Broken Inlet Valve Rockers
Here is a mystery I need help with.
My Dec 2007 159 JTDm 2.4 (done 35,000km's) has broken Inlet rockers on cylinders 1 and 4. I suspect bent valves as there is no compression on these cylinders. The cambelt and timing is fine so the mystery is how can this happen?
Whilst driving on a hilly and windy road and approaching yet another hill the engine seemed to loose power. No warning lights, no exhaust smoke, boost pressure seemed okay, temperature normal etc. As there was nothing telling me otherwise I suspected limp mode due to a failed sensor etc so drove on to my destination. Each new hill was a worry as I held up traffic barely able to maintain 90-100 kph.
Long story short the car would not restart so I had to transport it home to the local (main) Alfa dealer. They tried to start it and noticed a lazy cylinder. They did a compression test and found two! They have since removed the cam cover to find broken rockers on the inlet side cylinders 1 and 4. The exhaust side rockers are all fine. The Dealer is yet to establish a cause.
There is no debris, water, soot or anything in the cylinders they still look brand new.
My understanding is that if the cambelt was the cause then the exhaust side would be effected as well.
A mystery indeed - any ideas would be welcome