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mattomg
Trainee


Joined: 10 Apr 2019
Posts: 51
Location: Portsouth


PostPosted: Mon Sep 23, 2019 9:46 am    Post subject: Reply with quote

bazhart wrote:
I’ve taken pictures to help explain but can’t easily upload them – I can email them to someone to upload if there are any volunteers, otherwise similar pictures can be found on our website www.hartech.org

The normal potential problems with the cylinder design are scoring/scuffing & cracking.

Scoring isn’t as common in the 996 3.4 engine as the 3.6, 3.8 & 3.4 987 models but it can still happen, particularly with the Ferroprint pistons.

There are numerous contributory factors with scoring but the underlying issue is that the cylinder bore running face (Lokasil) isn’t quite up to the job in many cases. This is why we choose to go with Nickel Ceramic plating (like in the Metzger engine) as a running surface which is much more durable – it is electro plated onto an aluminium alloy wet liner which shares the same expansion and contraction rates as the rest of the block so is nice and stable in both the deck height and integrity of fit rather than a different material with half the expansion and contraction rate.

Cylinder cracking is a totally different issue and comes about because the original design is essentially a tube of metal just surrounded by water without any support at the top. The thrust loading over the years pushes against one portion of the cylinder and it gradually goes oval and eventually cracks. Our new cylinders are a “top hat” design so naturally stronger and are locked against the casting in a precision machined diameter - so cannot move so will not migrate oval and crack. The original design is an “open deck” whereas the wedging of our liner against the other part of the block makes it more of a “closed deck”. (Incidentally, this isn’t a classic problem with the smaller engines as the cylinder walls are thicker & stronger).

The “closed deck” element of our liner can be re-produced by infilling the space with a support ring of metal.

The pictures you showed me yesterday David are original Lokasil cylinders but with support rings fitted – hence them being described as “closed deck”. They are NOT liners nor Nikasil plated. They don’t look like our work either (well certainly not anything we’ve done for the last 15 years).

Going off tangent a little, there are 2 classic areas in these engines which will eventually lead to a failure through natural wear & tear/degradation – cylinders gradually migrating oval eventually cracking & crank shaft bearings wearing out. There’s a pattern where both seem to start happening at similar mileages (90k-100k upwards). There are obviously lots of cases where engines last longer but there are also others which don’t quite make it (we have 2 in at the moment – 1 at 75k and 1 at 80k).

Cylinder cracking isn’t too much of a drama – a re-build is needed but the damage is isolated but crank shaft bearing failure is another story and a disaster. The crank & rod will usually be wrecked and potentially the carrier. The debris then usually spreads and will kill the oil pumps and, more often than not gets into the cylinders damaging pistons and potentially the bore surface material. In the very worst cases the rod breaks and the whole engine can be smashed and written off. Cranks, carriers etc are getting much harder to source & second hand values are creeping up.

Consequently, there’s a very strong case for replacing the crank bearings as the mileage gets higher before they’ve failed, particularly if the owners plan is to keep the car for some time.

Hope that helps !

Grant
 
  
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bazhart
Approved Trader


Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Mon Sep 23, 2019 10:01 am    Post subject: Reply with quote

Not too sure why the earlier post has been reproduced mattong, but for clarification the report I mentioned on page 2 has 184 pages, 40,000 words and 88 illustrations.

Baz
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bazhart
Approved Trader


Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Mon Sep 23, 2019 10:11 am    Post subject: Reply with quote

Whilst there’s no harm in oil analysis there is a danger that too much reliance is put on it. If a crank bearing becomes so worn that the soft copper is exposed the rate of deterioration can be very quick. The situation could arise where the analysis is carried out just before the copper is exposed and then this soft metal quickly wears leading to a catastrophic failure.

We had an episode recently where an owner brought his 997 to us for a preventative re-build at around 120k miles. The bearings were down to the copper so he caught it just in-time but he had undertaken an oil analysis only a fortnight before and it was clear.

Grant
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coullstar
Albert Park


Joined: 15 Sep 2015
Posts: 1637
Location: Aberdeen/Torphins


PostPosted: Mon Sep 23, 2019 10:27 am    Post subject: Reply with quote

In that instance (I know its hard to definitively say) but what are we talking about in terms of mileage to a point where its then creating a hell of a lot more expense?
100's of miles or less?
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bazhart
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Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Mon Sep 23, 2019 11:50 am    Post subject: Reply with quote

That question would be very hard (if not impossible) to answer and you will probably find my attempt at it unsatisfactory as a result. You would have to first strip engines every say what? - 5,000 miles - and rebuild them with the same shells until after years of repeating it you eventually found one that had just worn through to the copper and then accept the full cost of rebuilding it with those worn parts still in it to see how long it lasted until the crank failed - and then add the cost of a rebuild with new crank etc (hoping the failure didn't snap the rod and destroy the whole engine).

Even if we did all that (which I do not propose), we would quite rightly then still get questions about if it is a tip or manual, what time of year was it driven (and ambient conditions), how long were the journeys, which Country was it in and most important how it had been driven since rebuilding with the worn shells.

You can see that to quantify all that would be beyond the resources of anyone.

However what we can do is to use the history of failed engines and the mileages they failed at (and the type of failure) to analyse the results and form a general advisory.

All engines we strip have a several pages long report on all the internal parts (primarily used for subsequent customer contact but also it builds pictures and correlations) that help us generalise.

However generalisation can always be flawed since everyone drives differently and it can only be an overall guide.

What Grant's post reveals is that using an oil analysis will not necessarily protect you from a failure and therefore our general advice may be more useful than relying too much on that even though it will vary by owner, model, conditions etc.

So despite some engines lasting for high mileages, on average most would benefit from a pre-emptive rebuild before they blow up and therefore if the owners like them enough to plan to keep them - that may be a sensible consideration in the 80 to 100K area (although some will fail before that and some will last well beyond it).

Baz
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coullstar
Albert Park


Joined: 15 Sep 2015
Posts: 1637
Location: Aberdeen/Torphins


PostPosted: Mon Sep 23, 2019 2:37 pm    Post subject: Reply with quote

Totally understand and I was hesitant in asking. I suppose it was more if you had some case history for this.
I suppose the reason for asking is that many people with these cars will do a limited mileage per year and they also (hopefully) will be doing an annual oil change so you could have some data to say that its occurred a number of times within a certain timeframe.
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GMG
Nürburgring


Joined: 07 Jan 2018
Posts: 464
Location: Devon


PostPosted: Mon Sep 23, 2019 3:47 pm    Post subject: Reply with quote

...interesting if rather sobering/disconcerting reading for owners with leggy (>80 k miles) 996/7s...reinforcing my view that given the fragility and known issues associated with these engines that only cars with rebuilt engines will find value in the future...
 
  
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mattomg
Trainee


Joined: 10 Apr 2019
Posts: 51
Location: Portsouth


PostPosted: Mon Sep 23, 2019 4:03 pm    Post subject: Reply with quote

Frankly if it's not the IMS it's the Bores Scoring or if not it's the Cracking unless of course the Crank bearings melt...

Honestly if you're unlucky, your unlucky but in the meantime drive these great machines until Europe & Sadiq Khan ban all internal combustion engines forever !
Life is too short
 
  
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bazhart
Approved Trader


Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Mon Sep 23, 2019 4:48 pm    Post subject: Reply with quote

This is why we developed the oversized engine conversions to offer a benefit for a pre-emotive rebuild through giving back a performance benefit that doesn’t have to be thrashed to enjoy through its much better mid-range.

Generally a 10% increase in capacity is perfect or the top end cannot offer as much of an increase that the extra airflow could enjoy. So our 3.4 to 3.7 and 3.6 to 3.9 work extremely well.

The 3.2 to 3.7 also works well because although the top end is not as much of an increase in proportion to the 500cc stretch, the light weight makes it very fast and might otherwise struggle for grip.

The 3.4 Cayman S to 3.9 is fantastic because it shares the 3.6/3.8 heads and camshaft variations and can breathe higher top end air flow and still give up good bottom end resulting from the more sophisticated induction system.

The 3.8 to 3.9 unfortunately only offers a 100 cc increase so is not as noticeable as the others.

Baz
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DAVIDGT996
Trainee


Joined: 24 Feb 2019
Posts: 76
Location: Colchester


PostPosted: Wed Nov 06, 2019 12:24 pm    Post subject: Rebuild Reply with quote

My 996 is back following its rebuild by Angus @ AMS Porsche. Went above and beyond by doing loads of extra stuff on the car FOC and sorting out the host of parts I left in the boot when the car was collected - sports headers, condensors, dansk exhaust clamps, titanium stud kit, Bosch spark plugs, brake pipe over engine. Also did some mesh grill for me on the front bumper.
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2001 C2 Coupe Tip
Black, GT3 kit, lowered
 



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maldren
Suzuka


Joined: 07 Oct 2016
Posts: 1197



PostPosted: Wed Nov 06, 2019 5:22 pm    Post subject: Reply with quote

Bet you're glad to get it back, what did AMS do in the rebuild? Can you share the details with us please?
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Mike
2003 996.2 C2 Coupe Arctic Silver
 
  
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DAVIDGT996
Trainee


Joined: 24 Feb 2019
Posts: 76
Location: Colchester


PostPosted: Thu Nov 07, 2019 9:49 am    Post subject: Rebuild Reply with quote

AMS Porsche - cant fault them, kept me informed all the way through.

Cylinder head reconditioned
Sourced used crank
2 new pistons & 6 piston rings
liners x 3 with closed deck retained
conrod bearings
main bearings, head bolts & conrod bolts
timing chains
cam chain tensioners & pads
AOS
Standard IMS, tensioner blade & link chain
Oil Pump
engine mounts
brake line over gearbox
low temp thermostat
waterpump
stud extraction and fitted my sports headers with ti studs & bolts
fitted my air condensors & rads
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2001 C2 Coupe Tip
Black, GT3 kit, lowered
 
  
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maldren
Suzuka


Joined: 07 Oct 2016
Posts: 1197



PostPosted: Sat Nov 09, 2019 9:23 am    Post subject: Reply with quote

A good list of extras for a rebuild, thanks
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Mike
2003 996.2 C2 Coupe Arctic Silver
 
  
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