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Timing Belts and Timing Chains on Cars and Trucks

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TIMING BELT REPLACEMENT: $150 to $500
TIMING CHAIN REPLACEMENT: $300 TO $500
(Prices good for most cars and light trucks)
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If there was a ticking time bomb under your hood, would you keep on driving until it went off?

Although a broken timing belt or chain won't kill you, it can certainly strand you in the middle of nowhere. (In these violent times that might just be a matter of life and death!) On some cars a broken timing belt could bend valves. This COULD DESTROY YOUR ENGINE: an expensive proposition indeed!


WHAT IS A TIMING BELT OR CHAIN? WHAT IS VALVE TIMING?


All current automobile piston engines have a camshaft and a crankshaft. The crankshaft transmits the power from the pistons as they move up and down and changes it to a rotating motion. (This is like the pedals on a bicycle changing the up and down motion of your legs to a rotating motion.) One end of the crankshaft drives the CAMSHAFT with a gear, chain , or belt. The other end of the crankshaft is connected to the transmission, which then powers your wheels.

The Camshaft opens and closes each intake and exhaust valve in the engine. A camshaft has eccentric LOBES or CAMS all in a row: one lobe for each valve. This lobe presses on a cam follower or valve lifter which opens the valve.

Different types of valvetrains exist,
but in all of them the cam presses
on a lifter or cam follower and the
lifter or follower opens the valve.
Some motors have a pushrod and
rocker arm linking the lifter and valve.

For each cylinder, the camshaft first opens the intake valve to let in fuel and air to be burned. After this, the camshaft opens the exhaust valve to release the burned fuel gasses, which pass out the exhaust pipe. The valve must open at exactly the right time. This coordination of the crankshaft with the opening and closing of the valves via the camshaft is called Valve Timing or Camshaft Timing.

If valve timing is incorrect a valve can open at the wrong time and bend the valve!!


SEE ALSO: IGNITION TIMING

Timing Gears, Chains, and Belts

The camshaft is turned by the crankshaft. 3 different methods are used to connect the crankshaft to the camshaft.

1) THE TWO GEAR METHOD

two gear cam drive method
This is the most reliable method. A gear on the crankshaft meshes directly to a gear on the camshaft. These gears last the life of the engine and almost never fail. The 2 gear method is used in big trucks and heavy equipment, as well as some cars. The only time I've seen a gear fail on a 2 gear drive camshaft is when a gear is made of nylon or fiber. This is always the camshaft gear: the crankshaft gear is always made of steel.

2) THE TIMING CHAIN METHOD

timing chain cam drive method

Although not as reliable as the gear to gear system, a timing chain still will last 80,000 to 100,000 miles or more before wearing out. As the chain stretches, however, performance will be affected. Also, on many vehicles the camshaft sprocket is made of plastic. When these vehicles are overheated even slightly this plastic can melt and the chain will skip teeth. The engine will stop immediately and will not run again until the chain is repaired. If a valve opens all the way at the same time as the piston comes up, it can bend the valve and possibly destroy the engine.

Symptoms or signs of a bad timing chain

Of the three methods of connecting the crankshaft to the camshaft, only the timing chain can actually give some signs before it fails.
Symptoms are:

1) Rattling noise from front of engine, especially at idle
This is especially true of overhead camshaft motors with timing chains. It also happens with timing chains with hydraulic tensioners (tensioned by a piston fed with oil pressure from the oil system)

2) Retarded ignition timing
In theory a vehicle with electronic ignition should never have to have the ignition timing adjusted or set unless the distributor is removed . As the timing chain stretches or as the gears wear, the camshaft "falls behind" where it originally was supposed to be, retarding the ignition timing as well as the valve timing. (Most engines drive the distributor off the camshaft). So if you have to advance the timing on a timing chain equipped motor with electronic ignition, the timing chain is probably stretched. If an engine will not run, but then starts after advancing the ignition timing A LOT then the timing chain has probably skipped a tooth and is about to fail altogether.

3) Plastic chunks in the oil
It's a good idea to watch your oil drain out, and to pour it through a screen to see what kind of chunks come out when you change the oil. Many camshaft gears are made of aluminum with plastic molded around the aluminum casting to form the gear teeth. When these plastic gears start to fail often chunks of plastic will break off and end up in the oil pan. If you find plastic fragments in your drained oil, you probably have a timing chain cam sprocket that's about to fail. Sometimes when a plastic gear fails the plastic chunks can get caught up in the oil pump screen and make the car lose oil pressure! All you can do then is to drop the oil pan and clean the oil pump inlet screen.

3) THE TIMING BELT METHOD


This method requires timing belt replacement every 40,000 to 60,000, (even 100,000+ miles according to some manufacturers). The camshaft sprocket is connected to the crankshaft sprocket by a toothed drive belt (Technical name: a Gilmer belt). This is becoming the dominant method. Over half of the cars on the road use timing belts. There are several reasons for this:
a) It's easier to connect the camshaft and crankshaft together with a belt when the camshaft is far away from the crankshaft (like with overhead cam engines).
b) They claim timing belts are quieter than chains, although personally I can't tell the difference.
c) Belts are lighter than chains, and every ounce counts to manufacturers, especially when they're trying to meet fuel economy standards.
d) It's much cheaper and simpler to make a belt drive engine than any other way.
e) When the belt breaks it can destroy the motor , so it increases new car sales or repairs for drivers who neglect proper maintenance.


Timing belts and water pumps

A lot of cars have timing belts which drive more things than the camshaft. Many have an auxillary shaft, balance shaft, or oil pump drive which either run off the timing belt or off an additional "toothed" belt positioned next to the timing belt.

The above stuff usually lasts the life of the timing belt plus some, but one common item often doesn't: THE WATER PUMP!!!

That's right: many cars run the water pump off the timing belt, and water pumps start failing at 75,000 miles. Timing belt driven water pumps normally last for the manufacturer's recommended interval for replacing the belt (100,000 miles or so) but if you're replacing the belt you might as well do the water pump, and vice versa!

Symptoms or signs of a bad timing belt

Timing belts give no easily noticed symptoms or signs that they are about to fail. That's why it's important to change them at the recommended interval. They DO SOMETIMES BUT NOT ALWAYS show some visible signs, if you can move the belt cover back enough to see the belt. Sometimes cracks can be seen on a timing belt that's about to fail, just like any other belt that's reached the end of its "lifespan".

A typical engine with a timing belt Timing belt with missing teeth or cogs


These cars that almost always bend valves when the belt breaks: If you own one of these cars, replace the belt every 50,000 mile or... "YOU'LL BE SORRY!!!"

ANY VEHICLE WITH MORE THAN 2 VALVES PER CYLINDER
MOST NISSANS, MITSUBISHIS, CHRYSLER COMPACTS LIKE LAZER AND NEON (A lot of Chryslers have Mitsubishi engines)
HONDAS WITH 16 VALVE 4 CYL. ENGINES

MOST HYUNDAIS
FIAT SPYDER AND SPYDER 2000 (FIAT SAYS 40,000 FOR THESE CARS, IF THEY'RE ANY OF THEM STILL AROUND)

I'm not sure there is a car that will NEVER bend valves, but the above cars almost ALWAYS bend one or more valves when their timing belt breaks.

Many Toyotas are "Free Runners", meaning they can break a timing belt and normally not bend valves.

The Gates Rubber Company website has a guide which tells which engines normally bend valves when the timing belt breaks (interference engines) and which ones don't bend valves.


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Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.


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Auto, Car, and Truck Article List

A
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
AUTOMATIC TRANSMISSIONS
B
BAD CAR DESIGNS
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BEARINGS
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
C
Car Washing and Care
CARBURETORS:Car & Truck
CHECK ENGINE LIGHT
CLEANING: Engine Cleaning
CLUTCH REPAIRS: Car & Truck
COMPRESSION: Car Engine
COMPUTER CAR CONTROLS
CV JOINT OR CV AXLES
D
DISTRIBUTORS (IGNITION)
E
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
ENGINE CLEANING
EXPANSION PLUGS
F
FREEZE PLUGS
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
G
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
H
HEADS & HEAD GASKET
HOSES AND BELTS
I
"IDIOT LIGHTS" AND GAGES
IGNITION TIMING: Car & Truck
J
AUTO JACKS: lifting cars safely
K
L
LEAN "Car runs lean"
LIGHTS: WARNING OR "IDIOT LIGHTS"
Limp Home Mode
M
MIL Light
MANUAL TRANSMISSIONS
N
NO START: Car Won't Start
O
OIL CHANGES
OIL: What's right for your car?
OIL LIGHT ON OR GAGE LOW
P
PCV Valve
Q
R
RADIATORS: Car and Truck
RICH: Car runs rich
S
SEALS AND GASKETS
SERVICE ENGINE SOON LIGHT
SPARK PLUGS
STARTERS: Auto, Truck
T
THERMOSTATS
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
TIRE REPAIR
TRANSMISSIONS: AUTOMATIC
TRANSMISSIONS: MANUAL
U
V
VACUUM ADVANCE
WARNING LIGHTS OR "IDIOT LIGHTS"
Car Washing and Care
W
WATER PUMP REPAIR
WINDOWS AND WINDSHIELDS
WIRING REPAIR
X
Y
Z

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