Timing Belts vs. Timing Chains

[Counterman]

If you were buying a new vehicle, what would you want the engine to have: a timing belt or a timing chain? You may have an opinion, you may not. Either way, let’s compare the two; then you can decide.

The Chain Gang

For many years, timing chains were the go-to for engine design. Generally speaking, they were dependable and didn’t require any specific maintenance. They were lubricated by the engine oil, so if you changed it on a regular basis, the timing chain would hold up well.

Or would they? A lot of people still say, “They don’t build them like they used to.”  This is true, and coming from someone who is an old-car enthusiast, I’ll defend a level of workmanship that we don’t see in today’s vehicle. But the statement, while true, doesn’t always mean they built them better.

In the case of timing chains, they sometimes wore quicker than a lot of people realized. What happened when they did? On an old car, nothing right away. At least nothing of which the owner was aware.

A timing chain, just like a belt, is there for one reason: to connect the crankshaft to the camshaft at exact points so the valves open and close at the correct time for engine operation. A traditional, old-school timing chain was tight upon installation, and the overall timing set consisted of a crankshaft gear, a camshaft gear and a chain. There was no adjustment or no tensioner.

When the chain or the drive gears began to wear, engine performance would suffer, but it would degrade slowly, and most vehicle owners had no idea there was a problem. They wouldn’t know at all until they started to get a hard-start or no-start symptom. And why? There was no crank sensor or cam sensor, and no computer to translate the signals into a crank/cam correlation diagnostic trouble code (DTC). So, we just drove the cars until they wouldn’t drive any more.

Early engine design was split between gears or chains, but chains ultimately became more popular because they took up less space and ran quieter, and by the early ‘80s, the majority of cars produced had timing chains.

An evolutionary change of timing-chain design included nylon-tooth cam gears. They ran quieter than a traditional steel gear, but they wore out a lot quicker and created problems long before vehicle owners expected, which didn’t do much for their reputation. The tried-and-true timing chain was simple and generally dependable, but times were changing.

Buckle Your Belt

As the ‘80s rolled on, electronics, emission controls and technology were on solid cruise control and like flipping a switch, timing belts were suddenly in the picture.

Although timing-belt-driven overhead camshaft engines weren’t new by any means, the value of the design began to be recognized and auto manufacturers started to change over to this concept. The camshaft was now located on the cylinder head, which eliminated push rods and, on some designs, the rocker arms were eliminated as well, saving weight, lowering cost, reducing valvetrain inertia and making multi-valve designs possible.

The easiest way to drive the camshaft was via a timing belt. Since timing chains suffered from inherent gear wear and stretching, engineers decided that belts were the way to go. They were quieter and lighter than a chain and less expensive to manufacture.

The tensioning systems were simple, and the belts remained tight for a long time without wearing the cam or crank gear.

Seemingly, all was good, but even with the advantages of a timing belt, they required replacement at specific intervals, and the one disadvantage that became known quickly was that if not replaced, they would break with no warning. Simple tensioning systems required adjustment from time to time, and oil leaks also were a problem with timing belts, as they would degrade the rubber quickly and lead to a broken belt. A broken belt could mean a very expensive repair on interference engines.

Belt quality and tensioner design improved quickly, eliminating many of the early timing belt troubles, and by the mid- to late-‘90s, timing belts were used on the majority of automobile engines. Belt-service intervals became longer, and consumers were getting used to this being a part of normal maintenance. But you still cannot ignore the replacement interval, and was it possible times were changing again?

The Old Ball and Chain

As we said “Happy New Year” to a whole new century, engine technology was a freight train out of control. Materials and manufacturing were better, RPMs were higher, turbochargers were boosting like never before and horsepower wars like we hadn’t seen since the ‘60s were heating up again.

Smaller engines were producing more power than ever, and variable valve timing was pushing engine performance to the limit. Just like that, engine design required something that was narrower, more durable and more dependable than a timing belt, and consumers no longer wanted the associated maintenance. Hello chains.

As of the last decade, timing chains have risen back to the top. Design is far different than that of old, with modern chains traveling around awkward paths of sprockets, hydraulic tensioners and chain guides, offering a high level of dependability and performance. But they couldn’t do it without one critical thing on their side: lubricant technology.

A primary reason for timing-chain wear always has been related to lack of oil changes, lower-quality oil, and poor or non-existent positive crankcase ventilation (PCV) systems, which wreaks havoc on engine oil.

Modern engine oil is not only far superior than it was just a few decades ago, but PCV technology also is eliminating the majority of blow-by-related contaminants and moisture from building up, resulting in cleaner oil and better lubrication throughout the engine.

Timing chains and variable valve timing systems are dependent on clean, healthy lubrication and now they have it, but then again, does everyone change oil as often as they should?

Talk to the Techs

Timing belts generally are easier to service. This is primarily because they’re located on the outside of the engine and run dry, with no lubrication. When replacing a belt, there’s less cleanup and no time required to reseal engine covers. On the other hand, the engine water pump is frequently driven by the timing belt, so when you replace it, it’s a good practice to replace the pump, as well as any tensioners or rollers.

Timing belts came into prominence along with the inline four-cylinder engine. What this brought was more than just cam/crank timing, but also balance shafts and intermediate shafts that often drove distributors and oil pumps. These weren’t hard to work with, but had to be timed correctly during belt replacement.

As the timing belt migrated to V-configuration engines, it became a lot longer with additional rollers and a more difficult installation, plus some components such as thermostats were all of a sudden underneath. Some things got better, some got worse.

Inspection is an advantage with a timing belt; it’s usually just a couple of bolts and you’re looking right at it. One problem, and a challenge especially on a second-owner vehicle: If the mileage is over that of recommended timing-belt replacement and the owner doesn’t know if it was done, replacement is always recommended.

Many belts can look great on the outside but strip the teeth off a day later. The only way to inspect them closely enough to really look at the integrity of the teeth can be to remove them. And then, does it make sense to put the old one back on, and is there a technician who would want to take that gamble? One solution to this is the bright yellow replacement decal that’s included in almost every timing-belt kit, for a technician to fill out and affix under the hood. If only they got used more often.

Timing chains, as good as they have become, are not without faults. They can be a bear to inspect and replace, mainly because they’re located inside the engine so they can be lubricated by the engine oil. There’s a lot more cleaning to do and usually a seal or two that needs replaced. Just as with belts, there’s often a water pump that’s driven by the chain that should be replaced.

While the chains are more durable and dependable, if oil changes aren’t religious, the guides have a tendency to wear out really quickly. Most guides are steel with some type of nylon or plastic that the chain rides along. Remember the nylon-tooth cam gears? These guides do the same thing and beyond a certain point in wear, the tensioner can no longer take up the slack in the chain.

This often leads to a rattling noise and a “Check Engine” light. Most engines still run perfectly fine at this point, with the most common complaint a “Check Engine” light and a cam/crank correlation DTC.

Timing-chain replacement is often very expensive due to labor time, but, then again, so is engine repair when a timing belt breaks. They both require special tools at times, so there’s no winner on that argument. And, one more thing: Did we mention the latest technology of belt-in-oil drive systems? Here we go again. So, do you have a preference, or do you agree with my conclusion?

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