Does anybody have a copy of the Caterpillar Failure Anaysis information they can post on this thread showing the reasons for exhaust valve face cracking? I have removed the cylinder head off a 120hp four cylinder diesel bulldozer engine due to low compression on #1 cylinder and found that the exhaust valves on all cylinders have cracks starting on the flame face of the valve. On #1 cylinder the crack has gone through to the exhaust port, I have not removed the valve from the head as yet, but the crack does not look as though it has reached the seating face but has started towards the centre of the valve and started working outwords.

All inlet valves look OK, engine starts and runs well with no white smoke or excessive black smoke. Any sugestions would be appreciated.

regards
Rob

I don't have the Cat failure analysis material but if you research the keyword "lamellar structure" it will explain how the metallurgy (austenitic matrix) structure deteriorates resulting in this type of failure.

What engine is involved? Couldn't find a 120hp 4-banger:)

Thanks Old Magnet,

I will do a search on your information. The engine is in an Komatsu D53 that a freind has asked me to help him with, not Cat I know, but this site is great for people willing to swap technical information.

Rob

RobertS,
Sounds like typical heat damage to a valve. Exhaust valve will show damage much sooner as the hot combustion gasses go over the exhaust valve whereas much cooler intake air passes over the intake. Several things can cause this to happen. Valve adjustment would be the first thing I would look at. Typically as the vlavle train wears, the valve head begins to wear further and further into the valve seat. This will reduce the amount of valve clearance that you will have and thus will effect the amount of time the the valve has in contact with the seat. This "time of contact" is when the primary cooling of the valve head and face happens, therefore making valve clearance very critical. If the clearance gets to the point where the valve is no longer making full contact with the seat the combustion gasses can force themselves past the face and seat and act like a mini torch and begin to erode the seat and valve face. The valve head over heats and the cracking begins. Look very closely at all of the exhaust valves and if it is not too late check the valve clearances before you take the top end apart.

"WyoCat" wrote:

RobertS,
Sounds like typical heat damage to a valve. Exhaust valve will show damage much sooner as the hot combustion gasses go over the exhaust valve whereas much cooler intake air passes over the intake. Several things can cause this to happen. Valve adjustment would be the first thing I would look at. Typically as the vlavle train wears, the valve head begins to wear further and further into the valve seat. This will reduce the amount of valve clearance that you will have and thus will effect the amount of time the the valve has in contact with the seat. This "time of contact" is when the primary cooling of the valve head and face happens, therefore making valve clearance very critical. If the clearance gets to the point where the valve is no longer making full contact with the seat the combustion gasses can force themselves past the face and seat and act like a mini torch and begin to erode the seat and valve face. The valve head over heats and the cracking begins. Look very closely at all of the exhaust valves and if it is not too late check the valve clearances before you take the top end apart.

I have also seen this condition on older Jhon Deere tractors if there is a build up of carbon not allowing the valve to seat all the way and thus not cooling properly

D2Darwin, Thats a good point you bring up. This would also be detected by checking the valve clearance prior to tear down. The big pictures that you need to find out if this is a situation going on with one cylinder or is it about to happen all over, etc.

As mentioned in the original post all the exhaust valves have cracks with one being worse than the rest. Sounds more like a metallurgical problem to me and is not unknown for certain valves that were prone to failure. I won't go on about Asian metals:rolleyes:

It would be interesting to know how many hours are on the machine and when its last tune up was. Since it is a Komatsu, there is a real good chance that it has a Cummins in it. Cummins are very picky when it comes to tune ups.
OM I would agree with metalurgy issues if the engine has been rebuilt as it is too easay for someone to put in cheap stuff from third world countries. If these are OEM components, I would have a real hard time believing metalurgy issues.

Here is a good summary on valve woes....
Note! Studies have shown up to 20% of valve failures are due to internal defects of the valves themselves.

www.aa1car.com/library/ar1192.htm

Thanks for all the replies,

We did check for clearance on the exhaust valve in question before removing the head, it wasn't measured but there was good clearance, not to tight or loose. The valves look to be OEM as you can just make out the Komatsu emblem in the centre, so this also rules out it being a Cummins. The engine is a genuine Komatsu, model # 4D130-1. Not sure of smu at last tune up, but it was on the list of tasks to do before we pulled the head off.

I tend to agree with Old Magnet that it is an issue with the valves as all the cylinders and exhaust ports relitavly clean with minimal buildup of carbon.. We will send the injectors to a shop and have them checked, but I don't think we will find a problem with them.

regards
Rob