This legacy YT Video shows an odd way of making the Engine Knock – Piston Slap in a then 10 Year Old GM 4.2L Engine subside. However, the VOP and his cohort were mistaken to conclude that the Engine 'goes into a vacuum' under these Test Conditions.
Conversely, the only thing I can figure is that enough pressure builds up when the PCV exit is blocked in this manner to either stabilize the idling engine Piston-To-Cylinder relationships… or enough Motor Oil is being pushed in between them to act as a sound cushion as the Gas Blow-By Pressure steadily increases.
There is always the chance that the Oil Wiper Rings are also involved by getting expanded outwards enough to ease the clatter of the “Piston Rock” that invariably occurs at or near Top Dead Center for all six cylinders.
I would not recommend doing this too often or too long as the Front and Rear PTFE Oil Seals around the Crankshaft might invert, become damaged or simply Blow Out.
Nonetheless… It’s an interesting phenomena.
Engines like this one might benefit greatly from having their Spark Plugs removed and get a thorough dousing of ACDelco Top Engine Foaming Cleaner for around (3) Hours to dissolve all of the Carbon Impacted Valve Seats and the two upper Compression Rings and perhaps substantially reduce these obvious effects of Gas Blow-By. If you've ever wondered why so much Engine Oil winds up getting ingested through the Throttle Body and your Oil Level is prematurely Three Quarts Low.. THIS is The Culprit
Conversely, the only thing I can figure is that enough pressure builds up when the PCV exit is blocked in this manner to either stabilize the idling engine Piston-To-Cylinder relationships… or enough Motor Oil is being pushed in between them to act as a sound cushion as the Gas Blow-By Pressure steadily increases.
There is always the chance that the Oil Wiper Rings are also involved by getting expanded outwards enough to ease the clatter of the “Piston Rock” that invariably occurs at or near Top Dead Center for all six cylinders.
I would not recommend doing this too often or too long as the Front and Rear PTFE Oil Seals around the Crankshaft might invert, become damaged or simply Blow Out.
Nonetheless… It’s an interesting phenomena.
Engines like this one might benefit greatly from having their Spark Plugs removed and get a thorough dousing of ACDelco Top Engine Foaming Cleaner for around (3) Hours to dissolve all of the Carbon Impacted Valve Seats and the two upper Compression Rings and perhaps substantially reduce these obvious effects of Gas Blow-By. If you've ever wondered why so much Engine Oil winds up getting ingested through the Throttle Body and your Oil Level is prematurely Three Quarts Low.. THIS is The Culprit
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