[v12-engine] It's the Chain Tensioner!

V12-Engine
1

I’m moving this over from the XJS side. A quick run down is the
car, just out of the blue, started making a rattly, chirping
sound. It was distinctly loudest from the left side valve cover.
Although I figured it was a lubrication issue trying to seize the
camshaft, when I pulled the left cover the only thing wrong is the
timing chain is loose. Conclusion…the tensioner must have blown
up.

I will be studying the manuals and ‘‘book’’, but just wanted to ask
for any tips you guys might have. Some of my obvious questions are:

  1. Aside from the top side gaskets, how far do I have to go into
    the front of the engine and what gaskets should I order.

  2. Is it best to drop the oil pan to chase the plastic pieces, or
    just let them ride?

  3. At about 90k miles is a new chain in order, or do they last
    much longer than that?

  4. Is it easiest to just pull the motor for this rather than
    working over the wings and condensor?

Any tips are greatly appreciated!–
John. '95 XJS 6.0L convertible. Southlake, TX
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2

In reply to a message from CJ95 sent Sat 18 Oct 2014:

john that is a royal PITA!

seems as tho Jag didnt put the right engineering in the tensioner
system V12, also on there newer V8s, they seem to have trouble
with some of them also.

just something I observe.–
The original message included these comments:

car, just out of the blue, started making a rattly, chirping
sound. It was distinctly loudest from the left side valve cover.
4) Is it easiest to just pull the motor for this rather than

–
Ronbros
daytona fl. / Austin TX., United States
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3

In reply to a message from Ronbros sent Sat 18 Oct 2014:

Isn’t that the truth! I’ve been checking on prices and
the tensioner alone is $300. I in sticker shock for a POS
part like that. At that price the thing should outlast
the rest of the engine.

Now Steve has me concerned that a failed tensioner may
result in the valves contacting the pistons. If that
turns out to be the case I’ll not be rebuilding…Time for
that electric conversion.

Does anyone know if the valve to piston clearance is so
close that loss of the tensioner allows them to hit?–
The original message included these comments:

seems as tho Jag didnt put the right engineering in the tensioner
system V12, also on there newer V8s, they seem to have trouble
with some of them also.

–
John. '95 XJS 6.0L convertible. Southlake, TX
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4

In reply to a message from CJ95 sent Sat 18 Oct 2014:

I can’t see how having the tensioner out of action would result in
any substantial valve clearance issues. The tensioner is on the
non drive side of the chain and the cams are not likely to overrun
the crank.
I recently replaced the same in mine so took the opportunity to do
a head job at the same time. I did replace the chain at the same
time but only because they are cheap.–
stephen davis 1976 XJ-S, 1989 XJR-S, Sl SWB XJ12 x 3
gorae, Australia
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5

In reply to a message from baxtor sent Sat 18 Oct 2014:

I hope you’re right, Stephen.

Did you pull the oil pan to get the timing cover off or just loosen
it? Also, were the dampening plates worn much?–
John. '95 XJS 6.0L convertible. Southlake, TX
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6

In reply to a message from CJ95 sent Sun 19 Oct 2014:

Update:

Got the right side stripped down to the valves today. That gave me
access to the top of the tensioner. The top pulled right out. I
see the bottom of the tensioner is anchored by a post at the
bottom.

On the bad side…I now see that to remove the timing cover the
heads, pan, and everything on the front of the motor have to come
off. Bummer.

On the good side…all of the tensioner is accounted for, so I do
not need to pull the pan to look for parts. I need to dive into
the ROM before I go farther, as it appears I may be able to pull
the tensioner anchor from the front of the cover without removing
the entire cover. That would be very nice.

Also, I pulled the spark plugs and scoped the cylinders. There is
no obvious damage, so chances are there was no valve to piston
contact. I will do a leak down check to confirm.

From what I can tell with half the tensioner in hand…it appears
the eye on the spring broke off, allowing the tensioner to go
limp. From there I assume the chain beat it to death. Luckily I
only drove it 8 miles max in that condition.

Oh…I also remembered that when I checked the cam timing just 6k
miles ago, the chain had not stretched enough to alter the cam
timing. So, if the chain was not too stretched 6k miles ago, I
don’t think I’ll change it now.

Seeing the tensioner up close and personal, all I gotta say is that
$300 is absolute highway robbery for such a chinsy plastic part.–
John. '95 XJS 6.0L convertible. Southlake, TX
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7

In reply to a message from CJ95 sent Sun 19 Oct 2014:

The heads or Pan or engine don’t have to be removed in order
to remove the timing chain cover. Three bolt’s on each head
hold the cover to the head. Drop the sandwich plate about
3/4’'from underneath. Don’t remove the bolts in the sandwich
plate, just loosen them. Read Kirby’s ‘‘Book’’ .
Larry
91 XJ-S 12cyl 5sp
95 VDP 6cyl–
The original message included these comments:

heads, pan, and everything on the front of the motor have to come

–
Larry Hartman
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8

In reply to a message from LarryHartman sent Sun 19 Oct 2014:

Thanks Larry,

I’ve done all the studying of the manual, ROM, and book. My plan
is to do exactly as you describe, although the amount of parts that
have to come off to even get to that stage is just boggling. I
have a complete 4’ by 8’ work table stacked 2 feet tall with parts,
and the floor is filling up fast.

I have learned a new respect for poor engineering. There is a
single post that holds the tensioner in place. If they simply made
the post a through bolt from the outside of the timing cover, the
bolt could be pulled and tensioner replaced by only removing a
single manifold and valve cover. ANYBODY who engineers an engine
with a critical component made of plastic that can only be replaced
by stripping the engine to a bare block should be shot. I will be
modifying the post to be accessable from the outside so I will not
have to go through this ever again.

I now know why my timing covers have always leaked on my XJS’s.
many of the accessory mounts are held with through studs for the
timing cover. So any time you mess with the accessories you are
also messing with the clamping force on the cover. A leak is
inevitable.

I should be down to the bottom, so to speak, tomorrow. I will post
a list of the parts it takes to complete this job once I get
there.

Has anybody out there actually gone through this…or has everyone
just farmed it out to shops?–
John. '95 XJS 6.0L convertible. Southlake, TX
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9

In reply to a message from CJ95 sent Mon 20 Oct 2014:

A few things to make it go faster: in order to reach the
sandwich plate bolts weld a 6’’ piece of stock onto a 9/16
box type ratchet. The idea is reaching those bolts between
the crossmember, that way you won’t have to jack up the
engine. use thread to hold up the head gasket when
reinstalling the cover. Trying getting Gortex gaskets for
everything if you can
Larry–
The original message included these comments:

Has anybody out there actually gone through this…or has everyone

–
Larry Hartman
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10

In reply to a message from CJ95 sent Mon 20 Oct 2014:

John:
I am afraid you are right – it is a big job and every part
you touch probably will have to be replaced

Marek has done this job, he might be able to offer some word
of advise:
http://www.jag-lovers.org/v.htm?id=1381505777

Richard is the other expert in-house on the tensioner, but I
understand he doesn’t have the updated version anymore:

http://www.jag-lovers.org/v.htm?id=1123672384

and

http://www.jag-lovers.org/v.htm?id=1105302943

Some other posters, who are not regular here anymore have
left this in the archives:

http://www.jag-lovers.org/v.htm?id=1173339314

Please take many pictures and share with us.

Good luck,
Steve–
The original message included these comments:

I’ve done all the studying of the manual, ROM, and book. My plan
is to do exactly as you describe, although the amount of parts that
have to come off to even get to that stage is just boggling. I
have a complete 4’ by 8’ work table stacked 2 feet tall with parts,
I should be down to the bottom, so to speak, tomorrow. I will post
a list of the parts it takes to complete this job once I get
there.
Has anybody out there actually gone through this…or has everyone
just farmed it out to shops?

–
'95 XJS convertible - V12 6.0L
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11

In reply to a message from sbobev sent Mon 20 Oct 2014:

Thanks again, Larry. All the lower end disassembly will be coming
tomorrow, so I am sure your tips will come in handy!

Steve, you are truly a master of the archives! So Richard found a
solution. I take it he was manufacturing the steel tensioner for a
while. I wonder what the long-term results were for them? I’ll
have to search for details.

Marek’s pics are extremely interesting. The range of the tensioner
is much more limited than you would think by the sprocket mount
bolt heads. I’ll have to study that closely once it’s all apart.
The spring on mine broke, with obvious fatigue striations. It make
me wonder if the chain bottomed as in the pics and set up a
vibration in the tensioner to fatigue the spring…or else just a
crappy spring to go with the crappy tensioner design!?!

Once I get the cover off, I will study the situation and see if
replacing the tensioner retaining post with a through bolt is
feasible. If it is, it would reduce the job from a week down to
about 4 hours.

Stand back…I’m going back in!–
John. '95 XJS 6.0L convertible. Southlake, TX
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12

There is a
single post that holds the tensioner in place. If they simply made
the post a through bolt from the outside of the timing cover, the bolt
could be pulled and tensioner replaced by only removing a single
manifold and valve cover.

Well, maybe. You might have to pull the cam sprocket off as well,
since the intact tensioner probably won’t fit between sprocket and
housing. Also, while removal might work OK, I dunno how much fun
you’ll have getting the new tensioner in and lined up to put that
bolt back into place.

ANYBODY who engineers an engine with a
critical component made of plastic that can only be replaced by
stripping the engine to a bare block should be shot.

One of the reasons I’ve urged development of a replacement arch for
the tensioner made out of spring steel with a nylon surface attached.
Somebody made a couple a few years back, but I haven’t heard any
more about it recently.

I now know why my timing covers have always leaked on my XJS’s. many
of the accessory mounts are held with through studs for the timing
cover. So any time you mess with the accessories you are also messing
with the clamping force on the cover. A leak is inevitable.

Well, perhaps not AS inevitable if the engine is assembled with the
upgraded gortex sandwich gaskets. But with paper gaskets, yeah, it’s
probably gonna leak.

I should be down to the bottom, so to speak, tomorrow. I will post a
list of the parts it takes to complete this job once I get there.

Has anybody out there actually gone through this…or has everyone
just farmed it out to shops?

Lots of us went through it. That’s how I wrote that whole section
about getting the timing cover off without pulling the heads.

– Kirbert

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !On 20 Oct 2014 at 10:11, CJ95 wrote:

13

In reply to a message from CJ95 sent Mon 20 Oct 2014:

Dear John,

You are going to have to remove the timing cover one way or another
and everything else will be clear once you’ve got that far.

The tensioner itself can be manipulated by hand quite easily once
you realise that its maximum resistance to being flexed is quite
early in its travel and not a progressive thing. This means that
you can work it in situ by hand without special tools to get it
into place. Then you’ll see whether you need a new chain. If you
do, Dremel a link off and roll the new chain in.

My pictures show that substantial chain wear had occurred and that
a new tensioner was only of limited help - a new chain was also
required to prevent metal to metal contact.

You’ll need at least the 3 new gaskets for the timing cover (and
perhaps more to seal the sump again once it is upset by being
partially lowered.) I have the rubbery goretex timing cover gaskets
but postage to the USA probably means you should source these
locally.

kind regards
Marek–
v12 E-type running MS3/3X sequential lpg and petrol
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14

One of the reasons I’ve urged development of a replacement arch for
the tensioner made out of spring steel with a nylon surface attached.
Somebody made a couple a few years back, but I haven’t heard any
more about it recently.

– Kirbert--------------------------------------------------------------------------------------------------

It was 9 years ago, and 25 were made.
This subject came up again on the forum in the last year or so.
I think you once asked for info and I sent you a Word document
complete with photos inserted.
If not, ask and it shall be yours.

There is one in the coupe HE engine I rebuilt.
There must be another 24 in V12s here and there.
To date nobody has reported a broken one.

I have no plan to make more, it was a labour of love.

The weapon of choice for the plastic is ( from memory ) graphite loaded Delrin.
At the time I could not find any the right thickness, so settled for
the non graphite version.
Graphite gives a slightly better temperature tolerance.

I still have Autocad files and info if anybody wants to make more.
Second time around you could improve on the detail of the design.
It was time consuming to make these things, be prepared to work for
about $5 an hour.
No wonder a machine moulded plastic OEM item looked attractive to Jaguar.

I think the weak point of the OEM tensioner is the hole at the bottom
where it fits over a steel pin.
I have seen at least 2 with fractures there.

Richard Dowling, Melbourne, Australia. 1979 coupe + HE V12 + manual;
1989 convertible; 2003 XJ350.

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15

In reply to a message from Richard Dowling sent Mon 20 Oct 2014:

Thank you Kirbert, Marek, and Richard.

Richard, I would be very interested in details of your
tensioner design. I am not interested in mass producing
them…but a one off to prevent this from repeating seems
worthwhile.–
John. '95 XJS 6.0L convertible. Southlake, TX
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16

In reply to a message from CJ95 sent Sun 19 Oct 2014:

Not 100% sure what ‘chinsy’ means. Since it is ‘highway
robbery’ you clearly have deep expertise in the design,
manufacture and inventory/warehousing/cataloging and
service supply of short-run technical plastic components
with a motor manufacturer for models up to forty years
old. What did your own calculations show to be the non-
highway robbery retail price? I’d be interested to compare
the numbers.

If, on the other hand, you were simply voicing an opinion,
then I can do that too. I might think that people who
expect pioneering complex old-school engines to be easy
and cheap to work on, probably have a few surprises in
store.

Pete–
The original message included these comments:

Seeing the tensioner up close and personal, all I gotta say is that
$300 is absolute highway robbery for such a chinsy plastic part.

–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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17

In reply to a message from PeterCrespin sent Tue 21 Oct 2014:

Pete, Quite obvious you haven’t changed YOUR tensioner
yet. Get back to me after you have. I have a higher
degree in engineering and spent a decade studying material
failures in aircraft. In all those years I have not seen
a poorer design. I’ll repeat…any engineer that uses a
critical plastic part that is prone to failure and buries
it down to the bare block has done a poor job.

Today I planned to pull the water pump, damper, and start
working on the lower oil pans. That plan went south fast.
I broke my 1/2’’ drive breaker bars (2) trying to unscrew
the damper bolt. I then proceeded to break one of my 3/4’’
drive breaker bars before finally loosening the nut with a
1’’ drive breaker. I think I bent the front wing frm
pulling so hard on a 5’ cheater pipe while leaning against
it. That’s tight!

I just had the damper off last year and assumed it would
be easier this time since I used ample anti-seize. The
lesson I get from this Excercise is that anti-seize
obviously lubes the threads so much that the published
torque allows the bolt to thread tighter than planned.
Note to self…if I use anti-seize reduce nstallation
torque accordingly!

4 years ago, when I first got up close and personal with
the front of this engine, I noticed the single posi-screw
holding the water pump…and told myself that ‘‘one day
that screw will frustrate me to no end’’ Today was that
day, and I was not wrong. After bending 2 posi bits and
having no luck with a chisel and punch…it got drilled
out.

So, I have to ask. I assume the posi screw on the water
pump was used originally for clearance. On my car there
is no clearance problem. Did there used to be something
that fouled that bolt hole?

I found the damper last night for $257. That’s the
cheapest I’ve seen after googling the world for 6 hours.
Pete, since you ask, this part is worth maybe $100…on
the outside…based on the pieces that comprise the
complete assembly. The Chinese could no doubt produce it
for less than $25. I will mail the broken pieces for you
to study if you still think I’m out of line. ‘‘Chinsy’’ has
a photo of this damper in the dictionary.–
The original message included these comments:

In reply to a message from CJ95 sent Sun 19 Oct 2014:
Not 100% sure what ‘chinsy’ means. Since it is ‘highway
robbery’ you clearly have deep expertise in the design,
manufacture and inventory/warehousing/cataloging and
service supply of short-run technical plastic components
with a motor manufacturer for models up to forty years
old. What did your own calculations show to be the non-
highway robbery retail price? I’d be interested to compare
the numbers.
If, on the other hand, you were simply voicing an opinion,
then I can do that too. I might think that people who

–
John. '95 XJS 6.0L convertible. Southlake, TX
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18

In reply to a message from PeterCrespin sent Tue 21 Oct 2014:

I’m sitting here killing time while my wife shops at
Dillard’s…so thought I would give you an example of what
I consider a well designed complex old school engine…a
Donovan Chevy style engine.

I once got a chance to play ‘‘roady’’ with a top fuel team.
The car would roll in from a 4000hp, 3.6 second run. We
could pull the heads and give it a valve job, replace the
rods, pistons, and flywheel with clutch pack. We replaced
the crank, lifters and timing chain on a run basis and had
it all back together…

…in an hour.

This was back in 1994. My jag with it’s plastic tension
had not even been built yet.–
John. '95 XJS 6.0L convertible. Southlake, TX
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19

In reply to a message from CJ95 sent Tue 21 Oct 2014:

I’m curious you kept saying ‘‘we’’ how many we’s were doing
this engine work, and how many times did this get done in a
year, repetitious work does beget efficiency you know if you
doubt that just ask any line technician working on
commision, also factor in the easy access also. But I bet
‘‘we’’ don’t want to consider all those factors do ‘‘we’’.–
The original message included these comments:

I once got a chance to play ‘‘roady’’ with a top fuel team.
The car would roll in from a 4000hp, 3.6 second run. We
could pull the heads and give it a valve job, replace the
rods, pistons, and flywheel with clutch pack. We replaced
the crank, lifters and timing chain on a run basis and had
it all back together…

–
1988 xjs Cabriolet
Mocksville NC, United States
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20

In reply to a message from Wayne Canter sent Tue 21 Oct 2014:

Does it matter…really? I could give you a thousand
techs and a Jag V12 on a stand and you would not be able
to change a single tensioner in an hour. Probably not in
6 hours. So what is Your point? Mine is that this
tensioner design was not engineered well.

If you guys can tell, I am not in a good mood right now.
If you can’t help then I’d appreciate not nit picking…or
st least don’t show up to the argument unarmed. If you
have not changed one of these then you have absolutely no
concept of what you are talking about. I notice nobody is
picking on Kirbert for having similar comments about this
POS tensioner.

The real joke is the manual lists replacing the tensioner
in only 3 steps…Remove engine and transmission. Remove
timing cover. Slide tensioner off. Honestly, that is the
biggest joke I’ve ever heard.–
The original message included these comments:

I’m curious you kept saying ‘‘we’’ how many we’s were doing
this engine work, and how many times did this get done in a
year, repetitious work does beget efficiency you know if you
doubt that just ask any line technician working on
commision, also factor in the easy access also. But I bet
‘‘we’’ don’t want to consider all those factors do ‘‘we’’.

–
John. '95 XJS 6.0L convertible. Southlake, TX
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