Piston Slap Diagnosis
#3
02-19-2011, 09:15 PM
The site formating is off. Maybe something on the server. Anyways I am posting this good info in here in case someone needs it or the site drops.
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There is a real nice yet little known test for piston slap I'll pass along. Some test results can be mixed or ambiguous but this one is 100% and I've never seen it wrong after using it for the last 10 years.
When the engine is cold, the aluminum piston is small in comparison to it's iron cylinder. Therefore the rather hollow slapping noise will be loudest first thing in the morning. After the engine warms up, the aluminum piston heats up faster than it's iron cylinder, cutting down on the excessive clearance between the piston and cylinder wall.
So, the test is this:
First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen.
If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back like a Marine Corps marching band coming toward you in the parade.
Valve train noises generally are loudest up to 1500 rpms. Lifters are also misdiagnosed commonly as the source of many noises when in reality they are quite trouble free, sorta. Dirt contamination on a sludged engine is the number one cause of true lifter noises, low oil pressure is number two, . Whatever you do, don't put engine flush in a sludged engine! We call it "Instant rod knock" because of the way it overloads the oil filter to the point of opening the filter bypass valve, flooding and destroying the engine bearings with mud. The only safe way to clean a sludged engine is to accelerate the oil changes and let the detergent in the oil do the cleaning at a controlled rate. Like every 500 miles
By the way, if you have low oil pressure, don't bother putzing around with the valve train because the damage you find will be the result of low oil pressure and will return after you spend a bunch of money on valve train parts.
Over nineteen engines out of twenty that we tear down with low oil pressure do NOT have bad oil pumps but have worn out bearings and journals so quit with the wishful thinking about just putting a pump in it.
Think about it, usually, an oil pump is two dumb ol' iron gears spinning around immersed completely in oil. EVERYTHING else in the engine has a tougher time of it than the oil pump.
Worn camshafts, low oil pressure, worn
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Old Wives Tale number 53.
The engine starts to use oil so a valve job is performed to correct the problem.
Immediately afterward the engine starts knocking or ticking.
The misdiagnosis is that the valve job gave the engine too much power making the weak bottom end fail.
What really happens is that mechanics all around the world burp the heads and timing covers off without draining the coolant from the engine first. The coolant spills into the bottom end of the engine. Even one oil change may not get all of the spilled glycol antifreeze out.
When you mix the smallest amount of antifreeze and water with motor oil you end up with a low grade acid that attacks the bearings. When you autopsy the engine you will find that the bearings are darkened and with time the bearing surface becomes rough.
That's why it developed a bearing knock immediately after the heads were done.
Carelessness or ignorance.
The right way is to open the drains or knock a freeze plug out.
Vee engines have two separate water jackets on each side so don't for get that you have two drains, one each for the right and left.
-------
---------------------------------------
There is a real nice yet little known test for piston slap I'll pass along. Some test results can be mixed or ambiguous but this one is 100% and I've never seen it wrong after using it for the last 10 years.
When the engine is cold, the aluminum piston is small in comparison to it's iron cylinder. Therefore the rather hollow slapping noise will be loudest first thing in the morning. After the engine warms up, the aluminum piston heats up faster than it's iron cylinder, cutting down on the excessive clearance between the piston and cylinder wall.
So, the test is this:
First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen.
If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back like a Marine Corps marching band coming toward you in the parade.
Valve train noises generally are loudest up to 1500 rpms. Lifters are also misdiagnosed commonly as the source of many noises when in reality they are quite trouble free, sorta. Dirt contamination on a sludged engine is the number one cause of true lifter noises, low oil pressure is number two, . Whatever you do, don't put engine flush in a sludged engine! We call it "Instant rod knock" because of the way it overloads the oil filter to the point of opening the filter bypass valve, flooding and destroying the engine bearings with mud. The only safe way to clean a sludged engine is to accelerate the oil changes and let the detergent in the oil do the cleaning at a controlled rate. Like every 500 miles
By the way, if you have low oil pressure, don't bother putzing around with the valve train because the damage you find will be the result of low oil pressure and will return after you spend a bunch of money on valve train parts.
Over nineteen engines out of twenty that we tear down with low oil pressure do NOT have bad oil pumps but have worn out bearings and journals so quit with the wishful thinking about just putting a pump in it.
Think about it, usually, an oil pump is two dumb ol' iron gears spinning around immersed completely in oil. EVERYTHING else in the engine has a tougher time of it than the oil pump.
Worn camshafts, low oil pressure, worn
-----------------
Old Wives Tale number 53.
The engine starts to use oil so a valve job is performed to correct the problem.
Immediately afterward the engine starts knocking or ticking.
The misdiagnosis is that the valve job gave the engine too much power making the weak bottom end fail.
What really happens is that mechanics all around the world burp the heads and timing covers off without draining the coolant from the engine first. The coolant spills into the bottom end of the engine. Even one oil change may not get all of the spilled glycol antifreeze out.
When you mix the smallest amount of antifreeze and water with motor oil you end up with a low grade acid that attacks the bearings. When you autopsy the engine you will find that the bearings are darkened and with time the bearing surface becomes rough.
That's why it developed a bearing knock immediately after the heads were done.
Carelessness or ignorance.
The right way is to open the drains or knock a freeze plug out.
Vee engines have two separate water jackets on each side so don't for get that you have two drains, one each for the right and left.
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MIKEGOTIT
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05-05-2011 04:20 PM
