Knackered old Porsche with loads of miles - 996 content
Discussion
J4CKO said:
This popped up on FB and thought it may be of interest.relevant, apologies if been posted before.
https://www.carthrottle.com/post/how-much-power-wi...
Brilliant! There are so many of these cars out there now with well over 200K on them and still going strong, yet so many internet folk will still tell you they'll explode at any second and cost you your house if you buy one https://www.carthrottle.com/post/how-much-power-wi...
EJH said:
A little o/t, but does Carthrottle generate *any* of its own content..as that's a video taken from a Jalopnik story published, I think, yesterday.
CarThrottle makes its own videos too, and Jalopnik posts many of those those, so it wouldn't surprise me if they have some sort of gentleman's agreement. Both sites aggregate others' content to some extent, although Jalopnik produces a good deal more original stuff I think. Just a little update, nothing broken and nothing falling off. It's off to Austria in a few days so we'll see how it copes with that.
As we all know at this time of year many Porsches are garaged or otherwise stored away for winter. Meanwhile I'm seriously considering washing mine and perhaps even refitting the arch liner properly.....:
Only 2000 miles of brake dust and grime
With the cold weather now back my rattle at start up has come back again, if the ambient is over 12 degrees or so it is silent but when it gets down to the temps we've been having recently I get a distinct rattle for 30 seconds or so. It's done this since I owned it so no major drama here, it seems to get a little worse each year but then it's got another 40K+ miles on it each year too
It's either the timing chain tensioners or a tappet that's lazy when the oil is thick. Hardly worth taking it apart to work out what at this stage - it would have made a bid for freedom by now if it was really bad and I've heart of freshly rebuild motors doing the same thing, clearly a feature 
As we all know at this time of year many Porsches are garaged or otherwise stored away for winter. Meanwhile I'm seriously considering washing mine and perhaps even refitting the arch liner properly.....:
Only 2000 miles of brake dust and grime
With the cold weather now back my rattle at start up has come back again, if the ambient is over 12 degrees or so it is silent but when it gets down to the temps we've been having recently I get a distinct rattle for 30 seconds or so. It's done this since I owned it so no major drama here, it seems to get a little worse each year but then it's got another 40K+ miles on it each year too
It's either the timing chain tensioners or a tappet that's lazy when the oil is thick. Hardly worth taking it apart to work out what at this stage - it would have made a bid for freedom by now if it was really bad and I've heart of freshly rebuild motors doing the same thing, clearly a feature Edited by poppopbangbang on Monday 7th November 23:10
poppopbangbang said:
J4CKO said:
This popped up on FB and thought it may be of interest.relevant, apologies if been posted before.
https://www.carthrottle.com/post/how-much-power-wi...
Brilliant! There are so many of these cars out there now with well over 200K on them and still going strong, yet so many internet folk will still tell you they'll explode at any second and cost you your house if you buy one https://www.carthrottle.com/post/how-much-power-wi...
Still loving the thread. Since its arrival I'm more and more tempted with a 996 at the 10-12k end of the spectrum.
A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
eltax91 said:
Still loving the thread. Since its arrival I'm more and more tempted with a 996 at the 10-12k end of the spectrum.
A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
Double row cars have something like a 0.7% failure rate, single row is nearer 7% although having said that if they're post 100K then either are probably going to be fine. On a double row engine other bits will wear out and break before the IMS fails...... unless it's a weird one like mine that keeps slogging on A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
A 98 or 99 car should be a dual row bearing engine which if it's made it to 80K odd is realistically going to go on until something else breaks.
I reckon mine has 50K or so left in it before it will need some serious work, the gearbox will need a rebuild at this point as the rear diff has just started to get a slight whine that's slowly increasing. At that point it would probably be worth pulling the engine apart to see what's what. It will have passed 600K KM by that point though so as life goes that's not bad for a road car!
poppopbangbang said:
eltax91 said:
Still loving the thread. Since its arrival I'm more and more tempted with a 996 at the 10-12k end of the spectrum.
A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
Double row cars have something like a 0.7% failure rate, single row is nearer 7% although having said that if they're post 100K then either are probably going to be fine. On a double row engine other bits will wear out and break before the IMS fails...... unless it's a weird one like mine that keeps slogging on A fair few adverts mention 'no IMS bearing issues at this mileage'. I've read the posts you made before about double or single row etc. Is there a common wisdom that, once the car has hit a certain mileage, then you've gone past the IMS failure window?
It's probably the only thing stopping me taking the plunge. The thought of a £5k engine rebuild with little or no warning of failure is horrifying!
A 98 or 99 car should be a dual row bearing engine which if it's made it to 80K odd is realistically going to go on until something else breaks.
I reckon mine has 50K or so left in it before it will need some serious work, the gearbox will need a rebuild at this point as the rear diff has just started to get a slight whine that's slowly increasing. At that point it would probably be worth pulling the engine apart to see what's what. It will have passed 600K KM by that point though so as life goes that's not bad for a road car!
fantastic thread, just read from cover to cover. The 'day to day' of it might be less glamorous than we assume but I can't help but think it's all very International Man of Mystery, hopefully without the goofy teeth
Superb.
I've just SORN'd the 986 and put it away in the garage for winter, a decision; having read the last few comments I'm beginning to regret! It's got 77k on it atm, this thread is a very good excuse to re tax and go drive it some more..
Superb.
I've just SORN'd the 986 and put it away in the garage for winter, a decision; having read the last few comments I'm beginning to regret! It's got 77k on it atm, this thread is a very good excuse to re tax and go drive it some more..
EJH said:
J4CKO said:
This popped up on FB and thought it may be of interest.relevant, apologies if been posted before.
https://www.carthrottle.com/post/how-much-power-wi...
A little o/t, but does Carthrottle generate *any* of its own content..as that's a video taken from a Jalopnik story published, I think, yesterday.https://www.carthrottle.com/post/how-much-power-wi...
They've gone from posting interesting articles to reposting articles weekly, usually robbed from Jalopnik or eBay and then when they get bored post s
t memes about their MX5, which no one is interested in anymore.Haven't been able to post since, think the owner took it badly
So update time and a fair bit is afoot......
The last oil test showed a high copper count compared to what is normal for the car, around 500ppm vs pretty much zero. It had also developed a bit more of a meaty rattle from cold start than usual shortly before this test. The engine was just North of half a million KM at this point.
Whilst performance was still good and there was no excess oil consumption or similar I made the decision to pull it at this point to investigate further as running it until it went pop was never the plan which revealed:
No 1 bearing showing wear to the copper, the failure mode for this was a timing chain guide starting to break up and shedding material which damaged number 1 crank bearing in turn leading to rapid wear. Just one of those things but a preventative change of timing chain guides every 200K miles would remove the chance of this happening. The crank is fine aside from some very slight marking on number 1 journal that will clear with a polish and no other bearings were overly worn. The big ends and all the remaining crank bearings were still totally serviceable and the rods still measured within spec for roundness on both ends.
The bores showed no scoring and were in great condition aside from normal wear at this mileage (beyond Porsche ovality limits but then it's got more than half a million KMs of up and downs on them so that is to be expected), pistons were fine and rings were still sealing well. The IMS bearing was mint and had absolutely zero play in it and the IMS shaft and sprocket were mint, timing chains were still in good condition so it was just a wear related failure of the guides which clearly are at life at 500K KM.
The oil pressure pump was in pretty decent condition with just a couple of minor scores in the ally housing from where the debris that had taken out no 1 crank bearing had gone through it. Both scavenge pumps were mint as were their drives. The cams and tappets were again mint with the surface hardening on the cams undamaged and no dished or soft tappets. The valve guides were well worn as were the valves, all 24 were still sealing but the stems measure thinner in the centers and at least two have a bit of stretch in them, again not surprising given how many KMs the engine has covered and how it has been used.
It's worth noting this car has always run 0W/40 Mobil 1 on a 10K - 12K mile service interval. It has always had coolant and oil temp before being heavily loaded but aside from that it's not been pampered or overly looked after. If anything a lot of what it has been through would be considered abuse by some as it's not shy of track work or donuts!
Based on this I'd say 500K KM is life for a 3.4 M96 used and serviced as this one has been - at this point the valves and guides are heavily worn, the bores are at the Porsche limit for ovality and the chain guides are worn to the point of fairly graceful failure. For a mass produced engine which makes just shy of 90bhp/litre I don't think that's bad at all, especially as it was making good power right up until I called time on it and to be fair to it would have gone a bit further still albeit at the risk of the crank being damaged beyond use.
So the plan:
As the bores are past the ovality limit then there are a few options to return them to round but in the interests of not messing about and given the opportunity for a performance increase then the block will be getting liners, which at the same time will convert it to a closed deck design and 100mm bore for 3.7L total capacity. Pistons will be low expansion forged items with a reduction in skirt and therefore friction and weight. Components will be made by Capricorn with Autofarm carrying out the engine build, Autofarm did my C2 which is still going (very) strong to this day. IMS bearing is a bit of an unknown as there are no more dual bearings available anywhere so short of running the old one again I am probably going to go with an oil fed roller bearing in place of a ball bearing. Heads will be refurbed with new valves, guides and seats freshened up but the majority of bits such as cams, crank, rods, major castings etc. will be used again. Having covered the distance they have it's pretty clear that all the castings are good (and well stress relieved given the amount of heat cycles they've done!) and there are no casting issues or material defects with rods, crank, cams etc. basically having got this far if they were going to fail they would have by now so I'm not keen on replacing them with unknown bits just for the sake of it.
Power should be in the region of 360bhp which compares nicely to a Mk1 GT3 and it should do half a million KM again without too much fuss, although this time around I will be doing chain guides at half that distance as they're a proven failure point.
Cost wise, you can buy quite a decent 996 for what this is going to cost but then again it costs £390PM to lease a diesel BMW on 20K miles a year and I do a lot more mileage than that so if I see another three years from the car then it's cost me no more than driving a diesel three series..... I know what I'd rather have
The last oil test showed a high copper count compared to what is normal for the car, around 500ppm vs pretty much zero. It had also developed a bit more of a meaty rattle from cold start than usual shortly before this test. The engine was just North of half a million KM at this point.
Whilst performance was still good and there was no excess oil consumption or similar I made the decision to pull it at this point to investigate further as running it until it went pop was never the plan which revealed:
No 1 bearing showing wear to the copper, the failure mode for this was a timing chain guide starting to break up and shedding material which damaged number 1 crank bearing in turn leading to rapid wear. Just one of those things but a preventative change of timing chain guides every 200K miles would remove the chance of this happening. The crank is fine aside from some very slight marking on number 1 journal that will clear with a polish and no other bearings were overly worn. The big ends and all the remaining crank bearings were still totally serviceable and the rods still measured within spec for roundness on both ends.
The bores showed no scoring and were in great condition aside from normal wear at this mileage (beyond Porsche ovality limits but then it's got more than half a million KMs of up and downs on them so that is to be expected), pistons were fine and rings were still sealing well. The IMS bearing was mint and had absolutely zero play in it and the IMS shaft and sprocket were mint, timing chains were still in good condition so it was just a wear related failure of the guides which clearly are at life at 500K KM.
The oil pressure pump was in pretty decent condition with just a couple of minor scores in the ally housing from where the debris that had taken out no 1 crank bearing had gone through it. Both scavenge pumps were mint as were their drives. The cams and tappets were again mint with the surface hardening on the cams undamaged and no dished or soft tappets. The valve guides were well worn as were the valves, all 24 were still sealing but the stems measure thinner in the centers and at least two have a bit of stretch in them, again not surprising given how many KMs the engine has covered and how it has been used.
It's worth noting this car has always run 0W/40 Mobil 1 on a 10K - 12K mile service interval. It has always had coolant and oil temp before being heavily loaded but aside from that it's not been pampered or overly looked after. If anything a lot of what it has been through would be considered abuse by some as it's not shy of track work or donuts!
Based on this I'd say 500K KM is life for a 3.4 M96 used and serviced as this one has been - at this point the valves and guides are heavily worn, the bores are at the Porsche limit for ovality and the chain guides are worn to the point of fairly graceful failure. For a mass produced engine which makes just shy of 90bhp/litre I don't think that's bad at all, especially as it was making good power right up until I called time on it and to be fair to it would have gone a bit further still albeit at the risk of the crank being damaged beyond use.
So the plan:
As the bores are past the ovality limit then there are a few options to return them to round but in the interests of not messing about and given the opportunity for a performance increase then the block will be getting liners, which at the same time will convert it to a closed deck design and 100mm bore for 3.7L total capacity. Pistons will be low expansion forged items with a reduction in skirt and therefore friction and weight. Components will be made by Capricorn with Autofarm carrying out the engine build, Autofarm did my C2 which is still going (very) strong to this day. IMS bearing is a bit of an unknown as there are no more dual bearings available anywhere so short of running the old one again I am probably going to go with an oil fed roller bearing in place of a ball bearing. Heads will be refurbed with new valves, guides and seats freshened up but the majority of bits such as cams, crank, rods, major castings etc. will be used again. Having covered the distance they have it's pretty clear that all the castings are good (and well stress relieved given the amount of heat cycles they've done!) and there are no casting issues or material defects with rods, crank, cams etc. basically having got this far if they were going to fail they would have by now so I'm not keen on replacing them with unknown bits just for the sake of it.
Power should be in the region of 360bhp which compares nicely to a Mk1 GT3 and it should do half a million KM again without too much fuss, although this time around I will be doing chain guides at half that distance as they're a proven failure point.
Cost wise, you can buy quite a decent 996 for what this is going to cost but then again it costs £390PM to lease a diesel BMW on 20K miles a year and I do a lot more mileage than that so if I see another three years from the car then it's cost me no more than driving a diesel three series..... I know what I'd rather have
Well that was unexpected!
Having got towards the bottom of the condition report I was expecting "put it all back together as standard and away we go", not "chuck a set of forged pistons in and give it a good going over".
At 500kKM that's not bad condition though, be interesting to see if you're the highest-mileage non-Porsche-owned M96.
Having got towards the bottom of the condition report I was expecting "put it all back together as standard and away we go", not "chuck a set of forged pistons in and give it a good going over".
At 500kKM that's not bad condition though, be interesting to see if you're the highest-mileage non-Porsche-owned M96.
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