[v12-engine] Main Bearing Replacement for Dummies

V12-Engine
1

I’ve had heaps of helpful feedback from the wonderful people on the
forum regarding bearing failure in my car causing low oil pressure.

There seems to be a better than good chance that if I replace the
main bearings I’ll be back in game.

So my questions are:

I’m a fairly average home mechanic but I’ve never replaced
anything ‘‘inside’’ an engine so am I going to bite off more than I
can chew?

Also Apart from bearings what else should I be looking at while the
sump is off?

What gotchas can I expect (XJS HE RHD V12)

I have workshop manuals and Kirby’s book what else should I know?–
1985 XJS V12 HE with TWR Engine Kit - www.bryansplace.net
Ashmore Qld, Australia
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2

In reply to a message from Bryan Burgess sent Sat 11 Dec 2004:

Your connecting rod bearings should also be replaced as well, I
would also pullout the the oil pump and check or have someone check
the tolerances. The best way to deal with the v-12 is to first have
a Haynes or Service manual in hand which can steer your efforts in
the right direction; you can most definately do this yourself
without problems so long as you take your time and dont get pissed
off ( this is when tools end up in the neighbours window or studs
get sheared off into their threads). A shop would be best, that way
you can hookup a chain hoist to the motor lift-eyes, unbolt the
engine mounts and lift the motor enough to service the bearings.
Just make sure that the engine is chained and blocked well as this
motor is around 900lbs with the tranny attatched. Learning is
fun…you will have lots. Good luck, informative people in this
site will be here to help you in your endevour.–
Regards, Keith Cox, 1987 Canadian VDP V-12
Salmon Arm, British Columbia, Canada
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3

In reply to a message from Bryan Burgess sent Sat 11 Dec 2004:

Hi Bryan,
Sent a reply off post, came back mail box full,
pls send me an email to let me know when to resend
Regards
Don–
The original message included these comments:

Also Apart from bearings what else should I be looking at while the

–
D W ANDERSON
SINGLETON NSW, Australia
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4

In reply to a message from V-12 King sent Mon 13 Dec 2004:

Well I’ve ordered the bearings so I hope it’s as easy as everyone
says.

Q: I have to dop the front crossmember right?

What about those BIG nasty coil springs are they safe in this
process?–
1985 XJS V12 HE with TWR Engine Kit - www.bryansplace.net
Ashmore Qld, Australia
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5

After having done this job both with the engine in and engine out, I would
pull the engine all the way out!!
Even if you are not going to take the heads etc off, you have WAY more room
to work.

Andrew Holley

Well I’ve ordered the bearings so I hope it’s as easy as everyone
says.

Q: I have to dop the front crossmember right?

What about those BIG nasty coil springs are they safe in this
process?

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6

Bryan, you ask

"…Q: I have to dop the front crossmember right?

What about those BIG nasty coil springs are they safe in this
process?–
I haven’t had to do this job on the 12 yet, but working on our 4.2 from
underneath was manageable, as long as you elevate the car high (and safe)
enough to give you room to work.

The suspension doesn’t have to be dismantled on the series 2 XJ. Best for
you to check out the XJS manual, which will explain how to support the
engine so that the subframe on which it is mounted can be removed. My
recollection of the series 2 is that after disconnecting some electrical
connections, the engine mounts, front dampers, anti-roll bar, lower steering
column, and power steering and brake hoses, the entire front subframe can be
lowered.

Instead of removing the subframe altogether, it is possible to merely
slacken its front mounting bolts slightly so that when you disconnect the
rear mount the subframe can be swung down to hang vertically. To achieve
this you will need to have the car high enough, and be prepared for the need
to control the rate of descent. If you are using a trolley jack under the
cross member, for example, the force you are trying to control will shift
suddenly from vertical to horizontal, so an assistant would be useful. By
this stage you would have reduced the assembly’s weight a little by removing
the front wheels.

Principal advantages of this method are savings in floor space and ease of
alignment when refitting. It’s also a good time to re-bush the rack if
needed.

Presumably you will check out the oil pump while you’re at it? Have you
been getting any of the other symptoms of bad main bearings, like rumble or
vibration? I guess these would be much less pronounced on a 12…I’ve
deleted our previous posts on this subject, but just wonder whether the
problem may be more connected with oil supply than bearing clearances. If
you haven’t exonerated the oil pump 100%, maybe the question of engine
removal turns on the accessibility of the oil pump. A quick look at my
series 1 V12 manual suggests it may not be as straightforward as the good
ol’ XK.

George

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7

Presumably you will check out the oil pump while you’re at it? Have you
been getting any of the other symptoms of bad main bearings, like rumble or
vibration? I guess these would be much less pronounced on a 12…I’ve
deleted our previous posts on this subject, but just wonder whether the
problem may be more connected with oil supply than bearing clearances. If
you haven’t exonerated the oil pump 100%, maybe the question of engine
removal turns on the accessibility of the oil pump. A quick look at my
series 1 V12 manual suggests it may not be as straightforward as the good
ol’ XK.

George----------------------------------------------------------------------

There do not seem to be many reports, if any, of oil pump failure on V12s.
However, Bryan’s is a rebuilt engine and it could happen.
The oil pump has a rear half of cast iron, but the front half is alloy and
shows some minor scoring on the HE engine I am rebuilding, although it is
not going to be a problem.
Possibly there is a problem with the pump or something else and nothing much
wrong with bearings.
Maybe the oil pipe from the pump to filter block has a poorly fitted O ring
and this is causing pressure loss.

It sure is no quick job to get at the oil pump, but listers have pulled the
timing cover off without taking the heads and sump cover off and then you
can get at the pump.

I guess if you could rig up a gauge to test the oil pump itself it would be
handy, but that is not easy. You need to take off the oil filter block and
put in something to measure oil pressure. In Bryan’s engine the pressure is
falling off when the engine is hot, so you have to test a hot engine. The
oil gallery to the bearings has to be shut off for a few seconds with a
running engine to see if the problem is pump or bearings.
With an engine doing 2000RPM on no load the bearings would not suffer if
pressure was lost for a few seconds.

I have a filter block in pieces, and my guess is an adaptor could be made to
bolt on the engine block and fitted with gauge plus changeover valve to
carry out this procedure. It can be a bit rough and ready, since the whole
thing only needs 15 minutes of use to let the engine warm up, and then a few
seconds for the test. If my life depended on it I think 4 hours work would
do it using an old filter block and a cheap industrial valve. There is
already a tapped hole with blanking plug on the rear of the filter block.

Of course, this does not cure the problem. It might tell you the pump is
shot or the bearings are shot or both are shot. One way or another you have
some serious work to do. It would be a pity to replace bearings, if ruined,
then ruin another set because the symptoms were cured but the cause overlooked.

Richard Dowling, Melbourne, Australia, 1979 XJ-S & 1985 XJ6.

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8

In reply to a message from George Morrell sent Sat 18 Dec 2004:

There is a bit of rumble which is getting worse (even my untrained
ear can hear it now) I’ll firstly look at the bearings and if they
are not obviously the problem I’ll check the oil pump clearances
too.

I bought a set of bushes for the steering a while ago so they will
be going in at the same time.

Ive been lead to believe the oil pumps in the V12 are near bullet
proof so I hadn’t planned to do anything unless the bearings look
good.–
The original message included these comments:

Presumably you will check out the oil pump while you’re at it? Have you
been getting any of the other symptoms of bad main bearings, like rumble or
vibration? I guess these would be much less pronounced on a 12…I’ve

–
1985 XJS V12 HE with TWR Engine Kit - www.bryansplace.net
Ashmore Qld, Australia
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9

Bryan, I think Richard and I are on the same wavelength on this one. Even
if the bearings are bad, the pump (or associated plumbing) may be the cause.

Good luck

George

“…There is a bit of rumble which is getting worse (even my untrained
ear can hear it now) I’ll firstly look at the bearings and if they
are not obviously the problem I’ll check the oil pump clearances
too…Ive been lead to believe the oil pumps in the V12 are near bullet
proof so I hadn’t planned to do anything unless the bearings look
good…”

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10

In reply to a message from George Morrell sent Sun 19 Dec 2004:

The bearings arrived today (BTW H&H in Melbourne have been great)
so after Christmas is over and done I’ll be into it.

Anyone got any tips for a beginner - I’ve already been given the
warning about taking extreme care not to damage the surfaces and
torque them up evenly etc

what about peoples past experience are the old ones easy to get out?–
1985 XJS V12 HE with TWR Engine Kit - www.bryansplace.net
Ashmore Qld, Australia
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11

The bearings arrived today (BTW H&H in Melbourne have been great)
so after Christmas is over and done I’ll be into it.

Anyone got any tips for a beginner - I’ve already been given the
warning about taking extreme care not to damage the surfaces and
torque them up evenly etc

what about peoples past experience are the old ones easy to get out?

1985 XJS V12 HE with TWR Engine Kit - www.bryansplace.net
Ashmore Qld, Australia-----------------------------------------------------------------------------------------

The hard part is holding up the engine and dropping or swivelling down the
cross member.
Once you get the sump covers off it is easy to remove the main bearing caps.
Probably a good idea to take 2 or 3 off and show them to an experienced
mechanic.
We are not 100% sure the bearings are the problem at this stage.

I guess no need to mention that gravity forbids you take all the main caps
off at once.
The rear cap is the one with the rope oil seal. Read Kirby’s Book about
that item.

Take a look in the bottom of the sump pan when you take it off.
Check for particles of metal. If any bearing metal is chewed up it should
end up in the sump.

In theory any bearing metal should come out of the bearing cap, but you
might find some lodged in the oil holes of the crank.
That is not a healthy place to leave it. You can buy pipe cleaners ( the
kind for lovers of lung cancer ) which are excellent for extracting muck out
of such holes. You can also take the oil filter body off and apply
compressed air into the oil gallery which should help force any stray metal
out of the crankshaft.

Note that there are endfloat spacers on the centre main bearing cap, check
them for wear.
Note that there is one main bearing shell which has no groove or something.
I forget the detail, but it has to be in the right place.

You can always try the Jag club in Brisbane, even if you do not join you
might find a member clued up on V12s who will call in and
look at your progress. That could save you a lot of heartache.

If you are stuck I have got heaps of 'photos taken of my HE engine rebuild
for the purpose of helping figure out what goes where - eventually they
will all be on a CD. There are detailed 'photos of all the individual parts
and the assembly of the bottom end.

Good luck,

Richard Dowling, Melbourne, Australia, 1979 XJ-S & 1985 XJ6.

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