<VV> Plateau honing

[BobHelt at aol.com]

In a message dated 3/29/05 11:02:40 PM US Mountain Standard Time, 
hmlinc at sbcglobal.net writes:

> Hi Bob,  Can you splain it a bit?  And does it apply to Vair engines?
> 

Plateau Honing

Cylinders, after boring, must be honed to set the exact cylinder dimensions 
and roundness. In addition the wall roughness must be very closely controlled. 
The honing operation should make the walls relatively smooth for little wear 
but also rough for oil retention. Previous practice was to use fairly rough 
stones to leave a fairly rough rough wall surface...like 220 or 280 grit stones. 
This would leave the oil retention grooves and the rings were expected to 
smooth out the surface during the breakin period.

The problem was that the rings were used to wear in the cylinder surface. 
This was undesirable for several reasons. It took many miles to get the rings to 
seat. The engines didn't develop full power until the rings seated. The engine 
may use oil until the rings seat. The engine didn't meet emissions 
requirements until the rings seated (for example, pity the poor customer who has his 
engine rebuilt and shortly thereafter is required to pass his state's smog test!) 
Another, maybe worse, problem was that the rings were wearing in the cylinder 
surface and releasing "tons" of small metal particles into the oil which 
could cause much damage elsewhere before they were removed by the filter (if they 
are ever removed. That's another subject for discussion.).

So the industry got smart, finally, What was required were two separate 
honings. The first was a rough hone to establish the wall dimensions and oil 
retention grooving. The second honing operation was with very fine stones (or 
brushes) to remove just the smallest amount of material, but to smooth the cylinder 
walls. Just as the rings would do during breakin. This is called plateau 
honing since a microscopic cross-section view of the cyl wall would show jagged 
valleys but with the top peaks all smoothed off like a plateau. Sort of like 
taking a mountain range and cutting off all the peaks to some level. All the new 
cars use this plateau honing technique and a few engine rebuilders do too.

I hope that this helps.
Regards,
Bob Helt