| Author | Message | ||
     Brian Vogel Grand Master Username: guyslp Post Number: 2364 Registered: 6-2009 |
There's no point in retyping, but I wanted to add this post here because it's the first time I've heard of a broken rocker arm tensioning spring being the culprit. See this thread on rollsroyceforums.com: http://www.rollsroyceforums.com/forums/26-sy-series-i-ii-1965-1980/19793-misfire-number-5-cylinder.html | ||
| David Gore Moderator Username: david_gore Post Number: 2610 Registered: 4-2003 |
Brian, Thanks for the link - one of those rare and hard-to-find failures........ Unfortunately, I could not view the photo of the spring not being a forum member. IMHO the probable cause of the failure would be a fatigue crack from mechanical damage to the surface or an internal non-metallic inclusion acting as a stress concentrator and the cyclic loads applied to the spring in use did the rest. * | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1433 Registered: 9-2004 |
Have seen this several times when the engine has been not used for a long period in damp environment. When a valve becomes seized in the guide whether in or ex. If the push rod does not bend then the spring lets the rocker do the rest. Have seen it once where the push rod was not located correctly! As David says stress. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 2365 Registered: 6-2009 |
Photo (quite fuzzy):  I didn't know that images didn't show up for non-member readers on rollsroyceforums.com. Brian | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 1438 Registered: 9-2004 |
This maybe a little better but not perfect  | ||
| David Gore Moderator Username: david_gore Post Number: 2612 Registered: 4-2003 |
Pity they are not high resolution and in focus - would really liked to see the fracture surface as this would most likely indicate where the breakage originated. One significant feature is the failure is close to equidistant from both ends - this raises the question whether it was due to an inherent defect or to localised over-stressing from unequal loads from each end due to unequal compression associated with lateral movement of the rocker arm on the shaft. I am always fascinated by material failures and the challenge of finding the reason[s] - makes life interesting and rewarding if the knowledge gained helps prevent future failures. * | ||
| David Gore Moderator Username: david_gore Post Number: 2613 Registered: 4-2003 |
Patrick, Your failures were probably related to fatigue cracking initiated by pitting corrosion from acidic moisture condensation during the extended periods of non-use. Heat-treated high strength low alloy ferrous materials are particularly susceptible to this problem. This is why desiccants are placed in shipping containers/storage shelters for expensive and/or classic cars which will remain immobile for extended periods of time or will be located in known contaminated environments. Moisture is a major concern due to its frequent association with damage to many materials if the conditions for corrosion/degradation exist. * | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 2366 Registered: 6-2009 |
David, I have asked Chris if he still has those springs, and particularly the one that broke, and if he could take a close-up, high resolution photo of the surfaces where the break occurred. If it is forthcoming I will make sure it gets posted here (and probably e-mailed, since I have to reduce resolution to post it here). Brian | ||
| David Gore Moderator Username: david_gore Post Number: 2615 Registered: 4-2003 |
Brian, Please, please let the springs be found and a camera with good depth of field capability be available..... Please send me the unprocessed images as I will Photoshop them to illustrate what needs to be shown to discuss the mode of failure. I can receive images up to 25Mb by email or download larger files from a Google Drive or similar storage service if an access link can be emailed privately to me. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 2367 Registered: 6-2009 |
David, I've posted your plea directly "on the other side" in hopes it spurs Chris on to action! Brian | ||
| David Gore Moderator Username: david_gore Post Number: 2616 Registered: 4-2003 |
I am waiting with anticipation........ | ||
| Alan Dibley Frequent User Username: alsdibley Post Number: 74 Registered: 10-2009 |
Why not mail the springs to David? Alan D. | ||
| David Gore Moderator Username: david_gore Post Number: 2617 Registered: 4-2003 |
Alan, I no longer have access to a fully equipped metallurgical laboratory for an in-depth investigation - a set of detailed photographs and past personal experience should allow me to determine the probable contributing factors to the failure. |
