[T2] re ceramic coatings

[Robert Mann]

	On the exterior of exhaust manifolds, pipes etc this has been 
commercial in NZ for a couple decades.
	On the inside of cylinders, I'd not heard of much ceramics. 
Pistons are coming along, I gather.  If the combustion chamber's 
several surfaces can be lined with ceramic, better specific power is 
expected.
	But the notion that intrigues me is ceramic added to valves. 
Exhaust valves are liable to wear, as are their seats, from the v 
high temperatures imposed on them by the exhaust gases pulsing past 
them.  They have been cooled in expensive engines this past 7 decades 
by a heat-pipe of sodium contained in the valve stem.  The idea is to 
conduct as much heat as possible away from the valve head & seat, 
thus tending to slow their wear.  That aim would appear to be opposed 
by slapping a relatively insulating layer of ceramic on the valve 
head.
	If someone is offering such aftermarket ceramics, ask to see 
the data compiled from failures so far.  Is the ceramic not falling 
off from time to time, in various sizes?  Are those fragments readily 
flushed out the exhaust valve, or do they sometimes cause damage? 
And anyhow, what is the plurry idea in the first place?

	I confess to the vice of theorising, with no facts  -  please 
supply the latter.



Robt Mann
Whangaparaoa, New Zealand
'73 VW 1600dp Devon camper
'53 Meteor V8
various Jawa-CZ and Jawa-NZ strokers

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