DUE TO HIJACKING I'LL ASK BARRY HART AGAIN!
Discussion
Thanks-some of it does but I still would like for Barry to clarify his findings on the design intergrity of the 3.6 vs 3.4.
I am glad Ballcock's and Versuvius' 996 are running well and I sincerely hope that they continue to do so. I will remind that I too had a 996 3.4 and enjoyed it but I if I am about to spend a reasonable amount on another I would rather buy one which is inherently better designed-saying all this I am trying to figure out if its worth spending the premium on a 3.6 i.e if I spend 7k more on one is there less chance of it suffering from a failure (AND YES I UNDERSTAND THAT THE CHANCE IS FAIRLY LOW EVEN ON A 3.4)
I am glad Ballcock's and Versuvius' 996 are running well and I sincerely hope that they continue to do so. I will remind that I too had a 996 3.4 and enjoyed it but I if I am about to spend a reasonable amount on another I would rather buy one which is inherently better designed-saying all this I am trying to figure out if its worth spending the premium on a 3.6 i.e if I spend 7k more on one is there less chance of it suffering from a failure (AND YES I UNDERSTAND THAT THE CHANCE IS FAIRLY LOW EVEN ON A 3.4)
Ok-had a brief read-
The 3.4 seems to suffer from a cracked liner in the middle of the engine block at between 14k to 67k miles-they (AUTOFARM) cannot work out why but feel its something to do with the structural integrity of the block. They have not seen a 3.6 suffering the same issue BUT....
The 2.5 and the 3.6 appear to be suffering from itermediate driveshaft failure-something that the 3.4 does not! doh!
The 3.4 seems to suffer from a cracked liner in the middle of the engine block at between 14k to 67k miles-they (AUTOFARM) cannot work out why but feel its something to do with the structural integrity of the block. They have not seen a 3.6 suffering the same issue BUT....
The 2.5 and the 3.6 appear to be suffering from itermediate driveshaft failure-something that the 3.4 does not! doh!
The realisation by independents - that there were a few problems with the 996 3.4 engine came early enough through rumours but understanding what the problems were - was perhaps delayed by the main agents replacing them early on and mainly sending them back to the factory for inspection.
This is good (originally particularly Japanese) practice so that the manufacturer gets to see the problems and keeps them away from public scrutiniy and also can assess common failures and try and design out a solution as quickly as possible in the next production run a.s.a.p.
It was only when older cars failed that were not covered by warranty that we started to need to strip them down and try and assess what the weak spots (if any) were.
Now the 3.6 has only just become old enough to be outside of the Porsche new warranty period - so I have not yet had to repair one. But I have also not heard about any similar problems and must assume that any initial difficulties with the original 3.4 new engines - have been addressed.
There have been a few attempts to improve the intermediate shaft - but in the middle they changed to a hivo chain (which I think increases loadings) so perhaps got sidetracked a bit.
The big ends may just have needed a higher quality shell material or better con rod inspection/rejection control - which I would assume is in place.
The problems with the Lokasil cylinder liners cracking - should have been resolved by now. I am still not sure if it is a casting or production design problem.
The early cylinders definitely go oval and I have machined a liner out and machined off the crankcase casting part to inspect the Lokasil liner and found it to be quite stiff but low in tensile strength (to resist hoop stress). It seems typical of a bonded matrix liner and so could crack through the heating/cooling cycle, through casting anomalies, through poor surface contact areas or because the original casting outer cylinder tube is not string ewnough (being unsupported).
I don't yet know the answer and all the ones I have machined out have had good apparent bonding but very uneven shape - despite being centralised in a very accurate crankcase casting the liner diameter is often up to 1mm out of centre. The jury is therefore still out on this one but I feel sure a change in composite design would improve it (like for example if the liner had an outer diameter of circumferential chopped strand carbon fibre added to improve tensile strength).
My guess is that the 3.6 is better - it certainly logically should be - and the evidence suggests it is - but sorry - only equivalent time and mileage will actually tell.
Baz Hartech
This is good (originally particularly Japanese) practice so that the manufacturer gets to see the problems and keeps them away from public scrutiniy and also can assess common failures and try and design out a solution as quickly as possible in the next production run a.s.a.p.
It was only when older cars failed that were not covered by warranty that we started to need to strip them down and try and assess what the weak spots (if any) were.
Now the 3.6 has only just become old enough to be outside of the Porsche new warranty period - so I have not yet had to repair one. But I have also not heard about any similar problems and must assume that any initial difficulties with the original 3.4 new engines - have been addressed.
There have been a few attempts to improve the intermediate shaft - but in the middle they changed to a hivo chain (which I think increases loadings) so perhaps got sidetracked a bit.
The big ends may just have needed a higher quality shell material or better con rod inspection/rejection control - which I would assume is in place.
The problems with the Lokasil cylinder liners cracking - should have been resolved by now. I am still not sure if it is a casting or production design problem.
The early cylinders definitely go oval and I have machined a liner out and machined off the crankcase casting part to inspect the Lokasil liner and found it to be quite stiff but low in tensile strength (to resist hoop stress). It seems typical of a bonded matrix liner and so could crack through the heating/cooling cycle, through casting anomalies, through poor surface contact areas or because the original casting outer cylinder tube is not string ewnough (being unsupported).
I don't yet know the answer and all the ones I have machined out have had good apparent bonding but very uneven shape - despite being centralised in a very accurate crankcase casting the liner diameter is often up to 1mm out of centre. The jury is therefore still out on this one but I feel sure a change in composite design would improve it (like for example if the liner had an outer diameter of circumferential chopped strand carbon fibre added to improve tensile strength).
My guess is that the 3.6 is better - it certainly logically should be - and the evidence suggests it is - but sorry - only equivalent time and mileage will actually tell.
Baz Hartech
paracetamol said:
Thanks for the response. I fully understand that engines wear-but would expect to achieve at least 120-140k miles on a modern engine with no significant issues
I agree. I'm in a position to spend up to 25K on an early 996, but have been put off by this issue. There are a lot of early 996's out there with replaced engines before 70K miles, so it seems there is a _significant_ problem with them. Unless you go back to the NSU RO80 or Triumph Stag, I don't remember another manufacturer with such an unreliable engine.
The problem with a 98 or 99 model 996 is that the OPC warantee won't last beyond the car's 9th birthday, and I can't afford to throw away 5K to 10K on a new engine or replacement.
So, what's the solution ? Buy a 993 or save up for a 3.6 engined model I guess ?
Diesel130 said:
paracetamol said:
Thanks for the response. I fully understand that engines wear-but would expect to achieve at least 120-140k miles on a modern engine with no significant issues
I agree. I'm in a position to spend up to 25K on an early 996, but have been put off by this issue. There are a lot of early 996's out there with replaced engines before 70K miles, so it seems there is a _significant_ problem with them. Unless you go back to the NSU RO80 or Triumph Stag, I don't remember another manufacturer with such an unreliable engine.
The problem with a 98 or 99 model 996 is that the OPC warantee won't last beyond the car's 9th birthday, and I can't afford to throw away 5K to 10K on a new engine or replacement.
So, what's the solution ? Buy a 993 or save up for a 3.6 engined model I guess ?
BMW and Jaguar have suffered similar issues with their nikesal based engines-decimated the values of late 98 7 series and Jags unless they had the replacement engines-the beauity of these was that the engines had the design fault ironed out-not simply replaced with the same flaw
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