A "new one" with regard to inexplicab... Log Out | Topics | Search
Moderators | Register | Edit Profile

Australian RR Forums » Silver Shadow Series » A "new one" with regard to inexplicable misfires « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 2364
Registered: 6-2009
Posted on Tuesday, 25 July, 2017 - 10:34 am:   Edit PostDelete PostView Post/Check IP

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
Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2610
Registered: 4-2003
Posted on Tuesday, 25 July, 2017 - 06:51 pm:   Edit PostDelete PostView Post/Check IP

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.

*
Top of pagePrevious messageNext messageBottom of page Link to this message

Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1433
Registered: 9-2004
Posted on Tuesday, 25 July, 2017 - 08:11 pm:   Edit PostDelete PostView Post/Check IP

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.
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 2365
Registered: 6-2009
Posted on Tuesday, 25 July, 2017 - 11:53 pm:   Edit PostDelete PostView Post/Check IP

Photo (quite fuzzy):

broken spring

I didn't know that images didn't show up for non-member readers on rollsroyceforums.com.

Brian
Top of pagePrevious messageNext messageBottom of page Link to this message

Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1438
Registered: 9-2004
Posted on Wednesday, 26 July, 2017 - 08:43 am:   Edit PostDelete PostView Post/Check IP

This maybe a little better but not perfect

Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2612
Registered: 4-2003
Posted on Wednesday, 26 July, 2017 - 09:54 am:   Edit PostDelete PostView Post/Check IP

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.

*
Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2613
Registered: 4-2003
Posted on Wednesday, 26 July, 2017 - 10:12 am:   Edit PostDelete PostView Post/Check IP

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.

*
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 2366
Registered: 6-2009
Posted on Wednesday, 26 July, 2017 - 10:42 am:   Edit PostDelete PostView Post/Check IP

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
Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2615
Registered: 4-2003
Posted on Wednesday, 26 July, 2017 - 02:29 pm:   Edit PostDelete PostView Post/Check IP

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.
Top of pagePrevious messageNext messageBottom of page Link to this message

Brian Vogel
Grand Master
Username: guyslp

Post Number: 2367
Registered: 6-2009
Posted on Thursday, 27 July, 2017 - 01:14 am:   Edit PostDelete PostView Post/Check IP

David,

I've posted your plea directly "on the other side" in hopes it spurs Chris on to action!

Brian
Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2616
Registered: 4-2003
Posted on Thursday, 27 July, 2017 - 10:38 am:   Edit PostDelete PostView Post/Check IP

I am waiting with anticipation........
Top of pagePrevious messageNext messageBottom of page Link to this message

Alan Dibley
Frequent User
Username: alsdibley

Post Number: 74
Registered: 10-2009
Posted on Thursday, 27 July, 2017 - 05:57 pm:   Edit PostDelete PostView Post/Check IP

Why not mail the springs to David?

Alan D.
Top of pagePrevious messageNext messageBottom of page Link to this message

David Gore
Moderator
Username: david_gore

Post Number: 2617
Registered: 4-2003
Posted on Thursday, 27 July, 2017 - 07:34 pm:   Edit PostDelete PostView Post/Check IP

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.

Add Your Message Here
Post:
Bold text Italics Underline Create a hyperlink Insert a clipart image

Username: Posting Information:
This is a public posting area. Enter your username and password if you have an account. Otherwise, enter your full name as your username and leave the password blank. Your e-mail address is optional.
Please quote Chassis Numbers for all vehicles mentioned.
Password:
E-mail:
Options: Enable HTML code in message
Automatically activate URLs in message
Action: