Bobbing oil dip stick?

[PTmowerMech]

The fuel is a little mirky and seems have a bit of water it in. Also the fuel solenoid was bad.

 

[StarTech]

Where does the extra pressure come from, since the only way from the combustion chamber to the sump is either through the valve guides or passed the rings.

You are forgetting the push galley on OHV engines that pass right the head gaskets. Briggs OHV Inteks are one that regularly blows the head gasket between the cylinder and the push rod galley.

Was the fuel solenoid actually bad or was it just needing a good ultrasonic cleaning?

 

[Scrubcadet10]

Stop & have a little think
As the pistons descend the crankcase is pressurised .
Air will take the path of leat resistance so it is simply a case that lifting the weight of the dip stick requires less energy .

Where does the extra pressure come from, since the only way from the combustion chamber to the sump is either through the valve guides or passed the rings.

The extra pressure comes from the crankcase area decreasing because the piston is traveling back down.

 

[PTmowerMech]

You are forgetting the push galley on OHV engines that pass right the head gaskets. Briggs OHV Inteks are one that regularly blows the head gasket between the cylinder and the push rod galley.

Was the fuel solenoid actually bad or was it just needing a good ultrasonic cleaning?

Probably just a good cleaning. It would move a little both ways, by turning the key off and on.


As far as the head gasket goes, I'd better do a leakdown before I start tearing into this. I bought the tool a few years ago, and have only used it once or twice.

 

[PTmowerMech]

The extra pressure comes from the crankcase area decreasing because the piston is traveling back down.

I'm talking about what Bert said about how one with a blown head gasket will make a dipstick jump several inches, if not all the way out the tube. This one is bobbing only a couple of inches. Same as the other one, that doesn't have a bad headgasket.

Plus something else I did, mowed for about 10 minutes. Killed it and pulled the dipstick. No smoke from the oil fill tube.

 

[7394]

A blown head gasket will allow the crankcase to inhale much more air thru the leak on down stroke, so more crankcase pressure is developed.

 

[bertsmobile1]

In theory when the piston rises, it creates a low pressure zone ( vacuum ) in the crank case and when the piston falls it creates a high pressure zone in the crank case that vents via the breather
In practice air gets sucked in past all of the seals , you get blow by on compression and a lot more on exhaust that will rush into the low pressure zone in the crank case
If the engine was in fact airtight then you would not need a breather .
The more the number of cylinders the less this effect and it becomes zero on horizontally opposed crankshafts
On race engines , particualry single cylinder ones you can get a couple of extra Hp by fitting a flow through crankcase venting system with a crank case inlet & outlet both fitted with one way check valves so less energy is lost through pulling a vacuum on up strokes and compressing on the down stroke
Piston rings do not create a seal
The oil gets behind them and on the upstroke pushes the ring into the cylinder wall
To do this the air above the piston has to be under pressure as is the case on the compression stroke
However on the exhaust stroke there is very little pressure because the exhaust valve is open thus the rings do not get forced hard onto the cylinder wall and you get blow by

 

[PTmowerMech]

Also, there is no oil around the fuel pump vent.

I mowed for about another 20 minutes, and during this time, I choked it a little at a time until the choke lever was in full position. This time, it did clear up the surging. Not sure why it didn't clear up the other two times I did it (even using my hand).
In the morning, after everything has settled, I'm going to drain out some gas. 1 quart at time, until it clears up. Then ad some fresh, high octane to it. I may also remove the float bowl and see what it looks like inside.

 

[PTmowerMech]

A blown head gasket will allow the crankcase to inhale much more air thru the leak on down stroke, so more crankcase pressure is developed.

That is IF it's blown around the edge, leading to the outside of the engine, right? Because the pressure inside the sump won't increase a whole lot, if it's an internal gasket leak. Will it?
Briggs don't normally fail from edges leading to the outside. I've only seen them leak between the valves and the opening to the push rods.

 

[Tiger Small Engine]

That is IF it's blown around the edge, leading to the outside of the engine, right? Because the pressure inside the sump won't increase a whole lot, if it's an internal gasket leak. Will it?
Briggs don't normally fail from edges leading to the outside. I've only seen them leak between the valves and the opening to the push rods.

Get an extractor (if you don’t already have one) and suck all that old bad cloudy fuel out, and blow out tank.
Suspected bad head gasket:
While at idle, quickly push throttle to WOT, then at WOT quickly go down to idle, waiting a few seconds in between. Does a puff of smoke come out? After running a bit, open dipstick and look for a little smoke coming out. Neither are definitive tests. Now perform a compression test and leak down test, watching for air escaping out of cylinder head with valve cover off. Just did one yesterday with 40% loss. Anything under 20% is acceptable. Single cylinder Briggs (ie: 31P677) is very common for bad head gasket.