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Timing Chain

Is It Time For A New Chain?

A broken timing chain can make quick work of destroying an engine - depending on when and where it decides to break.  A worn out timing chain is one that has stretched enough that its slack is altering the critical timing sequence of the motor.   The results aren't as catastrophic, but the motor's performance will still suffer.   So when the opportunity knocks, changing the timing chain can be good insurance against unwanted engine problems.

If so...

As with all chains and sprockets (or gears), it is ideal to replaced at the same time.  When looking for a replacement timing chain and gear set, note they come in different varieties.  Some gears are a composite and have plastic (or nylon) teeth attached to a metal center piece!  At the other extreme, there are double-row gears that are slightly wider.  These are suppose to be very strong and are also more expensive.  At a minimum, get an all-metal set if you're replacing an old chain/gear set on an older (not-so-new) motor. 

While you're at it, pick up a new timing chain cover gasket kit.   This kit will include the rubber gasket for the bottom of the cover (against the oil pan), a normal gasket for mating the cover to the front of the block, and an oil seal for the harmonic balancer opening.

How To:

Remove the radiator from engine bay. Drain the coolant and remove the upper and lower radiator hoses.   Remove the fan belt, radiator, fan shroud, and fan.  You need to expose the front of the motor.
Step 2 Remove the alternator and its bracket from to expose the entire front of the timing chain cover.
Pulling the harmonic balancer. Now the harmonic balancer can be removed.  An impact wrench works well for the extraction of the retaining bolt.  Using a harmonic balancer puller, remove the old harmonic balancer.  The face of the old harmonic balancer will probably need to be cleaned in order to get the puller's bolts installed.
Step 4 Remove all of the bolts (many different sizes) that hold the timing chain cover on.  Don't forget, there are four bolts across the bottom edge that essentially make the forward edge of the oil pan cover.  Once all the bolts are removed, LIFT the timing chain cover before pulling it off - so as to not ruin the separate seal of the oil pan/timing chain cover bottom edge.
A look inside the timing chain cover. A wire wheel on a bench grinder comes in handy for removing the old baked-on oil from inside the cover.  After you've cleaned this, remove the oil seal (at the round opening) from the cover and replace it with a new seal from your kit.
Here's what the old timing chain looks like on the motor. Remove the oil slinger (it just slides on the crankshaft end), the bolt holding the larger gear sprocket to the camshaft, and then remove the large gear sprocket (a slight tap with a rubber hammer on one edge will help pop it loose if it's tight).   Remove the timing chain.  Now remove the smaller gear from the crankshaft end (a two-jaw gear puller works great for this part of the job).
Step 7 Clean off the old gasket residue from the front of the engine block.
timing-chain-align.jpg (41344 bytes) Look at the new timing chain gears and note that each part has a small single "timing mark" that indexes one of the teeth (in this case, it's a punch just below the tooth).  Set both gears down so that each timing mark faces the other.  An imaginary line should be able to be drawn through the center of each gear, crossing over the two timing marks.   This "line" is represented by the upper edge of the white zip tie in the photo.  Set the new chain over the gears while maintaining the indexing of the two timing marks.
timing-chain-15pin.jpg (35204 bytes) Now the gears can be rotated accordingly so their keyways will fit onto their respective shaft ends.  Don't let the chain slip while rotating them!    Place the gears onto their shaft ends (they will only go one each shaft end one way).  Again, make sure the chain doesn't slip. 

Once both gears are on, check that the chain hasn't slipped.  There should be 15 chain link pins between the two timing marks (each mark is represented by a colored zip tie).

Step 10 Each gear needs to be pressed back onto the shaft ends.  The larger gear sprocket will be pressed on via its own bolt.  The smaller gear sprocket will necessitate the use of tap hammer and a large deep socket to press it back on.  Then replace the oil slinger.
Step 11 Back to the cover, find the rubber oil pan seal and attach it to the bottom of the cover.  This rubber seal will work both ways, the correct way is to have the two short ends facing toward the block (back side of the cover).  Some trimming may be necessary if these short ends are too long.  Silicon can also be used to supplement this seal.
Step 12 Find the correct gasket for your cover (the kit may include more than one) and use a gasket sealant to attach the gasket to the back of the cover.  Apply a small amount of oil to the oil seal that fits over the crankshaft end.
Step 13 Carefully install the cover over the crankshaft end, and while lifting slightly, ease the rubber seal at the bottom of the cover over the forward edge of the oil pan.  Loosely install the bolts onto the cover (don't forget those on the bottom).   Check to make sure the crankshaft end is centered in the oil seal so the harmonic balancer can fit back INTO the oil seal.  Then tighten all the bolts.
Step 14 Install remaining parts from Steps 3, 2, and 1 if this is all you are doing.