Joining the 996 engine rebuild club
Discussion
m444ttb said:
It was only for 6 months and having tried to claim for something else a waste of paper anyway. Given this is piston rings I suspect they would have declined it as wear and tear.
Keep in mind you may have a broken piston ring rather than advanced wear...possibly a case then for help from warranty claim. Good luck...Edited by m444ttb on Wednesday 15th July 21:19
Unfortunately Steve @ Autofarm had left and not given anyone else the prices so will have to wait until I can speak to him on Monday. My guess is £5k-£15k with the top end including 3.9L conversion with cams and re-map (c.390bhp apparently).
Anyhow what I do have are the results from the investigation work they did. All six bores look fine. The leakage test showed the following:
Cyl 1 10%
Cyl 2 10%
Cyl 3 8%
Cyl 4 9%
Cyl 5 13%
Cyl 6 8%
And the compression test the following:
Cyl 1 260psi
Cyl 2 270psi
Cyl 3 260psi
Cyl 4 260psi
Cyl 5 270psi
Cyl 6 270psi
I'm unsure what normal values are for an M96 or indeed any other engine but in told they've seen much worse than 13% leakage plenty of times.
Anyhow what I do have are the results from the investigation work they did. All six bores look fine. The leakage test showed the following:
Cyl 1 10%
Cyl 2 10%
Cyl 3 8%
Cyl 4 9%
Cyl 5 13%
Cyl 6 8%
And the compression test the following:
Cyl 1 260psi
Cyl 2 270psi
Cyl 3 260psi
Cyl 4 260psi
Cyl 5 270psi
Cyl 6 270psi
I'm unsure what normal values are for an M96 or indeed any other engine but in told they've seen much worse than 13% leakage plenty of times.
Edited by m444ttb on Saturday 18th July 16:16
Result. Honestly if it something like worn guides/seals I don't know why anyone would be surprised by this. People go on about how bullet proof the old cars are but pretty much every 968 with any amount of miles on it would have been down on power from worn guides. How many air-cooled motors had top end rebuilds at similar miles? blooming loads is the answer.
Trev450 said:
If the bores are fine I presume you are going for the 3.9 conversion purely for the extra performance it will give.
I'm probably not going for it, but if I end up doing something with the bores then it will be a consideration. The trouble is I'm reticent about spending a big wedge of cash (which it is regardless of what I do) and leaving some big worry like bore scoring there. I'd do the IMS shaft and bearing, chains, water pump, etc regardless though.rubystone said:
NJH said:
Result. Honestly if it something like worn guides/seals I don't know why anyone would be surprised by this. People go on about how bullet proof the old cars are but pretty much every 968 with any amount of miles on it would have been down on power from worn guides. How many air-cooled motors had top end rebuilds at similar miles? blooming loads is the answer.
thats what I thought it was originally.Sounds like top-end. surely a £3-£4k bill?
m444ttb said:
Trev450 said:
If the bores are fine I presume you are going for the 3.9 conversion purely for the extra performance it will give.
I'm probably not going for it, but if I end up doing something with the bores then it will be a consideration. The trouble is I'm reticent about spending a big wedge of cash (which it is regardless of what I do) and leaving some big worry like bore scoring there. I'd do the IMS shaft and bearing, chains, water pump, etc regardless though.It's hard to know who or what to believe on the liner front. However what Hartech say makes sense to me. Same material therefore same thermal expansion rate. How much of a problem is it though is the question. I wouldn't want to choose a liner solution where there's a chance or it becoming a new issue. Are all steel liners (like Autofarm's) created equal?
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
(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
I too found Baz's explanation as to the unsuitability of ferous liners interesting.
I had considered going for a 3.7 conversion if my liners were to require replacing, but think I would go with the Hartech fix, which I believe is only available in OE bore sizes, if the situation was to arise.
I had considered going for a 3.7 conversion if my liners were to require replacing, but think I would go with the Hartech fix, which I believe is only available in OE bore sizes, if the situation was to arise.
We have been fitting Nikasil alloy liners for about 10 years. The first ones were heat treated cast alloy (as strong as mild steel) but as numbers increased we couldn't cope with the quantities so now sub contract the production using an aerospace high silicon alloy that is even stronger.
Right from day one they have been fitted with a machined location for a top hat ring, converted to a closed deck design and featured increased coolant flow proportions (long before anyone knew about Porsche doing effectively the same for the Gen 2 engines years later).
We didn't keep numbers initially and I don't have time now to trawl back but because we have a variety of alternative solutions to re-round existing Lokasil cylinders and convert to a closed deck (with additional coolant), or fitting our replacement cylinders (to anything from one to all 6 bores) and cover all models from Boxsters to 3.8 997's - exact numbers of engines are difficult to confirm.
We are currently doing 4 to 5 engines a week and I guess it must be well over a thousand engines and we know it is over 2000 liners by now.
We could easily fit ferrous liners if we thought they were suitable and if we had not received so many already fitted with them to re-manufacture again - but instead stuck with the best solution and invested in machinery, staff and organisation to keep the price competitive with inferior solutions.
We have fitted ferrous liners to other engines (for staff and friends) where the bores were smaller in diameter and the crankcase design more suitable but these crankcases are not ideal and create problems best avoided.
I am not familiar with the BMW engine but would be interested to know the type of construction and typical bore sizes.
I don't want to make an issue of numbers with competitors - we have always concentrated and what we do and not what others do and there are always alternatives and some good options available - but I do believe that some of our competitors are in single annual rebuild figures.
We could make oversized engines quite easily (already have some piston manufacturers in tow) but the overhanging rear crankshaft already causes flexing that can wear the rear main bearing prematurely under duress and in so doing starves the big ends of an oil supply sometimes resulting in a seized big end, a broken rod and a scrap engine. Furthermore usually a reliable but standard engine holds a better long term re-sale price and parts are always still available. We feel if you want a faster car the GT3 or Turbo are already designed for increased performance and do not have an overhanging crank flywheel end, but do have Nikasil alloy cylinders and higher cylinder coolant flow rate - so seem to us a better way to go together with improved suspension, braking and handling to suit the additional performance.
One final technical point I should make is that (like the GT3 and Turbo versions) our cylinders are not held in with a heavy interference fit. They don't need to be because the heat is generated from the inside and so the inside is always trying to maintain a fit with any exterior crankcase part as it expands and the top (where the coolant flows) is one solid alloy cylinder (also made with convoluted exterior to increase the surface area and compensate for the rather poor coolant flow. Even alloy liners in alloy or ferrous liners in alloy reduce the stiffness of the resulting mechanical bi-construction compared with a solid cylinder and any interference fit with different material results in differential expansion of both parts and changes in the fit. Without going into too much detail our cylinders are more like a free standing solid alloy cylinder (with a Nikasil bore finish) and as a result expansion and contraction is only influenced by engine temperature with no other interfering factors.
Baz
Right from day one they have been fitted with a machined location for a top hat ring, converted to a closed deck design and featured increased coolant flow proportions (long before anyone knew about Porsche doing effectively the same for the Gen 2 engines years later).
We didn't keep numbers initially and I don't have time now to trawl back but because we have a variety of alternative solutions to re-round existing Lokasil cylinders and convert to a closed deck (with additional coolant), or fitting our replacement cylinders (to anything from one to all 6 bores) and cover all models from Boxsters to 3.8 997's - exact numbers of engines are difficult to confirm.
We are currently doing 4 to 5 engines a week and I guess it must be well over a thousand engines and we know it is over 2000 liners by now.
We could easily fit ferrous liners if we thought they were suitable and if we had not received so many already fitted with them to re-manufacture again - but instead stuck with the best solution and invested in machinery, staff and organisation to keep the price competitive with inferior solutions.
We have fitted ferrous liners to other engines (for staff and friends) where the bores were smaller in diameter and the crankcase design more suitable but these crankcases are not ideal and create problems best avoided.
I am not familiar with the BMW engine but would be interested to know the type of construction and typical bore sizes.
I don't want to make an issue of numbers with competitors - we have always concentrated and what we do and not what others do and there are always alternatives and some good options available - but I do believe that some of our competitors are in single annual rebuild figures.
We could make oversized engines quite easily (already have some piston manufacturers in tow) but the overhanging rear crankshaft already causes flexing that can wear the rear main bearing prematurely under duress and in so doing starves the big ends of an oil supply sometimes resulting in a seized big end, a broken rod and a scrap engine. Furthermore usually a reliable but standard engine holds a better long term re-sale price and parts are always still available. We feel if you want a faster car the GT3 or Turbo are already designed for increased performance and do not have an overhanging crank flywheel end, but do have Nikasil alloy cylinders and higher cylinder coolant flow rate - so seem to us a better way to go together with improved suspension, braking and handling to suit the additional performance.
One final technical point I should make is that (like the GT3 and Turbo versions) our cylinders are not held in with a heavy interference fit. They don't need to be because the heat is generated from the inside and so the inside is always trying to maintain a fit with any exterior crankcase part as it expands and the top (where the coolant flows) is one solid alloy cylinder (also made with convoluted exterior to increase the surface area and compensate for the rather poor coolant flow. Even alloy liners in alloy or ferrous liners in alloy reduce the stiffness of the resulting mechanical bi-construction compared with a solid cylinder and any interference fit with different material results in differential expansion of both parts and changes in the fit. Without going into too much detail our cylinders are more like a free standing solid alloy cylinder (with a Nikasil bore finish) and as a result expansion and contraction is only influenced by engine temperature with no other interfering factors.
Baz
Interesting reading as always. Thanks Baz.
I'm still not sure what I'm doing. Someone at Hartech was kind enough to give me a run down of an 'ultimate rebuild' package before i bought the car so I know what that will cost and what it will cover. I may leave it a few months as things stand. If i'm considering a full rebuild there isn't much more that can go wrong in the next couple of months.
I'm still not sure what I'm doing. Someone at Hartech was kind enough to give me a run down of an 'ultimate rebuild' package before i bought the car so I know what that will cost and what it will cover. I may leave it a few months as things stand. If i'm considering a full rebuild there isn't much more that can go wrong in the next couple of months.
dom1102 said:
Just a quick thumbs up for Baz and the guys at Hartech My 2002 996 3.6 engine was rebuilt using a Hartech sleeved set of crankcases. They were extremely knowledgeable and helpful through a fairly stressful time. My car has since covered 4k miles and runs like a dream.
Would you mind telling us what mileage yours gave up the ghost and how bad the symptoms were?Gassing Station | 911/Carrera GT | Top of Page | What's New | My Stuff