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Old 10-02-2014, 08:06 AM   #18
djmarchand
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City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23- outboard
Join Date: Aug 2012
Posts: 3,940
Quote:
Originally Posted by High Wire View Post
How does one measure blowby?
Blowby is exhaust gas that gets by worn rings and valve guides and into the crankcase. There is a vent for it. Some people have installed an Air Sep in the vent to catch the oil entrained and recycle it. A better idea is to use Sbmar's Envirovent device.

Cummins has published a procedure for accurately measuring blowby on their engines and gives new and worn specs. It consists of installing a temporary orifice in the vent tube and measuring the pressure drop across the orifice. More pressure drop equals more cfm of blowby. If anyone wants a copy, send me a PM with your email address and I will send you the procedure.

You can do a quick and dirty test by opening the oil fill cap, running the engine up under load and put your hand over the opening. If you feel a rush of pulsing gas that pushes your hand up, you have significant blowby.

David
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