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RE: Finding TDC

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Subject: RE: Finding TDC
From: "Tim Mullen" <>
Date: rro, 14 now 2000 09:46:15 -0800
Assuming that you just need to find close to TDC for the leak down test:

A simple way to find TDC of the compression stroke is to:

1 Remove all the plugs.
2 Put your thumb/finger over the hole for number 1 spark plug.
3 Crank engine (I use one of the hand held switches, but you 
      could have some one "bump" the starter with the key)
4 When you feel pressure under your thumb/finger, the piston is
      coming up on the compression stroke.
5 Use the timing marks to finish bringing it up to TDC (assuming 
      that you have timing marks that show TDC).  I.E. rotate the engine
      with the starter, wrench, or as others have suggested, by rolling the 
      car in gear.
6 Repeat for the other cylinders.

On four or eight cylinder cars, you can make a mark on the crank pulley/damper 
to indicate 180 and/or 90 degree increments.  On 6 cylinder cars, you will have 
to mark every 120 degrees (or something else if you have an odd firing V6).

I use some old, un-used nail polish - white or red - to make the marks.  The 
polish dries quickly, and usually lasts.  Note: Do not use your 
nail polish without permission!!  8-)

I doubt that you have to bee that accurate to do a leak down test, just pretty 
close.  The degree wheel is always useful, but it may not be necessary for the 
test, and they can be a hassle to install/use while the engine is in the car 
the radiator/fan(s) are in the way.  I assume that you just want the piston 
TDC to minimize the volume in the chamber...

Tim Mullen

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