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!
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.
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
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.
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.
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!
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
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.
Since the overlap period is only over a degree or two of camshaft rotation, the overlap period can be used to determine the correct valve timing on the camshaft. Assuming you've already determined TDC on the crankshaft, remove the valve cover over the cylinder 180 degrees opposite number one cylinder. (see above instructions) When this cylinder is in overlap, number one will be on TDC compression. This is useful to find the right timing marks to use. It's also a good way to find out if your chain or belt has skipped a tooth or two. V-8 and V-6 motors have tiing chains that are hard to get to to look at, but valve covers that remove fairly easily (sometimes)
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.
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
BAD CAR DESIGNS
Bad Drivers: How NOT to drive
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
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
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
FILTERS: OIL, AIR, ETC.
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
HEADS & HEAD GASKET
HOSES AND BELTS
"IDIOT LIGHTS" AND GAGES
IGNITION TIMING: Car & Truck
AUTO JACKS: lifting cars safely
LEAN "Car runs lean"
LIGHTS: WARNING OR "IDIOT LIGHTS"
Limp Home Mode
NO START: Car Won't Start
OIL: What's right for your car?
OIL LIGHT ON OR GAGE LOW
RADIATORS: Car and Truck
RICH: Car runs rich
SEALS AND GASKETS
SERVICE ENGINE SOON LIGHT
STARTERS: Auto, Truck
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
WARNING LIGHTS OR "IDIOT LIGHTS"
Car Washing and Care
WATER PUMP REPAIR
WINDOWS AND WINDSHIELDS