Anthony_Vince

I have recently bought a '97 993tt which was checked out by an official Porsche garage here in the UK. It was given the all clear. However 3 weeks later a noise appeared in the engine area, before a strip down it was diagnosed as a big end bearing failure!! This is so i am told unheard of, nonetheless the chains were changed first to no avail. A full engins strip down revealed #5 big end shell had failed and lightly damaged the conrod and crankshaft! The cause has still not been determined, the car is 4 years old with 39k miles and hasn't been driven particularly hard as far as any of us can tell. There does not appear to be evidence of oil starvation or problems in the oil galleries. The net result after 5 weeks by an official garage is new conrods, new crankshaft, new bearings and shells. The dealer at the same time managed to break a piston ring as well which will not be at my expense but nonetheless takes several days to order. It seems to me that this is a manufacturing fault on an engine component which Porsche admit to in my view by paying for the con-rods which incidentally were faulty themselves when they were renewed! Therefore the net cost is huge to me and not what i'd expect from an otherwise very competent Porsche. I'm wondering what other forum readers views are on this? similar experiences? should Porsche pay for more than just the con-rods? Does the old crankshaft and con-rods have a re-sale value to an engineering shop? Incidentally I didn't have a warranty with the car dealer (not official Porsche) nor with Porsche themselves since i trusted the 89 point check. The engine has still not been assembled.

many thanks

Kevin

Anthony;

Porsche decreased the size of the 993 rods (width) versus previous pcar rods. I would not blame Porsche for this problem, it is very easy to wipe out a bearing from missing a shift, or downshifting into a lower gear. Did your dealer have the other rods resized? If you believe that it was a material failure, there are testing labs that will do an analysis for you. Also, a bearing that was manufactured with a flaw will fail very quickly, not later in 39K. You should check your valve guide wear, to see how they are wearing. I would personally install Carrillo rods, with Carr rod bolts, $1,200, this is a worth while add on. Also, have them inspect the condition of your turbo's, having debris in your oil will lead to premature turbo failure. These stories touch home to all of us, and we do feel it, not in our wallet, but it does make us sick. Good luck.

Anthony_Vince

Kevin,
Thanks for your input, i wasn't aware of potential bearing damage from missing a shift. Since the damage to the crankshaft was superficial I tried to pursuade them to polish the mark out, which they initially agreed to without warranty but later retracted. I then tried to pursuade them to re-grind the crankshaft and fit oversized bearings which had a 964... part number. They were not happy with this and in the interests of time new parts have been ordered. In terms of fitting Carillo rods, as i'm sure you know they'll only fit genuine Porsche parts.

I believe i did 100 easy going miles with the engine in this state - and that was to get it to the garage for what appeared to be a very superficial noise. When i personally looked inside the engine at the garage there was a small amount of debris in the filter near the oil pump, which was the wear from the failed bearing shell but that was all; incidentally the oil pump was replaced as a precautionary measure.

They have broken a piston ring in the process which I find curious since they should just stay on the piston during dis-assembley and then be put back in, i wasn't aware that they are put under that much pressure when re-installed into the engine, perhaps i'm wrong or the part failed. I take your point about the valve guide wear and debris in the turbo, i'll be speaking to them about this. My main concern at the moment is that we have found the symptom (bearing) but not the cause and i'm afraid it might come back to haunt me. thanks again.

Kevin

Anthony;

I would request that the rods and crank be sent out to a independant machine shop that could handle the job. Porsche cranks are quite durable, however if the crank can be saved, I'd have it looked at. As for the rods, you didn't say whether they were checked out. Regardless with type of failure I would have the big ends of all the rods resized to factory specs.

Anthony_Vince

At last my car is back on the road after 2 months having the engine re-built. It appears they have done a good job and it certainly makes it all worhtwhile once you get back into one of these things. As with such a complex job I expected a few minor problems and sure enough I have them!

I have observed the 1000mile run in period (took me 1 weekend) which means keep the revs below 5k rpm. However, when I ask 90-100% performance from the car it cuts out like a rev-limiter at 3.5k rpm, i.e. it wont go past 3.5k rpm under load. It will do it if I go slowly through te revs but not under max or close to max acceleration. My only thoughts on this are that it could be a fuel related issue. I had to put about 1/4 tank of 95 octane unleaded in the car since super-unleaded 98 octane was not available. I have since filled it with 98 octane and re-filled again but the problem still persists. I believe it could be fuel related since i had a similar problem with a 944 Turbo, however the problem went with better fuel.

Anyone have any thoughts on this? It feels very much like a computer is stopping the car from delivering max performance because there is something not quite right.

thanks in advance.

mags993tt

I'm by no means an expert on this but think I read something on these boards (or in the manual - can't remember) that if there is any issue the ECU puts the car into 'limp' mode and max 0.5 bars of pressure are attainable from the turbos - it may be something to check on your boost guage if the 'rev limiting' effect takes place when u hit 0.5bars of pressure. I don't know how it limits the boost but one possibility is by cutting the fuel to the engine but I stress I am totally guessing here...I'm sure someone more knowledgeable will chime in shortly!!

Anthony_Vince

Thanks, i've just been back to the dealer and your not far off the mark. It was a vacuem hose on the waste gate that was not connected. This limited boost and in turn put the 'Check Engine' light on. All is well now.

The car is going back in next week for the remainder of the service, geometry and they are going to try and rectify the boost gauge. They have earthed the wire to the sensor which makes the gauge read 0.8 bar, which therefore indicates the sensor is faulty, however a new sensor hasn't cured it. Very strange!!

mags993tt

Anthony, noticed you live in London - not sure if you visit the 993 forum at all but there are a bunch of us 993 owning Rennlisters getting together on the evening of Jan 30 in Surrey to bore each others pants off with Porsche stories . The details are under the heading 'surrey beer night' (or something like that) on the 993 forum. You would be most welcome.
M

Anthony_Vince

Thanks, i've been there a few times with the 911 & Porsche world meets, I'll try and make it.