Joining the 996 engine rebuild club
Discussion
mollytherocker said:
bennyboysvuk said:
Would you mind telling us what mileage yours gave up the ghost and how bad the symptoms were?
I Understand there is no trend, they can let go whenever, so the answer wont really be of any help!
I thougthI'd up as the car has been at Hartech a couple of weeks and the engine has now been removed, stripped down and inspected.
In terms of oil usage there were no single big issues. The air-oil seperator wasn't great, there were a few leaks, valve guides worn and valve guide seals very hard. However no more scoring etc than would be expected for c.91k miles.
The more important findings, which are pleasing in terms of justifying the whole spend but otherwise quite alarming are that the IMS bearing was about to let go (by the sounds of it at any moment) and the crank bearings were just down to the copper. A very expensive job could have become very VERY expensive if the whole lot had grenaded and I'd needed a second hand engine on top.
So i'm sticking to the plan i had, which is Hartech's full works rebuild jsut for peace of mind. So 6x new bores & re-coated pistons, new 997 IMS shaft and bearing, timing chain set, etc etc etc. I'll also replace the AOS, clutch, water pump, valve guides & seals, a cam sensor, oil cooler, rubber proposhaft joints, both PSE valves, exhaust clamps and the brake pipes under the back end. The price is, of course, fairly eye watering and more so as a percentage of the car's value but I love it and want to keep it. Hopefully back with me pre-Christmas for running in.
In terms of oil usage there were no single big issues. The air-oil seperator wasn't great, there were a few leaks, valve guides worn and valve guide seals very hard. However no more scoring etc than would be expected for c.91k miles.
The more important findings, which are pleasing in terms of justifying the whole spend but otherwise quite alarming are that the IMS bearing was about to let go (by the sounds of it at any moment) and the crank bearings were just down to the copper. A very expensive job could have become very VERY expensive if the whole lot had grenaded and I'd needed a second hand engine on top.
So i'm sticking to the plan i had, which is Hartech's full works rebuild jsut for peace of mind. So 6x new bores & re-coated pistons, new 997 IMS shaft and bearing, timing chain set, etc etc etc. I'll also replace the AOS, clutch, water pump, valve guides & seals, a cam sensor, oil cooler, rubber proposhaft joints, both PSE valves, exhaust clamps and the brake pipes under the back end. The price is, of course, fairly eye watering and more so as a percentage of the car's value but I love it and want to keep it. Hopefully back with me pre-Christmas for running in.
My car is, subject to an MoT, all ready for collection. Unfortunately i can't make it up to Bolton until 9th January 
Grant @ Hartech thinks the car drives really well too. I wonder whether suspension work has taken place at some point. There's no receipt from a Porsche OPC (or other garage) for it amongst my folder of 'stuff' though. The engine will require a little running in, but pretty much involves me not driving it really hard but making sure i do use some revs. A further oil change in a couple of thousand miles onto the good stuff from Millers will then be required and I'm away. Just need to pay for it now.
Grant @ Hartech thinks the car drives really well too. I wonder whether suspension work has taken place at some point. There's no receipt from a Porsche OPC (or other garage) for it amongst my folder of 'stuff' though. The engine will require a little running in, but pretty much involves me not driving it really hard but making sure i do use some revs. A further oil change in a couple of thousand miles onto the good stuff from Millers will then be required and I'm away. Just need to pay for it now.hartech said:
Just a couple of additional points chaps.
(1) We have fitted over a thousand liners/year now without a problem. But before comparisons are made with other suppliers - I am in a difficult position because I have a good idea what the comparative numbers are between us and other suppliers (and of failures elsewhere) and without wishing to stir things up - can I just say there is simply no comparison between the success rate of our cylinders and others. Our cylinders are after all almost the same as the GT3 and Turbo versions (with other similarities with Gen 2 engine improvements) and are the solution Porsche themselves used to generate the superb reliability record their previous 6 cylinder models enjoyed for decades.
(2) We have identified why steel or iron liners that we have seen are a problem and why we get so many in to replace shortly after they have been fitted (and this will be revealed in a video in the not too distant future to prove the point). For those prepared to believe us meanwhile and to explain - the free standing cylinder tube that is left to fit the ferrous liner into is simply too thin and not stiff enough to prevent the piston from pushing the liner and in turn the liner pushing against the thin alloy tube in the thrust direction resulting in it gradually stretching the alloy tube it is fitted inside until it become lose (in much the same way and for much the same reason as the original Lokasil cylinders migrate oval). Because the alloy is thin and not strong - increasing the interference fit if the liner merely stretches the alloy more and ends up with the same problem.
None we have seen are fitted to a machined diameter into the top of the block to prevent any movement (although some look like they have been but actually don't quite touch the non machined cast surfaces). In fact I know of no other supplier that does locate the top in a precision machined recess (as we do) in either ferrous or alloy cylinders Worldwide.
The longitudinal differential expansion between the ferrous liner and the alloy crankcase casting means that as the engine heats up the squeeze from the tri-metallic steel head gasket loses its grip on the liner - promoting this movement and often even allowing it to spin or twist round in the cylinder bore as a consequence of the thrust load being in one direction against the honing ramp angles.
If the engines had a better head seal and a stronger alloy exterior to hold the ferrous liner in place - had a closed deck to start with or were machined in such a way that they could maintain the same head seal height (despite the differential expansion rates) then you would only be left with the problem of larger cold clearances, more dead weight, poorer heat transfer and cooling and higher wear rates.
Different engines (usually with stronger alloy cylinder tubes, closed deck tops and/or smaller pistons (but more of them) can be relatively successful with ferrous liners but this particular engine design simply does not lend itself to this alternative.
This is why an alloy Nikasil liner is the best solution (as long as it combines with a machined closed deck restraint). It combines light weight, equal expansion, tighter clearances and the longest lasting bore material yet proven for decades but more importantly it is the only way to properly replace the Lokasil failed liners with excellent proven reliability.
Baz
This really is a no brainer if you fully understood this post,and therefore definitely has my vote on Nikasil.. (1) We have fitted over a thousand liners/year now without a problem. But before comparisons are made with other suppliers - I am in a difficult position because I have a good idea what the comparative numbers are between us and other suppliers (and of failures elsewhere) and without wishing to stir things up - can I just say there is simply no comparison between the success rate of our cylinders and others. Our cylinders are after all almost the same as the GT3 and Turbo versions (with other similarities with Gen 2 engine improvements) and are the solution Porsche themselves used to generate the superb reliability record their previous 6 cylinder models enjoyed for decades.
(2) We have identified why steel or iron liners that we have seen are a problem and why we get so many in to replace shortly after they have been fitted (and this will be revealed in a video in the not too distant future to prove the point). For those prepared to believe us meanwhile and to explain - the free standing cylinder tube that is left to fit the ferrous liner into is simply too thin and not stiff enough to prevent the piston from pushing the liner and in turn the liner pushing against the thin alloy tube in the thrust direction resulting in it gradually stretching the alloy tube it is fitted inside until it become lose (in much the same way and for much the same reason as the original Lokasil cylinders migrate oval). Because the alloy is thin and not strong - increasing the interference fit if the liner merely stretches the alloy more and ends up with the same problem.
None we have seen are fitted to a machined diameter into the top of the block to prevent any movement (although some look like they have been but actually don't quite touch the non machined cast surfaces). In fact I know of no other supplier that does locate the top in a precision machined recess (as we do) in either ferrous or alloy cylinders Worldwide.
The longitudinal differential expansion between the ferrous liner and the alloy crankcase casting means that as the engine heats up the squeeze from the tri-metallic steel head gasket loses its grip on the liner - promoting this movement and often even allowing it to spin or twist round in the cylinder bore as a consequence of the thrust load being in one direction against the honing ramp angles.
If the engines had a better head seal and a stronger alloy exterior to hold the ferrous liner in place - had a closed deck to start with or were machined in such a way that they could maintain the same head seal height (despite the differential expansion rates) then you would only be left with the problem of larger cold clearances, more dead weight, poorer heat transfer and cooling and higher wear rates.
Different engines (usually with stronger alloy cylinder tubes, closed deck tops and/or smaller pistons (but more of them) can be relatively successful with ferrous liners but this particular engine design simply does not lend itself to this alternative.
This is why an alloy Nikasil liner is the best solution (as long as it combines with a machined closed deck restraint). It combines light weight, equal expansion, tighter clearances and the longest lasting bore material yet proven for decades but more importantly it is the only way to properly replace the Lokasil failed liners with excellent proven reliability.
Baz
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