Engine rebuild - rod bolt failure - Rennlist - Porsche Discussion Forums

Notices
997 Forum
Sponsored by:
Sponsored by:

Engine rebuild - rod bolt failure

Old 10-26-2018, 05:17 AM
  #1  
racer5j
Addict
Rennlist Member
Thread Starter
 
Join Date: Jun 2017
Location: Socal
Posts: 28
Default Engine rebuild - rod bolt failure

Not trying to spark fear but just wanna add another data point and share my story. I have a 2008 C2S with 78k miles. I bought it last November with 76k miles. Long story short, I blew the motor at an autox last weekend. Initially, I thought I spun a bearing due to oil starvation because I run wide sticky tires and the car generates a lot of grip. However, a motor teardown has revealed that a rod bolt on my #6 cylinder backed it's way out and chewed up the motor. A quick google search revealed that this is a known issue on high mileage M97s.

https://www.pelicanparts.com/techart...a_Problems.htm

Vision Motorsports is performing the rebuild and, per usual, they are great to work with. The block, crank and cradle have been sent out for inspection to determine if they're salvageable. If so, we'll likely move forward with building a 4.2L motor.

Like most who bought a higher mileage 997.1, I expected (but was hoping not) to rebuild the motor at some point. I just didn't expect it to be so soon. Still, I'm excited for the journey that lies ahead and can't wait to dive into the details of building a new motor.

Andrew
racer5j is offline  
Old 10-26-2018, 12:44 PM
  #2  
semicycler
User
 
semicycler's Avatar
 
Join Date: Jun 2012
Location: MN
Posts: 1,471
Default

4.2L is impressive. Would love to see a build thread if you go that route.
semicycler is offline  
Old 10-26-2018, 03:06 PM
  #3  
voiceprint1
User
 
Join Date: Aug 2011
Posts: 498
Default

does this problem extend to 997.2 DFI engine as well?
voiceprint1 is offline  
Old 10-26-2018, 03:09 PM
  #4  
Bruce In Philly
Addict
Rennlist Member
 
Bruce In Philly's Avatar
 
Join Date: Dec 2012
Location: Philadelphia
Posts: 3,076
Default

Originally Posted by voiceprint1 View Post
does this problem extend to 997.2 DFI engine as well?
I have not read of a single failure like this for the DFI engine.

Peace
Bruce in Philly
Bruce In Philly is offline  
Old 10-26-2018, 09:22 PM
  #5  
Iceter
User
 
Iceter's Avatar
 
Join Date: Feb 2012
Location: Raleigh, North Carolina
Posts: 1,618
Default

I would think a loosening rod bolt would get noisy as the big end of the rod got loose around the crank journal. What were the symptoms?
Iceter is offline  
Old 10-26-2018, 11:32 PM
  #6  
morefun
Addict
Rennlist Member
 
morefun's Avatar
 
Join Date: Jul 2002
Location: RI
Posts: 497
Default

Sorry to about about the unexpected expense. Just curious, any over rev or extensive track use history? Ive heard M97 rod bolts are prone to stretching when spun too fast and/or too long. Was a concern with my M97 Cayman that I sold with 63,000 miles and 65 track days in advanced run groups.
morefun is offline  
Old 10-27-2018, 04:18 AM
  #7  
racer5j
Addict
Rennlist Member
Thread Starter
 
Join Date: Jun 2017
Location: Socal
Posts: 28
Default

I've been replaying the final moments in my head over and over for the past 2 weeks. However, my local autox courses are generally pretty fast so I usually hit the soft rev limiter once or twice per lap. This particular course was quite fast and I intended trying out 3rd gear once the track rubbered in but I never got that chance.

On my second to last run before blowing up, I crossed the finish line after just hitting the rev limiter. As I was slowing down in the runoff area, I let in the clutch and when I was turning to get out of the course, I realized that I had no power assist. That's when I realized that the motor had shut down prematurely. I pulled off and restarted the car and it seemed to be running fine. In retrospect, perhaps there might have been slightly more clatter which I assumed was just lifter noise but there was definitely no obvious signs of something wrong. I sat in the staging until I deemed that the car was fine and then staged for my next run.

On my last run, the car seemed to run normally. However, when exiting a 180 degree corner just after a fast section of the course, I noticed the car was down on power and I heard a wheezing sound. I immediately shut it down and coasted to a stop. I restarted the car and there was a loud knocking sound so I shut it down again. At this point, it was pretty obvious that the rod had fully separated from the crank.

The previous owners did not track the car. I've only autoxed the car maybe 6 times since I've owned the car so the car doesn't have a long track history. Still, there are people in my region who have well over 100+k miles and heavily track and autox their M96 and M97 cars.

I was at Vision today and they said that there were some recent range 2 over revs, which would be consistent with my hitting of the limiter during my runs. Vision said that rod bolts may stretch and come loose when an engine is "back-holed", which is when a downshift is missed and the motor is instantly spun up due to being in the lower gear but perhaps not fast enough to overrev the motor. I've never back-holed the car and usually match revs on my downshifts but perhaps I did a poor job one too many times. Vision also said that as a precaution they usually recommend ARP rod bolts when rebuilding a motor regardless of whether using stock rods or Carillos.

Photos of the damage are forthcoming.
racer5j is offline  
Old 10-27-2018, 05:08 AM
  #8  
racer5j
Addict
Rennlist Member
Thread Starter
 
Join Date: Jun 2017
Location: Socal
Posts: 28
Default


Crank appears to be usable but will be inspected for cracks next week.

Closeup of crank damage

#6 piston and rod



Cylinder chunks

IMS is clearly not salveagable. IMSB (big bearing) was still in good shape tho.




Cracked cradle not salvageable

Closeup of the crack near the oiling hole

Thankfully no cylinder head damage
racer5j is offline  
Old 11-03-2018, 04:12 AM
  #9  
racer5j
Addict
Rennlist Member
Thread Starter
 
Join Date: Jun 2017
Location: Socal
Posts: 28
Default

Just a quick update. Thankfully, my block and crank are repairable so we should be able to proceed with a 4.2L build while staying within my budget. Shutting the motor down quickly saved me.

We haven't finalized the details for the build but will on Monday. I've been following a few other threads like Project Dora and Going Under the Knife for ideas on what to check/replace while the motor is out. Off the top of my head, I can only think of a handful of things:
  1. AOS
  2. plastic waterpump
  3. LNE IMS
  4. coolant tank
  5. starter cable
  6. oil pressure sensor
Please feel free to share other ideas. Thanks.
racer5j is offline  
Old 11-03-2018, 10:15 AM
  #10  
Petza914
Addict
Rennlist Member
 
Petza914's Avatar
 
Join Date: Oct 2007
Location: Clemson, SC
Posts: 9,142
Default

New chain tensioners and cam position sensors
Petza914 is online now  
Old 11-03-2018, 02:52 PM
  #11  
Hella-Buggin'
Super User
 
Hella-Buggin''s Avatar
 
Join Date: Nov 2009
Location: SF Bay Area
Posts: 2,200
Default

Go with the Motorsports AOS
Hella-Buggin' is online now  
Old 11-03-2018, 05:24 PM
  #12  
Coopduc
User
 
Join Date: Mar 2017
Location: Asheville NC
Posts: 297
Default

Racer- are you sure the crank can be saved? These main and con rod journals look bad, and there is indication of excessive heat in the area. Hope I’m wrong, and like to hear the shop’s rationale and/or plan to rework it. It may help others save their engines.




​​​​​​​
Coopduc is offline  
Old 11-03-2018, 07:20 PM
  #13  
JustinCase
User
 
JustinCase's Avatar
 
Join Date: Jan 2013
Location: Snohomish, WA
Posts: 190
Default

Originally Posted by racer5j View Post
Just a quick update. Thankfully, my block and crank are repairable so we should be able to proceed with a 4.2L build while staying within my budget. Shutting the motor down quickly saved me.

We haven't finalized the details for the build but will on Monday. I've been following a few other threads like Project Dora and Going Under the Knife for ideas on what to check/replace while the motor is out. Off the top of my head, I can only think of a handful of things:
  1. AOS
  2. plastic waterpump
  3. LNE IMS
  4. coolant tank
  5. starter cable
  6. oil pressure sensor
Please feel free to share other ideas. Thanks.
Based on what I did in my rebuild, everything you have above plus low temperature thermostat, LNE's billet aluminum paddle for the chain tensioner (and replacement guides), ARP carrier through bolts and head stud kit, and coated main and rod bearings. I assume you are getting the liners plated with Nickel Silicon Carbide ("Nickies") to replace factory Lokasil. I went with the pressure-fed oil plain bearing "IMS Solution" to avoid using a ball or roller bearing altogether as my extravagant upgrade, but if I could have afforded more, I would have upgraded the rods, too. I did take the opportunity to replace my clutch since the engine and transmission were already apart and it only really cost me the price of the parts (original clutch was at about 50%, so it was kind of a "push").

JustinCase is offline  
Old 11-03-2018, 08:25 PM
  #14  
racer5j
Addict
Rennlist Member
Thread Starter
 
Join Date: Jun 2017
Location: Socal
Posts: 28
Default

Coopduc- The crank has been confirmed to be repairable. Initially, Vision didn't think the damage was too bad. Mainly, they were concerned with whether the crank was cracked. I am going with their "sport" crank which is knife edged so perhaps some of the damage gets machined off in the process. Also, according to some websites, it seems that even significant damage (excepts cracks) can be repaired without compromising strength. The repair process involves welding on material and then machining the excess off. I'll ask about the heat discoloration on the journals. I used to run 5W-40 with high zinc content but will switch to 10w-60 in the new motor.

Thanks everyone for the input. Much appreciated. I have a feeling that I won't be able to replace/upgrade all these items but will do my best to cover as many of them as possible. Please keep it coming.
racer5j is offline  
Old 11-04-2018, 03:12 PM
  #15  
street rod
User
 
street rod's Avatar
 
Join Date: Nov 2011
Posts: 1,495
Default

What is the rationale for switching to 10w-60?
street rod is offline  

Thread Tools
Search this Thread

Contact Us About Us Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: