3.9 overheating yet more

Hello,

Finally managed to get a spare hour to check out the condition of the spark
plugs and do a compression test. All of the plugs looked "normal" with the
exception of 2 which were a bit black, but this may be down to the fact that
the plugs didnt seem that tight when I undid them.

However, below are the results of the test, I'd be grateful for your
opinion:

7: 142 8: 180
5: 150 6: 171
3: 160 4: 172
1: 153 2: 170
-----------------
<Radiator>

It's a 9.35:1 CR engine, so the right hand one appears OK, but the left hand
one is low. I've also noticed that the left hand head seems cleaner and
shinier than the right hand one, as if its been replaced at some point, and
also there are a couple of bolts missing which I've been told is due to some
gaskets not having the right holes in....is this true?

So does it appear if my left hand head gasket has gone? And would changing
the gasket alone do the job?

Thanks,
Paul
-------------------
1992 RR Vogue SE "Arthur"
2005 Baby Girl "Abigail"

On Thu, 7 Jul 2005 19:43:21 +0100, "Pacman" <[email protected]>
wrote:

>Hello,
>
>Finally managed to get a spare hour to check out the condition of the spark
>plugs and do a compression test. All of the plugs looked "normal" with the
>exception of 2 which were a bit black, but this may be down to the fact that
>the plugs didnt seem that tight when I undid them.
>
>However, below are the results of the test, I'd be grateful for your
>opinion:
>
>7: 142 8: 180
>5: 150 6: 171
>3: 160 4: 172
>1: 153 2: 170
>-----------------
> <Radiator>
>
>It's a 9.35:1 CR engine, so the right hand one appears OK, but the left hand
>one is low. I've also noticed that the left hand head seems cleaner and
>shinier than the right hand one, as if its been replaced at some point, and
>also there are a couple of bolts missing which I've been told is due to some
>gaskets not having the right holes in....is this true?
>
>So does it appear if my left hand head gasket has gone? And would changing
>the gasket alone do the job?
>
Are these readings wet or dry, and did you have the throttle fully
open when taking them?

Its a bit strange that all the left cyls (on yr diagram) are low
compared to the other side. But if that head has been replaced then it
could be a reason.
What makes the difference between the Hi and Lo comp engines? Head or
Piston, or both?

from the manual:
Compression pressure Test
snip
5. Expected readings, throttle fully open, battery
fully charged:
8.31:1 = 10.2-10.9 bar, 150-160lbf/in 2
9.35:1 = 11.5-12.2 bar, 170-180lbf/in 2

--
ColonelTupperware,
spouting bollocks on Usenet since 1997
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>>
> Are these readings wet or dry, and did you have the throttle fully
> open when taking them?
>
not sure what you mean by wet or dry (engine was warm). thrttle not open,
as it didn't mention throttle in the service manual under compression
testing.

> Its a bit strange that all the left cyls (on yr diagram) are low
> compared to the other side. But if that head has been replaced then it
> could be a reason.

could someone have put on the wrong head, therefore low compression readings
and therefore again, overheating?


Thanks,
Paul
-------------------
1992 RR Vogue SE "Arthur"
2005 Baby Girl "Abigail"

"Pacman" <[email protected]> wrote in message
news:[email protected]...
>
>
>>>
>> Are these readings wet or dry, and did you have the throttle fully
>> open when taking them?
>>
> not sure what you mean by wet or dry (engine was warm). thrttle not open,
> as it didn't mention throttle in the service manual under compression
> testing.
>
>> Its a bit strange that all the left cyls (on yr diagram) are low
>> compared to the other side. But if that head has been replaced then it
>> could be a reason.
>
> could someone have put on the wrong head, therefore low compression
> readings and therefore again, overheating?
>

Right, here goes. Compression is controlled by the size of the piston bowl,
not the head. All the heads have equal chamber volumes, assuming they are
the same heads to start with. 14 bolt heads (3.5, most 3.9, 4.2) are all the
same, and 10 bolt heads (late serpentine 3.9, all 4.0 and 4.6) are the same.
The compression can also be affected by the thickness of the gasket, the
original steel shim gaskets (crap, IMO) are only 0.45mm thick when
compressed, the aftermarket composite type gaskets (excellent, IMO) are
nearer 1.1mm compressed, a difference in compression ratio of around 0.6 to
0.8. Some of the aftermarket composite gaskets have only the 10 bolt holes,
so the outer row of 4 bolts are omitted on reassembly, as they really aren't
needed (They actually cause premature gasket failure if torqued to the same
value as the other 10 bolts, due to applying an uneven clamping force across
the head), hence landrover themselves doing away with them on the later
engines.
Do another compression test, but this time, do it as follows. Remove all 8
plugs and disconnect the low tension wires to the ignition coil. Squirt a
couple of cc's of engine oil down the plug hole of the cylinder under test,
fit the compression tester, press throttle fully down and crank for a count
of 5 seconds then record pressure. Repeat for the other 7 cylinders and see
what figures you get.
As an aside, one or two cylinders showing a lower value 'may not' be the
head gasket or even ring/bore wear, it is common on the V8 to find worn
camshaft lobes, causing some of the valves to not be opening fully and hence
causing the pressure differences.
No. 1 cylinder is the front passenger side (assuming right hand drive!),
no.2 is the drivers side.
It is possible that you have a tin gasket on one bank and a composite on the
other, not good for smooth running or power delivery.

Badger.
B.H.Engineering,
Rover V8 engine specialists.
www.bhengineering.co.uk
www.roverv8engines.com

On Thu, 7 Jul 2005 23:06:09 +0000 (UTC), "Badger"
<[email protected]> wrote:


>
>Right, here goes. Compression is controlled by the size of the piston bowl,
>not the head. All the heads have equal chamber volumes, assuming they are
>the same heads to start with.

According to a book I've just been reading at work, the head is what
determines the compression ratio. It even mentioned the different
sizes of combustion chamber. Our service manager confirmed this.

I can't remember the producer of the book, but it listed all the V8
varients and their catalog of rebuilt engines and parts.

But you have undoubtedly ripped apart and refettled far more V8s than
I have, so I'll take your word for it.

It would account for the OPs difference in readings if one Cyl head
were Low comp and the other Hi comp.
Ho hum.

--
ColonelTupperware,
spouting bollocks on Usenet since 1997
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"Colonel Tupperware" <[email protected]> wrote in message
news:[email protected]...
> On Thu, 7 Jul 2005 23:06:09 +0000 (UTC), "Badger"
> <[email protected]> wrote:
>
>
>>
>>Right, here goes. Compression is controlled by the size of the piston
>>bowl,
>>not the head. All the heads have equal chamber volumes, assuming they are
>>the same heads to start with.
>
> According to a book I've just been reading at work, the head is what
> determines the compression ratio.

No, the combustion volume is what determines the c.r., as a percentage of
the swept volume. The combustion volume is the total volume above the piston
at TDC, this volume includes the piston bowl capacity and the head chamber.

> It even mentioned the different
> sizes of combustion chamber. Our service manager confirmed this.

Sorry, your service manager is talking crap. That is bollox on a rover V8
engine, which is what is being referred to here. There are 4 different head
castings, but only 2 different chamber volumes, one being 28cc and I can't
remember the other off the top of my head (no pun intended!) but they are
effectively grouped by 10 bolt type and 14 bolt type. The 10 bolt variants
were skimmed extra to account for the thicker composite gasket that
landrover finally switched over to, so if you change from 14 bolt to 10 bolt
heads, and fit composite gaskets at the same time, the compression ratio is
unaltered.

> I can't remember the producer of the book, but it listed all the V8
> varients and their catalog of rebuilt engines and parts.

Just 'cos something is in a book, it doesn't mean the info is proven gospel.
There's a lot of factual inaccuracies in the 2 Hardcastle rover V8 books as
well, but then if you read them carefully, it's pretty obvious what
companies sponsored the writing of them. Good books as they are, though.

> But you have undoubtedly ripped apart and refettled far more V8s than
> I have, so I'll take your word for it.

There are different pistons for the following compression ratio's 10.5 (P5
and early P6 rover), 9.75 (SD1 Vitesse), 9.35 (Carb SD1, Rangie EFI, some
markets of carb landrover), 8.13 (Carb rangie, 90, 110, 101 etc). There are
also minor variants on the old P6 engines of 8.25 and 8.5, but the chances
of you stumbling across them are relatively remote nowadays, most people
rebuild the early engines using later high compression pistons. Go check out
the part numbers using EPC, you'll see the heads are the same part numbers
for many different compression engines but the pistons differ. All the
variants I have quoted are either 3.5 or 3.9, all with the same 14 bolt
heads.

> It would account for the OPs difference in readings if one Cyl head
> were Low comp and the other Hi comp.
> Ho hum.

Yes, but due to different gaskets maybe, not the heads themselves as he
already stated it was 14 bolt heads with the outer row not installed.

Badger.

On Thu, 7 Jul 2005 21:38:00 +0100, "Pacman" <[email protected]>
wrote:

>
>
>>>
>> Are these readings wet or dry, and did you have the throttle fully
>> open when taking them?
>>
>not sure what you mean by wet or dry (engine was warm). thrttle not open,
>as it didn't mention throttle in the service manual under compression
>testing.
>
Dry: without oil on the bores.
Wet: with oil in the bores.
It gives you a good impression of the state of the piston rings.

You need the throttle open to get a full charge of air in.

>> Its a bit strange that all the left cyls (on yr diagram) are low
>> compared to the other side. But if that head has been replaced then it
>> could be a reason.
>
>could someone have put on the wrong head, therefore low compression readings
>and therefore again, overheating?
>
Maybe, but I cant see a link to overheating. My guess would be a
furred up radiator or stcking thermostat.

--
ColonelTupperware,
spouting bollocks on Usenet since 1997
Usenet FAQ at
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On or around Fri, 08 Jul 2005 14:22:07 +0100, Colonel Tupperware
<[email protected]> enlightened us thusly:

>But you have undoubtedly ripped apart and refettled far more V8s than
>I have, so I'll take your word for it.
>

such V8s as I have seen differ only in the pistons. The later heads have
longer spark plug threads, but the same combustion chambers. The only
difference, as has been said, is the head gaskets - later head gaskets are
thicker, which has a minor effect on the C.R.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".