bob wrote:I have a Gardenway/Troybuilt rototiller with Tecumseth 6HP flat head engine. I do not understand how the breather works. All the breathers I have worked on have a breather tube that comes out and points straight down. This one comes out and connects to intake just below air filter. How does that works without sucking oil into the carb. Right now I have the engine running good at times and then all of sudden it will start smoking. I have taken the breather out and am cleaning now. I know oil seepage hole goes down which looks correct. What else am i looking for. Thanks
Blair
Well if you want the educational explanation... Crankcase breather , well, lets the engine breathe... As the piston is moving up in the crankcase, the change in crankcase volume will create a vacuum or suction effect (which is desirable) and then as the piston moves back down, it creates PRESSURE, which is not desirable (excessive pressure can blow out gaskets and seals, etc.) crankcase breather has a check valve / flapper valve, that opens to let pressure out and closes when vacuum begins (which helps keep oil in, helps keep gaskets in place, helps keep oil seals seated, among other duties) - However when the crankcase is pushing pressure out, there will be atomized (oil vapors) in that air (which is why you may see oil coming out - a little bit of oil vapor is normal) - most of the oil is captured by a breather filter in the breather chamber , which drains down and then exits back to the crankcase through a drainback hole.
Excessive oil coming out the breather on an L-Head is generally caused by a relatively few things - the more common one is, the drain-back hole gets plugged up with oil sludge over time - sometimes just simply cleaning that out solves the problem.. It can also be caused by a failing (or failed) breather check valve (broken reed or sludge/carbon holding it open, etc) which may also be accompanied by other crankcase leaks - and lastly, can also be caused by worn piston rings - allowing excessive combustion blow-by into the crankcase - breather can't control that much added pressure.. Breathers can fail the other way too and fail to open allowing excess crankcase pressures to build up which can blow out gaskets and pop oil seals out of their seats, even had one that kept blowing the oil dipstick out of its tube repeatedly..
In days gone by, there wasn't as much concern for the environment, so manufacturers went cheap and just vented crankcase vapors to the atmosphere.. although some would hook breather tube to air intake so as to help prevent dirty air from getting into the crankcase.. and of course the EPA steps in and then all engines had to have breather vented to the air intake (just like cars with their PCV valves had to hook to air filter housing)..
In an OHV engine, there's a new dimension added with possibly blown head gaskets that leak combustion to the crankcase via the pushrod galley - that can pump a whole lot of oil into the air intake in a hurry..
If your engine is operating normally and not using excessive oil, then you'll want to hook that breather tube back up to the air intake, or you're gonna be making things worse - with that air intake open, engine's gonna suck in dirty air.. Also first thing to check when excessive oil through breather tube and into the intake is suspected, would be to try a new air filter - even if it looks clean, if paper filter got wet the cellular composition of the filter media will change and acts just like a plugged up air filter... But if you are seeing a lot of oil pumping out the breather tube on an L-Head, first thing to do would be pop the breather off and clean it and be sure the oil return hole (can be quite tiny and hard to find) in both the breather and the valve box are clear, and visually inspect breather reed or plate (Briggs engines had a round fiber plate that isn't spring loaded but would close when air flow changed, so just because it doesn't seem to be closed, doesn't mean it is bad) and might want to do a compression test , check for worn rings, and make sure the crankcase is sealed (including dipstick and tube - failures in that area can cause breather to not operate properly) , and as a last resort, replace breather.. in my 40 odd years in this business, Ive only really seen a truly failed breather perhaps 3 or 4 times... lot of failures can be blamed on breather, but it isn't the breather's fault.. the root cause was found elsewhere.
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)