Is a timing belt better than a timing chain?
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QUESTION
Dear John,
I have a quandary. I currently own a 2015 Hyundai i30 diesel wagon (now done 145,000km).
My mechanic has said to me, on my latest trip for my bi-annual service, that my timing chain requires replacement. Always been a big fan of chain over belt because I have owned three cars prior to this that have all had timing chains and all cars have successfully gone well past 200,000km without any mention of timing chain replacement.
The cost to replace it is going to be $1850. So I’m currently seeking a second opinion and trying to weigh up whether I should sell the car and buy a different used or new car (need wagon space, limited options). Would that be better than repairing and keeping car for another 5-7 years? Not sure the longevity of the DCT will allow for this.
Your opinion would be appreciated. If I do get a new car, what is going to replace my wagon, like for like? I'm really against the SUV-style options.
Regards,
Conan.
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ANSWER
Conan,
Not trying to rip you a new one, mate, but I always hate it when people make statements like this: "Always been a big fan of chain over belt.”
It highlights a fundamental misunderstanding of how engineering actually works - because there are good chain designs and bad ones. Belts, ditto.
If you operate under the false presumption that chains are better than belts, you’re denying reality, which is that both work just fine, but the detail of the design and the execution really matters. Plus, they have different wear and failure mechanisms.
Belts tend to fail by breaking without warning, hence they do durability testing in R&D and arrive at a conservative replacement schedule.
Chains stretch (ie - they give you some warning they’re getting ready to fail). The stretching throws off the valve timing and gives the engine control ECU poor data about the ignition timing, etc, because cam position is derived from crank position and assumes a limited amount of stretch in the chain (ie - the computer can’t tell the chain has stretched excessively, so it tells the spark to fire at the wrong time relative to the position of the valves). Belts overcome this problem - they don’t stretch.
If a chain or a belt breaks, it will catastrophically destroy most engines because the piston(s) will hit the valves. After that, it’s just scrap metal.
And 145,000km is a reasonable service life for any timing chain, frankly. The cost you’ve been quoted is not excessive. It’s quite an involved disassembly and reassembly process.
If there’s no evidence of an impending DCT failure, then that’s just an irrational fear. You drive roughly double the national average, so I’m assuming you do a lot of highway driving, which is very easy on DCTs. (It’s very easy on all powertrain components.)
It’s going to cost you a lot more than $1850 to change cars, so if there’s nothing else wrong with the car, get the chain replaced. Nobody enjoys paying for repairs, obviously.
You’ve done almost four laps of the planet in this car - give the chain some credit.
JC
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