Hi guys, just thought I'd add my bit.
Lead is NOT used as a lubricant for exhaust valves - It is strictly there
to as an octane booster. Lead suppresses the the tendency for gasoline to
detonate in higher compression engines (i.e. anti-knock). I don't know
where the rumour started that it was added to lubricate valves.
The only time I had problems with exhaust valves sticking was on an older
C-85 after I started burning mogas. Having said that I switched back to
Avgas and it stuck on me again.
Interesting note that 80/87 has 0.5 ppm lead and 100LL has 2ppm.
You may also want to check that the exhaust valve guides were changed to a
Ni-Resist steel and are njot aluminum bronze.
Note the following excerpt from Avweb. it is for the O-470, but I suspect
the same guides are used on smaller engines. Hope this helps...
Older O-470 cylinders were equipped with aluminum-bronze intake and
exhaust valve guides. And while the intake guide performed well and is, in
fact, still used today, the exhaust guide didn't hold up to the heat
created in the exhaust port. When 100LL fuel was used, the exhaust guides
failed even faster due to the prolonged burning process of higher octane
fuels. The exhaust valve guide was then changed to a Ni-Resist steel guide
which is better suited to the higher temperatures encountered. After some
years of success with the Nitralloy guide in the 520 series engines, the
0-470 was given the option of using the same top end parts as the 520. As
a result, the use of the pre-sized Nitralloy guide, pre-sized
aluminum-bronze intake guide (with seal) and improved four-ring pistons
became the standard at engine overhaul.
In recent years, the Nitralloy guide has been replaced with a new version
of the old Ni-Resist guide due to some concerns about accelerated stem
wear and isolated cases of valve sticking due to corrosion in the guides
of inactive engines. TCM's SB #M90-13 talks about the corrosive
environment in which exhaust valves must operate and states that
accelerated stem wear is caused by these elements. More to the point would
be the elevated temperature the working Nitralloy guide creates by virtue
of the nitrided surface on the guide's inside diameter. This higher
temperature tends to flash (carbonize) the lubricating oil - especially at
shutdown - and can cause immediate and permanent valve seizure in the
guide.
Current issues of TCM's SB #M85-8 and #M85-19 define the options for
superseded piston assemblies and valve guide combinations. It's important
to be aware that older, outdated parts can still be purchased but they are
probably not the best option given the expectations put on our engines
today.
Tom Tonner
Date: Fri, 15 Oct 2010 20:27:48 -0700
From:
im_planecrazy@yahoo.com
Subject: Re: [rebel-builders] O-320 Exhaust valve guide wear
To:
rebel-builders@dcsol.com
Thanks Wayne! I do remember that now. I knew I was forgetting something.
Keith
--- On Fri, 10/15/10, Wayne G. O'Shea <
oifa@irishfield.on.ca> wrote:
From: Wayne G. O'Shea <
oifa@irishfield.on.ca>
Subject: Re: [rebel-builders] O-320 Exhaust valve guide wear
To:
rebel-builders@dcsol.com
Date: Friday, October 15, 2010, 10:23 PM
Yes lead is a lubricant to protect the valve seats... but it's content is
way too high in 100LL as Ken has pointed out and it becomes a valve
"sticking" and wearing problem.
----- Original Message -----
From: "Keith Leitch" <
im_planecrazy@yahoo.com>
To: <
rebel-builders@dcsol.com>
Sent: Friday, October 15, 2010 11:18 PM
Subject: Re: [rebel-builders] O-320 Exhaust valve guide wear
Have I been misunderstanding this all these years? I thought lead was
also
used in these old engines for a "lubricant" per se? Especially for the
valve guides. Besides an octane booster anti-detonation additive.Have
to
excuse me I may not be thinking correctly.
Keith
--- On Fri, 10/15/10, Ken <
klehman@albedo.net> wrote:
From: Ken <
klehman@albedo.net>
Subject: Re: [rebel-builders] O-320 Exhaust valve guide wear
To:
rebel-builders@dcsol.com
Date: Friday, October 15, 2010, 9:44 PM
That is one of the top couple of reasons to avoid avgas as much as
possible. Lead is very abrasive on valve guides. 100LL has about 5
times
the lead that 80/87 had and about 15 times the lead that leaded mogas
used to have. It is only 'low' compared to 100/130 and 115/145.
Ken
Wayne G. O'Shea wrote:
-----------------------------------------------------------------
List archives located at:
https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe:
rebel-builders-unsubscribe@dcsol.com
List administrator:
mike.davis@dcsol.com
-----------------------------------------------------------------
-----------------------------------------------------------------
List archives located at:
https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe:
rebel-builders-unsubscribe@dcsol.com
List administrator:
mike.davis@dcsol.com
-----------------------------------------------------------------
-----------------------------------------------------------------
List archives located at:
https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe:
rebel-builders-unsubscribe@dcsol.com
List administrator:
mike.davis@dcsol.com
-----------------------------------------------------------------
-----------------------------------------------------------------
List archives located at:
https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe:
rebel-builders-unsubscribe@dcsol.com
List administrator:
mike.davis@dcsol.com
-----------------------------------------------------------------
-----------------------------------------------------------------
List archives located at:
https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe:
rebel-builders-unsubscribe@dcsol.com
List administrator:
mike.davis@dcsol.com
-----------------------------------------------------------------
