| Re: BF (4.0) Dipstick blow-out fix [message #302972 is a reply to message #302754] |
Sat, 02 July 2016 20:24   |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
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Senior Member |
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Matt:
Small engines such the Onan use a PCV System that tries to keep a slight vacuum in the crankcase. That lower pressure helps to keep oil from going up the oil rings. (Small engines will burn more oil and leak more oil out gaskets without the low pressure) The PCV system uses a disk valve and spring that exhausts crankcase pressure on the down stroke of the piston and closes on the upstroke of the piston creating the vacuum in the crank case. Your blowing out of the dipstick is a indicator to me that the crancase is pressurizing and the PCV system may be inoperative or ring blowby has become bad enough to overwelm the system. My suggestion is to remove the breather plate and check and service the valve. This may help your problem, but you also do not have a seal which is also necessary for the PCV system to work.
If the crankcase is not properly sealed. The PCV system begins to move a lot of air into the carb. The high volume of air will bring oil mist from the crancase to the carburetor which will burn increasing the oil consumprion of the engine.
That PCV sytem is sure a bigger part of the engine operation than most are aware of, HUH??
Here is an illustration of the PCV Valve.
http://www.gmcmhphotos.com/photos/discussion-photos/p57964-onan-crankcase-vent-valve.html
I actually was a Briggs and Stratton/ Tecumseh, Clinton, Toro, and MTD dealer a long time ago)
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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