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Posted

Hello,

I've read about many 3.9, 4.0 and 4.6 engines that has the diagnose of a sunken cylinder liner.

How can they sink when the liners are pressed down to stops in the cylinder block? :huh:

When cylinder heads clamping the liners they should not be able to move in any direction? Or do they shrink? :rolleyes:

When they sink, how much will be enough to get compression out in the water?

Regards

Posted

The blocks are line bored and none too accurately depth wise, coupled with liners with iffy tolerances height wise then

when you shove the 2 together altough "Flush" when they leave the factory (the blocks are 'decked' so all is true and flat)

you can sometimes get a fingernail between the base of the liner and the block machined end.

Its not that the liners "Move" that causes the issues, is the fit between liner and block with crankcase pressures getting past

the joiner, this can cause the liner to move and sometimes you can even hear a knock, not all V8 blocks are the same they

are graded etc, and sometimes its just down to bad luck. One big cause is that 4.6 RR etc are ECU VE table to run lean - F LEAN

at crusiing speeds which can cause huge hot spots and heat build ups in the engine core - the temp gauge says fine,

but the liners don't like it. In general terms 4.6s are far far worse for this over 3.9/4.0/4.2s, althougfht they to can go its rareish compare

with the 4.6s, partly ECU tune and VE partly due to thinner coolant jacket as bored wider for cubic capacity

Mark Adams when he re chips 4.6s will richen up crusing to lower temps and risk of damage, I did write quite a lot on

this subject some while ago, so do a search for more info

Nige

Posted

Quick note on lean and what that means....

maximum EGTs in an engine occur when there is just enough fuel to burn all of the air. excess fuel cools it down, not enough fuel and obviously less heat is produced. For a homogenous charge mix this magic point is around 14.7:1 (the stoichometric point). this is the point that you need to be for a standard catalytic converter to work. Sadly this is not where the engine wants to be :(

Just to confuse the issue petrol engines rarely have a homogenous mixture, so to burn every last bit of air you need to add more fuel. Generally best power occurs around 13:1 AFR, with some helpful cooling from fuel you don't actually use. best economy occurs at the leanest point the engine will still run. 16:1 is usually the limit for that.

LPG by its nature generally IS far more homogenous, but EGTs are higher. There is just no free lunch :(

Posted

All good stuff Bill,but I'd like to add more too.Over the years alot of Rover V8's have suffered blown head gaskets,loose liners and cracked blocks.Many stories have been banded around to the cause of them.Often its just simple overheating from poor,(often zero.)maintenance,hoses failing etc,etc.Others have been down to the fact that the 94mm bore Rovers are weak - there is just not enough material supporting the liner and the quality of build was poor too.

The bit that really annoys me though is the "Excessively weak mixtures" that LR set them up to run at. Rubbish,spend any time tuning them in real world situations with modern monitoring kit and you realise how untrue it is.Any of the EFI RV8's are quite happy to go open loop - richer than stoich under heavy load / wide throttle openings.Yes,they are happily switching at cruise - just like any other closed loop cat equipped sparker.

Posted
The Titanic sank - and that had watertight bulkheads.

I'll get my coat!

Have you heard of the US senator Smith, who asked why the passengers did not go into the unsinkable watertight compartments and thereby save themselves.

He was informed the the watertight compartments were at the bottom of the Atlantic.

He was afterwards known as 'unsinkable Smith' :)

  • 1 month later...
Posted
The bit that really annoys me though is the "Excessively weak mixtures" that LR set them up to run at. Rubbish,spend any time tuning them in real world situations with modern monitoring kit and you realise how untrue it is.Any of the EFI RV8's are quite happy to go open loop - richer than stoich under heavy load / wide throttle openings.Yes,they are happily switching at cruise - just like any other closed loop cat equipped sparker.

Hi,

that´s what I wondered about. Didn´t Emission (NOx in mind) regulations demand the engine run at 14.7:1 as much as possible even 15-20 years ago (right until today). So there would not have been much "margin" in leaning any cruise areas. I would even think that these are the areas which were/are most important for emissions.

The modified chips usually claim more power with less fuel consumption. Is there any other option than richening WOT areas and leaning the cruise-areas ??

Bill,

I keep stumbling about people saying that lean mixtures cause hot combustion temperatures. To my knowledge that is untrue, because less fuel means less heat (enthalpy) to be emitted (hottest temp would be at 14.1, any richer than that temps fall again due to cooling effect of vapourizing fuel and some energy "inherent" in the then increasing amount of Carbonmonoxide).

BUT a few days I read an research summary about engine-knock (pity it is in german) so it should have been from people who probably are involved and I´d be inclined to subordinate in these conditions, but they wrote about temperatures being higher in lean conditions. That makes me unsure.

Now: Why on earth are these two rather contradictory information around ? Engines burn fuel for >100years. Enough time for people to agree ??

Posted

The 4.2s and 4.6s are designed to run hotter, couple that with crusising and lean VE for economy and thats why they get hot, its not just that they are too lean (they are OK but tabled for fuel consumption as good as poss) and are better if the Engine ran cooler,

Mark Adams (v8 guru) remaps thes as a 1st course and route, but also unleashes a bit more uMph at the same time. As with all thing a simple comment can have a wad of 'alsos' behind it,

Nige

Posted

Regardless of lean or rich ………………..I believe the issue is caused by the casting variations and the variable amount of ‘meat’ behind the liners. This variation creates local hot spots which cause cracking behind the liner into the water jacket. This is also the cause of the liner slip.

I think you will find that the special batch of cosworth blocks did not suffer from this issue as it was a thicker casting and I guess there are some Rover blocks that are still OK as those were the ones with more meat then others.

Top hat liners are a certain long term cure, but some well known motor machine shops seem to want to charge a premium for this service…….you can get it done to a very high standard for about 50% of the advertised figure.

:)

Posted
... and lean VE for economy and thats why they get hot, its not just that they are too lean (they are OK but tabled for fuel consumption as good as poss)

Nige, I am confused. Regulations for manufacturers are very strict today (as much that single misfire must not be allowed) and I suspected all engines to run 14.7 - just like the narrow-band AFR-table that the Megalogviewer uses.

I thought Rover just had to set up a VE table that takes care for an stochiometric AFR at all running conditions (unless at WOT) and just had to live with the fuel consumption that results from that.

Posted

another avenew which seems to have been missed is also the lack of earthing and also the build up of internal static electricity and piston to cylinder bore arching? now having stripped a few 4.2 with porus blocks when the problem first apeared at the main dealer i was working at, one thing was always apparent the piston had burn points in relation to the pit marks on the linner?

most of the vehicles that suffer lean running are also the closed loop emissions system rather than the non cat types

Posted

Ian (BBC) is also correct, there were 3 colours and qualities of block, with more or less meat behind the liners

depending which one you have, see other post I did around this, red blue and yellow blocks, this also goes into the equation

http://forums.lr4x4.com/index.php?showtopi...;hl=yellow+blue

At the end of the day you have what was a old 50s Buick block of 3.5 V8, in 2000 onwards producing far more horses

than 1st designed for by a company whos quality is like asking Forest Gump to do your dental work, even with quality

engineering the unit is on, or with some blocks past its edgem, build on this and its going to end in tears.

A good block, with THL, plateau honed balanced, and a few twaeks, set up right, built right and tunned is a very

different ball game o a std 4.6 owned for a few years and with iffy servicing, JED will build you a monster

5.2 / 5.3, it will not suffer from these issues, but your wallet will need after care and surgery, and something

like an LS1 will do all of this more and for a few % of the JED

There is a huge amount of Bo**&x sprouted around Rover V8s, but there are also some real problems too

Nige

Posted
most of the vehicles that suffer lean running are also the closed loop emissions system rather than the non cat types

:) "impossible is nothing" for a Rover

Could knock be an issue ? I think knock can cause pittings. Could it even cause peak pressures that might stretch the liner and put undue stress to the thin aluminium around the liner ? Would that be more likely than spark-pitting (alu cylinder heads are common on engines - is that observed elsewhere too?)

To explain - there´s again some observation of my knock sensor that I do not know what to do with - I am inclined to think that it is sensor-fault or "noise": I have mounted a knock sensor (knocksense). Knocksense uses a Bosch sensor and attaches it to small circuit which is tuned to the engine´s bore. All you have to do is to tune the sensitivity. MY problem is neither me nor many other folk seems to have experience with that thing. Maybe I´m the only one with it on a RV8 ? :) Now the strange behaviour is like I get signals at conditions like cranking, and regularaly above 3000Rpm. Even if I reduce the sensitivity a lot (knocksense recommends to turn the variable resistor 15-20° from start and I am at 45° now but have been further once - of which I don´t know whether that´s a lot or common) the >3000RPM signals are there (even with further reduced sensitivity). What I do get too is signals at 2100Rpm at 80-85kPa with advance of 16-17° - nothing really extreme. And that is with medium quality (95oct) fuel and 8.9 c/r of the 4.2l and sensor mounted same place as 4.0/4.6. My engine runs relatively cold with 82° thermostat. So this is best interpreted like all above is just noise. And I observe that warm-up makes things worse. The warm engine has much less signals than the cold one.

Well, would be nice if someone had some experience with sensors/knock and could advise me what to trust. But it really looks like I need to reduce the sensitivity further and live with doubts about the sensors effectiveness. At present I think I cannot rely on it while tuning which is what I had in mind with it (besides giving security with low quality fuel on travels).

OTOH I wonder if the OEM 4.6/4.0 have a similar behaviour concerning the "noise". Living with a non-operating sensor above 3000RPM will be ok because you don´t see this RPM-range very often, but leave that range "unprotected".

Does anyone know of a method to test the sensor ? I have heard about kind of self-made stethoscope (by means of wire or sth.) but cannot recall how it´s done. I try to listen to the engine, but my RRC is too noisy for the knock-unexperienced me to detect knock if it would occur.

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