Gordo,

Like you, I read all the posts on this subject and I don't remember seeing any primary chain/tensioner failures.  Since both the early plastic tensioner and chain guides are surly the same material as the the secondary ones I would think that the probably of failure would be the same.  Perhaps difference may be the number of teeth engaged.

Based on your pursuit of suspension problems I suspect that you are ultimately going to replace both.  Since you will have to remove all the things again that you will have removed doing the uppers I would do all at the same time, including the waterpump and serpentine belt tensioner.

I have continually been a little hesitant to tear into this strange piece of equipment but have found that it is really no different and the documentation is much better than the Haynes book I rebuilt that first Chevy engine with.

I was going to buy the aluminum T-stat housing from Black Dog Mfg (Britishparts.com)

Any brand recommendations on the Waterpump?

Thx Richyp.  I will sleep better now.  gordo

Cracking would usually be found on the tensioner body, under the shoe.You have to pull the tensioner to see the cracking here. Mine had one tensioner where the body just completely came apart, as well as losing the shoe. The other tensioner was still intact but had the body cracking, so I'm guessing it didn't have long to live.

My primaries were fine, but the primary chain guides all had cracking in the plastic. One guide was missing a small shard of plastic.

Also, the "whole job" in this case would include removing the oil pan to clean out the plastic shrapnel. This was an easy 30 minute job.

Dan

I have been on forums globally for many years, and I cannot remember to have read about a failing primary to underline Jagdocs experience.

However I have seen 1 primary guide that has completely failed, it was already deformed. Wish I have taken a picture as you would not believe it, the owner was very lucky that this was all that was destroyed.

My primary guides also where already cracked (the plastic around the metal), and small parts missing, I think it was around the 120Kmiles mark, or a little earlier. They obviously become more brittle with age and was glad that I changed it.

avos wrote:

My primary guides also where already cracked (the plastic around the metal), and small parts missing, I think it was around the 120Kmiles mark, or a little earlier. They obviously become more brittle with age and was glad that I changed it.

Hi Dennis. 

Torque values?  Why are you tightening the cam bearing caps? Not part of the project, are they loose?  Or were you simply noting the low values, which they do seem low.

The exhaust cam sprocket is spec'd high, because it is only that bolt tension which locks the cams, chains and crankshaft into place in the propert order.  There are no keyways or locating pins on the upper chain sprockets.

Use the temp thread locker on the tensioners, so you can break them loose again if need be. I didn't use anything to lock them down and feel OK about that.

No problems on what socket you use to turn the crankshaft bolt.  The engine assy rotates pretty easily. 

Good luck.  Gordo

Dennis: I packed xerox copies of the JTIS Service Manual instructions for replacing the secondary tensioners and another set for the primaries.  They were placed under the bubble wrap in the shipping box.  gordo

Dennis,
I don't doubt that you are reading those torque values, but the cam bearing cap value looks more like its for the coil cover.  Just a thought.

Gordo,
How did you torque your exhaust cam sprocket down?  I couldn't fit any torque wrenches in there so I had to go with the "calibrated arm".  Based on what it felt like coming off, I'm not concerned that I'm far off.  Just wondering what others are doing.

Mark R.

So I thought it might be worth posting a few observations after completing 1/2 of the job (the LH bank) and before I forget this stuff.

- things went pretty much as expected, with a few wrinkles and stop-and-think moments as follows ...

- A resident pro on the other form (Vic) noted a while back that that you really don't want to rotate an XK8 engine backwards during this job, since this can screw up the VVT timimg.  It occured to me that if you set a ratchet to tighten a normal right-hand thread, and use that instead of a box end wrench (which is what I first had in my hand) to turn the crank, you can't screw this up. 

- the exhaust sprocket securing bolt was really, really tight.  I had something like an 18" lever in play and still had to pull really hard to break it.  Scary.  I bet it was 100+ ft. lb.

- after this, the exhaust sprocket did not want to come off of the cam.  Could not get a puller on it.  Resorted to some prying and the like and it finally gave way.

- The removed 2nd gen tensioner was like new.  No cracking, and very little wear on the shoes.  Pictures later.  ~ 50k miles on the motor.  Everything is quite clean inside, so I'm thinking it was well cared for before I got it.


So: half-way home and all is well so far.  Unless Gordo is ready to go on his next job (Gorgo, please advise) I'll probably put off the RH bank until the weekend.

That's the story ...
Dennis

Here's what my removed original(?) secondaries looked like ('01 XK8, 49.6k miles):

Talk about your cognitive dissonance.  I'm delighted to see that these components survived in tact through that many miles.  It gives me high confidence in the condition of the primaries.  I also sort of wish they had been about to fail, so I would feel like the job really needed doing.  Anyway, each day's cold start will no longer be an adventure.

GordoCatCar wrote:

Is it true the Secondary Tensioners are more prone to failure than the Primary Tensioner system? 

After searching a dozen threads on the subject, it appears that Secondary Tensioners are more often the cause of catastrophic piston/valve interference.  Consequently they should be the first tensioners replaced.  Conversely, while Primary Tensioners (including the Guides and Rails)are subject to failures as any wearing part is wont to do; they are not as problematic as the 1st Generation Secondary Chain Tensioners. 

I have 4.0 AJ27 build date 3/97 with 65,000 miles.  Most likely it has 1st Gen Tensioners.  On startup there is a very slight chain slap which disappears after 30 seconds.  I assume this is the oil pressure building up in the tensioner body. 

Today the Secondary Tensioner replacement parts were ordered from JPLV; however, now I am having second thoughts about whether I should do the whole job at once. 

My logic is to first upgrade the Secondary with a 3rd Gen Metal Tensioner and see if that cures the symptom.  Later, when I get ready to upgrade the waterpump and thermostat, I will pull the front covers and closely examine what is needed regarding the primary chains.  For now I just want to immediately fix the chain slap on start up issue.

Is this reasonable thinking, as regards the Primary and Secondary Tensioners?