RE: TDC

Gentlemen:

I hate to tell you this, but at TDC, both valves will appear to be closed no matter which cycle the engine is in. At TDC on compression, both valves will be closed and will remain so for several degrees before and after TDC. When the crank is rotated another 180-degrees, both valves will appear closed again, but in reality they will be in transition, or overlap between the exhaust stroke and the beginning of the intake stroke. It is important to observe the operation of the valves as you rotate towards TDC. After the intake closes, as you rotate the crank, the piston will rise to TDC with no valve movement. If you are in the overlap portion of the cycle, the exhaust valve will close and the intake will immediately begin to open around TDC - depending on the cam specs, but that should help you spot the difference. Simply sticking your finger over the plug hole will quickly let you feel the compression stroke also, and at this time you can carefully rotate the crank (by hand) to TDC. Looking at the mark on the balancer can be a help as you rotate the crank close to TDC. If the balancer is bad (separating at the rubber), the mark may not be accurate. As Russ suggests, be careful sticking your finger in the plug hole! Should your finger actually fit inside the plug hole (my youngest son's will), a piston rising up into your figer tip might hurt a little! You'd have to shove your finger in there quite a bit though.

Hope this is helpful . . .

Bill Dettman

'74 Matador X 401, '70 Javelin 401 BBG

----Original Message Follows----

From: <mail@xxxxxxxxxxxx>

Reply-To: mail-From-javelinman-hotmail.com@xxxxxxxxxxxx

To: mail@xxxxxxxxxxxx

Subject: TDC

Date: Wed, 1 Dec 2004 13:28:37 -0800 (PST)

Having the piston at TDC will tell you that it is

either at exhaust or compression stroke, but by taking

off the valve cover and observing the rockers you can

tell the diff; compression stroke will have both

valves closed, exhaust stroke only one valve closed.

And please don't be sticking your finger into the

hole. Cover the hole with your finger, use a dowel or

spaghetti, a fancy TDC whistle or a good flashlight,

but don't stick yer finger in there.

All these suggestions from me and others are assuming

everything else is in good shape, and that you are

trying to adjust an engine with a jumped chain or

bent/broken valve. Take the time to start from square

one. An old Motors manual from the sixties will give

you a guideline to static time the engine when we all

kept our cars running from the shade of the old oak

tree, without the benefit of all that big city equipment......Russ

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