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PeppyDan

Briggs 16hp opposed twin breather blowing oil

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PeppyDan
I just got a Roper garden tractor with a Briggs 16hp opposed twin engine.The previous owner said it was working fine a few years ago and then the starter went out. He just left it set until this year when he changed the starter but still could not get it to run. He said he cleaned the carb and got it running but then after just a few minutes oil started blowing out of the left breather tube. I did not hear it run because the battery was dead and I seen no tools or clues at all that this guy worked on his own stuff so I think he may have just sprayed some carburetor cleaner in it. I have the breather out right now and do not see anything obvious wrong with it. I also drained and added new oil and did not see the presence of gasoline in the oil or overfilling. Does anyone have idea's where to look next or what else to check? Thanks for any help you can give me. Dan

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dlkelley713
If the breather valve isn't stuck open, then it's typically a head gasket or a bad seal somewhere like the oil dipstick tube. I'd check the head gasket on that side... Hope that helps narrow it a bit. Dan

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1Litre
The briggs manaual has the breather valve clearence from the valve disc to the opening that you measure with proper size wire with 90deg bend. dlkelly hit it on the head with crankcase venting of any place will cause that thing to blow oil out breather and past the rings. Last and worst is a broken rod and or piston. I have had two of the briggs twins like this and they pumped oil out the breaher.

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PeppyDan
Ok, I will check into the head gaskets and the seals though I don't understand why either of those items would cause it to blow oil through the breather tube. If there is positive crankcase pressure that is when the oil would be pushed out of the breather in my thinking and with a seal or gasket leaking it should allow that pressure to escape. Can someone please explain this more thoroughly so I can understand the reasoning behind it. Thanks, Dan

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1Litre
The breather valve is designed to keep the crankcase at less pressure than atmospheric pressure. When I was on one of the Briggs dyno's years back one of the factory techs showed me a 16 twin runnen at governed high rpm for longevity test of random pulled production unit. He reached over to the dipstick and twisted the cap loose and held it there so it would not spray oil vapor all over us. Less than a minute you could here the engine loose a little RPM and as we went further more RPM was lost and then engine was not running well at all. He pulled the exaust evac tube away from muffler outlet and that brand new engine was huffin blue smoke as if you took a oil ring off the piston. Most small engine breathers are designed to let out all the gases it can and very little back into the crankcase. This is what keeps crankcase at partial vacuum for oil control.

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dlkelley713
The breather has a one-way valve to allow extra gases and short bursts of positive crankcase pressure out. During the negative pressure cycle (in the crankcase), extra air is pulled in if a seal is bad (or a head gasket is bad). Then that leads to greater positive pressure than the breather can vent. As the oil heats up and the pressure increases, it comes up through the breather... Then the cycle starts over. Dan

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PeppyDan
Thanks for the explanations of how the breather works, I understand it a little better now. I will pull the engine and check all gaskets and seals since it will be easy at that point to replace any that are going bad. I was getting some blow-by from the other cylinder too so it will get checked too. Dan

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PeppyDan
I pulled the engine tonight and remove both heads. The head gaskets were not the problem at all. I needed to use a screwdriver to lightly pry them each off. The problem is both cylinders have some substantial scoring on the walls most of the way around. This engine is now going to get parted out since i do not need the engine or tractor and purchased it with the intent to repair and resell it. Now I will just part the entire tractor engine and snow blower instead. Dan

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PeppyDan
quote:
Originally posted by 1Litre
Oh no . Sorry Aluminum bore version?
Yes it isB):(!. I bought the tractor right so I know I can easily make money on it and will probably make more by parting it out. Dan

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