<VV> Re : dis-similar metals

[djtcz at comcast.net]

Avoiding  dissimilar metals is a good thing.  The piston/cylinder example stumbles only because the various cast irons with flakes or nuggets of carbon make them stand alone in terms of good wear resistance.

On water cooled engines Smokey Yunick was fond of iron guides, honed, not reamed to size.

Some (no lead) bronzes need copious lube to keep from seizing.  Some leaded bronzes survive skimpy lube conditions pretty well.  I've had a few problems with leaded bronze in rubbing situations when the relatively high thermal expansion made confined rings expand inward and grip a spinning shaft so tight they were welded (brazed?) together.  

An old air cooled Harley engine destroyed several name brand valve guides with spiral bronze inserts.  Iron guides ran just fine.  Looking back I suspect the expansion caused the problem.

I think valve/guide lubrication is another place where Mobil 1 is really needed.
--
Dan Timberlake

-------------- Original message -------------- 
In a message dated 3/8/2006 2:24:22 AM US Mountain Standard Time,  
lechevrier at earthlink.net writes:

The  resistance to seizing is due to dis-similar metals -- they don't use 
cast  iron pistons in cast iron bores, do they?