How to: Rear Timing Chain Tensioner Replacement

[2000StreetRod]

Background

The single overhead camshaft (SOHC) V6 engine may have as many as four timing chains with associated tensioners and guides. The main timing chain connects a sprocket on the crankshaft with a sprocket on the jackshaft as shown in the photo below by CDW6212R.

The jackshaft is in the same location as the camshaft on the overhead valve (OHV) V6 engine. The primary sprocket on the jackshaft is larger in diameter than the sprocket on the crankshaft. The secondary sprocket on the jackshaft is smaller than the sprocket on the camshaft. The combined ratios result in the crankshaft making two revolutions for one revolution of the camshaft. As the crankshaft sprocket rotates the teeth engaging the chain pull the jackshaft sprocket on one side. I call that side the traction side. The chain on the opposite side would be relaxed if it weren't for an installed tensioner. I call that side the slack side. The tensioner is only spring loaded unlike the OHV V6 tensioner that is spring and oil pressure loaded.

Behind the primary (large) jackshaft sprocket is the secondary (smaller) sprocket not visible in the above photo. This sprocket engages a chain that pulls a sprocket mounted on the camshaft located in the left (driver side) head. There is a guide assembly that limits the amount of side-to-side chain deflection and there is a spring/hydraulic tensioner on the slack side as shown in the photo below by CDW6212R.

The left upper chain guide assembly is shown in the photo below by ipwizard.

The guide assembly, chain and sprockets comprise the timing chain cassette.

The configuration of the camshaft chain drive for the right (passenger side) head is rather unique. A sprocket is mounted on the rear of the jackshaft and a sprocket is mounted on the rear of the right camshaft. The two sprockets are connected via a chain with associated guide assembly and tensioner on the slack side as shown in the photo below by CDW6212R.

The tensioner is at the very bottom center of the photo.

The engines in four wheel drive models and some of the later two wheel drive models have a balance shaft in the right side of the upper oil pan. On these engines there is another crankshaft sprocket located behind the front sprocket and a sprocket on the front of the balance shaft. The two sprockets are connected via a chain with associated guide on the traction side and tensioner on the slack side. Some of the components are visible in the first photo of this post.

 

[2000StreetRod]

Background continued

The rear timing chain cassette is shown in the photo below by ipwizard.

The following photo from an eBay vendor shows a 4WD timing chain kit.

The rear timing chain tensioner is the shorter cylindrical threaded housing with a hexagon head in the photo above. It is inserted/extracted in the rear of the right head on the side aft of the number three spark plug as shown in the photo below by CDW6212R.

A close up photo of the rear tensioner is shown below.

The red arrow identifies the hole that allows pressurized oil to enter the threaded cylindrical housing. The oil pressure forces the plunger against a projection on the guide resulting in chain tension. The blue arrow emphasizes the short distance between the under face (idenitified by the green arrow) of the hexagon head and the start of the hole. Installing a thick compression O ring will partially (if not totally) reduce the internally exposed oil passage and restrict oil flow to the plunger. Only install the very thin metal seal designed for the tensioner. It is important not to score the under face and the mating face on the head where the metal fits. Potential leaks can be prevented by keeping the tensioner installed when working on the engine except when the tensioner is being replaced. The metal seal can easily slip out of position when screwing in the tensioner. Grease can be applied to the metal seal to keep it in position.

I recommend that the rear timing chain tensioner be replaced every 75,000 miles or whenever chain rattle is detected at the rear of the right head. Chain rattle usually is first detected at engine cold start because the oil has had time to drain from the timing chain components. As the tensioners age the internal spring pressure weakens and the plunger exerts less force on the timing chain. This allows chain slap until oil pressure builds in the tensioner. Chain slap accelerates guide wear. As the guides wear eventually the chain comes into contact with metal surfaces resulting in chain wear and metallic particle contamination of the oil. The metallic particles in the oil accelerate oil pump wear and can accelerate wear in engine bearing surfaces unless a high quality filter traps them. Typically the rear chain cassette lasts longer than the front cassette because upon engine start the rear cassette receives oil sooner than the front cassette.

 

[2000StreetRod]

Tensioner removal

This post describes how to replace the SOHC V6 rear timing chain tensioner on my 2000 Sport.

1. Slightly loosen the right front wheel lug nuts.

2. Raise the right front of the vehicle. I used the original equipment bottle jack placed under the protrusion on the lower control arm.

3. Place a jack stand under the frame for safety and greater stability (considerable force may be required to loosen the tensioner). Lower the bottle jack until the jack stand is supporting the weight of the vehicle. Leaving the bottle jack in place provides additional safety.

4. Remove the wheel.

5. Remove the wheel well inner mud flap.

6. Working inside the engine compartment loosen the tensioner using a 27 mm shallow 6 point socket and a long breaker bar or torque wrench. The force required may exceed 75 ft-lbs.

The red arrow in the photo identifies the location of the socket fitted to the tensioner head. The shallower the socket the easier the loosening. If the socket is extremely shallow, there will be enough clearance for a breaker bar positioned vertically upward. An undersirable alternative to the socket/bar tool combination is a box or open end wrench. However, unless the handle is long there may not be adequate leverage to loosen the tensioner. Some members have successfully loosened the tensioner while working thru the wheel well. My attempt with a very deep well socket and various combinations of wobble and normal extensions was unsuccessful.

7. Working thru the wheel well unscrew and remove the tensioner.

 

[2000StreetRod]

Tensioner installation

CAUTION: McSlug has provided an excellent tip regarding the installation of the new tensioner. It is very important to ensure the washer/compression ring (if used) on the tensioner is centered when the hex head face contacts the head. If the compression ring is not centered then oil will leak profusely no matter how tight the tensioner. Applying a small amount of gasket sealer between the compression ring and the tensioner face will keep the ring in the correct position.

1. Make sure the tensioner sealing face, the washer/compression ring (if used) and the mating surface on the head are clean.

2. Working thru the wheel well with your hand screw the tensioner (with washer/compression ring) into the threaded hole in the head. Pressure will be required to compress the spring to start the threads. Be careful to keep the tensioner perpendicular to the head face to avoid cross threading.

3. Continue screwing the tensioner in by hand until the spring pressure prevents further rotation.

4. Use socket, extensions and ratchet/torque wrench thru the wheel well to screw in tensioner until it seats.

5. If using a new washer/compression ring torque the tensioner to 32 ft-lbs. If reusing the old washer/compression ring or none torque the tensioner to 49 ft-lbs. Torque the tensioner from the engine compartment if possible. Otherwise, torque the tensioner thru the wheel well realizing that the torque reading will be inaccurate if the wrench is not perpendicular to the axis of the socket.

6. Install the wheel well inner mud flap.

7. Install the wheel.

8. Raise the vehicle.

9. Remove the jack stand.

10. Lower the vehicle.

11. Torque the wheel lug nuts.

 

[Ritsui]

Thanks for the excellent info, writeup and pics

I can't see getting the rear tensioner loose from the top. In my 98 Sport, there simply isn't any room to move front/back even if I could get a bar up through that tight of a space. Fortunately, I was easily able to break it loose through the wheel well using a deep socket, two extenders and a 4 foot bar. With just a bit of upward leverage on the fender plastic, I was able to get the angle completely perpendicular. I imagine anyone with a body lift should be able to do it even easier.

Thanks again

 

[ExploringNC]

How much was the timimg chain kit?

 

[biggiesize]

I understand about changing this tensioner.But what good will that do if the plastic chain guide on the rear is worn?Am I missing something or does this tensioner wear down before the guide?From what I have read and seen in pics,alot of the problem comes from the plastic guides actually breaking.If I replace this tensioner,will that prevent that from happening?

 

[2000StreetRod]

cost & usefulness

I bought the tensioner for $5 with a lucky purchase on eBay. They're normally around $30.

The tensioner spring weakens with age accelerating the startup chain slap that accelerates guide wear. Replacing the tensioner will not repair worn chain guides.

 

[2000StreetRod]

tensioner not chain kit

How much was the timimg chain kit?

This thread was just on replacing the rear tensioner. A timing chain kit is much more expensive and replacing the rear chain or guide assembly requires either pulling the engine (preferred) or the transmission.

 

[Mark98]

I bought the tensioner for $5 with a lucky purchase on eBay. They're normally around $30.

The tensioner spring weakens with age accelerating the startup chain slap that accelerates guide wear. Replacing the tensioner will not repair worn chain guides.

Could you get a link? The only thing I can find is around $50 so I'm hoping I searched for the wrong thing.

 

[2000StreetRod]

tensioner source

Could you get a link? The only thing I can find is around $50 so I'm hoping I searched for the wrong thing.

XU3Z6K254BA, rear tensioner

tousleyfordparts.com
tascafordparts.com
silverstatefordparts.com
fordgenuinepartsonline.com

 

[biggiesize]

the inside of that engine sure looks clean compared to alot of other 4.0's that I have seen with sludge buildup.Do you use any kind of additive like seafoam or anything or is that just from regular oil changes?

 

[2000StreetRod]

CDW6212R's engine

Those photos are of CDW6212R's engine. I agree it looks very good. Mine looked like below when I pulled the valve cover off after owning the vehicle for about 2,000 miles.

 

[Mark98]

XU3Z6K254BA, rear tensioner

tousleyfordparts.com
tascafordparts.com
silverstatefordparts.com
fordgenuinepartsonline.com

Thanks!

 

[Vargas]

XU3Z6K254BA, rear tensioner

tousleyfordparts.com
tascafordparts.com
silverstatefordparts.com
fordgenuinepartsonline.com

I just received the parts I ordered from Tousley. For the rear tensioner, I ordered 7U3Z-6K254-A (a number I found here) which appears to be identical to the newer style (deep socket required) tensioner that is part of the 00M12 kit YL2Z-9E473-AA I ordered at the same time. I had not realized they were the same component. I don't know enough about Ford part numbering to tell if one of those numbers obviously supercedes the other or not. Based on your pictures/description, the rear tensioner does not have a washer under the head. I noticed that the 00M12 kit includes a washer for the front tensioner. Thoughts on that?

 

[2000StreetRod]

Rear tensioner part number

According to usallparts.com rear tensioner part numbers are XU3Z6K254BA superceded by 7U3Z-6K254-A and look like the one shown in this thread and not like the one included in the 00M12 kit. Is the part in a sealed bag with the later number on it? The longer barrel will increase the difficulty of installation and removal. The specified spring pressure may be different. I would question whether the correct part was shipped?

 

[Vargas]

According to usallparts.com rear tensioner part numbers are XU3Z6K254BA superceded by 7U3Z-6K254-A and look like the one shown in this thread and not like the one included in the 00M12 kit. Is the part in a sealed bag with the later number on it? The longer barrel will increase the difficulty of installation and removal. The specified spring pressure may be different. I would question whether the correct part was shipped?

Part number 7U3Z-6K254-B is on the box, tensioner wrapped in protective paper, inside box. Nothing sealed. Dimensionally identical to tensioner in 00M12 kit, and spring pressure feels the same, too. Firmer than I expected - not going to be fun to get the threads started.

 

[2000StreetRod]

tensioner PNs are different

Part number 7U3Z-6K254-A is on the box, tensioner wrapped in protective paper, inside box. Nothing sealed. Dimensionally identical to tensioner in 00M12 kit, and spring pressure feels the same, too. Firmer than I expected - not going to be fun to get the threads started.

I have just confirmed with a Tasca Ford parts sales representative that the part number for the left (front) tensioner is 7U3Z6K254B and the part number for the right (rear) tensioner is 7U3Z6K254A. You must have been sent the incorrect part. I would notify Tousley of the error.

 

[Vargas]

Thank for the very thorough research.

That is exactly what happened (they sent the wrong part). I ordered 7U3Z-6K254-A and they shipped 7U3Z-6K254-B in error. I contacted Tousley Ford and they corrected their mistake right away.

 

[Vargas]

I'd like to share my experience with replacing this part.

First a big THANK YOU to 2000StreetRod for his effort creating this (and other) helpful thread.

Armed with a 7U3Z-6K254-B from Tousley Ford and two new sockets, I tackled this seemingly small project this afternoon. Craftsman doesn't make (or at least local Sears didn't stock) 27mm 6pt sockets, so I purchased 1-1/16" 6pt 1/2" drive regular and deep sockets.

Once it was up on the jack and jackstand and I had the wheel off, I started by removing only the small flexible part of the fender liner. By the time the project was done, I ended up removing the rest of the liner, so you might decide to skip pulling off just the small piece. In my engine compartment, there is essentially no access from above, so I worked entirely from the wheel arch.

The extremely shallow head of the tensioner makes it tricky to keep the socket from slipping. The Craftsman sockets have a beveled lip at the edge which makes this even worse. If I was doing this more than once or twice, I would find or make/modify a flush faced socket.

I did not have a sufficient length of 1/2" drive extensions, so I ended up working with a combination of 1/2" and 3/8" with an adapter in between. This meant having to work with a 3/8" ratchet handle instead of my 1/2" breaker bar. This was annoying, and high on my list of tools to add soon will be a set of 1/2" extensions. At various times in the process, I was working with a total extension length of 12"-18" depending on socket and direction.

I was able to remove the old tensioner with only the small wheel liner removed. I swapped in my cheap ratchet and used a two foot pipe on it as a cheater. It is an awkward job due to the offset of the extensions. One hand (left) has to stabilize the ratchet head as a pivot point while the other hand is pulling on the cheater. I had the handle at about the 5 o'clock position. If you put a shop towel over the exhaust manifold/downpipe junction before removing the tensioner, it will catch the small amount of oil that will escape. Otherwise it ends up on the pipe and will smoke later.

I installed the new tensioner. I think there was a bit of spring resistance before the threads started - but I can't be certain after the fact. I was expecting to encounter some, and I don't recall being surprised at any lack thereof. I only doubt it in hindsight based on what happened - more on that later. The tensioner is easy enough to turn by hand so that you can be sure the threads are running smoothly. I had no trouble running it all the way flush with the head, just using my fingers. I assembled another slew of drive extensions and torqued the tensioner to 49 ft lbs. It is a major pain to torque things accurately in this circumstance, with the huge offset of the drive extensions.

Before buttoning things up, I started the engine to check for leakage. It was leaking quite badly. I shut the engine off and attempted to increase the torque on the tensioner. I simply could not get more force on it at the compromised angle I was working from. After having the socket slip off a couple of times, once marring the head of the tensioner and once bashing the knuckle of the owner, I decided I needed more room to work. At this point I began to remove the rest of the wheel arch liner.

Removing the liner -
There are two screws with 8mm heads at the forward edge of the liner.
There are two more screws of the same size in the top of the wheel arch.
The vacuum reservoir is attached to the liner.
I recommend separating them before removing the liner.
To do so, remove the two screws with 10mm heads near the front of the liner.
There is a clip holding the vacuum lines to the liner, installed from the engine compartment side of the liner.
You can poke it out from the wheel side, just look for the nub.
Lastly, there are four philips head screws along the lip of the fender.
The rear most screw is oriented vertically at the rear of the fender lip.
My Explorer has the tube style running boards, and the front portion curves under the fender lip, blocking access to that screw.
The curved piece is a separate part that comes off by removing two 13mm nuts.

With all of the fasteners removed, the liner was pulled out and set aside. Be gentle as you remove it, as the vacuum ball will drop down and you don't want to break one of the plastic lines.

With the full liner removed, I now had straight line to the tensioner, whereas before I was slightly off axis and constantly deflecting the liner.

To overcome the problem of torquing on a long extension, I found a simple solution using parts/tools at hand. I used the deep socket and one section of the bottle jack shaft to make a pedestal for the head of the torque wrench. With the wrench at 3 o'clock, the left hand on the wrench head can push toward the tensioner keeping the socket seated, and the right hand pushes down on the wrench handle. The pedestal keeps the wrench head from deflecting downward. I rechecked the torque on the tensioner and the wrench clicked without movement. I reset the wrench to 54 ft lbs and again the wrench clicked without movement. I decided to remove the new tensioner and reinspect the mating surfaces. Everything looked good.

I reinstalled the new tensioner and this time I am certain there was no spring pressure felt until the threads had been engaged for several turns. I torqued to 54 ft lbs and started the engine. The tensioner was still leaking so I shut the engine off. I loosened the tensioner and this time torqued it to 60 ft lbs. I started the engine and this time it was sealed. My torque wrench may be out of calibration, in which case my numbers are off. If not, I may have a devil of a time whenever I next change this tensioner. In the future, I think it would be worth the effort to obtain a washer to use under the right/rear tensioner - either like the steel one that comes with the left/front tensioner, or the copper substitute I have seen mentioned.

The real test comes in the morning, when I learn if or how much the start-up rattle is reduced or eliminated.