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I spent my birthday tearing down my 3.4 and found what failed
Some of you may recall last summer my engine failed on the track and Dundon Motorsports has been rebuilding and transforming my 996 in virtually every possible way including a 3.8 (that will be a separate post sometime in the future). Well, I got a great birthday present from Charles Dundon, when he invited me and a friend in yesterday on my birthday to tear apart my failed 3.4. Charles gave me a corner of his shop to do this with some guidance along the way. It was my first time taking an engine apart and it was a blast. In addition, we did find what failed (pic below)...the rod had broken, which looks like a result of oil starvation on the crank which is what we had diagnosed this summer. I was amazed about how simple the engine really is and really how few tools are actually needed to take it apart. While it is a messy job, I also found that the parts washer is my best friend really keeping the mess to a minimum. Finally, now I have a whole bunch of clean parts that I will likely sell on ebay but it you guys are interested in any of it let me know. The engine has 54K miles on it with a LN IMS with only 6k miles. I threw away anything that remotely could have been effected by the failure other than the case which Charles told me some folks would resleeve especially my case which has no porosity and low miles.
Nice, thanks for sharing. It's always fun to look at pix of the m96, as my knowledge base in that arena is limited. Normally, this would be a bittersweet experience, but given the sourness has had time to wear off I'm sure you had a blast.
Funny, i got a completely different (but similar) bday gift on my big day Friday: i had dropped my car off for a new clutch/ims/rms a couple weeks ago and my mechanic called out of the blue late Friday afternoon to let me know it was ready -- little did he know he was making my bday better than i could have hoped for. Needless to say I'm having a memorable bday weekend, hope your doing the same.
Thanks, I did it for a learning experience, and finally now I understand how all this works. It was a bummer when it happened, but I am now building a totally custom 996. Two years ago, I parted out GT3 and that was also a great experience in that I learned all of the non-engine parts of the car worked so I am not afraid to do myself. In the end....its all surprisingly simple to take both a car and an engine apart. The hard part is putting it back together...now that is the art!
Looks like cylinders #4,5,6 are heavily scored too. Do you have any photos of the failed bearing? Just curious.
Here is a picture of the crank shaft at the failed cylinder location. You can see the excessive wear....I would love to here Jake's opinion on this. You can also see that there is discoloration which I think was due to excessive temperature.
I have heard some experts say that starvation is an issue and some say it is not. I wish I knew the answer.
There’s no question in my mind that a stock 996 suffers from oil starvation at the track.
The evidence I’m basing this on is countless track videos that show oil pressure gauge readings that clearly show oil pressure drop on sweeping right handed turns. It’s either that all these cars have oil pressure sensor/gauge malfunctions, or that pressure drops are actually occurring. There is a saying in aviation that says something to the effect that - if an instrument tells a story, unless you have real evidence that the instrument is clearly wrong (an altimeter showing 80,000 feet while the aircraft is parked on the runway), you should trust the instrument and assume that it’s right.
Some folks think that oil pressure drops on these cars isn’t an issue because it doesn’t go to zero, so at least some pressure is better than no pressure. WRONG. Oil starvation due to air getting in or pressure being low results in one of two scenarios: either there isn’t going to be enough fluid moving and carrying away heat, which will lead to overheating or viscosity breakdown of the oil film, resulting in metal to metal contact, or, the air/oil mixture will be compressible in the bearing and lead to metal to metal contact. It’s metal to metal contact either way and will ultimately result in failed bearings.
If anyone is worried about this, simply position a camera to record your track event to read the oil pressure gauge. If there’s any oil pressures drops at all that aren’t in sync with RPMs, then it’s oil starvation or oil aeration. Temperature fluctuations and related viscosity changes won’t cause this problem.
Here is a picture of the crank shaft at the failed cylinder location. You can see the excessive wear....I would love to here Jake's opinion on this. You can also see that there is discoloration which I think was due to excessive temperature.
Man, if that’s not evidence, I don’t know what is. Question: what oil viscosity has you been running and what were your observed coolant temps? I have concerns that my 996 runs too hot. I’ve seen 110-111C temps at the track and even 107C at idle on a hot summer day.
Man, if that’s not evidence, I don’t know what is. Question: what oil viscosity has you been running and what were your observed coolant temps? I have concerns that my 996 runs too hot. I’ve seen 110-111C temps at the track and even 107C at idle on a hot summer day.
Yeah....that is a great point. I did put in a center radiator a few couple of years ago to get my coolant temps lower because they tended to be on the high side. In fact, I am so concerned about temps that even with the new 997S engine (expecting between 400-420HP) I am putting in 996 Turbo radiators which are much larger +center radiator cause I want to make sure the engine stays cool.
One thing I forgot to mention is the engine only had 54K miles on it but the car was tracked through its whole life....thus the starvation.
02-04-2018, 02:14 PM
I spent my birthday tearing down my 3.4 and found what failed
