Tech Tips:
Finding Top Dead Centre

From: rjquick [ronjohn(at)alphalink.com.au]
Sent: Wednesday, January 1, 2003 2:22 PM
To: hillman@can-inc.com
Subject: "Hillman " Hillman Hunter timing details please

This message forwarded by the Hillman List.

Hi There

I have an ancient Commer Motorhoma circa 1964 that has a Hillman Hunter motor 1725 cc installed.  I have just reconditioned the motor and am a bit puzzled on the timing markings on the crankshaft pulley.  There are I think 13 of them, each of which represents 5 degrees.  My problem is I am uncertain as to which one is TDC as there seems to be an additional mark on the pully edge where the fan belt goes around.  Is this TDC, approximately 5 divisions from one end or is it the marking at the end.

Any help would be appreciated.

Ps any help on the centrifical advance settings and vacuum advance setting would also be appreciated.

Thanking you for your assistance     Ron.

From: Alkon [alkon(at)bigpond.com.au]
Sent: Wednesday, January 1, 2003 3:42 PM
To: Hillman List
Subject: Re: "Hillman " Hillman Hunter timing details please

This message forwarded by the Hillman List.

Hi Ron

Usually the timing marks have a larger "tooth" for TDC and the others at 5 deg intervals.
Sometimes these timing marks can be out but there is a simple way to check.
Often there will be a saw cut in the pulley edge indicating TDC
Pull no 1 spark plug and turn the engine so that it is approaching TDC on No 1 compression stroke.  Now the professionals use a dial gauge to accuratelly measue where TDC is but us bush mechanics just poke a pencil or screwdriver down the spark plug hole so that the long end of it is able to move up and down as we carefully turn the engine.  Need to be carefull with the screwdriver not to jam it through the top of the piston.  As the engine is turned carefully through TDC the end of the screwdrive describes an arc.  The middle of the arc is TDC.  You will find that there is a very lttle movement as the piston passes TDC so you need to gauge the position by rocking the crank back and forth to find the middle position as the screwdrive swings up and down.  Even the professionals using a dial gauge measure the same piston height about 20 deg each side of TDC and split the difference.  Even in the absence of any visible timing marks it is possible to set timing using this technique.  I always start with static timing points open at TDC and work from there.
I find that slavish adherence to the "numbers" of advance is not really helpful with the poor fuels we have these days and always set my ignition timing by "ear" followed by the road test.  The maximum advance that will work without those engine destroying knocking noises is what I go for.

55 Californian

And again, in response to a later query.

From: Keith Johnson [keiths55(at)bigpond.net.au]
Sent: Saturday, October 02, 2004 2:49 PM
To: minx [hillman@can-inc.com]
Subject: Subject: Re: "Hillman " That'll teach me!

This message forwarded by the Hillman List.

Finding top dead centre.

Easy :-)
Pull out the spark plugs.
Turn engine until no 1 is at the top.
Stick a long piece of "something" about the diameter of a pencil in the spark plug hole.  Now I use a screwdriver but don't want to be responsible for somebody poking a hole in the piston :-)
With the "device" or "tool" resting on top of the piston and against the top edge of the spark plug hole, rock the crank back and forth.  You will find that the free end of your "tool" moves up and down as the piston goes up and down.  It is pretty easy to find the exact point of TDC this way.  Trick is to rock it between two points that push the "tool" the same amount and the halfway point is TDC.

Doesn't sound technical enough?
Well pull of the head obtain a dial gauge and do the same thing.  You will find for a part of the rotation through TDC the gauge does not move.  The engineers book says to turn it back until it starts to move.  Note the reading and mark the pulley.  Turn it forward till you get the same reading and mark the pulley.  TDC is half way between the two marks.
That backyard "tool" has an amplifier action as the short end moves a small amount and the hanging out bit a corresponding larger amount.  You may need a helper but it is dead easy to get two marks on the pulley equally spaced either side of TDC.  You can check if the timing mark on your pulley is correct this way as well.

Many clever engineering solutions from years ago never used sophisticated measuring intruments.

If you think about it the piston doesn't move much as the crank goes over TDC.

Keith    Agricultural engineering solutions :-)

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