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Tappet Stem Clearance On Briggs Engine

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  • Tappet Stem Clearance On Briggs Engine

    I'm just about ready to start putting this 12HP Briggs together. I bored and sleeved the cylinder back to standard bore and lined the valve stem guides. So everything is up to spec.
    The only question remaining is the clearance for the tappet stems. The book doesn't give a reject size for either the stem or the tappet guide hole. I guess they figure they never wear!!!!

    The new tappet stems measure .4305 in dia. I used a gage pins to check the holes, .432 goes and .433 goes about 3/4 of the way.
    So that leaves me with about .0025 clearance. Divide that by 2 and I get .00125 all the way around. A little sloppy as I can feel the wiggle. I have a newer made set of tappets, same PN# the stems on those measure almost .001 larger in dia. I probably should go with those, what do you think?????
    The newer made tappets are all ground, the older style new set are polished like a mirror. But the polish or tumbled finish may have been done after the grinding process. As we all know cost cutting steps have been taken on newer produced stuff. Which holds true with everything.

    JL...........

  • #2
    I'd run it. They live in oil.

    -D
    DZER

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    • #3
      If it was mine, on an air cooled engine I would rather it be a little on the loose side, than the other way. I would probably run the old ones also.
      James

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      • #4
        A little OT, but what did you use to bore it?

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        • #5
          I had the local motor shop bore and sleeve the cylinder for me. I couldn't do it on my BP, not enough down feed.

          JL...............

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          • #6
            Bore with the knee.

            -D
            DZER

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            • #7
              Is this a a 1920's-1960's cast iron 12 Clydesdale Horsepower engine, or a 1970's or later aluminum 12 Miniature Shetland Pony Horsepower engine? I don't know, but I've been told that there is a difference in specifications.

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              • #8
                briggs used to have a reject guage for that, maybe find an old mower sho and ask if you can mic their guage. I agree with the above loose is better than tight in the tappets, they are pretty short so there wont be that much deflection anyway. If memory serves, of the hundreds I have rebuilt I have never worried about the tappet bores just the valve guides and cylinder.

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                • #9
                  Because of the lifting action on the cam follower the bore will be egg shaped with some bell mouthing at the top away from the cam. Personally, I would run the original lifters unless you want to ream the bores out. To ream them you would have to be sure to align the lifter bore with the valve guide bore and for that reason I would leave it alone.
                  It's only ink and paper

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