Valve Bridges Failure Analysis

Did you know that when the valves fail on your diesel engine, it could be due to a failure in a specific area of the valve? Different types of failure cause damage in different areas of the valve, so identifying where the failure occurred can help you diagnose exactly what's  going on in your engine.

We're taking you through what happens to cause a failure in your valve bridges. Take a look at the images below to see if this is what's happening to you.


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Valve failure caused by turned valve bridge

Have you noticed that the valve head came off, damaging the cylinder kit and head? Below we go through how this can happen. 
Maybe something else is going on with your cylinder head? Read our post to find out when you need to replace your cylinder head

The first picture shows the valve head. The valve broke in the strongest part of the valve and not at the parting line between the valve head and stem. Breaks in this part of the valve occur when the valve is hit and the failure is caused by impact loading.


valve bridges failure analysis broken valve head | Highway & Heavy Parts
The next few pictures show a damaged valve bridge.


Damaged valve bridge | Highway & Heavy Parts


On the inboard side of valve bridge, note the limited contact area as indicated by the yellow arrow and edge damage pointed out by the blue arrow. The edge damage was caused when the bridge turned and the valve was in running contact with the outside of the bridge.


valve bridge damage indication | Highway & Heavy Parts


The next picture shows the out board side of the bridge. Note the witness marks, pointed out by the green arrows. These show running contact wear on the edge of normal contact area and on the outside edge of the bridge.


valve bridges witness marks | Highway & Heavy Parts

Conclusion: The most likely cause for the valve failure was found to be impact loading caused when the valve was momentarily locked in the open position by the turned valve bridge, allowing the piston to strike the valve, breaking it off from the stem.

Need more ideas of what might be going wrong with your valves? Check out our valves failure analysis


If you have a problem with your diesel engine, Highway & Heavy Parts can help you get the parts you need! We have ASE Certified Technicians on staff ready to help you out. Call them at 844-304-7688, or request a quote online!

Originally Posted November 18, 2015; Edited March 13, 2020