Home Forums Briggs & Stratton 4-Cycle Racing Briggs Stroke Motor Piston

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      James Frantz

      I was recently asked about piston pop up when using an aftermarket forged piston in a Briggs Animal engine. These pistons have a lot of material between the top ring and top of the piston. It’s not unusual to machine .100″ off the top of the piston to get the correct pop up. However, you can also shape the top to make it a domed piston.

      The following is something that you may find informative:
      The objective when doming the piston is to cut it in such a way that you build the desired compression with out having to machine the head gasket surface.
      This leaves all the original material on the head for more rigidity and strength.
      You can also either mill some of the combustion chamber out in the squish areas and leave more material on the OD of the piston.
      It’s easier to cut the piston flat and mill the head gasket surface and it works quite well with smaller bores.
      If you are going to maximize the bore of an Animal and use a stock head you may want all the strength you can get in the head.
      One of the biggest mistakes i see people make is putting so much compression in an Animal that they can’t keep from blowing head gaskets.

      Making a domed piston leaves you with a heavy piston so make sure you use a HD wrist pin. If you dome the piston you can remove material from the under side to lighten it up.


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