disco driver posted:

Hi furph,

Can you please elaborate on the reasons for this breakage so that others may benefit from your knowledge and perhaps be able to prevent the same occurring on their vehicles.

Thanks

Disco.

pepper2 posted:

click on members rig and profile anyone can do this and you will see the part

Redback posted:

There ya go, it is in his rig profile not on the post.



Baz.

Martyn (WA) posted:

Thanks Baz

Martyn (WA) posted:

Furph,
Mines one of the last 300TDIs, not a TD5. Tell me what the reasons are, for me it appeared random. Had all the others crack detected no issues found. Fourth valve in from the front of the engine is the one that broke if that tells you any more. Checked all the pushrods all straight, checked the valve clearances all good, couldn't check the broken one for obvious reasons. One thing I did find was slight pitting in the face of the rocker arm, nothing on any of the other seven.
Any help gratefully received. Thanks in anticipation.

furph posted:

Thanks Martyn.
If it had been td5, I could not help. However (opinion only, very difficult to prove conclusively).
1. There may have been a metallogenic flaw in the screw. In which case you were simply unlucky.
2. A small piece of metal/rock or other very hard material was injested by the engine, was between valve head and piston as piston went over tdc and result as occurred.
In the 300, when the timing belt breaks it bends pushrods, breaks rocker arms and adjusting screws and can lift the rocker arm shaft by stripping the threads on the holding down studs.
3. If the bearings wear/collapse in the timing belt idler wheels the timing gradually gets sufficiently out that the pistons
will "kiss" the valve heads at near tdc. Because this is a gradual deterioration the sound of the pistons touching the valves may not be noticed until too late.
The result from this is usually the rocker arm lifting as above.
Because the valve head is exactly parallel to the piston top, actual valve damage does not usually happen,
My feeling is that scenario 2 is the most likely. The fact that it was under the exhaust valve probably has no relevance.
Whilst you were replacing the screw, did you check the small
caps on top of the valve stems?
furph

Martyn (WA) posted:

Furph,
The parts arrived yesterday I haven't fitted them as yet and no I haven't checked the cap on top of the valve stem, thanks very much for reminding me, I was focused on the failure of the screw, from what I recall everything looked the same so at a first glance without specifically checking I would say that it's still there. I hope so that would be a bit ugly if it has fallen off.............
Again thanks for prompting me to check.