Discussion
Hi Guys,
I'm hoping your combined knowledge can help. My disco 2 needed a new motor and to give it a bit of upgrade in the process a fresh 4.8 was put in. First start up of the motor resulted in a bit of a knocking noise and the valve train sounded pretty noisy to me. The engine supplier was told about the noise and I got an email back after he head watched a video i sent of the engine running that he thought it was probably a lifter and it just needed a good run and it would clear. Anyway to cut a very long story short after high oil consumption and metallic flake being evident at each oil change the oil pressure light started to come at idle when it had warmed up so motor was pulled and sent back to the UK. (I'm living in Australia at the moment)
When the engine was pulled apart it looked more like it had done 200000km rather than 25000! The engine guy is trying to blame either the oil or me not changing the oil or something to do with the install for the state of the motor.
I've spoken to a couple of V8 specialists who made comment on short skirt pistons being a bad choice for anything other than a race engine and that might explain the noise and may be blow-by. Penrite running in oil for the first 1500km (changed every 500km) then Penrite 10w50 changed every 5000km. The engine temps were always good. The engine was supplied with oil pump and heads fitted.
I'll add some photos hopefully and see what you think. We're pretty desperate to get the car back on the road as it is only car and it has now been off the road since before christmas. I've contacted an independent assessor to look at but now the supplier won't let the engine leave until I've paid him for the shipping back to the UK as well as the import duty and VAT!! It's a bloody nightmare!
I'm hoping your combined knowledge can help. My disco 2 needed a new motor and to give it a bit of upgrade in the process a fresh 4.8 was put in. First start up of the motor resulted in a bit of a knocking noise and the valve train sounded pretty noisy to me. The engine supplier was told about the noise and I got an email back after he head watched a video i sent of the engine running that he thought it was probably a lifter and it just needed a good run and it would clear. Anyway to cut a very long story short after high oil consumption and metallic flake being evident at each oil change the oil pressure light started to come at idle when it had warmed up so motor was pulled and sent back to the UK. (I'm living in Australia at the moment)
When the engine was pulled apart it looked more like it had done 200000km rather than 25000! The engine guy is trying to blame either the oil or me not changing the oil or something to do with the install for the state of the motor.
I've spoken to a couple of V8 specialists who made comment on short skirt pistons being a bad choice for anything other than a race engine and that might explain the noise and may be blow-by. Penrite running in oil for the first 1500km (changed every 500km) then Penrite 10w50 changed every 5000km. The engine temps were always good. The engine was supplied with oil pump and heads fitted.
I'll add some photos hopefully and see what you think. We're pretty desperate to get the car back on the road as it is only car and it has now been off the road since before christmas. I've contacted an independent assessor to look at but now the supplier won't let the engine leave until I've paid him for the shipping back to the UK as well as the import duty and VAT!! It's a bloody nightmare!
Spot on advice Dave, tis very difficult and stressful when things go wrong, especially when sold abroad. We decided a few years ago to only sell engines abroad if we fit the engine, run it in and set it up properly, then we can give a watertight warranty( only sold one in two years but we, and the customer, were more than happy). Only exception is a customer who sells our engines in Germany and knows how to look after them and what can and does go wrong with setups.
Hopefully the owner will get sorted with the V8, mind you 'postage' must be horrendous to and from Australia!
Peter
Hopefully the owner will get sorted with the V8, mind you 'postage' must be horrendous to and from Australia!
Peter
PS - your original post is very unclear as to when this work was done, where it was done. - Engine went in last August. Fitted here in Australia.
why the engine has 25,000 km on it if it was faulty from the start. - After numerous emails and discussions we explored numerous potential causes of the knocking noise. It wasn't until the oil pressure light started to come on that he agreed take it out and get it back to the UK.
who stripped it and took photos? - The supplier.
what the supplier is demanding more money for? - He wants money for the shipping back to the UK and the import duty and VAT before he will let the assessor have the engine. I've had no definitive answer as to what happened......hence bringing in the Assessor.
why the engine has 25,000 km on it if it was faulty from the start. - After numerous emails and discussions we explored numerous potential causes of the knocking noise. It wasn't until the oil pressure light started to come on that he agreed take it out and get it back to the UK.
who stripped it and took photos? - The supplier.
what the supplier is demanding more money for? - He wants money for the shipping back to the UK and the import duty and VAT before he will let the assessor have the engine. I've had no definitive answer as to what happened......hence bringing in the Assessor.
So you're in Australia and you sourced a new ? used ? engine from the UK ?
It had problems throughout, and was removed...then you shipped entire engine back to the UK ???
Surely there has to be somewhere down under or local to you that is capable of working on a Rover V8 ?
Shipping such a relatively mundane and common engine around the world for work...seems almost crazy.
So currently you have no engine whatsover ? Or where are you left exactly ?
And although the engine is oily and dirty inside, no way does it have huge miles. Most old RV8's with huge miles are literally clogged thick with crap inside. Yours is dirty, but not that dirty.
Although combustion chambers do look well oiled up, but that could be for a few reasons.
But no oil pressure is certainly a problem regardless of miles, but again could have a few causes.
It had problems throughout, and was removed...then you shipped entire engine back to the UK ???
Surely there has to be somewhere down under or local to you that is capable of working on a Rover V8 ?
Shipping such a relatively mundane and common engine around the world for work...seems almost crazy.
So currently you have no engine whatsover ? Or where are you left exactly ?
And although the engine is oily and dirty inside, no way does it have huge miles. Most old RV8's with huge miles are literally clogged thick with crap inside. Yours is dirty, but not that dirty.
Although combustion chambers do look well oiled up, but that could be for a few reasons.
But no oil pressure is certainly a problem regardless of miles, but again could have a few causes.
combustable said:
Apparently there is a limited time period in which returns for repair have to be done. I'll be calling HMRC in a bit to find out if this is true or not.
I suspect there is some confusion here. If you return a faulty item that you bought from abroad for a refund of the purchase price you can reclaim the original import VAT and duty paid on the basis that the goods were worthless provided certain conditions are met. In the UK for goods bought from abroad that usually means returning the item as soon as you discover it's faulty and in any case within 12 months. What your regulations are in Australia I have no idea but they should be similar in concept.However if you return an item bought from abroad for repair the above does not of course apply and there should be no further tax or duty payable on receipt by the repairer or on reimportation by yourself as no value is being added - just the correcting of the original fault.
What may have happened is the engine was not properly declared to UK customs as being returned for repair and they have assessed an importation charge based on some declared value somewhere in the paperwork which will then have been passed on to your engine builder. You clearly need to fix that first but if he has already paid it and not queried it with customs then it might turn into quite a problem.
I honestly suspect that it may have been better to bite the bullet and pay someone in Australia to rebuild it than try to obtain redress at such long distance. Also it is pretty rocky ground from a legal standpoint if you did 25,000 km on it while knowing that metal flakes were in the oil at each change and it was noisy and had high oil consumption from the get go. The original build faults might have been fixable but obviously not now the engine is shagged.
Equally if you pay the costs the engine builder is demanding and get the engine repaired elsewhere you'll have to pay new import duties on their bill and then try and sue for the cost of everything which will be near as dammit impossible from so far away without paying a UK solicitor a fortune.
I would try and not fall out with the original engine builder because you're pretty much at his mercy now if he decides to give you the finger.
I think it's far to soon to blame the builder. We haven't seen a proper diagnosis, have no idea of operating conditions and it's probably speculation as to where the 'metal' flakes have come from. I think the builder (it's not me btw) should be allowed to carry out a thorough examination. the oil looks cooked to me and reminds me of a truly 'dog' ls1 that came from Oz. it was also cooked inside.
Is there any disadvantage of using short skirt pistons? Could this contribute to piston instability within the bore on an engine like this? I've been told by another RV8 builder that they only belong on rally engines which have rebuilds ever year. Could this lead to blow by of oil passed the rings into the combustion chamber?
This is the preliminary report that I had back after it was dismantled. Just to clarify the engine was "remanufactured" so came to me with 0km after a rebuild. The reason it was sent back to the UK was to comply with the builders wish to deal with it himself.
The piston to bore clearance when built was supposed to be 0.0035" according to the builder. It just struck me as odd that even though the noise that concerned me was there from the very first start up I was told categorically that it was not piston slap. Now when the engine is pulled apart the abnormal wear on one of the pistons was probably the noise. At the end of the day if it is something that was done or not done as part of the install I can accept that and take it on the chin. If it was something that was wrong in the block itself from the start then I want to know and someone else should be responsible. I know many people have different opinions on different oils but surely they are all of a good enough quality not to shag motor in that quickly?
This is the preliminary report that I had back after it was dismantled.
Externally the engine was in a clean condition, with no obvious
damage or defect. The temperature strips fitted to block and
heads indicated the external surface of the engine had reached
116' C at all three locations. We note that the sump was likely
removed before shipping back to UK, as there was little
residual oil within, which as not allowed us to collect a sample
for lab analysis.
On opening the engine, we were very surprised with how dirty
the interior was. ( See pictures ) All surfaces had a dark
coating of sludge like substance, deposited by lubricating oil.
Inspection of the combustion chambers and piston crowns showed
a heavy build up of carbon on all surfaces. ( see pictures )
Inspection of the pistons showed a very heavy build up of
carbon on lands, skirt and undersides. ( see pictures )
The engine and components were cleaned of dirt with our hot
wash process to allow measurement and further inspection.
Visual inspection of the valve train, camshaft, and followers
showed wear consistent with normal running in, and were
regarded as in excellent condition. The number 3 camshaft
bearing was found to have shifted from its fitted position.
Pistons and rings, once decoked, were found in good condition.
Rings had typical wear from bedding in, less than half the
second taper machined ring had bore contact, consistent with
good running in and use. Pistons were in good condition with
minor scuffing on lower skirt noted on several pistons on bank
one thrust side. No piston to cylinder contact was evident on
the ring lands or other areas not expected to contact the
cylinders.
Cylinder bores. An area extending down all the cylinders, but
particularly the thrust side of bank one was noted to be
scored. This area of damage corresponded with the area of the
lower piston skirts. No Specific embedment or scoring was found
outside of that area. Bore gauge measurement showed cylinder
sizing and shape to be virtually unchanged from new outside of
the damaged areas. Within the damaged spots the cylinder 7
showed worst increase in size, 0.002" over the size of the rest
of the cylinder.
Crank rods and bearings. Light scoring was noted on all
crankshaft surfaces, sizes were within tolerance, and no
ovality or wear could be measured. The Tin Aluminium main
bearings had evidence of some surface disruption. However wear
under the area of the bearings exposed to heaviest load was
found mimimal.
The big end bearings, of the traditional Lead Bronze with
Babbitt overlay type had evidence of disruption of the soft
babbit overlay. On one connecting rod bearing, the overlay had
been displaced to show the bronze backing at the point of very
highest load. All bearings could be described as scruffy, with
evidence of embedment in the Babbitt, yet careful measurement
with a ball point micrometer ( to avoid brinelling )the maximum
size difference of 0.0006" between unworn and most worn parts
of the bearing could be found.
Our view based on visual examination of the embedded particles
within the Babbitt would suggest they are comparatively soft
and colouration would suggest not ferrous.
Remainder of engine ancillaries etc
Oil pump was stripped and inspected. It was noted that at the
oil cooler connections, plugs were fitted, which indicate the
engine did not have an oil cooler fitted. Minor scoring
consistent with normal use and wear. oils seals and gaskets.
Rear crank seal seated and square to crankshaft. No wear groove
or scratches on crank running surface. No visible cuts or marks
on seal edge. Front pulley was missing from engine, so no
assessment can be made, seal visually ok.
Initial analysis.
I have read back at our correspondence since you purchased and
installed the engine. Early on, you reported high oil
consumption and a noise from within the engine to us. The first
fill of oil you recorded to have been drained at 400 KM, and
was reported as dark in colour, to which we replied was typical
of the initial running in period with this engine.
The oil was further reported to have been changed at 500 KM
intervals subsequently over the next 2000 KM.
Our initial finding on strip down was the heavy carbon build up
on the combustion chambers and piston ring lands. A build up
was found under the crowns too. This is in my experience very
unusual, and would not be expected to be found on an engine run
on today's oils. It is my view that the engine has not suffered
a combustion defect such as a lean mixture condition which
could raise piston crown temperatures to the point of
carbonizing the lubricating oil, without any other damage being
present. The engine gaskets, valves, guides, piston rings and
piston ring lands do not show any evidence of excess heat or
damage which could be caused by abnormal combustion.
Despite the fact that no oil cooler was fitted, and no
indication of the maximum temperature of the oil has been
recorded, It has to be noted that Land Rover only fitted oil
coolers to vehicles operating in certain conditions and
territories. I am not aware of the vehicle having been used to
heavy towing. I consider that the engine has been run with a
lubricating oil which has carbonized at normal engine operating
temperatures and conditions. Further strong evidence of the
poor performance of the oil is shown with the dirty condition of
the interior of the engine. Given the frequency of oil changes
reported, it would be expected that the interior of the engine
would be spotlessly clean, as engine lubricating oil contains
detergents and dispersents which maintain combustion products
in suspension within the lubricant. Clearly, it has not been the
case with this engine.
The abnormal damage to the cylinder walls on the contact area
of the piston skirts is in my view the cause for the noise from
within the engine. The 4.8 uses high silicon alloy forged
pistons, which have quite short skirts. The piston to cylinder
clearance has increased by 0.002" on the worst cylinder, and
whist the piston top land has not been making contact with the
cylinder ( generally a prime cause of piston slap noise ) the
piston skirt will have had more clearance than expected and
required. The reversal of piston skirt loading at end of stroke
will generate rythmic engine noise varying with load and speed.
I cannot attribute the damage to a typical dirt ingress
problem, as no damage is present other than on the skirt contact
areas. Dirt entering the engine through intake would be
expected to leave damage predominately above the piston rings.
If dirt was built into an engine, for example during assembly,
damage would be predominately below the rings. Furthermore, it
would be expected that contamination which is sufficiently hard
to cause a scoring type damage would embed in the softer
aluminium piston. It would also, regardless of source be more
generally spread around the cylinder. No embedment of material
is present. I attribute the damage as wear caused by a
lubrication break down on the loaded thrust face of the piston
and cylinder.
Crankshaft and bearings. The extent of the damage found has not
resulted in clearances opening up to the degree which would I
believe would cause excessive noise which could be identified
as an individual knocking or similar sound, but could possibly
result in the symptoms to be expected within a higher mileage
engine, ie typically a slight reduction in hot oil pressure,
and a more general increase in engine noise. Its not possible to
see any identifiable foreign bodies present within the Babbitt
overlay, the damage being I believe to be generated from within
the bearings themselves.
The piston to bore clearance when built was supposed to be 0.0035" according to the builder. It just struck me as odd that even though the noise that concerned me was there from the very first start up I was told categorically that it was not piston slap. Now when the engine is pulled apart the abnormal wear on one of the pistons was probably the noise. At the end of the day if it is something that was done or not done as part of the install I can accept that and take it on the chin. If it was something that was wrong in the block itself from the start then I want to know and someone else should be responsible. I know many people have different opinions on different oils but surely they are all of a good enough quality not to shag motor in that quickly?
This is the preliminary report that I had back after it was dismantled.
Externally the engine was in a clean condition, with no obvious
damage or defect. The temperature strips fitted to block and
heads indicated the external surface of the engine had reached
116' C at all three locations. We note that the sump was likely
removed before shipping back to UK, as there was little
residual oil within, which as not allowed us to collect a sample
for lab analysis.
On opening the engine, we were very surprised with how dirty
the interior was. ( See pictures ) All surfaces had a dark
coating of sludge like substance, deposited by lubricating oil.
Inspection of the combustion chambers and piston crowns showed
a heavy build up of carbon on all surfaces. ( see pictures )
Inspection of the pistons showed a very heavy build up of
carbon on lands, skirt and undersides. ( see pictures )
The engine and components were cleaned of dirt with our hot
wash process to allow measurement and further inspection.
Visual inspection of the valve train, camshaft, and followers
showed wear consistent with normal running in, and were
regarded as in excellent condition. The number 3 camshaft
bearing was found to have shifted from its fitted position.
Pistons and rings, once decoked, were found in good condition.
Rings had typical wear from bedding in, less than half the
second taper machined ring had bore contact, consistent with
good running in and use. Pistons were in good condition with
minor scuffing on lower skirt noted on several pistons on bank
one thrust side. No piston to cylinder contact was evident on
the ring lands or other areas not expected to contact the
cylinders.
Cylinder bores. An area extending down all the cylinders, but
particularly the thrust side of bank one was noted to be
scored. This area of damage corresponded with the area of the
lower piston skirts. No Specific embedment or scoring was found
outside of that area. Bore gauge measurement showed cylinder
sizing and shape to be virtually unchanged from new outside of
the damaged areas. Within the damaged spots the cylinder 7
showed worst increase in size, 0.002" over the size of the rest
of the cylinder.
Crank rods and bearings. Light scoring was noted on all
crankshaft surfaces, sizes were within tolerance, and no
ovality or wear could be measured. The Tin Aluminium main
bearings had evidence of some surface disruption. However wear
under the area of the bearings exposed to heaviest load was
found mimimal.
The big end bearings, of the traditional Lead Bronze with
Babbitt overlay type had evidence of disruption of the soft
babbit overlay. On one connecting rod bearing, the overlay had
been displaced to show the bronze backing at the point of very
highest load. All bearings could be described as scruffy, with
evidence of embedment in the Babbitt, yet careful measurement
with a ball point micrometer ( to avoid brinelling )the maximum
size difference of 0.0006" between unworn and most worn parts
of the bearing could be found.
Our view based on visual examination of the embedded particles
within the Babbitt would suggest they are comparatively soft
and colouration would suggest not ferrous.
Remainder of engine ancillaries etc
Oil pump was stripped and inspected. It was noted that at the
oil cooler connections, plugs were fitted, which indicate the
engine did not have an oil cooler fitted. Minor scoring
consistent with normal use and wear. oils seals and gaskets.
Rear crank seal seated and square to crankshaft. No wear groove
or scratches on crank running surface. No visible cuts or marks
on seal edge. Front pulley was missing from engine, so no
assessment can be made, seal visually ok.
Initial analysis.
I have read back at our correspondence since you purchased and
installed the engine. Early on, you reported high oil
consumption and a noise from within the engine to us. The first
fill of oil you recorded to have been drained at 400 KM, and
was reported as dark in colour, to which we replied was typical
of the initial running in period with this engine.
The oil was further reported to have been changed at 500 KM
intervals subsequently over the next 2000 KM.
Our initial finding on strip down was the heavy carbon build up
on the combustion chambers and piston ring lands. A build up
was found under the crowns too. This is in my experience very
unusual, and would not be expected to be found on an engine run
on today's oils. It is my view that the engine has not suffered
a combustion defect such as a lean mixture condition which
could raise piston crown temperatures to the point of
carbonizing the lubricating oil, without any other damage being
present. The engine gaskets, valves, guides, piston rings and
piston ring lands do not show any evidence of excess heat or
damage which could be caused by abnormal combustion.
Despite the fact that no oil cooler was fitted, and no
indication of the maximum temperature of the oil has been
recorded, It has to be noted that Land Rover only fitted oil
coolers to vehicles operating in certain conditions and
territories. I am not aware of the vehicle having been used to
heavy towing. I consider that the engine has been run with a
lubricating oil which has carbonized at normal engine operating
temperatures and conditions. Further strong evidence of the
poor performance of the oil is shown with the dirty condition of
the interior of the engine. Given the frequency of oil changes
reported, it would be expected that the interior of the engine
would be spotlessly clean, as engine lubricating oil contains
detergents and dispersents which maintain combustion products
in suspension within the lubricant. Clearly, it has not been the
case with this engine.
The abnormal damage to the cylinder walls on the contact area
of the piston skirts is in my view the cause for the noise from
within the engine. The 4.8 uses high silicon alloy forged
pistons, which have quite short skirts. The piston to cylinder
clearance has increased by 0.002" on the worst cylinder, and
whist the piston top land has not been making contact with the
cylinder ( generally a prime cause of piston slap noise ) the
piston skirt will have had more clearance than expected and
required. The reversal of piston skirt loading at end of stroke
will generate rythmic engine noise varying with load and speed.
I cannot attribute the damage to a typical dirt ingress
problem, as no damage is present other than on the skirt contact
areas. Dirt entering the engine through intake would be
expected to leave damage predominately above the piston rings.
If dirt was built into an engine, for example during assembly,
damage would be predominately below the rings. Furthermore, it
would be expected that contamination which is sufficiently hard
to cause a scoring type damage would embed in the softer
aluminium piston. It would also, regardless of source be more
generally spread around the cylinder. No embedment of material
is present. I attribute the damage as wear caused by a
lubrication break down on the loaded thrust face of the piston
and cylinder.
Crankshaft and bearings. The extent of the damage found has not
resulted in clearances opening up to the degree which would I
believe would cause excessive noise which could be identified
as an individual knocking or similar sound, but could possibly
result in the symptoms to be expected within a higher mileage
engine, ie typically a slight reduction in hot oil pressure,
and a more general increase in engine noise. Its not possible to
see any identifiable foreign bodies present within the Babbitt
overlay, the damage being I believe to be generated from within
the bearings themselves.
Firstly I suggest you read my posts in the following thread on forged vs cast pistons, particularly in respect to alloy types and bore clearances and how piston manufacturers try to cover their arses by specifying huge bore clearances so they don't get come backs due to seizures and sod how the engine performs in respect to piston slap and blow-by.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Your engine builder says the pistons used are high silicon forgings. Running high silicon, low expansion, short skirt pistons at 0.0035" clearance is going to lead to piston slap - end of. In fact running any piston at that clearance is going to but on a race engine it's sometimes part and parcel of avoiding seizure at extreme rpm and temperatures. Note in my posts above how tight OE forged pistons can be run when all the design work is done properly. 0.0015" for example in the Vauxhall engine mentioned.
Clearly on one of the combustion chambers, which I take to be number 1 cylinder after reading the builder's report, there is a particular problem and the ring blow-by has been especially severe leading to the badly clagged up chamber.
Your oil might not have been the best (you don't mention the specific part number or whether it was mineral or synthetic) but any modern oil should cope with normal use. Also sure as god made little green apples the oil didn't wear out just one cylinder and leave the other seven ok.
In my opinion the bore clearance used combined with the piston design has caused severe piston slap which has prevented the rings seating properly and in turn caused blow-by of oil up past the rings into the combustion chambers, the burnt by products also getting dragged back down into the sump, contaminating the sump oil and coating the engine interior with black products of combustion. Wear in the bores in the region of the piston skirts and wear on the skirts themselves is a classic symptom of piston slap. If the skirts aren't banging from side to side the oil film doesn't break down for no reason regardless of the type of oil used unless it's chip frying oil not engine oil! It's the piston slap that actually bangs the skirts through the oil film creating metal to metal contact and causing the wear.
My opinion on the especially bad cylinder is that it is far more likely, in fact near as dammit certainty, it had a particular problem from the start, maybe an oversized liner after honing, than being any result of the oil used. Just one bad cylinder with excessive blow-by will have contaminated the oil and started a chain reaction of wear and black deposits on the engine internals.
You can see the blow-by on the piston photos underneath the rings. That build up of brown under the oil ring and also the black deposits between the rings.
Photos of the bores and honing finish would be helpful.
Finally if the bearings and crank journals were not excessively worn as he says then what's the reason for the oil pressure light coming on at idle? Either they must be worn enough to cause the problem or the pump must be faulty, perhaps from the start. I don't see how one can have it both ways. However 0.0006" wear on each big end bearing shell = 0.0012" increase in bearing clearance and combined with a bit of wear on the crank I suspect that's getting close to causing oil pressure problems at idle with hot oil.
I don't think this is too much of a mystery. Piston slap => blow-by => oil contamination => wear.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Your engine builder says the pistons used are high silicon forgings. Running high silicon, low expansion, short skirt pistons at 0.0035" clearance is going to lead to piston slap - end of. In fact running any piston at that clearance is going to but on a race engine it's sometimes part and parcel of avoiding seizure at extreme rpm and temperatures. Note in my posts above how tight OE forged pistons can be run when all the design work is done properly. 0.0015" for example in the Vauxhall engine mentioned.
Clearly on one of the combustion chambers, which I take to be number 1 cylinder after reading the builder's report, there is a particular problem and the ring blow-by has been especially severe leading to the badly clagged up chamber.
Your oil might not have been the best (you don't mention the specific part number or whether it was mineral or synthetic) but any modern oil should cope with normal use. Also sure as god made little green apples the oil didn't wear out just one cylinder and leave the other seven ok.
In my opinion the bore clearance used combined with the piston design has caused severe piston slap which has prevented the rings seating properly and in turn caused blow-by of oil up past the rings into the combustion chambers, the burnt by products also getting dragged back down into the sump, contaminating the sump oil and coating the engine interior with black products of combustion. Wear in the bores in the region of the piston skirts and wear on the skirts themselves is a classic symptom of piston slap. If the skirts aren't banging from side to side the oil film doesn't break down for no reason regardless of the type of oil used unless it's chip frying oil not engine oil! It's the piston slap that actually bangs the skirts through the oil film creating metal to metal contact and causing the wear.
My opinion on the especially bad cylinder is that it is far more likely, in fact near as dammit certainty, it had a particular problem from the start, maybe an oversized liner after honing, than being any result of the oil used. Just one bad cylinder with excessive blow-by will have contaminated the oil and started a chain reaction of wear and black deposits on the engine internals.
You can see the blow-by on the piston photos underneath the rings. That build up of brown under the oil ring and also the black deposits between the rings.
Photos of the bores and honing finish would be helpful.
Finally if the bearings and crank journals were not excessively worn as he says then what's the reason for the oil pressure light coming on at idle? Either they must be worn enough to cause the problem or the pump must be faulty, perhaps from the start. I don't see how one can have it both ways. However 0.0006" wear on each big end bearing shell = 0.0012" increase in bearing clearance and combined with a bit of wear on the crank I suspect that's getting close to causing oil pressure problems at idle with hot oil.
I don't think this is too much of a mystery. Piston slap => blow-by => oil contamination => wear.
Edited by Pumaracing on Friday 11th April 05:06
I'll add one further thing for the sake of completeness which is gudgeon pin offset. Contrary to what one might assume gudgeon pins are not usually exactly central in the piston but offset by up to 1mm towards one of the skirts. This loads one side of the piston slightly more than the other and helps stop the piston slapping across the bore as it rocks over TDC and BDC as the conrod swaps its angularity.
This is not such a big factor with small bore long stroke engines with full skirt "baked bean can" type pistons of long ago but very important with modern short skirt slipper pistons and especially with large bore clearances.
It's not possible to tell from photos whether those pistons have offset pins or not but I've seen the same problem in the past with aftermarket forgings. If those pins are central then it will have exacerbated the problem considerably.
This is not such a big factor with small bore long stroke engines with full skirt "baked bean can" type pistons of long ago but very important with modern short skirt slipper pistons and especially with large bore clearances.
It's not possible to tell from photos whether those pistons have offset pins or not but I've seen the same problem in the past with aftermarket forgings. If those pins are central then it will have exacerbated the problem considerably.
Thank you Pumaracing.....this is exactly why I love Pistonheads!! This gives me a bit more ammo hopefully. My knowledge of engines falls away rapidly when you start talking about the internals but I know when something doesn't sound right!!
Is there any reason why the short skirt pistons were used or could something with a longer skirt have been used without any effect to something else inside the engine.
Cheers
Combustable
Is there any reason why the short skirt pistons were used or could something with a longer skirt have been used without any effect to something else inside the engine.
Cheers
Combustable
I have no idea what parts are available for your engine or even exactly what it is. I assume a 4.8 is an overbored 4.6 but it isn't an engine I've worked on. Others on here will know more. However for a non competition engine a cast piston with a longer skirt and a tighter bore clearance would be infinitely preferable as the thread on forged vs cast pistons describes. Unfortunately most "special" pistons are forgings with huge specified bore clearances as they're easier to make in small quantities hence the problems that so often result.
combustable said:
Forgot to add that the oil used was a Penrite 15w40 running in oil for the first 1500km (changed every 500km) then Penrite 10w50 fully synthetic after that. (Changed very 5000km)
I think that nails any oil related problems on the head then. Synthetics are excellent at preventing black build up inside engines and only ultra severe blow-by and products of combustion getting into the oil could have caused what looks more like 150,000 miles worth of mineral oil deposits rather than 15,000 on fully synth.Much of what your engine builder has written actually indicates a good knowledge of engine operation and fault diagnosis but unfortunately human beans tend to suffer very badly from "confirmation bias". The tendency to interpret evidence in accordance with the outcome you want rather than to correctly infer the outcome from the evidence. It's at the root of all religious beliefs for a start.
He wants to blame the oil because the alternative is to admit fault. In reality the oil was fine but the engine operational shortcomings shagged it.
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