OVERKILL
$100 Site Donor 2021
Originally Posted By: RI_RS4
Jeez, OVERK1LL, that was a quick post I made, not a technical paper. It might be good for you to ask questions, rather than assume and accuse. For example, "RI_RS4, could you clarify what you mean by iron bearings?" That would lead to a reasonable discussion.
My choice of words with regards to the cam lobes were imprecise. However, as far as the cam chain is concerned, there are quite a few sleeve or roller bearings involved in any chain. The point, which often gets overlooked, is that high Iron in a UOA is indicative of the wear of an Iron load bearing component in the engine. For engines with Aluminum cylinder walls, the Iron cannot be coming from the cylinders, thus it must be coming from someplace else. If it were coming from mixed-material bearings, you would see elevations of multiple metals in a UOA. In the case of recent Audi Alusil cylinder walled engines, the wear seems to be primarily iron, and not overlay metals in a bearing, or hard aluminum alloys (used in some of the bearings.) This leaves a very few sources ... Cams, and chains. In this case cams are ruled out, because roller followers are used, and several of the lobes are available for inspection through the oil fill hole.
Another clue, there are sharp changes in average FE levels as fuel dilution rises, and as oil chemistry is changed. A good working theory for this suggests that the wear is occurring in the mixed lubrication regime, where anti-wear films are especially important. Fuel seems to wash ZDDP deposition films away from critical load bearing surfaces, or at the least retards formation of the films.
The timing chain fits right into the mixed lubrication regime, and caries high loads. It is the most likely source of the Iron in my engines.
Great explanation! That's what I was looking for. And makes sense now that you've explained the system. Thank you.
As I stated, even though chains have their own little wear surfaces, most don't refer to them as bearings, more as the chain as a whole (which you've now explained and it makes sense) which is where you lost me on your original statement. As, which I'm sure you realized from reading, I was thinking you were talking about crank surfaces or had used the wrong term.
We are clear now
-Chris
Jeez, OVERK1LL, that was a quick post I made, not a technical paper. It might be good for you to ask questions, rather than assume and accuse. For example, "RI_RS4, could you clarify what you mean by iron bearings?" That would lead to a reasonable discussion.
My choice of words with regards to the cam lobes were imprecise. However, as far as the cam chain is concerned, there are quite a few sleeve or roller bearings involved in any chain. The point, which often gets overlooked, is that high Iron in a UOA is indicative of the wear of an Iron load bearing component in the engine. For engines with Aluminum cylinder walls, the Iron cannot be coming from the cylinders, thus it must be coming from someplace else. If it were coming from mixed-material bearings, you would see elevations of multiple metals in a UOA. In the case of recent Audi Alusil cylinder walled engines, the wear seems to be primarily iron, and not overlay metals in a bearing, or hard aluminum alloys (used in some of the bearings.) This leaves a very few sources ... Cams, and chains. In this case cams are ruled out, because roller followers are used, and several of the lobes are available for inspection through the oil fill hole.
Another clue, there are sharp changes in average FE levels as fuel dilution rises, and as oil chemistry is changed. A good working theory for this suggests that the wear is occurring in the mixed lubrication regime, where anti-wear films are especially important. Fuel seems to wash ZDDP deposition films away from critical load bearing surfaces, or at the least retards formation of the films.
The timing chain fits right into the mixed lubrication regime, and caries high loads. It is the most likely source of the Iron in my engines.
Great explanation! That's what I was looking for. And makes sense now that you've explained the system. Thank you.
As I stated, even though chains have their own little wear surfaces, most don't refer to them as bearings, more as the chain as a whole (which you've now explained and it makes sense) which is where you lost me on your original statement. As, which I'm sure you realized from reading, I was thinking you were talking about crank surfaces or had used the wrong term.
We are clear now
-Chris