Interference style engines and timing belts


#1

Why do manufacturers produce cars with timing belts instead of chains and why do they make interference style engines? Is there supposed to be some advantage in that for the buyer or are we being taken for a ride? No pun intended.


#2

Interference-design engines typically produce more power per cubic inch than non-interference design engines. As to timing belts vs timing chains, I believe that engines with timing belts are probably cheaper to manufacture than engines with timing chains.


#3

The rubber belt cam drive is considerably cheaper to manufacture than a roller chain in an oil bath…So the design has cost benefits…As far as interference or non-interference, who knows? The engineering team designing the head probably has no idea whether the valves can hit the piston or not…And they certainly don’t care…If consumers are lucky, somebody catches it and they cut some eyebrows in the piston tops to accommodate the valves and protect the power-train warranty…In the real world, consumers have rebelled and refuse to buy cars with belt-driven cams. They expect to get 250,000 miles out of a car without major repairs or staggering maintenance costs…As a result, timing belts are fast disappearing from the automotive scene…


#4

“consumers have rebelled and refuse to buy cars with belt-driven cams.”

Well, at least “informed consumers” have rebelled…
I could have…saved…a couple of thousand dollars on the purchase of my past two cars if I had been willing to accept the standard 4-cylinder engine with timing belt. Because of my aversion to that technology, I opted to spend more in order to get a 6-cylinder engine with a timing chain.

In addition to…effortless…acceleration on interstate entrance ramps, I got the benefit of not having to worry about a timing belt. IMHO–Saving a couple of bucks per week on gas is not worth the trade-off in terms of both increased maintenance expenses and slower acceleration.

IMHO, my money was well-spent on a larger engine w/o a timing belt.


#5

I am informed and I have not rebelled

I have had many cars with timing belts

I made my choice and am loving it

And I’ve always changed the timing belts at the factory specified intervals

No regrets whatsoever


#6

It is not some conspiracy and not that much is saved. It’s an engineering choice as most cars are significantly quieter with belts. "The engineering team designing the head probably has no idea whether the valves can hit the piston or not…And they certainly don’t care…"
With all due respect @Caddyman I can’t believe that is true. From what I was told, belts allow more flexibility in motor design and make it easier to build and design motors with multiple advantages. Unfortunately for that line of reasoning, people don’t want those advantages at the expense of reliability and are willing to accept noisier, less efficient motors to that end. IMHO, it’s a case of backward engineering where the consumer won out.


#7

Lower production cost is the impetus I believe. Higher maintenance cost is the result. Now in the overall scheme of things, it should not be so great a factor, as the water pump has it’s limited life expectancy also.

But I have to wonder why is that? Got a timing chain and a good water pump, 160k and going strong, bean counters and planned obsolescence coming into play?


#8

Cars are not built to last forever… They are disposable consumer products…


#9

Belts are quieter, if that’s important. Regarding interference design, it has to do with compression ratio-you get more out of your fuel when compression ratio goes up. That’s basic thermodynamics and that’s why diesel engines are more efficient. There are 2 ways to increase compression ratio. You can increase the bore and shorten the stroke. But the engine would be low on torque and needs to be revved to generate meaningful power. Imagine the average Camry driver revving the engine to7000 rpm to merge on the highway. The other way to increase compression ratio is using a long stroke design. That’s preserves the low end torque but requires an interference design .


#10
Cars are not built to last forever.. They are disposable consumer products..

Buy different cars if you can’t get them to last longer then the first, second or even third timing belt change.

Timing belts or timing chains…doesn’t matter to me. Either is fine. From 1987 thru 2005 when I bought my 4runner they all had belts. Now all our vehicles have chains.

My 4runner has over 260k miles and the chain isn’t making any noise…so I don’t see a need to change it any time soon. But plan on keeping it another 3-4 years and possibly 100k miles. We’ll see if the chain holds up. If not…then that ONE timing chain replacement will cost me more then all the timing belt changes I’ve done since 1987 COMBINED.

And I have 2 more vehicles with timing chains. The 4runner - if the chain needs replacing…I think I’ll do it. My wifes Lexus…no way. That transverse mounted engine is a royal pain to work on. Same with my 14 highlander.


#11

Several makers have switched to chains from belts, I’ll look for that in my future purchases. But no conspiracy, no ‘taken for a ride’, just an engineering choice.


#12

Interference engines are nothing new. They have been around for 50 years. A 1964 Cadillac has an interference engine. It has to do with the shape and size of the pistons, valves, and combustion chambers. Interference engines tend to provide more power than non-interference engines of the same size. So in that sense interference engines are better.

When overhead camshafts were introduced they needed a way to drive the camshaft. it had been driven by a chain previous engines. But a chain for an overhead cam would need to bo over twice as long, need adequate lubrication, would need some sort of tensioning device, and would tend to be loud. So a rubber belt outside the engine was the answer. Cheap, easy to change, and quiet.

Timing belts are still easier and cheaper than timing chains on overhead camshaft engines. Like @MikeInNH‌ just said, one chain replacement will easily cost as much as 3 or 4 belt replacements.


#13

There’s another thread on this subject, and I’ll repeat what I said there.

It’s possible that manufacturers have gone back to chains because of the new variable valve timing systems that use oil pressure to operate. Chains eliminate the concern for belts getting contaminated by oil and failing prematurely.

It’s also possible that customer satisfaction was a factor. The purchasing decision doesn’t consider belts vs. chains for most, but everyone complains when faced with such a large bill for scheduled maintenance, and when the vehicle comes back with operating problems, which is more common than it should be with timing belt replacements, they complain even louder.

I cannot get into the minds of manufacturers’ designers on this, none of us can. But those are my theories.


#14

A timing belt driven interference type engine should not even exist but engineers at the bottom of their profession have to design something in order to make a living.


#15

I’ve gotten mixed answers but just to clarify, does a timing chain ever need to be replaced?


#16

Not usually. A well maintained (oil changes) engine will typically keep its timing chain for the life of the car. There is no set time/miles limit. If there is a problem, noise will usually be an indicator.


#17

I had to replace one at 200,000 miles once. But generally, no, they last the life of the vehicle.
The chains do stretch over time, but generally it’s the sprockets and tensioners that wear out. The engine will start to make a rattling sound when that happens.


#18

The concept behind interference engines is that if the valves can open wider, the engine can breathe easier, making the engine more efficient. With a higher compression ratio, you tend to get better performance.

As to the VERY old chain vs. belt debate, you can find many heated debates about this issue in past discussions, but my take on it is that there are benefits for both options, and most of the other users in this forum prefer chains.

As a motorcyclist, I’ve often wondered why drive chains require so much maintenance and why Harley Davidson uses drive belts if chains are superior, but I guess that is a separate issue.


#19

Just a comment to those being critical of engineers designing interference engines. With all respect to the posters, you do not know how to design engines, they do.

Interference engines, as some have already indicated, are chosen as the design because the compression ratio needs to be high to improve engine efficiency. As high as 11:1 on modern, engines. (see Mazda SkyActive as an example) High lift cams make more power but smack the pistons when the timing belt or chain breaks. And, Yes, timing chains also break. The belts were used because they were quieter than chains and, yes, cheaper. Also consider that 950 hp, 9800 rpm NASCAR pushrod V8’s use timing BELTS, not chains, because they reduce camshaft vibration harmonics. They reduce those dynamics on a grocery-getter at 2000 rpm, too. Consider that when you disrespect the lowly belt.

That said, I prefer timing chains but would not reject a car because it had a timing belt. I’ve owned some and changed a few.


#20

As I posted in another thread, there are two types of interference engines. There are piston/valve interference engines, and there are valve/valve interference engines. Here is a video that explains the differences: