Question for Baz Hart

Hi Baz , I had a question that was prompted by your comment in the 996 sub section .
A while ago you were looking for doner 997.2 cars as you were seeing a very small % coming in for a rebuild ,I realise it is very very small numbers and you were looking for Doners to try and identify what , where and why these were having issues as Porsche suposedy overcame the Borescore from using sub standard cheap components that were happening to a small % of 996 and 997.1 cars. the 997.2 uses a different material for its liners . So I was wondering if you had started to reach any conclutions re the 997.2 is it a weakness in the liner or is it a weakness somewhere else thats then causing secondry damage to the liners is it on one bank or the other and do you have any new reccomendations for gen2 owners that are different to your current reccomendations for 996/997.1 cars . you mentioned seeing crank wear on older cars 996/997.1 and that could be risk reduced by using certain oils .I am using millers nano 10w 50 on my gen2 as I did on my gen1 . I did have a LTT on my gen1 but havent yet done it on my gen2 is it reccomended or will it make not much difference to the DFI engine.
And lastly have you yet got a gen2 bigger engine option maybe 4ltr.
I really just was wanting an update on your findings and any other reccomendations taken from your work on the 997.2 as I havent seen much todate from you guys about your findings . I know this is an imotive subject and gen2 owners will be freaking out :grin: but we do recognise that its a very low % and value any info that you are finding that will help us look after our cars the best we can especially as the DFI engine differs from the 997.1 and 996 engines and you may have other reccomendations that are specific to the DFI engine, so that hopefully the % of gen2 cars in for rebuild remains tiny.

:thumb: :thumb: :thumb:

Hi Phil, sorry if my reply has been delayed.

Although these cars can go over 150 mph - most owners rarely exceed 70 and the average speed recorded is often in the low 30's - so engines run most of the time with relatively little piston temperature and modest expansion. But the manufacturer still has to make them so they will withstand the occasional burst to top speed when the pistons expand more.

The amount pistons expand is a proportion of the diameter - so multi-cylinder engines with smaller pistons have a lower range of sizes between slow and fast motoring and the bigger the pistons the bigger the problem of keeping a small clearance in all running conditions. Iron liners (even cast in) would have to have too big a clearance for perfect running at low speeds to still be right for fast running and as most of the time the road sports cars run slowly - oil consumption and emissions would suffer.

To solve this - it was decades ago that manufacturers perfected using alloy cylinder blocks (so they expanded more like the pistons from cold to full hot) and managed to keep clearances down.

They introduced silicon into the alloy and created Alusil - but the aluminium piston surface would only survive if it had an electroplated hard iron surface to run against the silicon particles. This was super reliable with the 944/968 models but because the silicon was everywhere in the block they cost a small fortune to machine and manufacture. When Porsche were in danger of going bust (early @90's) they had to find less expensive production solutions to survive.

This created the idea of only putting the silicon near the cylinder bore surface locally (Lokasil) which cost less to produce and worked OK when iron coated pistons were used. The failure of the ovality and cracking was more to do with the design of the block to suit metal casting moulds that could be extracted but and left the top of the cylinders free and unsupported. Then the process by which the hard iron was electroplated was outlawed in Europe and hard iron piston coatings were no longer viable. The plastic piston coatings that replaced the hard iron were then found to be wear more quickly and be unable to resist the damage caused by occasional release of silicon from the cylinder bore and so eventually Lokasil was found to have too many adverse side effects to continue with and was abandoned in favour of a return to Alusil for Gen 2 models that had proven so reliable in earlier models.

So the Gen 2 engines returned to Alusil and with a different form of iron coating on the pistons.

In the same way that it was the design of the cylinder blocks that resulted in ovality and cracked cylinders (not the Lokasil) in Gen 1 engines, if there is a problem with the Gen 2 engines it is unlikely to have anything to do with the use of Alusil.

When we were testing different piston coatings in Lokasil – we found a hard iron coating similar to the original used in Alusil (but not the same) and looking exactly like the coating used now on Gen 2 pistons – was not quite as long lasting as the original type of coating. However the silicon in Alusil has smaller particles and unlike Lokasil (where the silicon particles are much bigger), the silicon content is not formed by trying to squeeze molten aluminium into a pre-formed porous tube during casting – but comes out of solution within the aluminium/silicon mix to grow into particles that are much more evenly distributed and I think more strongly retained.

So I would expect the Gen 2 Alusil block and iron coated pistons to provide a very good and reliable system and not lead to premature failures.

However we have had a small number that have scored bores and have found very minor evidence elsewhere. Our own investigation concluded that there could be a small problem over a long period of time that has nothing to do with the Alusil or the piston coating but is probably due to age related creep reducing the piston clearance at the bottom of the block and impinging on the piston during too quick a warm up from cold.

We do not know if the problem was solved during manufacture and therefore no longer applies, have no idea how many may be involved and the numbers we have investigated are too small to be sure of a firm conclusion. Evidence is that they seem perfectly OK if in cold weather the right warm up procedure is followed before driving flat out too soon.

We are involved in the 4 litre Gen 2 conversion but frankly have had too much on our plate with the oversized M96 engine range and getting them into production to turn our attention to developing it. However the good news is that I expect to have completed all the work on the '96 versions in 6 weeks and can then devote time to the Gen 2 car – so more on this later.

Baz

Baz, what a fantastic reply. I don't know you and as a recent owner of a Gen2 I hope I don't require your expertise personally but I would like to thank you for sharing your knowledge publicly. Thank you.
I hope you do share your future findings on the forum and help gen 2 owners maintain their cars accordingly.

Very imformative as usual from Baz :thumb:

Seems that Mechanical Sympathy is the way to go with any high performance engine.
Don't thrash it from cold is always best.

:worship: :worship:Thank you Baz, as always such a great and indepth reply while making it easy for non mechanical guys to grasp.I guess with all cars there will always be a % that are not driven or maintained simpatheticaly by their previous / current owners and I guess these are the ones that we may start to see fail over time. I will ensure I follow the reccomended warm up procedures especially in the cold.I will continue to use Millers nano+ 10w50 . whats your thoughts on a LTT on a 997.2 a good idea or not needed.
Please do keep us updated on any gen2 findings or reccomendations to keep them running well. I look foreward to following the development of the 4ltr gen2 :grin: :grin: 4ltr 911 just has such a good ring to it. :grin: :grin: :thumb:

Thanks Baz.

Can you elaborate on an appropriate warm up procedure for the 9972 DFI engine? I live in a (very) cold climate and I use an electric engine block heater from DEFA in the winter, which takes the coolant to about 36c for an easier start up, but the engine oil is still basically cold, so I'd be interested.

Clearly, I'm not the only guy in the world running a 997 in a cold climate, and I am aware that most engine wear happens at cold start, so I have a lot of mechanical sympathy, but would still like to hear your views.

MaxA

Max, you seem to be doing everything right so far - well done.

The problem we found was that pistons had scored themselves and the bores but not like the M96/7 Lokasil engines (where they usually still run - partly because when they gradually go oval it is in the same direction as the thrust direction where the piston is biggest - so it actually increases the clearances) but a proper traditional seize rendering the piston and bore fatally flawed and requiring immediate attention. When we measured some of the cylinders they were smaller at the bottom than the top reducing the clearance between the piston and the cylinder bore.

We measured 5 cases (another one imminent to check as well) and found the standard clearance round about 1.5 thou (0.00015" or 0.04mm) but some cylinders at the bottom had shrunk inwards in the direction the piston is biggest (the thrust direction) with the smallest clearance we found 0.0004" (or 0.01mm). Not all cylinders had shrunk - usually towards one end of the cases with one end parallel, the centre half shrunk and the other end most shrunk.


The owners had driven the cars much the same in similar conditions often for many miles and several years (impatient to drive off fast for a relatively short journey) but then they now had a problem. They all suffered the failures on very cold days after a short distance from cold.


Our conclusion (which I think is perfectly reasonable with the evidence available) was that the bores were parallel from new but gradually over many years and miles - the bottoms had slightly shrunk in until a rapid heat-up and expansion of the piston reduced the clearances enough to jam the piston in the bores.


If you drive off fast in cold conditions the piston will always heat up and expand quicker than the cylinder bore so the only way to avoid this happening is to drive more modestly for say 10 minutes and at least until the engine and oil are fully warmed up.


In very cold conditions partly blanking off a radiator with a removable blind would also help because it will reduce the temperature gradient inside the engine.


What we do not know is if this is a problem that will aflict more engines over time.


I guess those in climates that are never sub-zero might get away with it whereas those in places with extreme variances (like Canada) may incurr more failures.


Because there is no seperate crank carrier in the Gen 2 9A1 engines the bottom of the cylinder block has a large part of the casting (where the crankshaft shells sit) that is very thick and joines to the bottom of the cylinder area where the shrinkage we measured has ocurred.


It is a common problem in castings that residual stresses caused in the casting process can be present when they are machined and then over many hundreds or thousands of heat/cool cycles move minutely and change shape (especially where there are thick cross sections).


It seems possible that this thick area has done this especially since the failures are so far all in the first production models (but this could be because they have incurred the most thermal stress reversals).


What we don't know is if this is going to be the same in later models or if Porsche identified it early on and carried out either some post casting stress relieving (which is usually done by forced heat/cool cycles) or found a way to slow the cooling of the casting in production or found some other way to eliminate the problem.


Because it takes many thermal cycles to find evidence of the problem we doubt that anyone would have been aware of it until too many years later on - but that conclusion could prove to be wrong.

It would be theoretically possible to re-hone existing blocks that have shrunk but the cylinder has a blind bottom that prevents a hone passing out of the bottom and this would make it difficult to re-hone just the bottom.

Replacing pistons with smaller ones would also work or perhaps the profiles of the pistons have already been modified to allow for this eventuality - we simply don't kmow.

The apparent reluctance of Porsche to be open about similar technical issues (which is commercially understandable) makes the job of finding solutions (when the model range has finished production) - very difficult for small independents like us who try to find a better solution than replacing the failed part with one exactly the same.

So in the meantine we have made replacement cylinders and in the process a 4 litre conversion and when we have finished testing and found more evidence we will let you all know and meanwhile we will be ready if replacement cylnders are ever needed.

Baz

Thanks Baz. Fascinating stuff. I'll continue to take it easy for the first 10-15 minutes. On a typical day, that's easy. And then I sit on a highway at 85-90kmh for another 15-20 minutes so it's no big deal to be gentle.

Baz thats extremely interesting reading just as a note as its not mentioned were the five/six cars you have looked at manual, PDK or a mix , the reason I ask is that when I drive off from cold in my gen2 the engine feels tight as though you really would damage it if you pushed it hard , this usually feels like this for the first few miles and actually makes you want to keep below 3k revs mine is a manual. Not having driven a PDK from cold but having driven a TIP gen1 from cold this feeling of tightness was not present in the auto box even if driven in manual mode the gen1 felt looser when cold . I was wondering if they were PDKs if the box was pushing through the cold tight engine and the driver not feeling it thus adding potential damage. But this is just the info we gen2 owners need your last post where its clear that the gen2 maybe even more than the gen1 needs to be properly warmed up from cold before hooning. and even more so in colder sub zero climates which we southerners rearly see. :thumb: please keep this valuable info coming as you find things that gen2 owners can do to reduce risk . currently I follow all the Hartech reccomendations for the gen1 with the exception of not having fitted a LTT as I havent been told if its helps the gen2 or not. :thumb: :thumb: :thumb:

Thanks Phil,

we just don't have enough evidence yet to form reliable conclusions but the Gen 2 has Alusil bores it is run with tighter piston clearances than a Gen 1.


The Gen 1 distorts the bores oval. Some we have measured that are brand new and never been run (new cases) had already stress relieved oval in the thrust direction resulting in even more piston clearances and they then gradually go more and more oval increasing clearances as they do - so the problem of cold seizing as a result of too short a warm up time would have been very unlikely to strike at a Gen 1 car.


As a result perhaps some owners who have moved on to a Gen 2 have got used to getting away with short warm up times and found it was OK in the Gen 2 they own when they first used it (before the thermal stress relieving has shrunk the bores) - until that is - the bores on that model (that we have measured) go oval in the opposite direction (because of the different crankcase design) and pinch on the piston over time.


So - were the early ones we had to look at a rare unusual exception - or were they all like that but few ragged from cold on cold days after high mileages? Are there not enough of them that have had enough thermal stress cycles yet? did Porsche do something to fix the problem early on? was there a procedure after casting that some didn't spend long enough undergoing to stress relieve the castings? is it bad luck or a scenario that will re-occur?


We just don't know and only time will tell - but at least by analysing the few we have had to investigate and having found the same trend in all of them - the warning is out there and may-be fewer owners will be so impatient to drive fast from cold and the problem will reduce to zero?


The work we are doing for the 4 litre conversion is still valid as an exercise that will probably justify the cost when some owners take it up and if the issue does eventually mean more scored/seized Gen 2 engines we will already have produced, tested and have available an alternative solution to a new engine with the same issues and the option of a faster one.


Baz

Thanks Baz , I appreciate the time taken to answer my questions :worship: I will continue to follow your gen1 guidelines with my gen2 with particular attention to warming the car up and even more so during the colder months that way I hope to only bump into you for a coffee and chat or a 4ltr convertion because I want it not because I need it . and not because I have killed my engine :grin: :grin: :thumb:

Just a quick question. When ever i start my 997 i make sure to warm the car up to temperature, do i need to also wait for the oil temp to go up to temp aswell before i drive? I always give time before i drive, not in a hurry!!

Cheers

J

-- 997 -- said:

Just a quick question. When ever i start my 997 i make sure to warm the car up to temperature, do i need to also wait for the oil temp to go up to temp aswell before i drive? I always give time before i drive, not in a hurry!!

Cheers

J

Click to expand...

J , The rule of thumb is drive the car but stay under 3k revs until it;s all fully warmed up, I dont actually sit letting it warm up before I drive off once the start up revs have dropped 30 seconds or whatever it is your good to go. :thumb: was the way I understood it.

Phil 997 said:

-- 997 -- said:

Just a quick question. When ever i start my 997 i make sure to warm the car up to temperature, do i need to also wait for the oil temp to go up to temp aswell before i drive? I always give time before i drive, not in a hurry!!

Cheers

J

Click to expand...

J , The rule of thumb is drive the car but stay under 3k revs until it;s all fully warmed up, I dont actually sit letting it warm up before I drive off once the start up revs have dropped 30 seconds or whatever it is your good to go. :thumb: was the way I understood it.

Click to expand...

Cheers for that phil, i dont mind sitting and waiting for the car to warm up, its the way ive been doing for years, unless if im in a rush then id drive slow as said and keep under 3K. Otherwise if i sit and wait like i do then do i let the oil go up to temp like the water temp? Is it just as important on the 997 ?

Cheers

J

A new topic due shortly about bore scoring includes information relating to this subject

Baz