Distributer Cap...orientation?

BlueNote2

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Nov 30, 2014
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Hi,

I am changing out the distributer cap and wires on a Mercruiser 3.7 165hp 470.

When I changed to an electronic ignition, I lost track of which way the cap was oriented​
Does it matter which way a Distributer Cap is oriented? Or can I just attach the new wires and put it back on.


When I changed to an electronic ignition, I lost track of which way the cap was oriented.

Sorry if this is a dumb question. I really don't know if this is important or not. Thanks.
 
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Ostsideend

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Feb 2, 2009
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Distributor should have a notch and the cap should have a catch. Or vice versa depending on maker...
 

BlueNote2

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Thanks for answering, Ostsideend,
What about the order of wires clockwise...does that matter?
 

BlueNote2

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22.jpg

Thanks, I think I found the answer.
 
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BlueNote2

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Not sure how to do that (TDC) but was planning on having the yard set the timing, and check a few wires, etc.. in Spring just to be safe.
 
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stonyloam

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TDC is when the number one piston is at its highest point in the COMPRESSION stroke. Look at the timing cover and you will see a pointer with numbers on it. Now take a look at your rotor, and you will see a lined scribed in it. If you line that mark up with "0" on the pointer your #1 piston will be at the top of its stroke. Problem is that is not necessarily TDC, because, since you have a 4 stroke engine the mark will line up at both the compression and exhaust strokes. Couple of ways to figure it out. At TDC your rotor in the distributor will point toward the #1 spark plug wire (the distributor rotates once for every two revolutions of the crankshaft). Or pull the number one plug and hold your thumb over the hole, when the engine is turned over you will feel pressure build on the compression stroke. Lastly if you have the valve cover off, both of the rocker arms will be loose at TDC, on the exhaust stroke one valve will be compressed, the other loose.
 

BlueNote2

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stony,
great explanation. I have been trying to read about it, and that is the first time it made sense. thx.
 

stonyloam

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Thanks. So back to the original question. The cap should only go on one way and #1 plug wire should be marked in some way. Find TDC (if you pull all 4 plugs you should be able to turn the engine over by hand, or with a socket on the crankshaft nut of the rotor). With the cap on, mark the side of the distributor at the #1 terminal. Remove the cap and loosen the clamping screw on the distributor (might be two, can't remember) and rotate it so that the rotor points at the mark you made. Put the cap back on. Now you can get out your timing light and hook it up to #1 wire. Get a little white paint and fill in the timing mark on the crank rotor so you can see it better. With the plugs still out crank it over and note the position of the mark to the pointer on the timing cover. Should be at 4 degrees BTDC (before top dead center). Rember, since the distributor rotates clockwise, turn the distributor COUNTERCLOCKWISE to ADVANCE the timing. You can leave the plugs out when you spin it over.
 
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