Name that bolt.. most bazaar mode of failure yet!
11-02-2010, 01:59 AM
#16
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Should I pull the pan on my 15k mile '07 Cayman S 3.4 motor and check the rod bolts? Or just swap in some better ones?
11-02-2010, 02:23 AM
#18
Burning Brakes
Thread Starter
Came from cylinder #5
These are torque to yield bolts (stretch bolts) the only problem is that during operation they stretch farther than the torque values dictate, then they loosen.
This isn't our first exposure to this MOF, just the most bazaar considering the bolt was picked up by the timing chain. Generally the bolt is never found, it usually launches into orbit.
These are torque to yield bolts (stretch bolts) the only problem is that during operation they stretch farther than the torque values dictate, then they loosen.
This isn't our first exposure to this MOF, just the most bazaar considering the bolt was picked up by the timing chain. Generally the bolt is never found, it usually launches into orbit.
11-02-2010, 08:17 AM
#22
Burning Brakes
11-02-2010, 08:39 AM
#24
Unless Porsche got the torque value wrong such that bolt wasn't stretched to the proper yield point, I would imagine that the TSB also mandated new rod bolts too. Once a bolt reaches it's yield point, any more torquing after that will weaken it dramatically. I wouldn't trust a bolt that's been torqued past it's yield point, especially one holding my engine's bottom end together.
11-02-2010, 10:38 AM
#27
Drifting
It's called excessive deflection and it is a well known failure mode. It's the 'why' and 'how' that is the issue. It could be a single failure point where the product was missed in the QAR process (ie. heat treatment process failure) assembly error, product design issue, product material selection (ie low carbon (iron) steel instead of copper-nickel lets say). Even in the area identified as an 'assembly error' this could be an individual worker failure point or a production engineering issue (which is the worst for all of us) where Porsche based the design loads and set assembly requirements based upon faulty data. The same failure point can also be caused by a CFO interfering in the design process where by engineering request a budget for chromium metals and he tells them to pizz off and come back to him with an earth bound proposal using galvanized metals or something cheaper.
The other issue could be owner abuse although it is usually manifested in other parts first. Unless you send these pieces to a metallurgist you won’t know how it failed and if the material is appropriate for the intended use. I’m willing to bet it is either a production engineering issue (material changed) or a product material final finishing issue. The skeptic in me says it was the fault of the Porsche CFO being driven hard by Wankerboy in the 90's to cut costs!
The other issue could be owner abuse although it is usually manifested in other parts first. Unless you send these pieces to a metallurgist you won’t know how it failed and if the material is appropriate for the intended use. I’m willing to bet it is either a production engineering issue (material changed) or a product material final finishing issue. The skeptic in me says it was the fault of the Porsche CFO being driven hard by Wankerboy in the 90's to cut costs!
11-02-2010, 11:29 AM
#28
Burning Brakes
Thread Starter
The TSB I referenced was related to new engine builds or very deep internal repairs.. No way to access the rod bolts with the engine assembled.. Even if you could torque them the process would be wasted effort since the bolts are torque to yield.
Keep this in mind: The M96 engine in one of my cars has been used for all sorts of test work, I have held it at 7,400 RPM for 4 hours at a time on my chassis dyno, driven in second gear for 5 miles against the rev limiter, made abrupt downshifts that send the engine to a stage II over-rev and have generally tried to kill it. No luck, still going strong. I did that for 30K miles in 2007!
From what we've seen its really hard to force one of these engines to fail through abuse, makes no sense but they seem to fail more often and more explosively when just being driven normally.
We finished the autopsy of the engine this morning and will be inducting the entire assembly bottom end components onto our "trophy shelf" later this afternoon as more offerings to the Gods of Speed..
Here are a few more carnage pics...
Keep this in mind: The M96 engine in one of my cars has been used for all sorts of test work, I have held it at 7,400 RPM for 4 hours at a time on my chassis dyno, driven in second gear for 5 miles against the rev limiter, made abrupt downshifts that send the engine to a stage II over-rev and have generally tried to kill it. No luck, still going strong. I did that for 30K miles in 2007!
From what we've seen its really hard to force one of these engines to fail through abuse, makes no sense but they seem to fail more often and more explosively when just being driven normally.
We finished the autopsy of the engine this morning and will be inducting the entire assembly bottom end components onto our "trophy shelf" later this afternoon as more offerings to the Gods of Speed..
Here are a few more carnage pics...
Last edited by Jake Raby; 01-11-2015 at 11:56 PM.
11-02-2010, 12:18 PM
#30
Burning Brakes
Thread Starter