At 16:27 9/3/99 , Jeff Gilbert wrote:
>Ok, this seem pretty stupid, but would someone please explain to me what
>exactly a pushrod tube does?  I have read a lot of stuff in the archives

To amplify a little on Stuart's description -- the camshaft rotates and
shoves the hydraulic lifters out toward the heads.  The lifters push on
hollow tubes called pushrods.  They're hollow because oil gets pumped
through them to supply the valve train with oil.  The pushrods pass beneath
and into the heads, where they push on the rocker arms which in turn push
on the valves.  The valves push back b/c they have strong springs holding
them closed, so as the camshaft continues to rotate they push everything
back where it started.

The pushrods would be out in the air, except that they're covered by the
pushrod tubes which keep dirt away and give a return path for oil to get
from the head back into the crankcase.  The corrugations at the ends
provide spring pressure to keep the ends pushed firmly into their seals to
discourage oil leaks.  The regular ones can only be installed when
installing the head, but you can get (more $$) telescoping tubes with an
internal spring that can be installed with the head in place.

david
David Beierl - Providence, RI
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"