for interference engines on the web the other day. This reminded me that most people don’t really understand what and interference engine is.

To make a long story short and interference engine is one that will have parts interfere with one another when a key component such as a timing belt or chain is broken. Most of the time interference engines are discussed in relation to timing belts. Some of the older V-8 engines were also interference engines for example I remember several of the Ford 351M engines bending valves and push rods when the timing chain failed.

In my opinion the worst type of engine for interference between the valves and the pistons are the dual over head cam engines. Each cylinder head has two cam shafts that are connected by a chain, gears or the timing belt. The worst of these is the engine that has both cams driven by a common belt to the crank shaft.

Most overhead cam diesel engines are interference engines because of the tight space required to produce the compression necessary to ignite the fuel in a diesel engine. The Volkswagen indirect injected diesel engine is a prime example.

If you are going to change timing belts on your engine besure that you have correct information. One of the best sources of information can be found at Alldata.