The new section 5 of our Internet based buyers guide has now been uploaded (see www.hartech.org buyers guide). You will need a lot of time and probably a headache pill or two if you want to read the whole lot in one go.
It has been written to inform anyone at any level of relevant knowledge (from a non technical owner to an experienced qualified engineer) - that is interested in the problem of cylinder scoring in 996 and 997 3.6, 3.8 and Cayman S engines - what the many contributory factors are and why.
Briefly it covers why it is easy to design an engine so bullet proof that it never ever goes wrong but it would then be very expensive and heavy as a result. With pressures on profitability, low emissions and higher performance - manufacturers have been under pressure to trim designs, weights, costs, emissions and fuel economy while increasing performance - which inevitably moves their products closer to reliability or longevity limits.
This section gradually explains how some systems that worked OK in air cooled 911's and the 944/968 range had small subtle differences when applied across into the M96 engines that individually seemed insignificant but actually pushed each reliability issue slightly closer towards the limit - but insufficient to cause a problem (in other words pretty well perfectly designed for the needs of the modern World). Many of the changes and weaknesses seem also to concentrate the problem on bank 2 (where most of the failures are).
When the later bigger capacity and more powerful versions were built - instead of changing some of those marginal issues to compensate for the additional heat and loads - it seems that they were either left exactly the same or in one case while moving in the right direction for reducing costs - went entirely in the wrong direction for reliability - resulting in engines running so much closer to that boundary - that some - after ageing and with some wear and tear taking place and after experiencing different driving conditions and styles - simply slip over the boundary and become damaged (usually on bank 2).
The scenario is typical of many other historical engines from different manufacturers that following a capacity or performance increase - search out and find the weak spots in a previously reliable design.
Usually a small but significant modification eventually appears on the market to fix the problem - but more often from smaller specialist organisations (that is presently taking place with these engines).
Because this initial engine range was actually so very well designed to run really close to - but still inside those "safety margins" - the increased performance applied to later models without other supporting alterations - has revealed a complex list of contributory weak spots - each even closer to the limits - such that a particular mix of sometimes different circumstances can push the engine over them.
It is therefore a complex problem requiring lengthy investigation and testing, proving good well founded solutions while exposing some other inadequate ones recently coming to the market.
This 25,000 word section explains each issue with both simple explanations and analogies backed up with technical and scientific facts so anyone should be able to grasp the salient points and realise that there are several issues to consider and several modifications that are beneficial during a rebuild and not one simple fix. It also includes further new developments that may help owners avoid the problem.
Before readers start with responding with typical criticism "" please remember that I don't need to write this stuff for my benefit (I already understand it) and furthermore if I spent the same amount of time and effort it took to write this section on promoting our business in other advertising or marketing ways "" it would certainly result in greater financial rewards. It has been written to inform others about the problem "" what we know about it and what we do about it "" to prevent misleading alternatives from confusing owners "" empowering them to make informed decisions if they need help or advice.
Although many with more experience would not need to read the whole of it to understand what it contains, I do not intend to respond to any criticism unless every word has already been read.
Best regards and happy reading,
Barry Hart
It has been written to inform anyone at any level of relevant knowledge (from a non technical owner to an experienced qualified engineer) - that is interested in the problem of cylinder scoring in 996 and 997 3.6, 3.8 and Cayman S engines - what the many contributory factors are and why.
Briefly it covers why it is easy to design an engine so bullet proof that it never ever goes wrong but it would then be very expensive and heavy as a result. With pressures on profitability, low emissions and higher performance - manufacturers have been under pressure to trim designs, weights, costs, emissions and fuel economy while increasing performance - which inevitably moves their products closer to reliability or longevity limits.
This section gradually explains how some systems that worked OK in air cooled 911's and the 944/968 range had small subtle differences when applied across into the M96 engines that individually seemed insignificant but actually pushed each reliability issue slightly closer towards the limit - but insufficient to cause a problem (in other words pretty well perfectly designed for the needs of the modern World). Many of the changes and weaknesses seem also to concentrate the problem on bank 2 (where most of the failures are).
When the later bigger capacity and more powerful versions were built - instead of changing some of those marginal issues to compensate for the additional heat and loads - it seems that they were either left exactly the same or in one case while moving in the right direction for reducing costs - went entirely in the wrong direction for reliability - resulting in engines running so much closer to that boundary - that some - after ageing and with some wear and tear taking place and after experiencing different driving conditions and styles - simply slip over the boundary and become damaged (usually on bank 2).
The scenario is typical of many other historical engines from different manufacturers that following a capacity or performance increase - search out and find the weak spots in a previously reliable design.
Usually a small but significant modification eventually appears on the market to fix the problem - but more often from smaller specialist organisations (that is presently taking place with these engines).
Because this initial engine range was actually so very well designed to run really close to - but still inside those "safety margins" - the increased performance applied to later models without other supporting alterations - has revealed a complex list of contributory weak spots - each even closer to the limits - such that a particular mix of sometimes different circumstances can push the engine over them.
It is therefore a complex problem requiring lengthy investigation and testing, proving good well founded solutions while exposing some other inadequate ones recently coming to the market.
This 25,000 word section explains each issue with both simple explanations and analogies backed up with technical and scientific facts so anyone should be able to grasp the salient points and realise that there are several issues to consider and several modifications that are beneficial during a rebuild and not one simple fix. It also includes further new developments that may help owners avoid the problem.
Before readers start with responding with typical criticism "" please remember that I don't need to write this stuff for my benefit (I already understand it) and furthermore if I spent the same amount of time and effort it took to write this section on promoting our business in other advertising or marketing ways "" it would certainly result in greater financial rewards. It has been written to inform others about the problem "" what we know about it and what we do about it "" to prevent misleading alternatives from confusing owners "" empowering them to make informed decisions if they need help or advice.
Although many with more experience would not need to read the whole of it to understand what it contains, I do not intend to respond to any criticism unless every word has already been read.
Best regards and happy reading,
Barry Hart
