Timing belts and chains


#1

When buying a used car, how can you tell whether in has a timing belt or a chain? Also whether it has an interference or non-interference style engine?


#2

Go to the Gates timing belt site, see if they list a part for it, and see if they indicate whether it’s an interference engine.


#3

+1 to texases’ comment.

Also, the OP can look at the maintenance schedule that should be sitting in the glove compartment. (the absence of an Owner’s Manual and/or a Maintenance Schedule should be considered as a major red flag with a used vehicle)

If the maintenance schedule lists timing belt replacement (also called a cam belt by some manufacturers) at…60k…90k…105k, then you know that it has a timing belt. Failure to list timing belt maintenance indicates the use of a timing chain.

However, the maintenance schedule will not tell you if the engine is of the interference design, so ultimately, the Gates site is very useful for answering the OP’s questions.


#4

Interference design is more lack of design than anything else…It tells me the design team was under great pressure and in a hurry when they designed the engine…Too late to put some eyebrows in the pistons…


#5

To make room for valve clearance reliefs in the pistions the compresion rings must be located lower on the pistion. This increases the amount of space/depth of dead space between the top of the piston and the first compresion ring resulting is higher emission output.


#6

That’s interesting. So there’s a design compromise, a non-interference engine will tend to have higher emissions than an interference design, and therefore might not pass the gov’t emissions regulations. I can see why car manufacturers might lean toward interference engines. They save money on the design, and by the time an interference problem occurs, the warranty is expired and they are off the hook.


#7

Putting reliefs in pistons isn’t the answer, depending on how far the valve travels and the size of the combustion chamber you may have to relieve clear through the piston. Also reliefs tend to create spots of different temperature and can change the propagation of the flame front. Lowering compression could reduce the interference but that would be going backwards in engine design.

In DOHC engines it’s not just pistons hitting valves, it’s intake and exhaust valves hitting each other. If you want your engine to breathe and squeeze, it’s probably going to be an interference engine.

@gimmeit‌ Is there a specific car or engine you are looking at?


#8

If you are going to build and sell an interference engine, at least you could make changing the belt a simple, straightforward procedure not involving the water pump or removing the R/F suspension…Give the second and third owners of these cars a break…


#9

Caddyman, in theory I agree with your last comment, however engines are also designed to make the best use of available space and to keep manufacturing costs (and thus vehicle costs) reasonable. Making the timing belt an external belt, and not using the available belt to drive the water pump, would compromise these goals.

For the record, I hate designs with timing belts too. The cost of the “routine scheduled maintenance” is too high, and far too many vehicles end up with operating problems introduced during the process. The work just doesn’t seem to be as error-resistant as a routine maintenance operation should be. I suspect that timing belts have been enough of a PITA for the customer base to be the reason that manufacturers have gone back to more expensive chains.


#10

If you see plastic covers over the belt area, you have a belt.


#11

I have some additional theories as to why engines tend to use chains nowadays

Engines are becoming ever more powerful

Very sophisticated valve timing

I’m not an engineer, but is it possible both of these lend themselves better to engines using a chain?

I don’t really buy the theory that the customer is so informed now, that they won’t stand for a timing belt anymore

That would imply that customers were not informed before, which I don’t believe

Plus somebody needs to show me numbers to back up the claim that customers were consciously choosing chains over belts

I truly think it’s an engineering thing, not a global customer awareness thing

Let’s also not forget that some of the best selling cars had belts for years, if not decades. And people kept buying them, and were happy with them

Perhaps an automotive engineer can chime in . . .


#12

Points well made.
It’s also true that designers are using variable valve timing systems operated with oil pressure, and chains eliminate concerns about protecting the cam-driving system (belt or chain) from oil exposure.

I doubt of belt vs. chain is a factor in purchasing decisions, but perhaps customer complaints were a factor. In my experience, very, very, very few customers are informed until they face a large bill, but many complain when that time arrives. I also realize I’m giving manufacturers more credit for caring about customer satisfaction than they probably deserve.


#13

mountainbike

If customers were so upset with belts, WHY did they keep buying belt driven Camrys, Accords, Corollas, and any other number of cars

Let’s not forget that the Domestic manufacturers also had their fair share of belt drive engines

For decades . . . !


#14

It has absolutely nothing to do with country of corporate office. It’s just a belt vs. chain question. Let’s not turn everything into an “American vs. foreign cars” debate.

IMHO they kept buying these cars because overall they had reputations for reliability and longevity, and for most their experiences supported the reputations. So they became repeat customers. I think many also complained when they were faced with the cost of replacing the belt as scheduled maintenance, and I know many complained when the service introduced operating problems, which in the case of timing belt replacements was too often.

Look, I cannot get into the mind of the manufacturers. Neither of us can. My statements on the reasons are only theories.


#15

“Let’s not turn everything into an “American vs. foreign cars” debate.”

That is why I mentioned that the domestics ALSO used timing belts for years

Car manufacturers from different continents were all using timing belts


#16

Many cars today have a timing belt service interval of 120,000 miles. I remember when 120,000 miles was about what you’d expect your timing chain to last before the gear stripped out.

So what’s the difference?


#17

Ha!


Here to represent my ride: F150 with the 300 I-6 engine. Timing GEARS. (Of course, Ford just had to decontent mine with those Bakelite Point-Of-Sale gears!)


If and when it ever fails, metal gear upgrade: last forever, and good and noisy, too. Oh, and it’s non-interference.


#18

MJ-one good engine!-Kevin


#19

pdxinspections.com


#20

Ase, I can remember when 120,000 miles was a good lifespan for the CAR!