Re: IML: Old Engines, Oil Pressure, Compression, Fun

[randalpark@xxxxxxx]

This leads to a sweeping statement and some general commentary.

I find that the two most basic & revealing tests to determine wear on 
an old engine are measuring the actual oil pressure, and checking 
compression. Noise and smoke are pretty obvious, but they can be 
"covered up". Sometimes they just don't occur in an engine needing 
major work. Checking these two things on a seemingly good, warmed up 
engine is the best way to tell if it's time for an overhaul.

Worn rod bearings usually are the first major cause of low oil pressure 
in a prematurely worn engine. Often this is due to incorrect fuel 
and/or tuning which leads to pre-ignition, and extra pounding on the 
crank. I have seen this happen in engines with less than 25,000 miles 
on them. Premature top end engine failure is usually next, since most 
of the oil flows the path of least resistance, it will go through the 
damaged bearings, leaving the tight parts dry. All surfaces gradually 
wear, so in high mileage engines, anything goes, including worn cam 
shaft bearings, main bearings, and even the oil pump itself. Frequent 
oil changes/pcv system checks are a critical part of good maintenance 
in order to maximize engine life. This keeps oil passages clean, 
prevents clogs from sludge, and the subsequent lack of lubrication to 
specific and otherwise long lasting parts.

Low compression can be caused by many different problems, but uniformly 
low compression in a worn engine is normally caused by worn out rings. 
Premature ring failure is often due to overheating. Poor tuning, 
improper torquing of bolts, and lack of maintenance, such as leaky 
vacuum lines, can lead to common non-uniform compression problems such 
as those resulting from burned valves, cracked pistons, warped heads, 
and blown head gaskets.

All engines wear out and eventually need to be overhauled. I think that 
there is value and merit in discussions about the causes and 
differences between normal wear and premature wear. I also think it is 
useful to distinguish between premature failure due to poor maintenance 
practices vs. sub-standard design on the part of the manufacturer. 
Luckily, in most cases, our cars well very well designed to begin with. 
Imperials from the 1950's and '60s are among the very best American 
cars ever put on the road.

One of the most rewarding aspects of this hobby for me is maximizing 
engine life. I have a great deal of respect for an old sweet running 
engine that has been well maintained, with exceptionally high miles. I 
despise waste. A low mileage engine destroyed by lack of maintenance 
and incompetent repairs is one form of it that I find intolerable.

Paul W.
-----Original Message-----
From: mikanlin62@xxxxxxxxxxx
To: mailing-list@xxxxxxxxxxxxxxxx
Sent: Fri, 30 Mar 2007 5:08 PM
Subject: IML: Re : pressure vs volume

This comes up all the time in various forms. Follow along....your oil 
pump is a positive displacement pump meaning it can move a set amount 
of oil each time it rotates, whether it is a spur gear style or a rotor 
style like Chrysler uses. So for EXAMPLE, if it can displace an ounce 
of oil for each revolution of the pump it will move 1000 ounces at 1000 
engine rpm. Now, if the various clearances in the engine bearings, 
crankshaft, connecting rods, lifters, pushrods, let less oil past them 
than the pump can move you will get pressure.

If this doesnt seem clear, remember that we are talking FLOW here, and 
resistance to FLOW causes PRESSURE. Dont think so..go turn on the 
garden hose and let it run, youll see flow. Then put your finger over 
the end of the hose and close it off about half way, you reduce the 
flow but increase the pressure. Its not quite the same as the kind of 
flow vs pressure you see in hydraulics where there isnt any leakage 
desired because in an engine its a given that you will have oil leaking 
past the various clearances in the engine, thats how it is designed. 
The oil cools as well as lubricates.

This is also why as an engine wears out the pressure will drop, because 
the clearances get larger as the bearings and other surfaces wear. 
Since the pump can still only move a set amount of oil, whatever that 
amount is, the resistance to the flow of the oil lessens and the 
pressure drops accordingly.

Use a high volume pump as opposed to a high pressure pump. The only 
difference between standard and high pressure is the relief spring and 
you dont need higher pressure anyway. A high volume pump will give you 
more than enough oil flow to create good oil pressure.

Mikey
62 Crown Coupe

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