Re: IML: Unleaded gas effects

[RandalPark@xxxxxxx]

I can't say too much about all the rest of this, but one thing I know for sure is, when my parents 1968 Imperial LeBaron was brand new, it got 15 - 17 mpg on high speed runs (on cruise, A/C off) frequently. I realize that Dick was running with the A/C on, so maybe that was enough to make the difference.

On an intuitive note, even though the "lack of uniformity" regarding wear on the valve seats would suggest a problem, I have never heard of a case where all 16 valves failed at the same time. In cases of valve recession, I have especially noticed one or two valves in a given engine being much worse that the rest, although damage is generally present for all. It seems that this is due to normal differences, how ever slight, in fuel delivery and other heat issues (such as coolant passages) between the different cylinders.

I believe that most engines have a predictable pattern of wear that varies from cylinder to cylinder. This is usually based on these and other factors, not necessarily relating to a lack of precision that the time of manufacture or reconditioning.

Paul W.

Paul W.

In an email dated Thu, 17 11 2005 7:30:04 am GMT, "Brent Covey" <brentcovey@xxxxxxxxxxx> writes:

>I think maybe its time for some reflection-
>
>If some valves are receding and others arent, whats different about the
>situation? They all ran the same RPM on the same fuel at pretty much the
>same temperature, so what is different enough that some failed and others
>didnt?
>
>The weakness of original carb jetting and the common need to slightly retard
>ignition settings from the original spec to prevent ping both increase
>exhaust valve temperatures enough to impact longevity, and might bear a
>little extra attention- the standard rule of thumb is re-jet any 'smog'
>carburetor about 3-5 thou richer than 'stock' spec. on the primary circuit
>to restore the original thermal energy of the non oxygenated, high Btu fuels
>that were availible prior to the late 1970's. Current fuels are quite a bit
>weaker than 1960's blends many places, as much as ~10% or so. That you're
>getting 17 mpg at 75+ mph suggests its running pretty darn lean indeed. That
>will make a blowtorch out of any valve face/seat flaws in a hurry.
>
>The fact that valve work was performed 16,000 miles prior is a prime
>suspect- the removal of seat material may have allowed some pitting in the
>seats to surface which will adversely effect some valves and not others.
>Depending on the workmanship and techniques used, the seats might have been
>poorly matched to the valve faces or may have been ground out of round from
>indexing the seat cutter to a slightly worn valve guide- theres a ton of
>variables when you service heads that are not much of a factor in factory
>assembled heads. Sometimes the valves dont have enough margin to cover the
>seat face adequately to protect it from the blast of combustion. Even weak
>springs might cause pounding damage from valve lofting at speeds not much
>over 3000 rpm if the engine is operated for extended periods at highish
>temperatures, or perhaps the valves are not rotating adequately from the
>weak springs . A used engine with even modest oil consuption (say a quart in
>1200 miles or so) blows enough oil thru the exhaust valve to provide many
>times the seat protection any amount of lead ever could have provided.
>
>I would not implicate the unleaded fuels in the seat damage. There is likely
>a combination of causes for the damage where it has occurred, and they
>probably can be corrected pretty easily. Hardened inserts are a pretty good
>solution however there are other risks related to them, such as cracking the
>heads or hitting the water jackets by using too deep a seat, or having them
>drop out of the head entirely from inadequate tension. Charging up the
>mountain one side getting everything hot and coasting down the other with
>closed throttle cools the seat faster than the head and can occasionally let
>an insert drop. After recession has already occurred you're kinda stuck with
>inserts if you plan to retain the heads of course.
>
>I certainly do not mean to criticise your workmanship but the head service
>likely is where the problem originates and the operation of the car at
>elevated speeds and temperatures just aggravated a flawed situation. I
>belive your original point of view regarding the lack of neccessity for
>leaded fuels is correct and feel you'll likely discover other reasons for
>the seat recession if you inspect the heads and engine calibration much more
>closely. I dont think leaded gas would have saved the day for you, Dick-
>
>Very sorry to hear theres been troubles whatever the cause,
>Brent Covey
>Vancouver BC
>
>
>----------------- ?http://www.imperialclub.com ?-----------------
>This message was sent to you by the Imperial Mailing List. Please 
>reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be 
>shared with everyone. Private messages (and attachments) for the
>Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx
>To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm
>
>


-----------------  http://www.imperialclub.com  -----------------
This message was sent to you by the Imperial Mailing List. Please 
reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be 
shared with everyone. Private messages (and attachments) for the
Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx
To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm