Worn cams 2.0 16V TB

[evo1]

Hi Guy Croft, first of all happy 2008 and i hope you are well.

Last night, i took my valve cover off to check the tappet clearance and discovered some strange coloration on the cam lobes, both the inlet cam and exhaust cam. The cams are OE ones, factory fitted and have run about 60K now. I'm a bit worried because i know several cases of extremely rapid wearing cam lobes on 2.0 16V turbo engines, my friend had 2 delta's where the cam lobes were virtually gone in as fast as a month of driving.
this is my friends cam one month later after being fine and running the recommended tappet clearance:
http://img405.imageshack.us/img405/4007 ... amsas3.jpg

this is how my cams look at the moment:



my question is now, why would this be the case, what makes some cams wear so fast and why do i have these strange (heat?) marks on my cams. Are they on the way out?
Is it a matter of wrong oil or just the hardened layer that wears off?

Our theory for now is the wrong type of oil, all of the cars with worn cams were running on Castrol RS 10W60 which is supposed to be good oil but not really a 100% synthetic oil. My car had the Castrol once after running on 10W40 selenia but now runs on Motul 300V 15W50 since.


Your advise would really be appreciated, i'm really getting a bit worried to be honnest.

Thanks, Xavier.

[Guy Croft]

OK,

First off: OE Fiat cams are (- I guess, because I don't know the factory process route for certain -) chill-cast nodular (spheroidal grahite) high silicon/moly/nickel cast iron and the chill-cast method is excellent fro thru-hardness and durability. The molten iron is poured into steel molds that cool it fast, resulting in the formation of hard carbides. No coatings or heat treatment are needed, the material is naturally oil-retentive. Second: It's vital to use new OE spec shims when building up or reshimming, because the cams will wear quick if worn shims (where the oil retentive layer is worn off) are used.

Your wear pattern looks normal to me, what you are most likely seeing (and no, I know you can't see everything in a photo, even a good one like yours..) is the grain of the material nicely polished and running quite properly. If the lobe is smooth and not 'pointy' and the clearances are good they're probably fine.

In the case of your friend's cams what I see is wear all the way round the cam which is usually a sign of the running clearances being way too tight. The follower is in almost constant contact with the lobe from base circle to nose.

Apart from the above, there are as many other causes of cam wear as the day is long!
eg:
1. Contamination of the oil by gasoline (especially common on modified turbocharged engines where the fuelling is over-rich)
2. Low oil level
3. Low grade oil
4. Water in the oil
5. Defective cam material (never seen that from an OE source although years ago before everyone knew better, some aftermarket low-grade sand-cast cast iron cams used to be prone to it)
6. Wrong valve springs for that profile
7. Overheating oil
8. Dry start-up
9. Follower material or hardness/heat treatment wrong...

GC

[evo1]

Hi GC,

The best way to describe the striation marks that they resemble a lot to the layered damascus steel knive blades, that's why i was a bit worried that the marks were different worn off layers but yes the lobes are smooth and other than the marks i can't see/feel anything unusual.

The clearances are a bit on the high side, i need to reshim them soon but nothing dramatic, i have 0.50mm on the exhaust cam now, and 0.40mm on inlet.


About my friends car, it really remains a mistery. Both of his engines died that way, and there are a couple of more cases around.
He's a Fiat mechanic and set the clearances himself with new OE shims according to factory spec.


1) The car is running a stock chip and not overfueling and had an oil change.
2) Oil level was ok
3) the oil was Castrol RS 10W60
4) I doubt there is/was water in the oil but it's a possibility.
5) I've seen several cases of worn cams now, both inlet and or exhaust that lose one or more lobes, so can't really rule out the possibility but then again you have never had a case of a bad quality Fiat cam.
6) Valve springs are original OE
7) The oil was overheating in the end because of the worn lobes which probably made them wear even faster.
8) The head was transfered to another engine which had a snapped timing belt but the system was primed till there was sufficient oil pressure prior to firing up the engine and cams lubrificated
9) Possible

[Guy Croft]

Good reply, well done. Sometimes cam failure remains a 'mystery' because you need a metallurgical lab & consultant to diagnose some failures, an expensive and time-consumng thing I avoid where possible, but insofar as this is concerned;

The oil was overheating in the end because of the worn lobes which probably made them wear even faster


..yes, when the lobe profile (esp ramp or nose) is disrupted all cams wear pretty fast, esp cast iron ones.

GC