My Dad used light to look for uneven surfaces.  I was only eight years old
so I don't remember all the details or results but he was a full time
mechanic all his life and this was a routine.  He had a tail light bulb
soldered to a twisted pair.  He dropped it into each spark plug hole, threw
a rag over it, got under a tarp to eyeball.

We used light tables to check flatness of carbon seals for jet engines but
that was a tad more sophisticated than what Dad did.

Harry Watkins
Newton, MS
86 SDL Silver
85 300D Euro
86 SDL Gold
81 240D manual trans

----- Original Message ----- 
From: "Jim Cathey" <[EMAIL PROTECTED]>
To: "Mercedes Discussion List" <[EMAIL PROTECTED]>
Sent: Tuesday, January 03, 2006 10:28 AM
Subject: Re: [MBZ] OT: Genset

> I found my 18" Starrett rule and my feeler gauges.  I wiped down the
> head and block and went looking for warpage.  Using the 0.004" gauge
> (limit is supposedly 0.006") I walked all over the head, both
> directions, and nowhere did the feeler even begin to come close to
> fitting under the rule.  Ditto the block.
> I next calipered the head gasket, which is 0.068" thick.  The old
> gasket is about 0.070" thick, less of a difference than I thought
> based upon handling them.
> Next I placed the head on the block sans gasket.  I had some real
> trouble getting it to sit flat, it looked like there was some
> interference from the locating dowel pins.  I was able to use three
> head nuts to pull it down on that (away from the pushrods) side, then
> I removed the nuts.  It looked pretty good by eye, and probing all
> around it with my 0.004" gauge it only wanted to nose in a bit in some
> places, and only slipped in at one corner of #1, which is not one of
> the places I was seeing leaks.
> Looking at all the studs I found no place where there were
> insufficient threads protruding.  So _that's_ not it.
> So, from yesterday's list I'm only left with surface roughness as a
> potential culprit, and that seems unlikely to be responsible for such
> widespread leaking, especially as the gasket is a rubberized (?) one.
> It seems pretty grippy, unlike the old 2-layer metal one.
> Sigh, no real smoking guns.  I suppose it is possible that the
> business with the dowel pins could have been responsible.  If the head
> got started clamping down while it was not seated flat to begin with
> it could have gotten 'trapped' at a bad angle and leaked, even though
> it looked OK by eye.
> The current plan is to put it back on again but this time paying more
> attention to getting it flat before I start torquing the nuts down.
> If it leaks again the plan is to remove the head and use that spray-on
> copper gasket sealant I bought yesterday.  If _that_ doesn't work
> I'm not sure what I will do.
> -- Jim

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