Oil in Carb B&S OHV 15.5HP

Discussion in 'Mechanic and Repair' started by Jeffandtamara, Apr 2, 2006.

  1. Jeffandtamara

    Jeffandtamara LawnSite Member
    from KY
    Posts: 26

    I have a B&S 15.5 OHV that started spewing Blue smoke. I checked the air cleaner and the filter and breather area was soaked with oil. I suspected the crankcase flapper valve that vents into the breather was bad. Put in a new one. Some better,,, but there is still a lot of oily blowby coming back into the carb. In fact after about an hour of use, the filter was pretty soaked again.
    Also...This engine was not run for about 3 years and sat in storage, and has only a very small amout of hours on it.... Any ideas.
    I am curious, if the valves are not fully closing, seems like that might drive excess combustion gas into the crankcase through push rod seals and have to go to the crankcase, so into the breather...I hope I'm wrong, but I know there is a expert out there somewhere who can put me on the right path...Thanks for your help!!!
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    There are no push rod seals, If the valves were not closing or out of adjustment the engine would not turn over easily due to the compression release on the camshaft. I suspect fuel contamination in the oil and or too high of oil level, Too thin of oil. HD30 is most common around here. If the unit sat that long the float valve or float could have stuck and flooded the cylinder with fuel that seeped past the rings into the crankcase thinning the oil or causing a high level.
  3. Jeffandtamara

    Jeffandtamara LawnSite Member
    from KY
    Posts: 26

    Thanks Rob...
    I think the oil level is OK. Service manual called for 48 oz and it brought it right to the full mark on Dipstick...Oil level OK..Halfway on the stick due to the amount of oil sucked into the carb. Can't detect gas in the oil. Although it the oil is quite a bit darker than I would expected to see with it just being changed. Seems like most engines keep that clear oil look for several mowing cycles at least...
    The motor starts good and reacts to the throttle as expected, would that be what is expected, if the float was stuck?
    How bout the head gasket??? is there a posiiblity of a problem there,,,How to check or diagnose??

    Thanks for your help...This site is great and very informative!!!!!1
  4. randy448

    randy448 LawnSite Member
    Posts: 39

    If engine sat for 3 years I would guess the rings are stuck and compression is pushing oil out the breather.
  5. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    That is a good point randy, Since the oil is fine.

    A cylinder leak-down test would give all the answers, But this test requires special tools to be done accurately. Call your local shops to see if they have the tools to perform this test.
  6. lucforce

    lucforce LawnSite Member
    Posts: 223

    If the air filter is not free flowing the manifold "vacum" will pull oil through the breather.
  7. oldrustycars

    oldrustycars LawnSite Senior Member
    Posts: 301

    restrorob brings up a good point, and if i may jump on my soapbox just a second...all you guys with mowing equipment need to own a leakdown tester.
    its a way better test than just a compression test, although i still do that on 2 cycle engines. it will help you pinpoint where the problems are. compressed air goes into the cylinder, one gauge shows how much. the other gauge shows actual cylinder pressure. then you can see where your trouble is. oil bubbling? then its getting past the piston, or possibly a head gasket on an OHV. feel it coming out the muffler? exhaust valve. they cost about 100 bucks, any tool guy can get you one.
  8. Jeffandtamara

    Jeffandtamara LawnSite Member
    from KY
    Posts: 26

    Thanks for all the responses. Some pretty Good ideas...

    New Air filter. So Air filter "Was" free flowing. Now probably enough oil benn sucked into the breather, that it is no longer as free flowing as it once was. I think the majority of the oil is coming in the breather through the crankcase vent. If I run the engine in the shop with the breather off I can see a lot of fumes coming out of the vent. Like I said I put in a new flapper valve. Is there anything that would put more pressure in the crankcasel such that ultimately make more oil/fumes go into the breather...
    I have an old compression tester not a leak down. To use it, I think I would turn the engine over and get a reading, then add some oil to the cylinder, then check again. If the compression reading goes up, Probably rings....If no change then,,, Well, I'm not sure what that proves.
  9. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Explain this flapper valve you keep calling it, What doe's it look like and where doe's it go ? Aside from that it looks like a ring problem.
  10. Jeffandtamara

    Jeffandtamara LawnSite Member
    from KY
    Posts: 26

    I am looking in the B&S service manual and so far I can't find it, but..it is the equilivent of a PCV valve. I think it is supposed to work like this.... It allows clean air to enter the crankcase when the piston goes to TDC and keeps air from going out when the piston comes back. It has two screws 1 top and bottom. Approximately 1" wide by 2" tall and 1/2" thick. I got the a new one at my local B&S shop. They knew exactly what I was talking about, (I was impressed)...

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