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Re: Valve seats

To: Datsun Roadster List <datsun-roadsters@autox.team.net>
Subject: Re: Valve seats
From: Marc Sayer <marcsayer@home.com>
Date: Tue, 14 Aug 2001 20:15:59 -0700
As usual I'm going to chime in here with an opinion that is slightly off center
from most folks. I agree completely about using hardened seats for the exhausts.
But most places will also try to sell you on a set of steel, iron, or some other
harder material, for the intake seats as well. This is where I diverge from the
"common sense" approach most shops have. This hard intake seats idea is BS.
Datsun is one of the few companies to use high-quality bronze intake seats. If
you do some checking, you'll find out they are in very good company with this
concept. Most folks will eventually find that their bronze seats are worn out
(usually pounded out is a better description). In fact in 510s this a very
common occurrence now. The symptoms are a sudden loss is power and smoothness
coinciding with a marked valve noise. This situation will crop up fairly
quickly, last a while and then suddenly disappear. It is the symptom of a
pounded out intake seat. But, just because the seats all seem to pound out
eventually is not a reason to condemn them. *ALL* seats will wear or otherwise
lose serviceability over time. But a hard seat will begin to leak slightly very
quickly, and the leakage will just get worse and worse. OTOH a "soft" bronze
seat will seal well for 100k to 200k miles! Yes, when it goes, it has to be
replaced rather than just resurfaced, but think about this for a second.
Wouldn't you rather have a seat that seals 100% for 100k, than one that lasts
for 300K+ but needs resurfacing every 20K-30K and does a relatively poor job of
sealing after only 10k or so? Besides, as Les can attest, even the so called
"soft" bronze seats usually outlast the valves themselves. Sadly, common wisdom
has decreed that bronze seats are bad and so they are nearly impossible to find
now, but the fact is they are a superior material spec for an intake seat and
worth the extra cost of finding a source. Last time I checked, a company called
PEP did supply bronze seat blanks, and most engine builders know of them or can
find them. So I recommend good hard seats (stellite is a good material
generally) for the exhaust but those so-called "soft" bronze seats for the
intakes. And yes, bronze seats are safe to run with unleaded gas.


Thomas Walter wrote:
> 
> Soft bonze was originally used.
> 
> If you are having the head reworked, cheap insurance
> to have the exhaust valve seats replaced with Stellite,
> or another modern material (Stellite has been around
> since the 1930's!)
> 
> Cheers,
> 
> Tom Walter
> Austin, TX
> 
> Roadster wrote:
> 
> > Howdy All!
> >
> > Are the original valve seats in a U20 hardened?  Or, do they need to be
> > replaced to run unleaded gas?
> >
> > --
> > Best regards,
> >
> > Fred Schroeder
> > '70 2000
> > SRL311-13359

-- 
Marc Sayer
82 280ZXT
71 510 2.5 Trans Am vintage racer

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