<VV> Valve Guides

[Tony Underwood]

At 06:52 hours 03/07/2006, Ron Guy wrote:
>Two questions.
>1. What exactly are the advantages to bronze valve guides?
>Heat? Lack of lubricant in that area?


Bronze is malleable and thus won't gall the valve stem if it's forced 
to run in situations where there's very little lube available or the 
lube is thinned severely such as when very hot.


>2. Are stem seals just for older worn engines or do builders
>use them on rebuilds?


Most engines when new used some sort of stem seal.   If the guides 
are in top notch shape, stem seals aren't needed unless the valve 
gear is swimming in oil.   If intake guides are worn, intake vacuum 
will suck oil down the valve stems and the engine will smoke, 
especially if allowed to idle a lot.

On Vair engines, if I have a head apart etc and if the guides are in 
decent shape upon reassembly, I do *Not* use stem seals at 
all.    I'll trade a puff of smoke on occasion for clean unscuffed 
valve stems.    Vair valve stems don't get that much oil in the first 
place, and since they're horizontally positioned instead 
of  vertically like in most other engines (which obviously would 
benefit more from stem seals since oil weeps down the stems into the 
guides) and could likely appreciate a little extra oil, especially 
since the heads are hot and the oil isn't doing its best work there 
in the first place.

...this only works if the guides are OK.   If you have worn intake 
guides and no stem seals, you can expect coking behind the valve heads.


>Seems they restrict any lubricant from the valve stem area.


Tight stem seals do restrict most oil... not sure I really like such 
seals (those Teflon pressed-on seals come to mind) since they allow 
almost nothing past them.  If I use seals, I'd rather do with the 
umbrella type floating seals (in a vertical configuration 
engine).    Again, I don't put stem seals back in Vair engines.   I'd 
rather put up with an occasional puff than deal with scuffed stems 
and rattling guides.

By the way...  worn valve guides do NOT help keep seats in place.


tony..