why do car makers still make interference engines with timing belts.
Because they can.
More power from a given engine size because there is less wasted space in each cylinder.
Higher compression means better energy efficiency. But, leaves less room for valves and pistons to interact. Most non-interference engines are designed for low compression engines that easily run on regular fuel. Higher performance engines are typically interference design due to higher compression ratios. They also require mid grade or premium.
Why don’t people just learn to replace their timing belts at the correct interval?
If you don’t like timing belts, buy a vehicle that doesn’t have one.
Others explained the technical reason for interference engines, VDC driver gave the correct answer to the question.
Purchase price drives a lot of sales. Every day, thousands of purchase decisions are made between an Accord or a Camry based on which dealer gives the best deal on a car that day. A few dollars makes the difference between sale or no sale.
It is cheaper to design and build an engine with a timing belt. Belts are light and quiet and gentle on the valve train.
Cars are built with front wheel drive for EXACTLY the same reason. A front wheel drive car is significantly cheaper to build on an assembly line. They are also lighter and leave more available interior space. Cars that are built for a market that is more focused on handling, quality, and longevity rather than initial purchase price (e.g BMW, Mercedes, and the higher end models of other brands) tend to build rear wheel drive cars with timing chains.
Although I often think it’s crazy that after 100+ years we’re still tinkering around with internal combustion piston engines in cars, I have an observation.
Just a few decades back cars needed valve jobs, bearings, timing gears/chains and piston rings often times before today’s cars need timing belts replaced. Major engine overhauls were common before reaching our present day spark plug replacement intervals.
Buying and replacing spark plugs and adjusting valves every 6000 miles and the items mentioned aboved were a bigger pain. Next, it sounds like soon, we are going to look back on the days when we had to go to a gas station every few hundred miles and recall how inconvenient it was.
We’ve come a long way!
I still wonder, “Have we taken the old piston engine about as far as we can take it?”
Having a timing chain is not always an advantage. My brother-in law’s Saturn S-series is headed to the scrap yard to a broken timing chain at 165,000 miles/9 years old. The engine is interference.
Interference engines are efficient. By allowing the valves to open more, the engine breathes better. More fuel can flow into the cylinders and it takes less energy to push the exhaust out of the cylinders. Your question seems to suggest interference engines are a problem from the past that should be solved. The opposite is the case. Interference engines are a part of the solution because they increase fuel efficiency.
Timing belts also add to efficiency. Using a timing belt instead of a timing chain makes the car lighter. In addition, timing belt jobs routinely include replacement of the water pump and timing belt tensioner pulley. This decreases the chances of water pump failure, which increases the life span of the average car, as long as you keep up with the routine maintenance.
Timing belt driven systems are simply easier and cheaper to manufacture than chain driven systems. Yes, they have less mass for the crank to drive, and it takes more energy to continually change the direction of the heavier chain (that energy comes from the crank…originating in the gasoline), but it’s really just a cost-of-manufacture decision. Either works just as well mechanically.
The most precise and reliable system would actually be a gear train. You can buy aftermarket geartrains too drive the cams on some models of engine that get retrofitted for racing. However the expense to do that on a mass production engine would be prohibitive.
Usually, worn timing chains will start making noise long before they break.