I think the water and tube method will work quite well if you shape the tube
into a vertical U about 24" tall. This is called a water manometer. If you
are worried about sucking in water you can place a container of some type
between the cylinder and manometer that exceeds the displacement of the
cylinder. If you happen to turn the engine all the way over the water will
end up in the container and not the engine.
By marking the height of the water column in the tube at its highest point
you can pretty accurately determine the point where the piston breaks over
TDC. There are a few degrees on both sides of TDC where there is not much
piston movement. This method may be accurate enough so that doesn't matter,
but in case it is too difficult to determine the exact highest point the
fall back is to mark both the pulley and the manometer at a point a few
degrees on one side of TDC, move the crank until the piston passes beyond
TDC and the water level comes back to the same point on the manometer, mark
the pulley at that point, measure between the two marks on the pulley and
mark a point exactly half way between them. that is TDC.
Bill Lawrence
>From: bspidell@comcast.net (Bob Spidell)
>To: "Steve B. Gerow" <steveg@abrazosdata.com>, Healeys
>Newsgroup<healeys@autox.team.net>
>Subject: Re: [Healeys] Finding TDC
>Date: Mon, 07 Jul 2008 21:57:50 +0000
>
>Sure, but go a few degrees past TDC and you're sucking water into the
>cylinder (might try it with oil instead of water, however). How do you
>turn an engine at a steady rate--no more than a few degrees a
>minute--anyway?
>
>Used to know an aircraft mechanic who liked to find TDC by putting his
>thumb over the spark plug hole while someone turned the prop. The end of
>his thumb ended up in a cylinder (and no, the mechanic was no longer
>attached to it).
>
>
>bs
>--
>***************************************************************
>Bob Spidell San Jose, CA bspidell@comcast.net
>'67 Austin-Healey 3000 '56 Austin-Healey 100M
>***************************************************************
>
> -------------- Original message ----------------------
>From: "Steve B. Gerow" <steveg@abrazosdata.com>
> > > Bob Spidell wrote:
> > >
> > > Sounds like a great way to suck water into the cylinder.
> > >
> >
> > Haven't done it but can imagine it to be very accurate in that on the up
> > stroke bubbles would appear in the jar and would stop as soon as TDC was
> > reached. If you had a thin transparent tube at the end in the jar, TDC
>would
> > be when the last bubble left and water was just ready to go up the tube.
> >
> > --
> > Steve Gerow
> > Pasadena CA
> > 59 BN6
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