Very rare cylinder scoring problem explained

[bazhart]

I have been asked to edit this posting to ensure forum rules about promoting products and servicesw are not broken. So if anyone is interested in the problems that can occur rarely to a Cayman S (but for interest sakes more likely to a 996 3.6 or 997 3.6 or 3.8) then we have just managed to complete section 5 of our buyers guide available on the Internet by going to our web site www.hartech.org and buyers guide section 5 or by this link
http://www.hartech.org/docs/buyers%20guide%20web%20format%20Dec%202010%20part%205.pdf . (please note the section 5 starts after the foreward). This is purely an information tool and by going directly to the link - you can avoid seeing anything else about Hartech - as there are no prices or direct sales information in the section. The forward does contain some generalisations but if all you want to read is technical information please skip that and go directly to section 5 a few pages further on.

If the moderator wants to alter this message to satisfy the rules pllease feel free to do so or remove it if neccessary.




The section 5 explains in detail the differences between the 3.4 Cayman S, 3.6 and 3.8 engines (the models that exhibit cylinder scoring problems) and earlier engines, the potential causes and various new solutions and road test results INCLUDING A RELATIVELY INEXPENSIVE SOLUTION.

For those wanting faster answers "" whilst increased piston to cylinder wall loading results from increased bottom end torque "" at the same time changes to the coolant flow and distribution increase the temperature of localised hot spots and in some combinations of driver style, other older typical wear/age related problems, and general deterioration - push them beyond safe levels in an engine type already running hotter (but previously better balanced) temperatures than older typical designs. The result in some combinations of circumstances is too thin an oil film being unable to keep the piston and cylinder wall apart safely and resulting scoring of the piston and cylinder.

Fitting a lower temperature thermostat (while checking out other contributory factors) will lower the odds of you experiencing this failure while new exclusive pistons and modifications to the inside of the engine during a rebuild - will reduce repair costs further and protect against a reoccurrence.

All this research, design, rebuilding, testing and sharing our results with everyone takes up enormous amounts of time and energy "" hence often too little left to promote our excellent standard products and services in a more market orientated "" reader friendly style "" sorry - but I hope the information will help those unsure what to do to protect their interests, enable them to fully enjoy this fantastic model range and if they are unfortunate enough to experience the consequences (which is extremely unlikely) "" remember you can potentially incur unnecessary expense by not checking what your chosen investigative would or could do and what it would cost before authorising it.

The Cayman S is the least likely to suffer this problem but we have repaired some already and it may be worth checking up on, protecting against.

My very best wishes and good luck for the New Year "" until then

Baz

 

[ChrisW]

Very interesting Baz, particularly in terms of maintaining residuals for these cars and accepting the generality that the smaller capacity engines have less risk due to the thicker cylinder walls and therefore lesser likely-hood of hot-spotting. Given your analysis, does the new DI engine ameliorate these issues --- and or is it likely to suffer it's own ?[]

 

[bazhart]

Chris w - all this work, research testing, re-designing solutions, manufacturing and explaining etc is all focussed on the M96 and M97 engines. It looks to me that the Gen 2 engines have designed out the potential for similar problems but I have not yet got inside one or heard of any failures (apart from the consequence of carbon build up on inlet valves). In time any weak areas or not will eventually come to our attention and I will (as usual) be happy to share our thoughts on the subject if and when it emerges. Baz

 

[ChrisW]

Thanks Baz, As far as I can see it's a very worthy investment and I hope and trust that it will pay a tangible dividend for both you and your business [] I hear that some of the Audi DI engines have suffered carbon build up but Porsche were late in the game with theirs, and so will hopefully have learned also from this unanticipated consequence ! The worst I guess is de-cokes, --- now where have I heard that before [][] Though it was incredibly simply on the old side valve engines !!

 

[bazhart]

Just to confirm that on other forums a member called GT4 explained how to use/re-program the air con unit to find the true coolant temperature and the result confirms that the dashboard guage reads about 10 degrees lower than the coolant actual temperature (as our tests confirmed) and proves that the whole argument we raised was valid and can be confimed using a Porsche system already fitted to the car. Baz

 

[Alex Postan]

This happened to me in 2008 at 23500 miles. Five cylinders and swarf in sump. New engine, no quibble; first Cayman engine problem seen by Dick Lovett Porsche.

 

[bazhart]

Thanks Alex - it is quite a problem when we warn people of a rare but potentially expensive problem (and a solution) and they rubbish the advice on various grounds - which your photo and experience proves is a rare but is a genuine possible outcome exactly as shown in our own photographs. It is difficult to know exaclty what sequence of events and failings in the general condition of the car all combine to make some cars suffer while others don't. I think one problem is that the radiators are a long way from the engine and the thermostat quite slow to react (and on the engine inlet side so slowing reaction time) and the dash board analogue temperature guage is also slow to react (you can prove this using the air con read out to display digital engine temperature) so anyone suddenly increasing the temperature of the pistons by putting a lot of load on them (probably especially at lower revs while the coolant pump is relatively slow) can briefly just get too high a temperature rise at the psiton face before the thermostat opens and the whole system cools again. It may be that slightly low coolant may be a factor or slightly low pressure - but basically they are running a bit closer to the perfect set up than older typical examples - so any small influence can push the critical areas over the edge. This is why - despite the fact that by providing a method of reducing the potential for failure (in our lower temperature thermostat) we will reduce demand for our engine rebuilding services - we feel it was a higher priority to try and advise owners how to minimise their risk by this simple and effective change that - by running the engine a little cooler - gives some breathing space to the system to run a bit outside the designed settings, perhaps be driven agressively, yet still not reach the critical temperatures before the system has caught up. Baz

 

[jetbox]

Baz, Interesting stuff. not wanting to change the thread subject but I see you are saying a thicker oil is beneficial in higher mileage M96 engines to improve the oil film strength. What specifically do you recommend? Changing to a 10w-50 oil? thanks Jetbox

 

[Alex Postan]

My neighbouring farmer has a dizzying array of diesel powered farm kit and his observation is that if you are too easy on a new engine it always goes on to give trouble so he "rags 'em from day 1 and they never give a problem" So I didn't treat the replacement engine with kid gloves, I just used it as if it was run in. Dick Lovett Porsche were outstanding in how they dealt with me and with the problem. Top Marks.

 

[bazhart]

How many miles have you done on the new engine Alex? This problem seems to relate to deterioration of several parts as they age - so the question is relevant - and where owners have owned the same car for a long time there is some correlation of them having the second engine fail as well in time. I sincerely hope yours is perfectly OK fo ever and proves this wrong and there must be an element of luck relating to quality and build issues influencing some cars and engines more than others. Bye the way - when we receive a car for service that has been regularly serviced elsewhere we (and all the other caring specialists) get to know how good or indifferent other service centres are. Dick Lovett are on such business and their cars are always in good serviced conditions with the right things done as they should. I whish I could say the same about some others. Baz

 

[Alex Postan]

Sorry about the delay. I did another 10,000ish before I sold it. I kept the gurantee up and advised the new owner to do the same. I have a theory that with cars like the Cayman that are capable of 170 MPH and 8,000 rpm is that they never get used hard enough and fail through faint heart, so to speak.

 

[bazhart]

Juat by way of information - the next Cayman has come in with three seized pistons/scored bores on bank 2 again - so we are going to order our oversized pistons for this model as well now. Warranties adviseable. Baz