Briggs & Stratton 16.5 smokes

Discussion in 'Mechanic and Repair' started by johnhartlove, Aug 29, 2007.

  1. johnhartlove

    johnhartlove LawnSite Member
    Messages: 2

    I'm not in the landscaping business but I have lots of grass to cut each week!
    I have a 2004 B/S 16.5 model #310707 that smokes when the blades are engaged or when it is run at full throttle.

    The engine will also foul the plug with oil in 20-30 minutes.

    I do no see any oil in the carburetor or the breather tube.

    The oil also becomes dark quickly.

    I have done some preliminary test and inspections:


    The compression is 90-100 psi

    I did not do was a leak down test.

    removed and inspected breather

    disassembled and inspected carburetor

    installed new carburetor

    removed cylinder head and disassembled.

    I found oil in the intake pocket of the cylinder.

    I also found oil deposits on the back of the exhaust valves.

    the cylinder bore still has a nice cross hatch.

    when I coat the bore with oil and turn the engine by hand the rings seem to clean the cylinder OK.

    At this point I'm planning on cleaning and lapping the valves,replacing the head gasket,changing the oil,replacing the breather,replacing the dipstick tube o-rings.

    If any one has seen this before or has any ideas that could help I would appreciate it.

  2. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 965

    Replace the seal on the intake valve. B&S PN 690968.
    If you haven't cleaned the block surface yet, look for a thin line between the push rod chamber and the bore for a potential leaky head gasket.
    Your problem does sound a bit strange!
    Something to check though is the oil. Smell it for gasoline fumes. If gas was leaking past the carb, it could dilute & overfill the oil. This could cause it to get past the rings pretty easy. As the gas "cooked off", it would disappear pretty fast, which would make it appear to be using lots of oil.
  3. johnhartlove

    johnhartlove LawnSite Member
    Messages: 2

    Thanks for the ideas!

    I ordered a cylinder head gasket set on-line which I received today. The kit came with the valve seal,head gasket,cover gasket and exhaust gasket.

    I have already drained the oil so I can't check for gas.

    I have installed a new carburetor so hopefully that will eliminate any fuel issues.

    I will re-assemble it this weekend. I think the headgasket is the culprit.

  4. topsites

    topsites LawnSite Fanatic
    Messages: 21,652

    If it's not the head gasket it could be your problem is worn rings, how else would oil get into the combustion chamber, and turn it dark?

    At least on cars I've had, anytime they've smoked and turned oil dark, it was lost compression due to worn rings, I could be mistaken but I believe pressure for these engines should be closer to the 100-120 psi range, but you'd want to check the specs, I'm just not sure.

    As for me I got tired of it, I run synthetic oil in the lawn beasts nowadays, cars and truck as well.
    Far less problems, pay now or pay later.
  5. hr214_boy

    hr214_boy LawnSite Member
    from Ohio
    Messages: 8

    Same problem with Honda mower. I replaced the valve seals/guides (same thing different names) and it stopped smoking.

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