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How to possibly avoid cylinder scoring

Yet another reason not to buy a London car!
 
GT4 said:
Yet another reason not to buy a London car!

Yet another reason to buy a turbo / GT3

MC
 
The worst scoring is always on bank 2 and always on the top of the engine (the opposite side to gravity effects which have nothing to do with it). The thrust side on bank 2 is the top where the coolant is exiting the cylinder (hence also hottest).

The thrust side on bank 1 is at the bottom where the coolant enters and is therefore coolest and almost never has scoring.

Just another example of well meaning posts that through lack of proper knowledge of the engine seem to contradict my posts when actually they are not only wrong but the complete opposite is true.

The obvious answer would have been an electric operated pump at low engine speed and a thermostat on the top of the engine block plus a re-routing of the entry point of the coolant on bank 2 - but it is too late for any of this to be applied to existing engines - hence I have been trying to think of ways to help those who presently do not have scored bores - to keep it that way without any expense or modification.

Ignore this advice at your peril (and if you do ignore it - please bring the car to me to fix it).


Baz
 
Perhaps this thread should be a sticky....?? - MOD anyone?
 
@Baz: Interesting theory. Your work on the failed engines has naturally prompted you to put a lot of thought into the causes and possible remedies and your extensive experience has provided you with the observations on which to build up a well-founded theory.
I do have a question on your advice to 996 drivers based on your conclusions, but want you to understand beforehand that I'm just trying to pick your brain and not pick holes in your theory.

Since we're talking about cars capable of 0-60 mph in around 5 seconds, the unfavourable conditions prone to causing cylinder scoring in the most endangered cylinders would not last very long at all if the driver opens the throttle wide in an appropriately low gear, as the increased coolant flow and oil spray jets would kick in very quickly (though maybe still not quickly enough).
Don't you think that a more dangerous scenario based on your theory might be if a driver (starting from the same conditions) were to open the throttle wide from a low road speed in too high a gear, so that the pistons would experience a high lateral thrust load for a much longer period without benefiting from increasing coolant and oil flow, due to the leisurely rate of acceleration?
This would mean that the advice should really be not to "flog" the engine by opening the throttle wide in too high a gear for the speed or incline, particularly with a hot engine.
It would also explain why tracked cars which are regularly subjected to wide open throttle from a standstill while hot do not appear, as far as I am aware, to be over-represented amongst those suffering from cylinder scoring.

As I said, I'm not questioning the validity of your theory. I'd just be interested to hear your views on this interpretation of the possible conclusions to be drawn from it.
 
bazhart said:
The worst scoring is always on bank 2 and always on the top of the engine (the opposite side to gravity effects which have nothing to do with it). The thrust side on bank 2 is the top where the coolant is exiting the cylinder (hence also hottest).

The thrust side on bank 1 is at the bottom where the coolant enters and is therefore coolest and almost never has scoring.

Just another example of well meaning posts that through lack of proper knowledge of the engine seem to contradict my posts when actually they are not only wrong but the complete opposite is true.

Baz

OK, I was obviously wrongly informed regarding which bank suffered the scoring, but I was certain I was told it was the bank where the thrust stroke was at the 'bottom' of the cylinder (if you see what I mean)!

I am still unconvinced about the water theory though... Is it not likely that the scoring is simply a result of gravity reducing the amount of oil available for lubrication at the top of the cylinder, then? I understand that the material used for the cylinder liners is different in water-cooled engines and could explain why they suffer more than air-cooled engines, perhaps?

The reason I am sceptical is that I don't understand how the bore can be hotter in a water-cooled engine, than in an air-cooled (or oil-cooled, if you want to be really pedantic) engine? Surely the water won't be hotter than if it wasn't any water there at all?

Maybe I am wrong, but I did study engine thermodynamics as part of my Automotive Engineering degree (albeit many years ago) and I am struggling to understand the physics here!

Either way - not thrashing the engine when there is insufficient oil pressure sounds like a good strategy to me!
 
pawmaro said:
Buy a mercedes

Well done, is that what you did?

~ Maxie :wack:
 
like a racehorse

Yes nurtured never ranted from cold but still engine knackerd at 50k and no goodwill from Porsche. No warning just check engine light and a smoky left hand bank. Bloody rubbish now not like they used to be
 
Always a pleasure to hear you Baz.

All those who have experienced the exceptional quality of your rebuilt units can affirm that your experience in engine design means great gains for the owners of such cars.

After over 4000 miles (not including the oil change after 2000 mi run in) I have not needed to top up the oil, the temperature runs steadily at 80 even when going (not) full tilt up at 165 leptons, and the car purrs and gently whines as all those handbuilt cogs tooth and spool in tight lockstep after precision manufacturing from Hartech.

Speaking from experience, though, I must also say that it is a sorry state of affairs that Porsche have been stumped on build quality, and that all these years later there is no admission of the faults inherent in these engines. One expects issues in older cars but those younger 997's? Such a shame.

I have now passed on from the Porsche fraternity. ELA is the new owner and I can tell you he is very happy with his new unit - no Porsche Paranoia Syndrome for him!

It is a pleasure to have made your acquaintance Baz..



:bye:
 

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