> This is more of a question for the rest of the list than an answer as
> I'll
> be pulling my own head for a bi-opsy next month. Would it be
> worthwhile to
> give the rest of the valves a grinding by hand while the head is off?
> Or is
> this reserved only for old Briggs and Stratton mower engines?
Personally, I would throw in an entire set of new exhaust valves, have
hardened seats installed if the head does not have any, have the head
magnafluxed and checked for flatness. It is a lot of work getting the
head off & you might as well make sure everything else is hunky dory
while you are at it.
If you have the old style 7:1 head, no raised platform adjacent to the
valve cover at the place closest to the carb, do not mill the head
beyond a clean up mill. There is not a lot of metal between the head
bottom and the water jacket and milling the head a point will invite
head cracks.
If you have the raised rectangular surface look carefully to see if
there is a number stamped on that surface. If there is no number or a 7
stamped there then you have a late 7:1 head.
If there is an 8 stamped there (Mine looked like two zeros that were
stamped to make an 8) then you have an 8:1 head.
Only heads with the raised flat surface that have an 8 stamped on it
are factory 8:1 heads.
The later head castings are thicker between the bottom head surface and
the water jacket. This makes the head less prone to cracking and
provides enough metal to mill the head to 8:1 compression.
A late 7:1 head can be milled to provide 8:1 compression by milling off
100 thousandths from the head surface. A 7:1 head that has not been
shaved is 3.690 inches thick from the bottom surface to the valve cover
mating surface. Before milling a head check to see how much may have
been removed in the past and subtract that from the 100 thousandths
needed to bring the head to 8:1. A 7:1 head can not reliably be milled
to 9:1
TeriAnn J. Wakeman
Marigold Ltd.
www.marigoldltd.com
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