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OT - Small engine repair

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  • OT - Small engine repair

    Had a Briggs & Stratton 5.5 HP engine dropped off to fix as it "wasn't running right". There is a rubber hose that runs from the valve cover to the air filter housing, assuming it does some sort of crankcase ventilation. The air filter is soaked with oil. What is causing the oil to come into the air filter housing? Worn oil rings on the piston? Worn valve guides? Some other part that is clogged? The spark plug has a fair amount of carbon from running rich but is not oil contaminated. The top of the piston has carbon deposits but nothing excessive.

    Last edited by SteveF; 05-25-2012, 10:34 AM.

  • #2
    Excessive crankcase pressure is usually caused by high blowby (piston rings) or crankcase ventilation device (if fitted) restricted. Pull the hose off, start the engine and watch what comes out of the valve cover with the engine under load. If it's smoking heavily and has much pressure behind it, rebuild time.

    If not, check the hose and the valve cover to make sure they're not restricted. I think they have a baffle with a filter screen or the like in the valve cover. Could be clogged causing pressure build up.

    Good luck!

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


    • #3
      From what a neighbor who teaches small engines at the trade school has suggested in other cases, valve guides can be a problem, not suggesting that rings might not be either.


      • #4
        One time my neighbor's riding lawn mower started blowing white smoke like a fogging machine. It turned out that the air filter was clogged with debris and manifold vacuum was being applied to the crankcase ventilation hose because it entered the manifold down stream of the filter element. So it was sucking oil out of the crankcase and into the manifold. A new filter fixed it.



        • #5
          The hose you mention is a crankcase vent hose. as others have mentioned, high crankcase pressure can cause oil to be blown out of this hose. Another source of the problem can be oil level too high or using the equipment on a hill (angle) that allows the oil to cover the internal vent hole that the normal blow by gasses take to escape. If angle or level isn't your problem it's probably rings, a crack or small hole in the piston (with associated reduced compression). There is what amounts to the Briggs & Stratton version of a PCV valve called a Crankcase Breather, which the hose is connected to on the block, usually held in place by two screws. If the internals of that part are missing or inoperative that could also cause the problem. Follow this link: and look about halfway down the page for Crankcase Breather maintenance information.


          • #6
            How old is the motor? Is it overfull of oil?
            I've run into this problem a couple of times. The steel seat in the alum. block comes loose and jams under the exhaust valve.


            • #7
              Small gas engine equals consumable. Why fart around spending your valuable time and cash when you can replace it for a HF Honda knockoff for less than $100 and be done with it. I have one that always starts within a pull or two. If your in the repair business then buy a bunch when on sale and resell them as replacements. You'll make more money/hour but will have to endure the rathe of people who think you should we working for $5.00 an hour to fix this crap.
              Last edited by 914Wilhelm; 05-25-2012, 07:26 PM.


              • #8
                small briggs, oil spewing out breather, like some suggest I would look at rings/piston or bore damage. And if its a non IC variant, it wont have a cylinder liner, they just ran the piston right in the crankcase material after boring it and called it "cool wall technology". You can't even compression test them to see if they're good without dismantling because the "easystart" cam grind keeps the ex valve open till a set rpm to give the crappy underpowered starter motor a chance to spin it up without cylinder pressure to load it up.

                I'd just open the lid, see the oil, note it was a briggs then go off to buy a honda engine to replace it.


                • #9
                  re: Wilhem's post-"Why fart around, go buy a new one"----

                  There ARE people who enjoy diagnosing a problem and fixing it.


                  • #10
                    I see a couple of Briggs bashing posts here and find it a little it a little unfair. Maybe Honda makes a better small engine, maybe not.

                    I've had Briggs & Stratton engines on my equipment since my Dad's lawn equipment in the late 50's and had great luck with them. We ran them on home made mini bikes using bicycle frames, wheelbarrow wheels, Speed Queen washing machine clutches, belt drive and dryer pulleys on the back wheels through mud, sand and over dirt roads when I was 14, under loads and conditions that were never envisioned by the manufacturer and they held up fine. These were plain bearing, aluminum cylinder without cast iron sleeve engines to boot. Many of those engines were put together from parts of many worn out engines found in the trash or at the dump. In all that time I've had one failure in a 12 HP vertical shaft Industrial engine which threw a rod within a week of purchase on a commercial lawnmower. That engine was replaced, no questions asked, under warranty with a 12.5 HP version. That was at least 15 years ago and that mower still runs great today, with the same engine.

                    B&S makes engines to meet different markets and sometimes they are blamed for something the manufacturer of a product did. Using a plain bearing engine in an application where the all the load is borne by the crankshaft bearing is a recipe for sure failure. I saw that with a Craftsman mulching machine. Sometimes manufacturers cut corners to remain competitive or make more money and choose a less than ideal engine series for their product. Honda and Briggs both make different levels of engines and when chosen properly either will perform well for many years.

                    Maintenance, or lack of, is another issue. Those little engines put out all they have with little complaint. So little, in fact, it's easy to overlook oil changes, cleaning air filters, spark plug replacement or other maintenance. Gas is left in them until it's rancid between uses as well, but still they run until they break or won't run in may cases then the engine gets blamed not the lack of maintenance.

                    Then there is the government and it's regulations. Emission and safety regulations have made these engines more vulnerable to breakdowns yet when they quit the engine gets blamed, not over regulation.

                    Competition from copycat foreign manufacturers, mostly Chinese, will take their toll of Honda engines eventually, if they haven't already. Honda will be forced to use cheaper materials and engineer weaker designs to compete with the Chinese knock offs and eventually will be put in the same category as some here have put the B&S engines.


                    • #11
                      One of the very best engines i ever had was a 9Hp B&S "Vanguard".

                      Got it on a Lincoln 125 amp welder generator.

                      Used it to weld but also used it to run my AC power while i was living off grid in the bush.
                      Had it for 13 years and put over 7000 hours on it ,,when i sold the place it went with it.
                      When i got it, it burnt 1 liter of fuel per hour @ 1/2 load, when i sold the place it still was using 1 liter per hour.
                      All i ever did, was plug changes , steady oil and air filter changes,,,AND it usually started first pull! At -20-30F it would require 2-3 pulls.

                      Oh, and i put one recoil spring in it and 3 starter ropes.

                      One hell of a GOOD engine!!


                      • #12
                        Everybody's pretty much covered most of the stuff I would look for - high oil level - running on a slant - excessive blowbye,

                        Sometimes you think oil level is fine cuz you changed or checked it recently but rich mixtures or leaky needle and seats with higher fuel tanks can up the ante on the oil level because its diluted with fuel...

                        also make sure the air cleaner is not restrictive and that the internal crankcase baffling is in tact...


                        • #13
                          I just rebuilt our briggs (15hp I believe) in our 0 turn. Same thing, running bad, using oil. I thought for sure the rings were shot because someone hadn't checked the oil before mowing the whole block.

                          Well after pulling the motor off the chassis (pain in the arse) and tearing it down I soon realived it was justa blown head gasket between the cylinder and valve chamber (push rods next to the cylinder). So in the end I could have left the motor on the mower and just pulled the head off and threw a new gasket in...

                          otherwise looks like everything has been covered. Not much to these motors, quite fun to work on honestly because everything is small and easy to work with. Working on heavy diesel engines all the time make you appreciate small light things.


                          • #14
                            The cause of the oil in the carb is there is a flapper valve in the valve cover. If the flapper valve does not close the back pressure from the crankcase will blow into the carb and will migrate into the air filter.

                            Replace the valve cover, DO NOT rebuild the engine.
                            It's only ink and paper


                            • #15
                              Originally posted by firbikrhd1
                              I see a couple of Briggs bashing posts here and find it a little it a little unfair. Maybe Honda makes a better small engine, maybe not.
                              I don't think its unfair at all. I spent 6 years fixing lawncare equipment as a profession and my opinion is based entirely on what I experienced in that job.
                              And I saw a LOT of dead brigg's motors, most of which I would lay firmly at the door of that piston and oil flinger design.
                              Are the other manufacturing entities mentioned subject to the same regulation changes? Perhaps they just had a better design and didn't cut corners to be the cheapest engine on the shelf in the pursuit of the almighty $ regardless of quality.

                              I think the chinese copies of the honda will eat brigg's lunch, not honda's. Because all the people who buy on price point will buy them instead, and then we will all see engines failing from poor quality control and materials instead of design shortcuts.

                              Saasquatch, the vanguard and the IC series motors are a different beast to the small engined briggs you see in lawnmower's and sit&ride mowers etc. They are actually designed well with a oil pump and a cylinder liner amongst other innovations.

                              I post too much, off the shed instead.