14.5 Briggs IC Gold with Oil Back Pressure

11 years ago

I have an otherwise good running 14.5hp Briggs IC Gold on a craftsman mower.

It has low hours and starts and runs easily.

For some reason, I'm detecting some pressure in the crankcase. There are two signs of it......A fair amount of oil leaking somewhere around the OHV cover, and when you shut off the motor,and open the oil filler, you can hear a whoosh sound like there may have been a few psi of pressure built up there.

Shame on me, I've been occasionally working on small engines here and there for over 50 years and this is my first encounter of this type!

Tips are most welcome!

14.5 Briggs IC Gold with Oil Back Pressure

Comments (7)

1saxman
11 years ago
It's got to have a crankcase vent tube that goes to the carb or some other arrangement to relieve blow-by pressure. On an engine that big there might even be a valve in that line.
walt2002
11 years ago
Well of course a 14.5 hp B&S engine has the same crankcase breather and valve used on most B&S engines from 8 hp up until the 31 with letter series.

" when you shut off the motor,and open the oil filler,"

Is that really what you mean?

If it isn't causing any problem, why are you worrying about it?

Walt Conner
wayne440
11 years ago
My take- inspect said breather and valve, then if it still leaks, replace the valve cover gasket and use it.
etbrown4
Original Author
11 years ago
Greetings to Walt, Wayne and Saxman.

Your comments are much appreciated.

The oil seeping or dripping off of the ohv cover is unusual, messy, and smokes a lot when the motor gets hot.

Nobody I know wants a motor acting this way!

Otherwise, I've never seen a lawn mower motor holding a few psi of pressure, and yielding a whoosh sound when you open the oil filler, and that covers maybe 50-60 motors I've worked on.

Something is definitively wrong, and I'm going to try to figure out what it is!

One adviser suggested that I might have a blown head gasket or one that's ready to blow. Possible maybe, but I'm not so sure.

I did notice something else unusual. when I shut the motor off, there is a ton of vapor/smoke exiting the carb intake. While it's clearly not supposed to be like that, it seems to suggest that the pcv or equivalent valve is open and allowing ventilation out to the carb.

Assuming that I've got excessive pressure at that hose to the carb when the motor is running, what is the most likely cause and the most likely cure?

Has anyone experienced this?

Constructive tips much appreciated!
rustyj14
11 years ago
Is the crank-case breather unit clogged up? It resides near the carburetor on some engines, and on the larger ones, it exits the crank-case on the top of the block, near the carb, and it is a fairly large rubber tube, about 1/2 inch I.D., and it fits on the carb intake, near the choke plate.
etbrown4
Original Author
11 years ago
not sure about the valve itself, but the hose is clear and very clean
roadbike
11 years ago
Try removing and cleaning the breather valve. If that doesn't help then replace the valve.