From: karish@pangea.Stanford.EDU (Chuck Karish)
Subject: Re: tune-up (and Fiamms)
Organization: Mindcraft, Inc.
Date: Wed, 26 Aug 1992 23:32:02 GMT

In article <1992Aug25.151400.8551@sifon.cc.mcgill.ca>
loki@nazgul.physics.mcgill.ca (Loki Jorgenson) writes:
>	Anyways, I finally got down and dirty and cracked the valve cover
>on my '84 FJ for the first time.  I figured that, since I don't have a
>second bike or a complete shim kit, I would go through the motions,
>note what I would do if I had the shims, close it back up and then let
>the mechanic do it.  Then if his choices compared favourably with mine,
>I'd make arrangements to do the whole thing myself next time.  So call
>me cautious.

Why do all that work, then pay somebody to do it again?
After you do the measurements, go get the shims you need
and install them.  Then chech the valve clearances again.
Iterate until the clearances are all correct.

You'll do a better job than most shop mechanics, because
you can afford to be patient.

>	1) My plugs were a whitish-yellow instead of the usual tan; I can't
>	  remember what that is supposed to mean.  Mixture is too lean?
>	  What do I do?

It probably means that you're running unleaded gas, like the
rest of us.  The brown color was a coating of lead compounds,
and spark plug reading is a different art these days.

>	2) The plug gap was on the narrow side of specs.  I widened them
>	  to sit in the middle of the range.  This should advance my
>	  timing a bit and heat up the spark.  It also seems to have
>	  improved my power a bit.  Any comments?

Changing the plug gap has no appreciable effect on
timing.  Widening the gap should makes a bigger spark
which should do a better job in the marginal, lean
mixture they use in the mid-throttle range these
days, to give us cleaner air.  This makes some
bikes a bit harder to start, though.

>	3) As was advised in a posting long ago, I started out measuring
>	  the valve gap at about 5 different places around the back of the
>	  cam lobe.  I got tired of this pretty quick and realized that I
>	  could reduce the hassle by just selecting the two feeler gauges
>	  on either end of the spec range, poking the thinner one in at
>	  each of the five (or so) points until it passed through and
>	  then poking the thicker one in.  If the thin one didn't pass
>	  through at any point or the thick one did, then I went back
>	  and did a full set of measurements.  Does that sound
>	  alright?

Yes.

>	4) I have the dreaded Yamaha valve gasket leak, both from before and
>	  after my sojourn.  What can I use (besides a new gasket and bolt
>	  washers) to seal it against leaks?  I have heard about using 
>	  silicon rubber but I'd like to hear it from a Denizen that I 
>	  trust (know any?).

Silicone seal will work, but it will mean lots of time and
solvents to get everything clean enough for it to stick
properly.  And the next time you take the cover off you'll
have to scrape out all the silocone goo; you do NOT want
silicone rubber loose in your engine, where it might
somehow plug an oil passage.

On the other hand, those specially molded rubber gaskets are
EXPENSIVE, so the silicone approach has its appeal.

>	5) Several of the valve clearances were just below or just above
>	  the spec limits.  Since the range is only 0.04mm and shims come
>	  in 0.05mm steps, is there any point worrying about these ones?
>	  Is it better to be slightly over-loose or slightly over-tight?

No.  Loose is safer.
--

    Chuck Karish          karish@mindcraft.com
    (415) 323-9000 x117   karish@forel.stanford.edu