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How-to: timing chain replacement


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Thought I’d throw up a little old-school tech for the group. Although most of the component removal I did wasn’t absolutely necessary, I was doing some other maintenance and mods at the same time, and the pics are a lot better to see what I’m describing.

 

After listening to my timing chain slapping around for the last 30K miles, I decided to replace it over the weekend. Special thanks to Chuck (cmcolfax) for giving me half of his garage to work in :cheers: If anyone’s thinking about doing this who hasn’t done it before, I’ll try to make this as all-inclusive as I can. Feel free to ask any questions if I don’t cover everything (or if I left anything out….I was working solo and taking pics as I thought I should for a good writeup). My MJ is a 2.5L, but both the 2.5 and the 4.0 share the same bottom end, so the procedure is identical for either engine. Your alternator bracket will be a bit different than mine, and I don’t have AC so I didn’t have to work around AC lines or a condenser, either. YMMV ;)

 

OK, here we go…here’s the patient, my 87 MJ 2.5L with 174K miles on it, and a slapping timing chain:

 

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Start by removing the battery, drain the cooling system and remove the radiator (and if you have AC, deal with the condenser somehow):

 

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With the radiator out of the way, you can see the harmonic balancer bolt that needs to be loosened. At this point, leave the serpentine belt intact (the tension will help hold the balancer stationary while you loosen the bolt):

 

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There’s a couple different ways to break that bolt loose (which I won’t mention), but I prefer this for a quick-and-easy method:

 

 

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Break the bolt loose, but do not remove it yet. Now you can remove the serp belt. First, loosen the tension in the belt via the power steering pump (all bolts are ½” hex head, FYI). There are 2 bolts to loosen that hold the pump, one trunion nut that holds the tensioner bolt, and one tensioner bolt you turn counter-clockwise to move the pump toward the engine. Remove the airbox for complete, hassle-free access to these. The two bolts in the back of the pump are these:

 

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The trunion nut is in the front, at about 7 o’clock:

 

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And the tensioner bolt is under the pump, pointing toward the driverside fender. Turn it counterclockwise to loosen the pump (you may have to persuade the pump to move if it hasn’t in a while):

 

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Remove the belt. At this point, I also removed the radiator shroud, fan, and water pump pulley for better access to the timing cover. Next step (if you haven’t already) is to set the engine to TDC, using the harmonic balancer bolt that you loosened above. Rotate the engine clockwise with a ¾” socket until the timing mark on the balancer lines up with the “0” mark on the timing tab on the cover:

 

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Verify TDC by rotor position. The rotor tip should be pointing directly at the #1 tower on the distributor cap:

 

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Once you are at TDC, remove the harmonic balancer. Use a balancer puller, like this…

 

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It attaches to the HB and pulls it off the crank snout cleanly and easily. Do not redneck engineer this process, and do not rotate the engine.

 

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With the HB off, you can see what they are famous for….they are a two piece construction, with rubber sandwiched inbetween the inner and outer parts, and the rubber starts to migrate out, and start gringing away on the front of the timing cover (not a good thing). Here’s what mine looked like:

 

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And this is what the back of the HB looked like. See the rubber ring :cry: ?

 

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We’ll deal with that in a bit. For now, go ahead and remove the myriad of fasteners that hold the timing cover to the block. The larger studs are 11/16”, and the smaller bolts on the face are 10 mm. There are 4 bolts that hold the bottom of the cover to the front lip of the oil pan, and they are 8mm. I like to keep track of multiple fasteners using a piece of cardboard, like this:

 

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Finally, you arrive at the timing set. Stop and have 10 beers.

 

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At this point, if you’ve done what I did, you will have roughly a pile of removed parts that looks something like this:

 

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And your engine bay will look something similar to this:

 

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Good enough for today, I’ll finish tomorrow:

 

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OK, to continue. I cleaned up the timing cover, and the damage from the balancer was minimal (not enough to warrant replacement):

 

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The only difference between the 2.5 and 4.0 timing sets (the parts themselves are identical) is that the 2.5 uses a spring-loaded tensioner. Mine tensioner was shot, causing the clacking sound, and the chain was stretched somewhat. Here’s the gears and chain with the tensioner removed. Not cool:

 

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Verify the timing marks on the sprockets are lined up, remove the oil slinger on the end of the crank (the dish shaped thingy) and remove the chain and both sprockets together as an assembly. The cam sprocket is held on with a ¾” bolt (use the impact gun again so you don’t rotate the engine), but the crank sprocket is pressed onto the crank and is held with a machined keeway. A little gentle prying may be necessary to remove the sprockets. It’s a good idea to stuff some rags into the oil pan at the bottom front of the block to prevent anything from falling into the pan while you are working/cleaning. Once removed, you will have this:

 

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At this point, DO NOT rotate either the crankshaft or the camshaft or you will have to reset the valve timing. Lay the old timing set next to the new set, and align the new set exactly like the old. Notice the timing marks on the sprockets (6 o’clock on the cam gear and 12 o’clock on the crank gear):

 

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Clean off the face of the block and mating surface of the cover while the gears are off, and install the new gears and chain, again as an assembly.

 

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The crank sprocket is keyed, and the cam sprocket has a small hole machined into the back of it that lines up with a pin (I forgot to get a pic of this, sorry), so the gears can only go on one way. Fiddle around with them until it all lines up, then push the sprockets on alternately, so the chain doesn’t bind. Once they are on as far as you can push them, I used a rubber mallet to give each a couple taps to make sure they were seated. Spin the cam sprocket bolt back on with the impact (torque to 80 lb/ft), and reinstall the oil slinger:

 

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One thing (probably the most important, actually) I forgot to get a pic of is to verify the timing marks by rotating the engine (use the HB bolt in the front of the crank snout again) until the timing mark on the cam sprocket is at 3 o’clock. Once there, stop rotating and count the number of chain pins between it and the timing mark on the crank sprocket. There must be 20 pins (15 pins for a 4.0L per the manual) If you didn’t move anything when you took the old sprockets off, and installed the new ones with the chain taught, you shouldn’t have a problem. If you don’t have 20 pins, you have issues, and you’ll have to start all over again :cry:

 

Got 20 pins? Good. Stop and have a beer or five, then proceed. For us 2.5 guys, install the new tensioner. It is held to the bottom of the block with a bracket held by two bolts…to access them, you have to drop the oil pan (which I wasn’t going to do ;)) Instead, the tensioner itself pivots on a post inside the front of the cover, easily accessible. It is held by a circlip that you remove and pull the tensioner off the post. Slip the old one and replace with the new one, and reinstall the circlip. Make sure the tensioner is UNLOCKED before you button everything up. Once the tensioner is installed, and the oil slinger is put back on the front of the crank (dish shape facing OUT), you can reinstall the cover.

 

But first, install a new oil seal on the cover. Tap it in with a large socket (or block of wood) squarely into the cover until it sits flush:

 

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Install the rubber gasket onto the bottom of the cover. There are little tabs that fit thru predrilled holes to align it and hold it in place (no pic…sorry I forgot). Make sure both the cover face and the block mating surface is sqeaky clean, apply gasket sealer to both surfaces:

 

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I use Indian Head gasket shellac:

 

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Let it tack up a few minutes, install the paper gasket, then install the cover on the engine. Thread all the fasteners finger tight (this is where you’re carboard template comes in handy). Have fun aligning the 4 oilpan-to-cover bolts on the bottom of the cover. Once all fasteners are installed, torque the small bolts to 5 lb/ft and the large studs to 16 lb/ft. Make sure the oil pan rubber gasket is aligned properly or it will leak.

 

Reinstall the harmonic balancer (make sure the woodruff key is still there to align it). Do NOT hammer it back on to the crank snout....line up the keyway with the woodruff key and push it on as far as you can, evenly. Then, thread the the 3/4" bolt and washer back into the front of the crank and tighten it down. It will draw the balancer back onto the crank as you tighten it down. Wipe some clean engine oil around the sealing surface of the balancer so that the new front seal you just installed doesn’t rip when you first start the engine. Verify timing one last time by rotating the engine around until the timing mark on the HB aligns with “0” on the timing tab (TDC) and verify rotor position on the distributor. If you did everything right, it should be pointing to #1.

 

 

 

I didn’t take any pics of the reinstallation of everything else, but if you took it off you ought to be able to put it all back together ;) I completed the work with a coolant flush and new radiator hoses (upper, lower, and heater, with new clamps). Don’t forget to remove the overflow bottle (if you have an open system) and flush/clean it also). I also changed the oil just in case anything nasty found it’s way into the oilpan while I was working.

 

Once you get it all buttoned up, fire it up. If it runs, you did good….have another beer. If it doesn’t, have a beer anyway ‘cause you’re going to have to rip it all back apart:

 

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Hope this helps somebody!

 

Jeff

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Got some better pics of the tensioner today, to show just how worn out it was :cry: Here it is, assembled as it came off the engine. The little block at the end of the spring starts it's life at the other end of the assembly, up where the little locking handle is on the far left. This thing has gone the whole way to the end of it's adjustment range:

 

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Here you can see how worn the face of it is, where the chain rides. See the nice, chain-shaped grooves worn into it? They are about 1/4" deep :eek:

 

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This isn't the best pic, but it shows the wear on the inside, where the snubber block rests against the inside of the tensioner arm. Both surfaces have teeth cut into them (to prevent the snubber from moving backward as the assembly wears...it ratchets it's way up the tension arm as it goes thru it's life. It's hard to see, but the snubber teeth are completey worn away, as are the teeth on the inside of the arm. You can see where the block has been sitting (at the end of it's adjustment range) for the last 30K miles on my engine.....

 

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Jeff

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  • 2 years later...

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