In truth it’s all economics. Belts are cheaper to manufacture into the engine than chains. And the belts themselves are cheaper. There are also some technical reasons (see below) but it’s really just cost-based. If chains were cheaper to make and install they’d all be chains.
Personally I far prefer chains. I consider having to have the belt changed as just another opportunity for a screw-up. But as has been pointed out, on V-style engines with dual camshafts on each head the convolutions in the chain can become difficult to cope with. Chains are much heavier than belts, and as they run they want to form a circle due to the physics involved, much like a lariat (sp?) forms a circle for a cowboy. It’s easier to control a belt in a convaluted path simply due to the weight involved. And the lateral stresses on the rotating components around which the device travels are far lower.
Water pumps…it’s simply easier, cheaper, and more space effective to add the water pump to the belt drive, especially on transverse mounted engines where space around the engine is at a premium. In trucks, where longitudinally mounted engines are the norm, the water pump will still typically be a bolted on component driven by a fanbelt.
I agree about the fuel pumps. But, again, it’s a cost of manufacture issue. I’d guess it’s probably cheaper to put the pump with float and tank together as a subassembly and mount it than to mount both seperately to the unibody. If you seperate them you also have to then add a fuel level measuring system as a whole additional subassembly, so it makes sense for the pump and th efloat to be in one unit. Saves an assembly operation. There’s no technical reason that I can see.
In design, everything has a tradeoff. They’re basically trading off ease of repair for lower cost of manufacture…which also keeps the final cost of the vehicle down.
But, if they follow the “lifetime fluids” rule, then that means once the belt breaks, that’s considered the life of the engine. Also, most people trade their car in before it needs replacing anyways, or trade it in once they see how expensive it is to change out.
Chain Noisy? We Have Cars With Both Chains And Belts.
I Don’t Think My Bonneville Engine With Single Chain Could Be Much Quieter. It’s Like A Library Inside The Car, Very Quiet And Pleasant, The Quietest Of Our Fleet. I Love It!
In order to get the high specific output (HP per displacement) expected in modern engines compression must be fairly high and valves must open pretty wide. That means little or no dish in the piston tops and the valve heads can reach out and touch someone, like the pistons, if the belt or chain stops doing its job. So interference engines are here to stay if you want high performance.
…interference engines are here to stay if you want high performance.
I thought so. I really don’t have an issue with interference engines or timing belts. If you buy a reliable car, take care of it, and get the timing belt changed when you should, you should end up with all of the benefits of an interference engine with none of the disadvantages.
The way I see it, spending $400-$550 every 90,000 miles ends up being a wash when you consider the added fuel efficiency of an interference engine. If making an engine an interference engine with a timing belt lets a car average 33 MPGs instead of 30 MPGs, that ends up saving 273 gallons over 90,000 miles. At $2.50/gallon, you save $682. I would rather give that money to my trusted mechanic than the oil companies. At $4.00/gallon, you actually save money. $1,091 in fuel savings minus $550 for a timing belt job equals $541 in your pocket.
In the end, having a non-interference engine with a timing chain instead of an interference engine with a timing belt will cost you money and make the oil companies richer. I am sure the CEOs of Exxon-Mobil, Chevron-Texaco, and Shell would like to thank those of you who want non-interference engines with timing chains. When gas goes back up to $4/gallon, you will make them very happy.
Interference vs non-interference was never mentioned that I could hear in the world of cars until timing belts arrived. Because that concern arrived with timing belts, the implication is that timing belts are overall less durable than chain or gear cam drives.
I’d also like to point out that the $500 needed for a timing belt and water pump change can be saved for other repairs with a car with no cam belt drive.
A person dealing on a new car with a belt cam drive could ask the salesman to discount the price for enough money to cover the first cam belt and water pump change or else threaten to buy another brand with a chain drive cam that will not need that service.
One very rarely seen approach to driving the cam(s) is a gear train. That’s the most infallable, but also the most costly.
Ultimately we may be seeing valves driven by some other method such as a solenoid, leveraged with an eccentric rocker arm for added force. The thing that makes me think this is variabble valve timing. Controlling it with a computer would open up better control possibilities. I’m also aware, however, of the technical challanges.
Or perhaps we’ll be all electric soon and all of these problems will disappear. But that’s another thread.
I agree with the OP’s logic on both counts: why not a timing chain rather than a belt, and why not mount the fuel pump externally? Some cars do, that’s why I bought a Mercedes.
Believe Me Greg, I Share The Same Concerns And They Factored Into My Choosing A 3.8L Bonneville, And For Cal, His Purchase Of A MB.
See my previous post.
Consumers can vote for easier/cheaper cars to service with their purchase decisions. A company that promoted these features for consumers could possible win a market share from folks who do their homework and keep cars for a long time. I know of 3 of us who are interested and there are others who responded, too.
KISS Method = Keep It Simple, Stupid - (Method of engineering).
CSA
P.S. Many people can’t believe the MPG these 200HP 3.8s deliver in these large GM cars out on the open road, often 30+. Most don’t use oil after 150,000 miles. I love it.
I am sure the CEOs of Exxon-Mobil, Chevron-Texaco, and Shell would like to thank those of you who want non-interference engines with timing chains. When gas goes back up to $4/gallon, you will make them very happy.