Porsche 911UK Forum

Welcome to the @Porsche911UK website. Register a free account today to become a member! Sign up is quick and easy, then you can view, participate in topics and posts across the site that covers all things Porsche.

Already registered and looking to recovery your account, select 'login in' and then the 'forget your password' option.

Borescore - How do you know ?

We can only form opinions and judge the origin of faults based on the engines we see and repair.

When the first ones fail they are usually repaired by replacing the engine with a new one via a main Porsche agent and we do not get to see them or assess causes.

Eventually they come our way and then initially we have to base our conclusions on what we see, can measure and assessing the type of damage.

All the Gen 2's we have seen so far have siezed the bore for a different reason than the 996/7 Gen 1 type engines.

All of them so far have had age and temperature cycle stress relieving result in the clearances between the piston and the cylinder bore reducing at the bottom of the cylinder block until from cold the piston expands bigger and quicker than the bore and is too tight and fully seizes on both front and back faces.


The typical Lokasil bore scores only occur on one side of the piston because the problem is not that the piston is bigger than the bore but that a piece of loose silicon was trapped between the piston and the cylinder bore and as there is only one face that is under thrust load - that is the face that the damage is located on.


This is also the reason why bank 2 always scores first - because bank 2 thrust face is on the top of the engine while bank 1 thrust face is on the bottom - and the coolant flows into the bottom of both banks resulting in bank 2 running hotter on the thrust face than bank 1 because the coolant on that side has picked up heat as it rises through the block whereas the thrust face of bank 1 receives the coldest coolant before rising through the block. This in turn results in the oil being thinner between the piston and cylinder and reduces the clearance that could be between the 2 parts for silicon to escape between.


Gen 2 (9A1) piston clearances are generally tighter than their earlier 996/7 gen 1 cousins so anything else that could make them run hotter could also contribute to scoring. Typical issues could be mixtures and so there is every chance that some engines ran weaker if the injector seal was loose - or any other typical cause of engines running weak or hot.


The Gen 2 engines are so much more reliable than the earlier engines that it may well be some time before we have seen enough failures to form conclusions about the most common causes.


Baz
 
bazhart said:
We can only form opinions and judge the origin of faults based on the engines we see and repair.

When the first ones fail they are usually repaired by replacing the engine with a new one via a main Porsche agent and we do not get to see them or assess causes.

Eventually they come our way and then initially we have to base our conclusions on what we see, can measure and assessing the type of damage.

All the Gen 2's we have seen so far have siezed the bore for a different reason than the 996/7 Gen 1 type engines.

All of them so far have had age and temperature cycle stress relieving result in the clearances between the piston and the cylinder bore reducing at the bottom of the cylinder block until from cold the piston expands bigger and quicker than the bore and is too tight and fully seizes on both front and back faces.


The typical Lokasil bore scores only occur on one side of the piston because the problem is not that the piston is bigger than the bore but that a piece of loose silicon was trapped between the piston and the cylinder bore and as there is only one face that is under thrust load - that is the face that the damage is located on.


This is also the reason why bank 2 always scores first - because bank 2 thrust face is on the top of the engine while bank 1 thrust face is on the bottom - and the coolant flows into the bottom of both banks resulting in bank 2 running hotter on the thrust face than bank 1 because the coolant on that side has picked up heat as it rises through the block whereas the thrust face of bank 1 receives the coldest coolant before rising through the block. This in turn results in the oil being thinner between the piston and cylinder and reduces the clearance that could be between the 2 parts for silicon to escape between.


Gen 2 (9A1) piston clearances are generally tighter than their earlier 996/7 gen 1 cousins so anything else that could make them run hotter could also contribute to scoring. Typical issues could be mixtures and so there is every chance that some engines ran weaker if the injector seal was loose - or any other typical cause of engines running weak or hot.


The Gen 2 engines are so much more reliable than the earlier engines that it may well be some time before we have seen enough failures to form conclusions about the most common causes.


Baz

Very interesting. Thanks for taking the time to post :thumbs:
 
OP, I wouldn't bother checking it if there are no signs showing, it's a waste of time and money.

Do as people say, don't rag it until warm etc etc, change the oil every year, use good oil (I am on Millers) and generally look after it.

You can get it checked, but what are you going to do if it shows signs? Some cars have some scuffing which as someone said some slightly less knowledgeable will say is scoring, so make sure you get it done by someone who knows what they are looking at, get the pictures, ask Baz and/or demort to have a look, but only if you want the peace of mind......
 

New Threads

Forum statistics

Threads
124,354
Messages
1,439,460
Members
48,712
Latest member
golfguy11800
Back
Top