by Bob Belding

Bent rod
Connecting rods are not meant to bend like this

Here’s a story I hear too often after a customer’s car has come into the
garage on the back of a tow truck. What happened? While driving down
the highway, they heard a loud bang and the engine suddenly stopped.
They are baffled because they rigorously maintained their 120,000
kilometre car, with regular oil changes and periodic tuneups.

But they forgot one very important maintenance chore. They didn’t
change the timing belt.

I’ve heard the excuses too. They just didn’t get around to it. Or they
hadn’t read their owner’s manual in four years. Or they thought the
cost of changing the belt was too much and decided to take a chance.
Bad decision.

If your engine uses a timing belt for valve timing (check that owner’s
manual), you will need to replace the timing belt at a recommended time
usually between ninety thousand and one hundred thousand kilometers.

What is valve timing? Each cylinder on an engine has at least one intake
valve and one exhaust valve. The intake valve opens to let a mixture of
air and fuel into the cylinder. As this happens the piston is moving
down creating a vacuum in the cylinder which helps suck in the air/fuel
mixture. As the piston moves back up on the compression stroke, both
intake and exhaust valves are closed, compressing the mixture. When the
piston is about to reach the top, spark will occur from the spark plug,
igniting the air and fuel and slamming the piston down on the power
stroke. Once again the piston moves up in the cylinder and the exhaust
valve opens to let exhaust gases out into the exhaust system.

As you can see, the intake and exhaust valves open at a specific time
and close at a specific time. The opening and closing of the valves is
controlled by a camshaft, which lets the valves open and close when
they’re supposed to. The camshaft is driven by a rubber belt connected
to the engine’s crankshaft.

While chains, sprockets and gears are also used to turn camshafts, the
rubber timing belt is the most common. And if you think it’s just
economy cars that use this device, you’re wrong. Most manufacturers,
including Lexus, BMW and even Porsche, use rubber timing belts. They are
as good or better than other devices. And like all other cam turning
devices, they will wear out over time.

A valve.... before and after
With the end of the valve completely gone, compression is at and all time low… if the engine will actually spin to check it!

If a worn out timing belt breaks, some of the valves will stay open and,
as the piston moves up in the cylinder, it will crash into one or both
valves, damaging the engine beyond your wildest imagination. If there
was ever any doubt about changing your timing belt, I hope its cleared
up now!

Try to imagine a five ton truck traveling at 100KM/H colliding with a
Chevette – kinda messy eh? Replacing the timing belt can cost anywhere
from $150 to $1000 depending on the engine and labour time involved in
the repair. Skip this service to save a few dollars and it might be a
mistake that could cost you as much as $3000 (the going price for a used
engine that may have been maintained no better than the one your just
trashed – or worse). Keep your money in your pocket and replace the

If you bring your vehicle to the same repair shop on a regular basis
they will let you know when your vehicle needs a new timing belt. If
they don’t, you should be looking for a new place to have your vehicle
serviced because that repair shop is doing you no favours by not telling

Unless you know what you’re doing, I wouldn’t recommend trying this
service yourself at home. If you don’t install the timing belt on the
pullies properly you may cost yourself an engine! But if you’re really stubborn and prefer to ignore my last sentence, please, get yourself a
repair manual for your vehicle from the dealer. Make sure you have a
very good set of tools, jack stands and a good jacking device. The only
thing worse than trashing your engine is having your car land on you. So
be careful and use common sense.

Bob Belding is a licensed automotive technician at Acacia Motors in Ottawa, Ontario.

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