Normally, I stumble across these trivial thoughts by screwing around on the web because I’m bored. Recently, I’ve been very busy and haven’t really had the time to surf around and stumble. Today, I have a good one that not only did I stumble across, I tripped, fell down and bloodied my nose over it.
Engines: Interference and Non-Interference.
The simple explination: When the timing belt breaks on a non-interference design, the pistons and valves don’t collide because there is enough clearance between the two.
On an interference engine there is insufficient clearance between those parts. A broken timing belt results in open valves being struck by the top of the pistons and major engine damage. Most likely, replacing the engine.
According to the lists I saw, Nissan and Isuzu (my 2 cars) don’t make a Non-Interference engine. Most of the lists I saw showed that a little more than half of the domestics and a vast majority of the foreigns are interference types.
Now we run into the “why”. Why aren’t all engines non-interference if the damage can be so catastrophic?
It has to do with (surprise!) manufacturing costs. But, efficiency also plays a part in this too. In the interference engines, the larger valves open further into the combustion chamber allowing more outside air. This allows a smaller engine to create just as much power as a larger non-interference or “free-running” engine. Smaller engines, less cost to produce but it also allows for smaller, lighter cars.
Steel timing chains can last for 150,000 to 200,000 miles. Since there is no way to measure the wear on rubber timing belts they are recommended to be replaced at 60,000. That’s where I think they get us. I can see the reason behind the smaller engines but why couldn’t they use steel timing chains on them?
Here’s an illustration of just how lucky I am. My engine is the one on the bottom.
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