Chuck -
D@%n. You're right. I should never post before coffee...
Chris K.
> *sigh*
> the valve stems expand due to their captive heating from
> exhaust gases and combustion(and their being shrouded by
> the guides). and the lifters and push rods do expand to
> some degree under the warming up process to normal
> operating temperature. these combined factors contribute
> to a valve to rocker clearance deminishing as an engine
> heats up. the most expansion is in the valve stem. some
> manufacturers give hot and cold lash settings. cold is
> always more clearance than hot. experimentation on the
> dyno back in the 70's yeilded little suprise to improved
> performance with reduced valve lash. but! there is a
> point where under normal operating temperatures some lash
> must exist to allow for extreme heat (excessive abuse or
> sustained high RPM's for long periods) for aditional
> expansion! or uh-oh! i think we burned a valve (or it's
> nasty relative..) i think we holed a piston...it seems to
> have no compression..........yup! going fast has some
> up's and down's...... that's why a daily driver is always
> best left stock or near stock.....(it's a reliability
> thang....) :).
> chuck.
> been there.....broke that! :)
> ----- Original Message -----
> From: <ckotting@wideopenwest.com>
> To: <spridgets@autox.team.net>
> Sent: Thursday, March 20, 2003 7:13 AM
> Subject: RE: Cold vs. Hot valve lash
>
>
> > Crash -
> >
> > They do loosen when hot. As the hot metal expands, the
> > pushrods stay relatively cooler than the block and head.
> > As the distance between the camshaft and the rocker
> > shaft increases, the length of the pushrods increases
> > less, making the valves looser.
> >
> > However, that being said, I'd just set them at factory
> > "hot" spec, even though the engine is cold. At the
> > first start up, you've got to run it for at least 30
> > minutes to get the cam and tappets bedded in together
> > (assuming you're using new ones), which is going to make
> > the valve lash change anyway.
> >
> > You're not going to do any damage in 30 minutes of
> > running, and you're going to have to readjust the valves
> > after that initial bed-in anyway, and the engine will be
> > at operating temp at that point. So just figure that
> > things will be a bit rough at first, and do a complete
> > valve lash - balance carbs - set mixture after that
> first run-in. >
> > At least that's how I've always done it.
> >
> > > I don't think so, do you think they will looser when
> > > hot? Maybe add ..02?
> > > Crash
> > >
> > > Chris:
> > >
> > > minus .02
>
> /// unsubscribe/change address requests to
> majordomo@autox.team.net or try ///
> http://www.team.net/cgi-bin/majorcool ///
> http://www.team.net/mailman/listinfo /// Archives at
> http://www.team.net/archive/spridgets /// Send list
> postings to spridgets@autox.team.net /// Edit your
> replies! If they include this trailer, they will NOT be
> sent.
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/spridgets
|