Note:  This maintenance write-up for a TJ 4.0L engine timing chain replacement is provided courtesy of Mike Forbes.  Mike was doing some work on his 2005 TJ and asked if I wanted to put the info on the site.  Since I had nothing on the site that addressed a timing chain replacement, I was happy to accept his offer.  So here it is, direct from Mike.   And Mike….thanks again for providing this info for everyone else to use.

While changing the rear main seal, I took a look at the timing chain.  It flexed just over half an inch which, according to the factory service manual, means it’s up for replacement.  All in all about 4 hours.

Mopar Timing Chain
Mopar Camshaft Gear
Mopar Crankshaft Gear
Mopar front crankshaft seal
Mopar Timing Chain Cover Gasket
RTV Black

Tools Needed:
Factory Service Manual (FSM)
Inch Lbs Torque Wrench
Torque wrench that can go to 80 ft lbs
Seal Installer
Harmonic Balancer Puller
Harmonic Balancer installer
1/2″ Breaker Bar
Socket extensions
Gasket Scraper
Wire Brush
10 MM socket
11 MM Socket
13 MM socket
14 MM socket
15 MM socket
16 MM Socket
19 mm socket
Large Crescent

The parts, 2 gears, a chain, a new crankshaft seal and a cover gasket.

This is easiest with the water pump out of the way.  Either replace the gasket if the pump is new or the pump if it hasn’t been changed in a while.  Note: I don’t think you have to remove the water pump and will attempt this on my TJ in a few weeks, I will update if different.  I picked up this LJ at 91,000 miles so I did not know the previous maintenance and chose to replace the water pump, thermostat and hoses at the same time.

Step 1:  Remove the radiator overflow container.  Simply push on the plastic nub that sticks through the shroud and lift up.  Disconnect the hose from the radiator neck.


Step 2:  Remove the fan and fan shroud.  The fan requires a big crescent wrench, quite big, looks to be 36mm.  Whack it with a 5 lb hammer is usually enough to break it free.  Once it is lose, remove the 4 11mm bolts holding the shroud to the radiator.  There are two on each side, the bottom ones are bit of a pain but are reachable from the top.

NOTE:  DO NOT STORE THE FAN FLAT. The fan MUST be stored VERTICAL.  It has to do with the thermal viscous fan drive so be careful and don’t lay it on its side.

TJ 4.0L Timing Chain Replacement

Step 3:  Using a 19mm socket and a large breaker bar break free the crankshaft bolt.  I have a manual transmission, so I just put the jeep in gear with the parking brake on.  It broke free rather easily.

Step 4:  Drain the radiator.

Step 5:  Remove the water pump, thermostat, and radiator hoses.  Refer to the water pump/thermostat replacement write-up.

Step 6:  Remove the radiator by removing the 4 10mm bolts, 2 on each side.  I found a deep well worked well, a regular socket with an extension would have worked as well.

Step 7:  Using a 1/2 inch breaker bar insert the bar into the belt tensioner and remove the belt while levering the breaker bar to relieve tension.

TJ 4.0L Timing Chain Replacement

Step 8:  Remove the alternator bracket as the belt tensioner is attached to it and is blocking bolts on the timing chain cover.  The two bolts holding the alternator in the bracket are 15mm, the 4 bolts holding the bracket to the engine are 14mm.

Step 9:  Remove the crankshaft bolt with a 19mm socket and be sure to remove the washer or you will not be able to remove the vibration damper.  Notice the washer is still on in this photo!

Step 10:  Using the harmonic balancer remover, make sure the tip is on it it or it will destroy your crankshaft threads.  Note, I missed this part :(, I thought the end was bigger than the bolt hole, I was wrong and got lucky and figured it out before I did much damage to the crankshaft threads.  DOH!  Read all directions on tools you are not familiar with!!!  Remove the vibration damper with the remove and set aside.

Step 11:  Remove the the bolts in the timing cover, most of them are 10mm and there are two 16mm bolts, and four 11mm oil pan bolts.  I use a piece of cardboard so I know where the bolts go.  Just stick them through the cardboard as you take them out in the same position.  Strangely on mine 1 bolt was missing, it had apparently been taken apart before and not put back together correctly.  I found the bolt stuck in some engine grease on the block, very strange.

Step 12: Slide the cover off. Note the chain guide likes to slip out. Just make sure not to lose it.

Step 13:  The timing marks need to line up on both the crankshaft and the timing gears before you can remove them.  You can see them in this photo near the edge of the gears, they are 2 lines.

I had to slide the vibration damper back on just a bit to turn the crank to get the timing marks to line up.

Step 14:  Once lined up remove the camshaft bolt and washer with a 16mm socket.

TJ 4.0L Timing Chain Replacement

Step 15:  Remove the large sprocket and chain being careful not to turn anything.  Not likely as the engine is hard to turn.

Step 16:  Remove the key from the crankshaft and remove the lower gear.  Note: I could not get the small sprocket off.  I realized I had not removed the key in the crankshaft.  But since my near disaster with the crankshaft threads I was not excited to screw something else up. I had read the gears were hardened steel so I replaced the top one only on the camshaft.  The lower crankshaft gear looked fine anyways.  I will be doing this on our TJ in the near future and will do both gears. I will provide an update if anything changes.

Step 17:  Replace the chain and gears in the same position making sure the timing marks align.  This is critical!!! Reinsert the key into the crankshaft with some RTV.

Step 18:  Reinstall camshaft bolt and washer tighten the bolt to 68 Nm (50 ft. lbs.) torque.  Useful to put the jeep back into gear at this point.

Step 19:  Remove the seal from the cover with a seal puller.

Step 20:  Install a new seal while supporting the cover.  The FSM states to put some rtv on the outside of the seal before tapping in and to lubricate the seal with oil before installing.  I recommend the mopar tool but you could just use a socket.  I found the tool on e-bay for 24 bucks.

Step 21:  Clean the surface of the timing chain cover and engine block

Step 22:  RTV the timing cover gasket on both sides as my friend says jeeps like to leak.

Step 23:  RTV the bottom of the timing cover where it has the sharp corners.

Step 24: Reinstall cover using the seal installer as a guide on the crankshaft. Be careful not to lose the chain guide.

Step 25:  Tighten the 1/4 inch cover-to-block bolts to 7Nm (60 in. lbs.).  Tighten the 5/16 inch front cover-to-block bolts to 22 Nm (192 in. lbs.).  Tighten the oil pan-to-cover 1/4 inch bolts to 9.5 Nm (84 in. lbs.)

Step 26:  Using the harmonic balancer installer reinstall the vibration damper.  This tool is great, it threads into the crankshaft and has a larger bolt that goes over that one allowing you to put a nut on the outbound side of the damper.  You just crank it on.

Step 27:  Install the crankshaft bolt and washer and Tighten the bolt to 108 Nm (80 ft. lbs.) torque.  I put some RTV under the washer, not sure if that is needed but it looked like there was some there previously.

Step 28:  You are done, reinstall in the reverse, alternator, water pump, thermostat, radiator, fan and shroud.

The FSM said there was a oil slinger on the crankshaft. I did not see one and maybe that has something to do with the missing bolt on the timing cover and previous maintenance.I will update if the TJ has one, if it does I will have to reopen this up and correct it. It helps to deflect oil from the front crankshaft seal.

Things I have learned from this install is to have lots of degreaser on hand to clean things up.  You will notice that timing cover wasn’t as clean as I would have liked.  The bolt I found caused a leak and greased up the entire front.  Not sure why someone would not put all the bolts back in a timing cover?  Next time lots more cleaner!