OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S Vanguard breather issue

Hi all,

I have a 21 hp Vanguard engine powering a Grillo ride on mower. This mower is specifically designed to tackle steep slopes. For the most part is does this well. However, if mowing a steep slope without turning (i.e. reversing down, mowing up) for a decent length of times as is sometimes necessary, oil flows into the air filter (and, I presume, in the carb) via the crankcase breather. From there it can drip oil onto the exhaust creating a very smokey mess, or, as I say, into the carb creating a very oily combustion which can't be doing the engine much good. Oil level is good (I keep it about 3/4 full, which I consider optimum for slopes); breather reed valve is fine.

I'm no expert, but I think this is a design fault for this type of mower, as oil is inevitably going to build up in the little breather tank and has nowhere to go but, eventually, into the air cleaner and carb. So I am thinking the following:

Plug the hole for the breather pipe that feeds into the air cleaner
Re-route the breather tube so it T's back into the oil filler tube so that any oil build up flows back into the case via the filler tube.
T into that new breather tube to mount a small external breather filter so any pressure can vent to the atmosphere.

Anyone see any problems with this idea?

Briggs engines are only rated for a maximum slope of 15 degrees. If you do not exceed that angle, I doubt you'll have any problems with the breather flooding. If you exceed 15 degrees, you are likely to have problems with the engine lubrication system. The fact that you have lowered the oil level will make this a lot worse.

Thanks Grumpy, the mower is rated to do 30 degrees up and down and 17 degrees side to side. Do you see any problems with bypassing the breather-to-air filter and feeding to oil feeder pipe with a small vent?

A belated welcome to Outdoorking, RedKev - I didn't notice initially that you are a new member.

As far as I can tell from on-line information, the Vanguard engines, which were designed by Daihatsu, are permitted to operate at greater angles than the Briggs-designed engines. It appears that the petrol versions of Vanguard can operate at a maximum of 25 degrees continuously, and 30 degrees intermittently. The diesel versions can operate at 30 degrees continuously. That is based on information from a mower supplier who appears to be quoting Briggs - it was not obtained directly from Briggs, so please do not rely on it. So, are you sure you are not attempting to operate the engine at more than 25 degrees continuously? To do so would presumably void your warranty on the engine.

Your proposal to create a new vent from the crankcase ventilation system to the outside atmosphere, instead of to the carburetor air intake, does not comply with emission control requirements just about anywhere in the world that has emission control requirements. I understand that you would try to separate most of the liquid oil from the gases emitted, but there would still be considerable oil droplets and vapour, and the gases will still consist primarily of blow-by gas, made up of combustion products containing substantial proportions of hydrocarbons and probably carbon monoxide. In addition of course, the modification would void the warranty on both mower and engine.

As you can see, I'm voting no on your proposal. I do sometimes help people to modify machines for which parts are no longer available, to keep them operating, but I don't support anyone operating outside the machine's original design parameters, and I don't support modifying modern machines for which proper parts are still available.