You miss the point. The difference in sprocket phase IS NOT due to a difference in tension. It is due to the path being a different length as it chords from the sprockets to the fixed (non tensioned) side of the tensioner which is a different dimension. If the path is a different length, the phase of the sprockets changes. You use the word exact twice, and the timing will NOT be exact if the tight side chain path changes.

Now, if you want to argue that the 1-2 degree timing shift is immaterial, I would say you have a good argument. But the timing is not exact if you use the zip tie method.

 

The second gen, plastic Sach design, was excellent; regretfully plastic was crap: as we MEs learned years ago, design is one thing, strength and materials is equally . . . .

 

I have seen threads on here where cars with only 50k miles have cracked tensioners. Being well maintained, having a clean car fax, etc. isn't saying much. Heat and oil affects the plastic regardless of how well maintained it is.

I would make it a priority to check them and replace if they are original.

 

I'm having trouble picturing this. If the phase of one cam sprocket changes by 1°, wouldn't the phases of the other sprockets change by the same amount, thereby perserving the same timing? The five sprockets, (crankshaft, 2 intake cams and 2 exhaust cams) all remain locked together in the same place by their chains. A 1° change in one should result in the same 1° change on the other four.

 

Everyone thinks if they carry out the secondaries its all fixed. Why don't you consider the primaries and guides, as they're made out of the same plastic fantasic and just as prone to fail?

Thinking goes along the lines of, well the secondary failure is a destroyed top end, with the primaries its a noisey chain, wrong.

It's a bigger job that can't be bodged. The timing cover need to comes off, factory tools HAVE to be used. I've seen so many pulley pullers, pro and homemade bent in a U shape that have just not been designed for this work.

The ziptie method is a bodge, any process that carries an element of risk isn't the right way. I've not recommended this style of replacement on this board because of that risk.

Factory tools - these have been designed to take that risk out of the equation, for every 10 ziptie successes there's usually 1 bad one.

 

First, understand that when I compared the two tensioners, the position of the non moveable slipper shoe was different. I do not remember if it was positioned to push the chain out more or less from the most direct path between the sprockets, but it was different.

Just imagine two sprockets connected by a chain with some slack. If one sprocket is held, and the other sprocket rotates, the slack will move from one chain path to the other. Remember that the path without the tensioner action is the one that sets the phase. So, if you were to move the chain on that side, as that path changes distance, it rotates the non held sprocket in relation to the held one.

If anyone wants to confirm how much it changes the timing, you would just do the zip tie method, pull the slack to the moveable tensioner side of the path, assure that the VVT is bottomed out, and check how much the two flats are out of line.

Let me say, it would be foolish to delay doing the tensioners by the zip tie method just because one was waiting for the tools to do it "right"! I have done it both ways myself.

 

Sean:
I agree with you about doing both primary and secondary tensioners now that I have seen the condition of several of the primary tensioners! However, many years ago Jagtech Ohio (as I recall it was him, anyway) challenged anyone to claim that an engine crash had occurred because of failure of the primary chain tensioners. He claimed that they made so much noise when they were failing that the owner would fix it before the chains actually jumped teeth. I do not recall anyone here ever taking up that challenge.

Because of that, and the much higher propensity for secondary tensioners to fail early, I would say that it is foolish to wait to do the secondaries if you just cannot bring yourself to do both immediately!

Oh, and i will re-issue Jagtech's challenge.

 

Would anyone be able to provide some images of failed/failing primary tensioners?

I've not heard many issues with the primaries, however, I have seen plenty of images of cracked and broken guides.

 

Every time I read one of these threads I feel a little better about the awful amount of money I paid the local Jaguar dealer to do all my tensioners and a new timing chain. I probably wouldn't have had them do it, except that they had tracked down an oil leak to a cracked timing cover, and "as long as you're in there...." But, man, looking at those pictures at the top of the thread would be driving me nuts right now otherwise.

 

. . . which is why you race to upgrade the secondaries . .

Both Ross and Sean are correct: if you can afford it, or have the skills, tools, or space to do it right, DO IT RIGHT; if not, at least do the secondaries IMMEDIATELY!

 

Saying that there is "NO REASON" to use the proper tools is like saying, "I had sex with a prostitute and did not get a disease so therefore no one needs to use protection".

The tools are cheap to rent and take all the risk out of doing the job. If your valve timing is off at all, the tools will bring everything back to spec.

 

In North America, there is a phrase ... "the buck stops here".

It means that the responsiblity lies with the decision maker.

In this case, that would be the british JAGUAR engine engineering team.

The original SACHS design is actually nicer than the replacement.

The problem was the fetish for weight reduction taken to extreme.

Look at the voids in the castings which could have been left solid,
and the main tube which could have had reinforcement right out
to the edge.

They all crack in the same place, and thus, for the same reason.

++

 

I have no images or pics of failed plastic body primaries but I replaced 2 or 3 in Jaguar Factory Warranty when I worked at the dealer back ten or fifteen years ago.

The piston in the metal bore has an 'O'ring that can fail and the tensioner looses it's ability to maintain pressure on the curved guide. The bottom of the 'O'ring holder comes loose, the 'O'ring disintegrates and guide 'chatters' and breaks apart.

I called tech line and was authorized to replace all guides, tensioners, and chains on an engine that had this fault.

The later 'all metal' primary tensioners have a ratchet mechanism to prevent the 'chattering' from using oil pressure alone.

The primary chains did not fail, but he NOISE at idle was enough to warrant engine repair!!!!!!!!!!!

YES the primaries can fail!!!!!!!!!!!!!!! The noise is ANNOYING!!!!!!
The tensioner blade disintegrates and the parts fall into the oil pan!!!!!!!!!!!!!!

Just keep driving until the oil light comes on and then pull the pan and remove the debris from the pickup screen. Then drive some more and if the engine fails, replace the engine!!!!!!!!!!

It's that easy.

bob gauff

 

The tensioners would be on the slack run of the chain and not the
working run.

Therefore, the timing would not change at all as that is determined
by the number of links running from driving sprocket to the driven
sprocket.

As I have pointed out in the past, given the limited number of
teeth on the driven sprocket, any mistiming is grossly obvious.

For example, if there were 20 teeth, a single tooth misalignment
would be 18 degrees.

 

Answered earlier before completing the thread, but as explained in that
post, sprocket timing is purely a function of the number of links being
maintained on the working run. The tensioner is only there to take
up slack on the return run.

 

As put directly to that member, it was ultimately his team's decision to incorporate these
tensioners, and therefore the outcome is on their heads. In fact he hints that his main
responsibility was the cylinder heads. I would say that the timing drive would have
been an allied responsibility.

He has never responded to that to my knowledge, although he is eager to bash the
driveline team's decision to change differentials, going so far as to name names.

I believe the differentials fail much more infrequently.

Would they be better with a LSD option? Yes.

Could they be setup tighter? Again yes.

But, they aren't bone china teacups either. Unlike the tensioners that his
team decided to adopt.

 

I used the ziptie method without concern, other than introducing the
idea of using multiple zip ties.

In fact, I have employed similar methods on other engines by simply
marking the relationships using whiteout.

It is only on JF where the idea of adding zipties came to light given
the hoo-hah about using the factory tools. Other forums for other
makes quite happily go about the task without zipties.

A little bit of hillbilly engineering neve hurt anyone.

 

Good to know.

I guess if the noise is too annoying, one could always install a sport exhaust!!!

 

Well, Plums, again you spout off about something you have no direct knowledge of; There might be many motivations for using a plastic design, and you have determined which one it was by claivoyance, I guess.

And... If you have actually been inside the AJ26 or AJ27 engine, you should have noticed that there there is a slipper on the tight side of the chain, integral to the tensioner assembly that does set the tight side path. I suppose your clairvoyance let your down on that one!

 

So, on the primary tensioners, there is no reason for "immediate" concern so to speak unless it's chattering?
I only ask, because I would like to better understand the risks of potential primary timing chain failure, and the likelihood of it... Thanks.