Pay very close attention to John Grady's recommendations and his analytics involving supposed need for engine rebuild based on the results of a compression test. He's RIGHT ON!!!
All too often the results a grossly flawed, not only because of errors in procedure, but also because of errors in knowledge of how to interpret the readings.
Important clues regarding condition of engine are numerous: rate of oil consumption, smoothness of engine at idle and especially loaded at slow rpm, noise from valves, noises from crankshaft bearings (rods and/or mains, oil leaks can be a clue, but not usually indicating mechanical trouble, difficulty in obtaining consistent/satisfactory ignition timing (suggests timing chain wear likely). Listen to the engine's exhaust-----all 8 cylinders should sound nearly the same. Leaky exhaust valve will likely make an audible WHOOSH sound each time that cylinder has compression/combustion, intake valve leakage is uncommon and not easy to detect by sound. Loose pistons (worn cylinders) might give an audible light thump as slow idle when cold, but likely will go away as warm-up occurs. Aircraft engines usually have quite audible piston noise for a few minutes after start-up (air cooled engines generally have very loose fit pistons compared with liquid cooled engines.
Please note: message attached
From: John Grady <
jkg@xxxxxxxxxxxxxxxxx>
To: Nick Taylor <
nicksgaragesd@xxxxxxxxx>
Cc: Matt Allyn <
allynentertainment@xxxxxxxxx>, Chrysler 300 Club International <
chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} Compression Test - 413
Date: Sun, 4 Sep 2022 09:20:42 -0400
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Subject: Re: {Chrysler 300} Compression Test - 413
Date: September 4, 2022 at 7:20:42 AM MDT
That’s perfect . Don’t rebuild your motor for nothing !
So many in club do , can cause way more trouble than help — so dependent on skill of machinist . One of 100 ‘s of possible errors, you own it . Been there .
If you really want an accurate test , drive at least 30-40 miles and do it . But why if running ok?
It is normal for variations to happen in ring seal etc at slow crank . Unless using a lot of oil or there is antifreeze in the oil , or something broken leave it alone .
A bad valve would drop one cylinder a lot .a bad cylinder would repetitively foul a plug and burn oil .
Remember Jerry Kocur ? 330 k(?) on first 413 , another 300 k on second build .
392 were known to hit 300 . Mileage is the parameter if no oil burn .Even then a timing chain ( check) and reseal leaks would come first
I have had two Jeep 4.0 go over 300 , one I have now at 280 k uses no oil ( mobil one) between 10 k mile changes . I read research by SAE on oil durability , they used 350 chev . They kept running it ( various kinds) and doing careful lab tests every 1 k or so — NO degradation of Mobil one at 17000 miles . Frequent oil changes sell oil and make profitable work . And at 17 k it was a slow decrease in additives. The AMC 4.0 series are great motors like the slant six , although chrysler messed them up in 2000-2002 with a bad “new design” head castings ( crack) and cheap pistons (skirts break off)
Get involved with mechanics , what needs rebuilding is your wallet .
Mho John
Sent from my iPhone
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