Can I safely modify a Briggs exhaust?

Discussion in 'Lawn Care/Landscaping' started by leejosepho, Aug 25, 2009.

  1. leejosepho

    leejosepho DIY scratch-pad engineer

    I just posted this question at a Q&A site, but then thought about all the experts here ...

    My old 8hp Briggs engine (170702-1017-01) on my old JD mower recently lost most of its compression over a period of a few weeks (due to bad valves, I believe, since it did not use any oil or smoke), and I wonder whether I might have caused the problem. I had recently added an elbow, a 3" nipple and a second elbow to get the muffler away from a tire and underneath my mower.

    Question: Does anyone here know whether 2 ells and a 3" nipple (all 3/4" pipe) between the exhaust port and the muffler on an 8hp Briggs could cause valve trouble?

    I have just replaced that engine with another one (195702-4020-01), and I will leave the muffler in the exhaust port if my "extension" could cause engine trouble.
  2. Cookie

    Cookie .

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    Last edited: Aug 25, 2009
  3. leejosepho

    leejosepho DIY scratch-pad engineer

    No, I doubt the valves are sticking, and no, I do not leave the mower out in the weather.

    The last time I mowed, I had a very difficult time getting the engine started, and I believe the problem is low compression. Even after installing a new plug and even though the plug was dry, I finally got it going by holding a gap between the wire and the spark plug to get a hotter spark (like you can do when an engine is flooded). And, I use a drill motor to start my mower.

    I do not understand precisely how or why a modified exhaust system can affect engine performance, but I suspect my adding the elbows and nipple might have caused too much back pressure or some excessive heat that has warped or burned the exhaust valve. But, that engine is quite old and might have just finally given up anyway.
    Last edited: Aug 26, 2009
  4. hj

    hj Moderator & Master Plumber Staff Member

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    valve

    You probably upset the dynamics of the engine so that the gases stayed in the cylinder longer creating heat which would burn the valve seats. If you had increased the size of the pipe for the extension it might not have happened.
  5. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, that is what I am thinking. Briggs lists a street ell as an exhaust component for pointing a muffler, but nothing more than that. So, I suspect my two ells and a nipple might have been too much restriction. But, that engine was old and had a lot of hours before I did that.

    I might try using a 3/4" x 1" ell to step up to a 1" configuration with this newer engine, but not until after I have good reason to believe I will *not* burn a valve by doing so!
  6. Cookie

    Cookie .

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    Joe,

    Did you get it fixed?
  7. leejosepho

    leejosepho DIY scratch-pad engineer

    I got the new engine on the mower and it works great, but I did not relocate the muffler.
  8. Cookie

    Cookie .

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    So, Joe, you are back in business, glad to hear. I got burned one year really bad, they don't call them second or third degree burns anymore, I forget what they called mine, but, said, if they were still referring to them as such, mine would had been a third degree; I was fixing my mower and rested my hand on the carburetor. Like my kid would had said, when little... hot, hot, hot...

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