The engine camshaft has to turn at precisely half the crankshaft speed. There can be no deviation and no room for error. The earliest method for achieving this was with a simple set of gears.
Actual gear-to-gear timing gear arrangements instead of chains used to be far more common than they are now. With the proliferation of overhead cam engines, their use has dwindled a just a few types of engines. Even many engines where the camshaft is located in the block have gone to timing chains rather than gears mostly because they are quieter and cheaper to manufacture. However, the term timing gear has hung on and is still in common use to describe the sprockets that drive timing chains and timing belts as well. Changing the actual gears and the replacement of sprockets on other types of engines is similar, but often more complicated because of overhead camshaft layouts.
A worn timing gear may become noisy or it may show no symptom at all. They rarely fail completely but if they do, you may have other serious damage to the engine. At the very least you will be stranded. So a worn timing gear should not be neglected.
Part 1 of 3: Remove the timing cover
Materials Needed
- Belt tensioner tool
- Breaker bar
- Combination wrenches
- Crankshaft holding tool
- Dead blow hammer
- Drain pan and jugs for storage
- Gear puller or harmonic balancer puller
- Impact wrench (air or electric)
- Jack and jack stands
- Safety glasses
- Screwdrivers (Phillips and straight)
- Socket wrench set
- Workshop manual
Step 1: Jack up the car. Make sure the car is in Park, or in first gear if it is a manual. Set the brake and put wheel chocks under the rear wheels.
Jack the front of the car and place it on good jack stands. Working underneath a car is potentially one of the most dangerous things a home mechanic will do, so you don’t want to take any chance that the car can shift and fall on you while you’re working underneath.
Step 2: Drain the coolant. There are a few types of engines that don’t have coolant passages in the timing cover.
A good visual inspection can tell you if that’s the case. Older cars had drain cocks or plugs in the radiators and engine, many newer cars don’t have a drain in the radiator, but most of them still have engine drains.
Remove the radiator or coolant reservoir cap, locate the drains with your workshop manual and let the coolant out into your drain pan. If your car doesn’t have a drain, you may have to loosen a hose at a low spot on the engine
Be sure you know where your dogs or cats are during this step! Automotive antifreeze tastes good to them. They will drink it down if they find a pan or a puddle of it and it will destroy their kidneys! Drain your coolant from the pan into your gallon jugs to re-use it or dispose of it.
Step 3: Remove the radiator. Not all cars require radiator removal. If there is enough space to work in front of the engine, leave it alone! If there isn’t enough space to work, It needs to come out.
Remove the hose clamps and disconnect the hoses. If your car has an automatic transmission, disconnect the oil cooler lines as well. Unbolt the mounts and remove the radiator.
Step 4: Remove the drive belt(s). Your car will have one or more drive belts that have to come off. It may be a question of loosening the mount on an alternator or other accessory, or if it is a late model car, it will have a spring-loaded tensioner that you need to loosen. These are often difficult to reach and having the appropriate belt tensioner tool will make all the difference.
When the belt is loosened, it still may be necessary to turn the engine with a wrench while you “walk” the belt off of the pulley.
Step 5: Remove the water pump. This is another step that may not be necessary on your engine. On some in-line engines, the water pump is off to the side of the timing cover and can be left in place. On most V-type engines, the water pump straddles or bolts directly to the timing cover so it has to come off.
Step 6: Remove the drive pulley. On the front of the engine is a large pulley or harmonic balancer that comes through the timing cover. Getting the bolt off of this pulley can be a challenge, even for professionals because the engine tries to turn while you attempt to loosen the bolt. You will need to use a crankshaft holding tool or an impact wrench to take this bolt out.
Once the center bolt is out, you should be able to pull the pulley off of the crankshaft with little more than a few strikes on the side from a dead blow hammer. If it is stubborn, a gear puller or harmonic balancer puller will do the trick. Watch carefully for any loose key that may slide out with it.
Step 7: Remove the timing cover. Use your small pry bar or a large screwdriver to gain a purchase under the timing cover and work it off of the block. Some engines have bolts that come up from the bottom through the oil sump into the timing cover. Be extra careful not to tear the oil pan gasket while sliding it off.
Part 2 of X: Replacing the timing gears
Materials Needed
- Combination wrenches
- Crankshaft holding tool
- Dead blow hammer
- Gear puller or harmonic balancer puller
- RTV gasket sealant
- Screwdrivers (Phillips and straight)
- Socket wrench set
- Torque wrench
- Workshop manual
Step 1: Set up the timing marks. Check the workshop manual. There are as many different kinds of timing marks as there are engines. Usually they are a series of dots that are lined up when the engine is at TDC.
Put the bolt back in the crankshaft temporarily to enable you to turn the engine. Rotate the engine until the marks line up as described in the manual.
Step 2: Remove the timing gears. Remove the nuts or bolts that hold the gears to the camshaft. The bolt for the crankshaft gear was the same as the one holding the front pulley and was removed earlier.
The gears may slide right off of their respective shafts, or it may be necessary to use a gear puller. With gears, you may take them off one at a time, but if you can slide them off simultaneously it will go a little easier. The camshaft may have to turn slightly when the gear comes off because of the helical cut of the teeth.
Step 3: Install the new gears. Slide the new gears up onto their respective shafts simultaneously. You will have to line up the timing marks, and hold them in position as the gears slide up onto their keys.
Once they are in place, a few taps with the dead blow hammer will seat them fully. Put the crankshaft bolt back in so you can rotate the engine with a wrench. Turn the engine through two full revolutions to be sure the timing marks align properly. Take the crankshaft bolt back out.
Step 4: Reinstall the timing cover. Clean the timing cover and scrape the old gasket off. Install a new seal in the cover.
Apply some RTV sealant to the surface of the engine and to the timing cover and stick the new gasket in place on the engine. Install the cover and the bolts finger tight, then tighten the bolts evenly in a criss cross pattern to seat the cover.
If the cover had bolts coming up through the oil pan, tighten them last.
Step 5: Reinstall the front pulley. Install the front pulley and the center bolt. Use a crankshaft holding tool and a torque wrench to tighten it to factory specifications. This is a big one! It will probably need to be tightened to 180 ft lbs or more!
Part 3 of 3: Finishing the reassembly
Materials Needed
- Belt tensioner tool
- Breaker bar
- Combination wrenches
- Dead blow hammer
- Drain pan and jugs for storage
- Safety glasses
- Screwdrivers (Phillips and straight)
- Socket wrench set
- Workshop manual
Step 1: Reinstall the water pump and belts. If the water pump is old, it’s a good idea to replace it now. It’s relatively inexpensive and will eventually fail so you can save yourself some trouble later.
Likewise, it’s good practice to install new belts at this time since you already have them all off. Use a little RTV sealer on the new water pump gasket when you put it on.
Step 2: Reinstall the radiator and fill the cooling system. If there is a coolant bleeder, open it up. If not, remove a heater hose at a high spot on the engine. Then pour the coolant in through the reservoir.
If the coolant you drained out is more than two years old, replace it with fresh coolant. Keep pouring until coolant runs out the bleeder or the hose that you disconnected. Close the bleeder and reconnect the hose.
Set the heater on High, and run the car until the temp gauge comes up and you feel heat coming out of the vents. Continue topping up the reservoir while the engine is warming up. When the car is fully warmed up and the coolant is at the correct level, Install the pressure cap on the reservoir.
Check the engine for oil or coolant leaks, then take it off the jack stands and take it out for a drive. Check again for leaks after driving around for a few minutes.
This is a job that will take you at least a day on the most basic arrangements. On the more complicated engines, it could take two or more. If your idea of a fun weekend doesn’t include spending it bent over the hood of your car, YourMechanic can replace your timing cover at your home or business to do the job at your convenience.
