Silver's cam

[dardal@xxxxxxxxxxxxxxx]

> Someone else can talk about why cams don't produce
> sharp metal fragments.
> 
> Kerryp
> 
Kerryp, the cam wear you are talking about is "normal" wear that happens over a 
relatively long period of time, right?  The wear particles are very small, and 
show up gradually enough such that the filter grabs them.  Also, cast iron (cam 
material) has graphite in it, so the particles are probably not as abrassive as 
say, sand.  Now, what happens as a cam brakes?  This failure is probaby fatigue 
related, so I am not sure if the brakeage has sharp edges that can readily 
scratch one another and create shavings. The back firing that Mike noticed 
however indicated that the broken part of the cam was possibly rotating after 
the fructure, possibly by the friction of the two separated surfaces 
(backfiring occurs due to totaly incorect timing in those cylinders).  However, 
cast iron is tribologically very compatible with cast iron, so the amount of 
shavings was probably limited, till the two surfaces wore in to each other.   
Or, the part that kept the two pieces together got real thin and twisted just 
before braking, messing up the valve timing on the other 4 cylinders.  In this 
case, there would be fewer of any particles.   

Now, can these shavings damage bearings?  The real big ones won't go through 
the screen as mentioned, but the smaller ones could reach the bearings through 
the by-pass (not all the oil goes through the filter from the oil pump, even 
though its called full flow filtration).  However, when they do reach the 
bearings, they will imbed them selves in the soft babbitt material right away.  
The crank is a much harger material to be scratched by cast iron savings 
though, so I see no catastrophic failures from this.  An oil pressure 
measurement can tell, but if the engine has to come off, these can be readily 
changed just in case.  As the engine keeps on turning, more and more oil 
eventually flows through the filter, so very quickly the shavings are not in 
circulation.  Its only the first few minutes-seconds (?) that potential damage 
can occur.   Can these shavings affect the rings and liners?  The real small 
ones going through the screen could, theoretically.  But, a compression test 
will tell.
D^2