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JohnBolton

13 posts

34 months

[news] 
Tuesday 7th February 2012 quote quote all
Good post, lets get some data.

Only just got mine so hopefully it is not too bad a result.

cmoose

26,634 posts

117 months

[news] 
Tuesday 7th February 2012 quote quote all
Gary11 said:
IIRC its the 3.4 that doesnt D chunk as much the bores are thinner on 3.6/3.8 units.
Which makes the odd low mileage 2.9 Boxster engine with scored bores a strange one,have seen 2 and know of one on here.
You've got to be kidding? The bores on the 3.8 are even thinner than the 3.4? If that's true, it can't be long before the failure rate gets really gruesome. If the walls of the 300hp 3.4 are thin enough for Baz to observe that they all appear to go oval with time, what's it going to be like with the 355hp 3.8?

doneitnow

594 posts

36 months

[news] 
Tuesday 7th February 2012 quote quote all
I am a little confused here, I can understand all the issues with the 3.4,3.6 and 3.8 but where do the problems with the Cayman S engines come from being derived from the 3.2(M96.26)that was used in the Boxster S but with the cylinder head from the 997 S 3.8(M97.01)?


cmoose

26,634 posts

117 months

[news] 
Tuesday 7th February 2012 quote quote all
Gen 1 Cayman S issues are chiefly, I believe, IMS and bore scoring. Neither are related to bore thickness.

doneitnow

594 posts

36 months

[news] 
Tuesday 7th February 2012 quote quote all
It is hard to take it all in as there seems to be a lot of issues with quite a few different engines.
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hartech

1,617 posts

105 months

[news] 
Wednesday 8th February 2012 quote quote all
It is very confusing and yet the general thrust of what has changed is relativley straight forward - perhaps the following will help.

Basically all models run hotter than many older model designs to assist with the reduced emission standards. The 2.5, 2.7 and 3.2 Boxster S had relativley thick cylinder walls but the 996 3.4 was made by boring out the 3.2 Boxster S block bigger in bore diameter (without increasing the outside diameter) - so that model had thinner cylinder walls.

The 3.4 Cayman S, 3.6 996 and 3.6 and 3.8 997's retained about the same cylinder wall thickness as the 996 3.4 (thinner than the first engines again but similar to each other).

The 3.4 Cayman S, 3.6 and 3.8 engines also had a different head gasket that allowed more coolant to flow into the cylinder heads (and therefore less into the cylinder blocks) - so they run slightly hotter cylinder wall temperatures.

The IMS bearing was made bigger for later models (and is much more reliable) but there is a confusing mixture of new bigger engines fitted with old smaller IMS bearings - so there is a mixture that is a little unpredictable.

The general flow of changes is that as the engines got bigger and more powerful - while they gradually fitted the larger IMS bearing (a benefit) the cylinder wall temperatures at maximum output would be higher and some scoring started.

If we forget the IMS issue for now - it is clear that as the engines had bigger pistons or stroke (more capacity) and worked harder (if they were driven to their limit) the cylinder wall temperatures were at the same time moving in the direction of going slightly higher.

When a piston scores it is usually because the friction has increased and with it the temperature of the piston surface - suddenly reaching the limit - and within a few seconds melting at the surface and setting again - the lumps created scoring the bore.

The oil between the piston and the cylinder wall is thinner if the temperature is higher and so as the friction increases - the ability of the oil to protect the running surfaces diminishes and as it does so the oil gets even hotter and therefore even thinner until damage occurs.

The side of the piston that gets hottest is the side running with the most friction and this is the "thrust side" where the piston pushed against the cylinder wall to drive the car along.

On bank 1 this is the bottom of the engine and on bank 2 it is the top.

The coolant enters at the bottom on both sides and the oil spray jets (that lubricate the cylinders and pistons) are directed at the lower part of the pistons - so in both cases - bank 2 has both less oil on the thrust face and runs at a higher temperature - and this is why that side has all the problems.

It is obviously very marginal because only a small % fail and anyway driving modestly will run the enginess further away from the critical temperatures.

Because the cylinder wall thicknesses of all the later engines are similar to the 996 3.4 (that cracks and "D" chunks) I would expect them to eventually do the same (and we have repaired some accordingly) but scoring seems to occur before that mileage has been reached (in those that have scored).

Piston loads and lubrication are worst at low revs and high loads (or throttle openings) and also at full throttle maximum revs runs. Because the engine sits with horizontal pistons - oil does not drain away from the cylinder bores when the car is idle. Because the pistons have to be designed to cope with expanding to their maximum at full throttle (and huge horsepower) they must be made with more taper than if they were less powerful and because of these 2 facts - sometimes - on start-up - the combination of that additional taper and sitting horizontally allows the oil that has collected on the cylinder bore to allow a brief puff of oil to burn (but has very little effect on the overall oil consumption).

Cylinders on all models are "open deck" and creep oval with time and this increases the piston clearance allowing increasing blow by to heat up the piston more than when the engine was newer and therefore gradually move the engine more towards running at a cylinder wall temperature that approaches critical limits.

Because the radiators are at the other end of the car to the engine and because the thermostat is fitted at entry to the engine (rather than exit from it) - sudden changes from modest driving to flat out can result in a relatively slow cooling response and temporarlily raise cylinder block temperatures higher than they may settle down to (even resulting in some localised boiling or bubbling).

Therefore (apart from the cloudy IMS issue of which bearing was fitted on 2002 to say 2005 models) you have engines that gradually increase bore ovality, runn slightly hotter cylinder wall temperatures than earlier engines, have the potential to run with higher piston to cylinder wall loads (either at low revs as a result of increased torque or high revs as a result of increased bhp) - so if the owner utilises all that potential torque and power - will run with higher cylinder wall loads and temperatures and may eventually score, crack or "D" chunk a cylinder - in a relatively small number of engines (increasing numbers with age).

Several businesses can now rebuild the engines (fixing the fault often with cheap short lived solutions) or new engines are available (with the same spec as had the failure).

Only one business adresses ALL the problems listed and optionally offers to re-round the oval cylinders (while stabilising them so they will not "D" chunk or crack", to replace a scored, cracked or "D" chunk liner (with a special alloy as strong as steel) - coated in Nikasil - the preferred finish for turbos and GT3's etc), to reduce the cylinder wall temperatures *by increasing cylinder block coolant flow), reduce running temperatures (by offering a lower temperature thermostat) and replaces the smaller IMS bearing with a better lubricated one with stronger spindle. That same business also carries out all that work "IN HOUSE" - in their own precision machine shop - but their contribution to this problem does not stop there.

Presently they are testing oversized pistons in Lokasil bores (to reduce rebuild costs). This has involved high investment in machinery and test cars - but ultimately will be able to provide the most cost effective solution, and manufacturing their own replacment IMS shaft (to suit earlier roller chain systems or later Hivo cahin systems) fitted with the larger improved IMS bearing. They have also successfully tested long term replacement parts for crankshafts and bearings (etc) in case critical parts ever dry up (or become too expensive) - to they can continue to rebuild customer engines to their own exact requirements and incorporate improvements in every area suspected of contributing to the problems some suffer from.

That business is Hartech and I am proud of the extent of the work we do and the options available (to fit in with customers future intentions for their car and their budgets) and the fact that we also provide a scheme to limit the cost of an engine rebuild (if it even happened) while gradually paying monthly for the future servicing and labour for repairs.

There is no single cause (hence the large number that are still perfectly OK) and instead a small number of issues conspire together to contribute to a failure in a variable range of circumstances that is difficult to make exact predictions about of a set of rules to try and avoid.

We continue to try and increase the range of solutions and reduce the potential for problems in every engine we rebuild - still at prices between a third and a half of that generally charged for replacement with a new engine with all the same features as the one that failed.

Further information available on our web site www.hartech.org buyers guide section 4 and 5.

Baz







doneitnow

594 posts

36 months

[news] 
Wednesday 8th February 2012 quote quote all
Hi Baz

Thanks for taking the time to explain it does make a lot more sense when reading it like that, I think the main bit I had missed was that the 3.2 engine has been bored out effectively making it weaker in the 3,4 cayman s.

How hard is it to self install the low temp thermostat?

And when are you going to open a branch for us southerners so we can all get on your scheme?

Alan

uktrailmonster

4,678 posts

88 months

[news] 
Wednesday 8th February 2012 quote quote all
Great post Baz. All makes perfect sense and a very pragmatic approach to identifying and solving the various problems. I'm very pleased my 996 has one of your rebuilt engines, otherwise I'd be cacking myself on every drive wink

hartech

1,617 posts

105 months

[news] 
Wednesday 8th February 2012 quote quote all
Anyone capable of some home mechanics work should be able to install it - but bleeding the coolant system is not easy and you need to read up on it - if you can - before attempting it and then expect some air entrapped to gradually bleed out afterwards after driving cautiously while the levels settle down.

Baz

doneitnow

594 posts

36 months

[news] 
Wednesday 8th February 2012 quote quote all
hartech said:
Anyone capable of some home mechanics work should be able to install it - but bleeding the coolant system is not easy and you need to read up on it - if you can - before attempting it and then expect some air entrapped to gradually bleed out afterwards after driving cautiously while the levels settle down.

Baz
Thanks Baz

But you ignored the important question, "when are you going to open a branch for us southerners so we can all get on your scheme?"

It's 250miles of boring motorways for some of us.biggrin

Alan


Edited by doneitnow on Wednesday 8th February 12:59

hartech

1,617 posts

105 months

[news] 
Wednesday 8th February 2012 quote quote all
Unless you could fit a camera to continuously record the state of the cylinder walls and the engine running parameters - I don't think it would be possible to ever be certain exactly at what point and under what circumstances the engines score the bores (well I cannot think of any other way perhaps someone else can!).

That being the case it is only possible to use such comparisons combined with general engineering experience and motor vehicle experience (plus engine design and manufacture) to work out likely causes and solutions.

It is definitely a problem of cylinder wall lubrication, temperatures and oil viscosity but scoring is a known phenomenon of other engines at high torque and low revs (which these newer engines have more of) and also a phenomenon of other engines with high revs and full throttle running.

Add to that the higher coolant temperatures and relatively slow coolant temperature response times to sudden increased loads and the gradual increase in cylinder to piston clearances and the different usage owners put their cars to (from driving around towns and cities modestly to full blown race track days) - coming up with one explanation proves impossible - when engines come in damaged from all different types of care, driving styles and mileages.

Some say it is pistons (but then bank 1 is OK with the same pistons), some say replacement steel liners are OK (but we have already had to repair 2 different versions and they are generally understood to be unsuitable for such applications - see section 5), some say it is the Lokasil (but then it is OK in earlier models and bank 1), at least our explanations (while picking on a number of different general design weaknesses) all add together to make sense of the rarity of the failures and the different circumstances that cause them (and that is why we incorporate all the improvements we can think of to try and cover every eventuality - and still keep costs reasonable).

Our latest "belt and braces" option is to fit additional spray jets to spray cool oil directly at the part of the cylinders that the scoring occurs at. The logic behind this is similar to our general approach to these repairs. At the moment it is spray oil that lubricates the bores (not splash oil from the crankshaft as in more traditional engines). But the oil is sprayed into the lower area - which doesn't help bank 2 pistons much (especially as the oil will fall downwards away from the thrust face under gravity).

Oil spray quickly picks up heat and the quantity is less than by directly spraying neat, cooler de-aerated oil onto that critical area - and as the volume of oil is then higher - it not only provides better oil film characteristics to the cylinder wall but also takes more heat away from it and from the piston. Furthermore it sprays that fresh oil on every single stroke. Tests so far show a slight increase in hot tickover oil pressure (demonstrating the reduction in overall oil temperatures - which is a very good thing to achieve). Initial tests suggested a slight increase in that puff of oil on start-up (probably due to the additional oil on top of the piston and cylinder wall when the car is turned off) but now the test cars are getting more run in - that seems to be going away (or even if it didn't it would be my preferred option to live with it than score a bore again).

Unfortunately we are not yet prepared to offer it generally until more tests are completed satisfactorily - but we have high hopes that added to all our other options - it may just provide the ultimate belt and braces solution.

It is however a very difficult engine type to sort out (when in essence Porsche gave up and re-designed out those weak areas in the generation 2 versions) and our resources are miniscule compared to theirs - so it is no easy task and especially when rebuilding engines with a number of general weaknesses that only afflict a very small number of examples while others seem perfectly OK.

Our view is that by improving all the weaknesses that we can identify that individually have a logical and a correct engineering technical benefit (or compensate for a definite potential technical problem) and in view of the very small number that fail anyway - there is the strongest likelihood that all these small changes combined will enable reliability to improve to an acceptable level.

Rebuilding old engines requires a very high degree of skill and equipment because - like all engines manufactured by modern cost effective methods - there is (and has always been) a minute number of random component failures that are insufficient in number to do anything serious about but that may still - on very rare occasions - afflict any engine rebuilt or not (though not connected with the original or general failure or the rebuild). This is made more difficult when a non-runner is delivered - so any other problems the car may have been running around with (not connected to the obvious failure) may still be there after the rebuild and complicate the outcome (especially if we only received and rebuilt the engine).

Finally you may be aware that we are involved with our racing team and Millers oils - in testing and developing improved oils to assist in this process of making these engines bullet proof and future proof - including Nano oil derivatives – that – like our lower temperature thermostat – could help engines that are presently running perfectly OK to avoid such problems altogether.

Baz

KeithRobinson

100 posts

34 months

[news] 
Tuesday 6th March 2012 quote quote all
I've just purchased a 1999 996 with 85k miles. The owner heard a noise, turned it off, took it to a specialist who told him the engine was destroyed, had water in the cylinders and needed replaced. He thought this was crazy and got a second opinion from Hartec. On Hartec's further inspection it was only the water pump, however whilst at with them he had the engine rebuilt, bores reshaped, new pumps and new IMS bearing etc (Total invoice cost is £6700 which includes collection, fuel, airflow meter etc).

It just goes to show how many cowboy outfits exist, so called specialists can be total rip off merchants. Hartec were honest with the previous owner and from what I can tell did a fantastic job.

It's my first 911 and after a years research I felt this was the best car for me as the engine gives me peace of mind. Only had it two days, however I'm hoping it will give me many years of enjoyment.

I'll pop some photos up on another thread.

Keith

Gary11

3,885 posts

89 months

[news] 
Wednesday 7th March 2012 quote quote all
cmoose said:
You've got to be kidding? The bores on the 3.8 are even thinner than the 3.4? If that's true, it can't be long before the failure rate gets really gruesome. If the walls of the 300hp 3.4 are thin enough for Baz to observe that they all appear to go oval with time, what's it going to be like with the 355hp 3.8?
CM
I think its heat dissipation rather than weakness beacause its thinner that makes them oval,I think for obvious reasons the internal tempreatures and stresses are higher with the larger capacity engines and move nearer danger levels,sympathetic driving style really does help here.
Guided by Bazs post I stand corrected with the D chunk rate on 3.4 engines I was basing that on cars I have inspected with replaced units rather than the mechanical reasons for failure.I see more 3.6/3.8 engines of late with problems.

hartech

1,617 posts

105 months

[news] 
Wednesday 7th March 2012 quote quote all
Basically the "D" chunk is caused by metal fatigue because the cylinders flex and alloy always has a failure eventually. The thinner the walls the shorter the life.

That flexing is influenced by throttle opening and conbustion pressures, and/or revs, and or temperatures before after and during fast work, also throttle opening (or torque) at low revs, the orignal quality of the Lokasil, the centralisation of the liner during casting (which is not perfect) and finally the number of relevant stress cycles (as with all metal fatigue failures).

The irony is that people now assume the later engines don't "D" chunk because they are actually scoring bores before they have reached that point - but we have had some higher mileage ones through with cracks and "D" chunks - so it will occur eventually.

But then I also had a 3.4 that lasted for 153K before it cracked a liner - so it is still a relatively rare occurence.

At least our securing rings fix that problem by converting the block to a "closed deck" (and we are the only suppliers offering that) while others use stiffer alloy (which may still fatigue one day in the future) or steel/iron tubes (which have differential expansion potential problems) and leave them "open deck" as it is cheaper to make a thin tube in either material than fix it our way.

If we need to fit a liner we machine a homogeneous top hat flange on it that fits into the block as well so both our liners and/or original bores are converted to the closed deck design - at extra cost but better long term security.

Baz



KeithRobinson

100 posts

34 months

[news] 
Wednesday 7th March 2012 quote quote all
Gary11 said:
Hi this is not meant to be peadantic but why?

"It's my first 911 and after a years research I felt this was the best car for me as the engine gives me peace of mind"
Because the engine was rebuilt by hartec, has all new belts, pumps, IMS bearing etc. so it gives me a good chance of trouble free motoring. If I bought one without a rebuilt, I may never have any trouble either, however I just felt more comfortable knowing he engine has been refreshed.

Keith

Gary11

3,885 posts

89 months

[news] 
Wednesday 7th March 2012 quote quote all
Looking at todays poll, adding the engine failure numbers to the 59 people not buying due to the potential failure these issues are affecting almost half of polled owners and potential owners thinking,it really highlights the reason for the fall in values trying to compensate for undesireability.
G

Edited by Gary11 on Wednesday 7th March 20:04

Gary11

3,885 posts

89 months

[news] 
Wednesday 7th March 2012 quote quote all
KeithRobinson said:
Because the engine was rebuilt by hartec, has all new belts, pumps, IMS bearing etc. so it gives me a good chance of trouble free motoring. If I bought one without a rebuilt, I may never have any trouble either, however I just felt more comfortable knowing he engine has been refreshed.

Keith
Sorry Keith only read bottom of your post on BB, sorry I didnt see the Hartech part hence my confusion,Im sure your engine will be fine now its been modified.

Globs

13,131 posts

119 months

[news] 
Wednesday 7th March 2012 quote quote all
Gary11 said:
Looking at todays poll, adding the engine failure numbers to the 59 people not buying due to the potential failure these issues are affecting almost half of owners and potential owners thinking,it really highlights the reason for the fall in values trying to compensate for undesireability.
G
I'm not sure it is affecting prices much TBH, looking at these cars compared to performance BMWs, Mercedes etc their values seem to be holding up pretty well.

Try buying a Porsche that cost the same as a BMW 740 from 2001 and you'll find it's a multiple of the BMW's value now.
Look at the 987, still over £15k for a 7 year old non-S model, show me another performance car that holds value like that.

cmoose

26,634 posts

117 months

[news] 
Wednesday 7th March 2012 quote quote all
Globs said:
Gary11 said:
Looking at todays poll, adding the engine failure numbers to the 59 people not buying due to the potential failure these issues are affecting almost half of owners and potential owners thinking,it really highlights the reason for the fall in values trying to compensate for undesireability.
G
I'm not sure it is affecting prices much TBH, looking at these cars compared to performance BMWs, Mercedes etc their values seem to be holding up pretty well.

Try buying a Porsche that cost the same as a BMW 740 from 2001 and you'll find it's a multiple of the BMW's value now.
Look at the 987, still over £15k for a 7 year old non-S model, show me another performance car that holds value like that.
I agree - I don't think reliability concerns have had much impact on values of 996s or 997s. It's all about big production numbers and the fact that none are yet old enough to really be considered classics.

Gary11

3,885 posts

89 months

[news] 
Wednesday 7th March 2012 quote quote all
Globs said:
I'm not sure it is affecting prices much TBH, looking at these cars compared to performance BMWs, Mercedes etc their values seem to be holding up pretty well.

Try buying a Porsche that cost the same as a BMW 740 from 2001 and you'll find it's a multiple of the BMW's value now.
Look at the 987, still over £15k for a 7 year old non-S model, show me another performance car that holds value like that.
I was comparing values across the Porsche range not comparing with other marques I feel they should be higher than 9-10k for an early 996 and 5k for a Boxster this is at a price range where people are buying them as you say just like any other car and sadly this reflects in the way they are looked after and without sounding Porscheist people buying them beacause they can afford the purchase sadly not the maintainence.
I feel a juice guzzling 740 saloon isnt a compareable,perhaps a 350z or an Audi TT neither of which are miles away from the values mentioned above,and are sold without the influence of the topic poll and are "just cars" in comparison to the Porsche marque.
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