Knackered old Porsche with loads of miles - 996 content
Discussion
poppopbangbang said:
Doofus said:
FEAD?
Front Engine?
Front End Accessory Drive - essentially everything on the engine which is belt driven from the crank pulley including all the power transfer and tensioning elements of that belt. Front Engine?
Although I suppose on a 911 it's at the back not the front, even though that's still the front but at the back....so maybe it should be BTFEAD - Back To Front End Accessory Drive?
How do you find out the "life" of these components - is it a Porsche thing?
B'stard Child said:
Had me scratching my head too - thanks for explaining
How do you find out the "life" of these components - is it a Porsche thing?
More experience of lifing things on racing cars - although aerospace principles apply too! How do you find out the "life" of these components - is it a Porsche thing?
The aim with lifing any component is to ensure you get the maximum reliable life from it, where reliability is quantified by the effects/acceptability of a failure. In a competition car a component failure may be race loosing so you'll determine the useful life of the component and then divide that by an agreed number (usually two or three) to arrive at a life which is such that the component is reliable during that length of operation i.e. you should never have a failure. You then further refine this with real world data if required.
For the vast majority of components they live on the bathtub curve:
The infant mortality of components is such that if you REALLY need to ensure reliability you'll run the first part of life in a none critical situation where ever possible. When you hear about race engines going on the dyno etc. this is partly why, when you release the assembly/part for use in the live environment it is past the stage of infant mortality and should be within the zone of low failure rate.
One of the key aspects of lifing any component is data - you get more real world data on reliability from using the component than you possibly can any other way. So you track stuff in operation - partly to record where you are in life of that component and partly to understand how worn/close to failure it was when it came off. You may have environmental issues that apply here too so you may wish to understand how much greater the wear rate is in an new operating regime.
If you were to look at a lot of the components on the 996 this thread is about you'll see these stickers on things:
The lifing code relates to version of the component on the car. So in this case that's the third one of those rad fans and second set of those uprights which have been fitted to the car. Each set is tracked for mileage and if applicable failure mode. Where it's not just about tracking an individual component the assembly is issued with a part number and the whole assembly covered by the lifing code.
Rad Fans on my car lasted 200K miles'ish the first time around. So now it gets new rad fans every 140K Miles (at 70% of the last failure life), hence we're now on L03 Rad Fans as they were up on mileage. When inspected the bearings were properly gritty and there was some minor damage to the blades from debris etc. so that's a pretty good mileage to be working on.
Of course when you're doing this on a privately owned vehicle and where you have no control over suppliers etc. you have to take it with a pinch of salt as someone changing the end supplier of a part that goes through three rebrands before you can buy it obviously has the potential to cock up your data.... likewise components becoming NLA in the spec you were using, like I now have a quarter of a million miles of useless data on a certain manufacturers metal impellor M96 water pump that they don't make any more
Given my usage of this vehicle, especially in the old days, I think this approach does play out very well. It's had two car stopping failures in 350K miles. One was a Crank Sensor which died of old age (these are so cheap they subsequently got changed yearly) and one was an outer Lobro joint which failed within the first 1000 miles (there's that component infant mortality
). Taking into account it's use now and the refocused purpose of the car it's not really worth still recording component life etc. but I've started so I'll finish applies! 
Fascinating stuff!
I'm looking at rebuilding the front suspension on my 211 Mercedes E-Class. I usually use Febi / Lemforder parts but reading your last comment about supplier rebrands etc and not being able to be confident of the quality / life of aftermarket components - would you be able to offer an opinion on what you think the best aftermarket brands are these days?
Im looking at TRW bits on Autodoc but also Febi can be had at good prices on eBay especially when 20% codes are available. However, ive noticed NAPA and SKF are appearing too - do you have an opinion on those? The prices are quite a bit cheaper. Im looking at suspension arms and ball joints rather than shock absorbers.
Thanks!
I'm looking at rebuilding the front suspension on my 211 Mercedes E-Class. I usually use Febi / Lemforder parts but reading your last comment about supplier rebrands etc and not being able to be confident of the quality / life of aftermarket components - would you be able to offer an opinion on what you think the best aftermarket brands are these days?
Im looking at TRW bits on Autodoc but also Febi can be had at good prices on eBay especially when 20% codes are available. However, ive noticed NAPA and SKF are appearing too - do you have an opinion on those? The prices are quite a bit cheaper. Im looking at suspension arms and ball joints rather than shock absorbers.
Thanks!
B'stard Child said:
Thank you for that reply - really bloody interesting and not something I've ever thought about - despite running cars with quite high mileages in the past
PPBB has put some excellent info up there already but I feel its my duty to add a little, especially as this is a thread with a history of detailed discussion and inputs...B'stard Child said:
How do you find out the "life" of these components - is it a Porsche thing?
Absolutely not just Porsche - my background is Reliability Engineering, which is what we are talking about.Firstly for commercial vehicles, and latterly airliners. The principles are exactly the same, just as they are with motorsport. Things will break - that is guaranteed. But in all cases we want to avoid unplanned maintenance, whether that is a broken down truck or bus not delivering its load, a Jet aircraft that has to divert or a race car that doesnt finish the race. Or indeed, a steallthy overnight express parts delivery 911 that doesnt deliver its race car parts to the team on time!
poppopbangbang said:
The infant mortality of components is such that if you REALLY need to ensure reliability you'll run the first part of life in a none critical situation where ever possible.
The middle of a race, or a passenger flight, would be your 'critical' situation, as explained above, that we want to avoid. The relaibility engineer is trying to ensure that we get the maximum good life from our components, without letting them fail - and that all replacements are done in a controlled situation.
The bathtub curve posted above is Reliability Engineering 101, following from that there are other analysis tools such as Weibull Analysis, all of which is dependent on data, the more of it the better. Hence the logging of components, hours and cycles is key.
Halving the predicted life and replacing pre-emptively at that point would be a pretty blunt way of ensuring reliability, In a larger organisation where the economies are different, the Reliability Engineers job is then to start pushing that out, without letting it fail. Effectively, a game of shove halfpenny - who can push the component further, to the end of the board, but woe betide anyone who pushes it off the end!
There are even certain situations where it pays to use the "less reliable" (sic) component!
Component A we can see from our Data lasts on average 1000 hours, however the spread of failures is quite broad, some have failed at 400 hours, some not failed at 2000 hours...
Component B lasts on average 500 hours, but our failures are all at 498, 512, 504, 461, 522 hours etc... quite predictable.
This component might also be quite easy and quick to replace under planned maintenance (in the aircraft hangar, or at the race teams HQ between races), but would be a show stopper if it failed, ruining your flight or race.
After analysis, the most effective way to run this component is to run Component B, and plan to change it every 400 hours, easily and cheaply in your planned downtime. - even though on first look we saw that "A lasts longer than B!" We might use more of them, but we never ever experience a failure in service.
The counter to the above situation, is maintenance induced error!
https://www.weibull.com/hotwire/issue174/hottopics...
In short - sometimes the worse thing we can do is to mess with things that dont need it, and to 'over maintain' items, as the actual process of component service or replacement is far more damaging than simply leaving things as they are. See also the infant mortality mentioned above.
The Reliability Engineers role is balancing all these factors, and the goal is the same whether its a truck, bus, helicopter, F1 car - avoid unplanned maintenance.
The process that PPBB is going through is the same as any vehicle manufacturer, operator, race team etc...Its a very interesting sector of design and engineering that I fell into but really enjoy.
I would be interested to know from PPBB if their analysis is purely based on hours, or cycles too?
Edited by snotrag on Friday 5th May 09:06
poppopbangbang said:
...Crank Sensor which died of old age (these are so cheap they subsequently got changed yearly)
Thanks for the insight on how you life components.When I bought mine I created a service schedule in excel, based on the schedule RPM Technik had on their website at the time (I haven't checked if it's still there), plus a few bits from this and other threads. You'd previously said waterpump annual; coil packs, cam & crank sensors and MAF every 2 years/100k miles, clutch kit fork and pivot 100k. And I can now add Rad fans - 140k!
I mainly use the car for fun, it's non-safety or time critical, so I'm looking at these more as sensible preventative maintenance, so in my sheet have pushed the time interval out, but not the mileage. For those of us wanting to keep these cars in fine fettle but only doing a modest mileage of a few thousand a year is there anything else you'd recommend that these cars have periodically beyond the standard servicing?
I have added removing the precat lambdas, cleaning the threads and reinstalling every 2 years, as I currently have one original failed and seized into the cat
Happy to share the sheet if anyone wants.
Edited by HughG on Friday 5th May 10:31
Well this week has been a busy one, but here's my whiteboard as it currently stands!
Suspension setup is one for CofG to do later this month so I'm down to the last few items. Building a car up post paint is usually quite good fun as it's all clean and nice to work on and this was no exception. I'd pushed the boat out and ordered a ridiculous amount of new fasteners, clips, fittings etc. from Porsche so I had the pleasure of building it back up with all new fasteners too!
So to recap the week:
Out of the trailer and fresh from the paint booth with everything floating in approximately the correct place... mostly on a single bolt.
Tuesday morning, In the air and ready for build up. The job list for this stood at:
- Build up door cards and refit mirrors.
- Underseal, cavity wax and rustproof all the areas where 996s are generally prone to grow orange fail.
- Fit the front and rear bumpers properly and replace the rear bumper hangers.
- Refit the carbon canister and screen wash bottle.
- Refit the arch liners with all the associated bolt on bits that had been cleaved off over the years.
- Fit the side skirts and get them as straight as possible (the skirts are NLA so this was a case of do the best possible with the 23 year old ones).
- Fit the fuel filler cap.
- Bleed the brakes.
- Fit the floor panels/undertrays
.... and a load of little fettling bits...
Undersealing / cavity waxing it was easy enough. I always use Bilt Hamber stuff, specifically their S50 stuff as it creeps so much better than anything else. I coated the inside of the sills from the front and rear arches. They were already amazingly good inside given the age and mileage but it seemed rude not to belt and braces this for the sake of a kilo or so!
Photos in no particular order
Doors built up and mirrors refitted, the original seals etc. went back on without any dramas so this was all pretty easy and straight forward. Took the opportunity to fix the pas door handle which has been none working since Monaco 2017
Front bumper properly mounted (or at least as good as a 20+ year old four time repaired one will ), arch liners fitted and rad exit gurneys fitted.
Rear arch liners fitted, the easiest job out of everything!
Fuel filler cap fitted, the biggest, most pain in the arse, unenjoyable, downright annoying job out of everything.... I cannot emphasize what a total knob this was to get to a point I was happy with. It was an actual days worth of bolting on and off, fettling and general backwards and forwards'ing chasing the last 1mm of gap in the wrong place. It was a total arse but it got there in the end and I am very happy with the gap and alignment..... and the fact it's got a later spec hinge in there now too so it flips open a treat and springs shut with a reassuring thud.
This was absolutely the hardest part of going to carbon wings though as it's so noticeable there's no escape from getting it right. In the end I salvaged the bracket/hinge carrier from the original wing by drilling out the spot welds, drilled them out, slotted them to provide adjustment in Y, drilled and slotted the wing inside the filler cap to provide adjustment in X, drew up and 3D printed a stop (that would also carry the original rubber stop), drilled and slotted the wing to provide Y adjustment for this and then spent the aforementioned day getting it all to line up..... vs a standard metal wing where you just dead blow/screw driver the bracket/hinge carrier and bend the stop to suit - easy on metal but carbon doesn't bend
On the subject of carbon wings, with the bonnet open you'd be hard pressed to tell they weren't standard aside from a few rivet heads that aren't there as standard. They go in with all the standard fasteners which have been painted in place just like they would be on the line back in 1999.
Side skirts fitted, this is the second biggest arse of a job on the car aside from the fuel filler flap but this is mainly because these parts are 23 years old and have lived ALL of the life the car has to be in with the best fighting chance of getting them to sit straight, tight against the body and look presentable I replaced every fitting, screw and mounting for them. The clips which mount them clip to the sill seam under the car, this seam gets pretty grotty on all 986 and 996 but especially those with skirts so I was keen to make sure this wasn't a pain point in future. The sills have been treated and any corrosion or grot removed along with being recoated in PU, I made a template up to locate the clips in the correct place based on the skirts and all new clips went on before being doused in Bilthamber UB Wax to make sure that over time they didn't also corrode (which pushes the clip off and the skirt out) as well as further protect the sill seams.
With that all done it was just a case of backwards and forwarding to get an acceptable fit in terms of flushness and straightness. This is the first time since I've owned the car that both skirts have actually been straight and fitted well the drivers side used to be so bad you couldn't see the swage line detail on that side of the car! They're pretty battered on the wheel arch side of things but hey you can't really see that and you can't hide all the 500K KM patina right
Tomorrow should be a fun day doing the last bits and bobs and expect some photos of it outside a garage and not in bits in due course.
Still a few things that are on the list to do like wheel centre caps, steering wheel dash, it's due some exhaust manifolds this winter but for the most part it's now cleaner, tidier, better presented and far more sorted than it has been for years!
Suspension setup is one for CofG to do later this month so I'm down to the last few items. Building a car up post paint is usually quite good fun as it's all clean and nice to work on and this was no exception. I'd pushed the boat out and ordered a ridiculous amount of new fasteners, clips, fittings etc. from Porsche so I had the pleasure of building it back up with all new fasteners too!
So to recap the week:
Out of the trailer and fresh from the paint booth with everything floating in approximately the correct place... mostly on a single bolt.
Tuesday morning, In the air and ready for build up. The job list for this stood at:
- Build up door cards and refit mirrors.
- Underseal, cavity wax and rustproof all the areas where 996s are generally prone to grow orange fail.
- Fit the front and rear bumpers properly and replace the rear bumper hangers.
- Refit the carbon canister and screen wash bottle.
- Refit the arch liners with all the associated bolt on bits that had been cleaved off over the years.
- Fit the side skirts and get them as straight as possible (the skirts are NLA so this was a case of do the best possible with the 23 year old ones).
- Fit the fuel filler cap.
- Bleed the brakes.
- Fit the floor panels/undertrays
.... and a load of little fettling bits...
Undersealing / cavity waxing it was easy enough. I always use Bilt Hamber stuff, specifically their S50 stuff as it creeps so much better than anything else. I coated the inside of the sills from the front and rear arches. They were already amazingly good inside given the age and mileage but it seemed rude not to belt and braces this for the sake of a kilo or so!
Photos in no particular order
Doors built up and mirrors refitted, the original seals etc. went back on without any dramas so this was all pretty easy and straight forward. Took the opportunity to fix the pas door handle which has been none working since Monaco 2017
Front bumper properly mounted (or at least as good as a 20+ year old four time repaired one will
), arch liners fitted and rad exit gurneys fitted.Rear arch liners fitted, the easiest job out of everything!
Fuel filler cap fitted, the biggest, most pain in the arse, unenjoyable, downright annoying job out of everything.... I cannot emphasize what a total knob this was to get to a point I was happy with. It was an actual days worth of bolting on and off, fettling and general backwards and forwards'ing chasing the last 1mm of gap in the wrong place. It was a total arse but it got there in the end and I am very happy with the gap and alignment..... and the fact it's got a later spec hinge in there now too so it flips open a treat and springs shut with a reassuring thud.
This was absolutely the hardest part of going to carbon wings though as it's so noticeable there's no escape from getting it right. In the end I salvaged the bracket/hinge carrier from the original wing by drilling out the spot welds, drilled them out, slotted them to provide adjustment in Y, drilled and slotted the wing inside the filler cap to provide adjustment in X, drew up and 3D printed a stop (that would also carry the original rubber stop), drilled and slotted the wing to provide Y adjustment for this and then spent the aforementioned day getting it all to line up..... vs a standard metal wing where you just dead blow/screw driver the bracket/hinge carrier and bend the stop to suit - easy on metal but carbon doesn't bend
On the subject of carbon wings, with the bonnet open you'd be hard pressed to tell they weren't standard aside from a few rivet heads that aren't there as standard. They go in with all the standard fasteners which have been painted in place just like they would be on the line back in 1999.
Side skirts fitted, this is the second biggest arse of a job on the car aside from the fuel filler flap but this is mainly because these parts are 23 years old and have lived ALL of the life the car has
to be in with the best fighting chance of getting them to sit straight, tight against the body and look presentable I replaced every fitting, screw and mounting for them. The clips which mount them clip to the sill seam under the car, this seam gets pretty grotty on all 986 and 996 but especially those with skirts so I was keen to make sure this wasn't a pain point in future. The sills have been treated and any corrosion or grot removed along with being recoated in PU, I made a template up to locate the clips in the correct place based on the skirts and all new clips went on before being doused in Bilthamber UB Wax to make sure that over time they didn't also corrode (which pushes the clip off and the skirt out) as well as further protect the sill seams. With that all done it was just a case of backwards and forwarding to get an acceptable fit in terms of flushness and straightness. This is the first time since I've owned the car that both skirts have actually been straight and fitted well
the drivers side used to be so bad you couldn't see the swage line detail on that side of the car! They're pretty battered on the wheel arch side of things but hey you can't really see that and you can't hide all the 500K KM patina right Tomorrow should be a fun day doing the last bits and bobs and expect some photos of it outside a garage and not in bits in due course.
Still a few things that are on the list to do like wheel centre caps, steering wheel dash, it's due some exhaust manifolds this winter but for the most part it's now cleaner, tidier, better presented and far more sorted than it has been for years!
Don1 said:
Awesome stuff.
God help me, I've been thinking indecent thoughts about a cheap 996 and some Dakar-esque suspension....
So have I! The problem is you can only go so far with subframe spacers and long shocks and that's not really Safari enough for me.... I've got a set of rear uprights in CAD at the moment that will do that trick which relocate the upper and lower links accordingly but I need to do some research into drive shaft angles (although 996 uses Lobros on both ends so pretty extreme is likely possible). The front McPherson setup will go quite a long way up just by moving the coffin arm and tuning fork arm mounts to the bottom of the subframe and spacing the subframe down.God help me, I've been thinking indecent thoughts about a cheap 996 and some Dakar-esque suspension....
I'd go to 280mm brakes all round to allow 15" wheels (probably Braid like my Cayenne runs) with some proper tyres, massive rock sliders, two piece Kevlar floor (just to allow easy engine and gearbox access), weld some mounts to the standard crash bars to receive some Safari style front protection, delete the silencers and run a Y piece single exit box, roof rack with a spare wheel on it and job jobbed.
A lightly crashed C2 would be perfect, especially if it's already ripped a corner off as I don't need any of those bits and cars that don't roll generally go pretty cheap
poppopbangbang said:
I'd go to 280mm brakes all round to allow 15" wheels
I tried to fit a 16 inch 986 rear wheel but It didn't go on. It fouled on the mounting point for the rear camber arm to the hub. I think that's what it's called.
Cleared the disc and caliper fine. I didn't bother to try a front as I believe they don't clear the front brakes.
Hopefully you can see in the pic.
ATM said:
I tried to fit a 16 inch 986 rear wheel but It didn't go on. It fouled on the mounting point for the rear camber arm to the hub.
There's loads of room! If the toe arm link mounted from the top To get the ride height into it without creating lots of "bad" geometry in the rear suspension it's necessary to move the pick up points so everything runs at sensible angles. Think about that rear upright another 100mm down and you'll see how the toe link would top out (even if the wheel fitted), but move it to the top and all is good, of course on a standard upright the ball joint taper is now the wrong way around but you can solve that by machining a taper that provides a thread for a clevis to receive a spherical link..... or just do a new rear upright as you have to move the top and bottom pickups anyway! The key to doing a Safari 996 properly is in the uprights as the most height you can get with subframe spacers and long shocks is just enough to make it look weird rather than Dakar
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