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 Tech
- Base Gasket Leak
Almost all Harley Davidson evolution  motorcycles
have had a base gasket leak at one time or an other . there are many
fixes but few of them are correct. In order to make a permanent fix
we need to understand why they leak . Im going to explain to you what
the problem is and then how to cure it . After the cylinders have been
heated up and cooled down a few times ( called heat cycling ) they warp
its a natural stress relieving of the metal . not only do the bases
warp but so do the bores and head gasket surfaces . the common thing
to do is replace the base gasket with a thicker one or a James silicone
steel gasket . The problem is that the thicker gasket raises the cylinder
and raises hell with the compression and the steel gaskets wont seal
a warped surface.
What we need to do is repair the cylinder so its not
warped . I take the cylinder and hone it .050 over size to bring the
back round and then machine the base of the cylinder flat in a lathe
them machine the top of the cylinder flat in a mill I have found that
when I mill the head gasket surface if I remove .015 to .018 I can correct
the squish band to a better dimension.
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