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Old 07-01-2022, 04:45 PM   #21
KR500
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Default Re: How in heck does this thing work? (Nu rex)

Some newbies put to much strain on the wrench when turning the distributor cam ( which they have not sufficiently loosened) and then bend the wrench causing in accuracy which Bob Gray pointed out to me on one of my supplied photos,
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Old 07-01-2022, 04:52 PM   #22
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Default Re: How in heck does this thing work? (Nu rex)

Why must you time the engine perfect?
Gap the points correctly. The starting point is, timing pin in dimple, distributor body on distributor base, then move the spark lever until the upper plate arm just touches the distributor body. Then by some means of your choice adjust the cam to the proper position. The distributor body can be off or on depending what method you use while timing. The reason you start with the distributor body on is to get the upper plate arm in the correct position.
If the body is off when setting the spark lever, you could start out being to retarded. Use the body as a limit stop, not the steering column.
I like using a light across the points. When I pull the spark lever down 2-3 notches the light comes on. There is plenty of movement in the spark lever to make up for a few degrees of miss timing.
A properly timed Model A should never be run with spark lever all the way down.
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Old 07-02-2022, 05:47 AM   #23
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Default Re: How in heck does this thing work? (Nu rex)

Quote:
Originally Posted by aermotor View Post
Piston movement is nearly undetectable moving the crankshaft a few degrees left or right. I think we are overthinking getting within a gnats a**. After starting the advance is determined by depending on the ear and feel, which will not be able to detect a couple degrees either way.
John
Yep.
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Old 07-02-2022, 05:52 AM   #24
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Default Re: How in heck does this thing work? (Nu rex)

Quote:
Originally Posted by Eccentric Old Guy View Post
To get the timing absolutely perfect, the only way to do that is a perfect TDC in #1 cyl, and a timing light that will determine the very instant when the points open.

To find perfect TDC, the timing pin will serve as a reference point, but removing the spark plug in #1 cyl, and rotating the crankshaft while observing the piston through the spark plug hole, is the only real way to find a perfect TDC.

Is there a more perfect way to do it?....and, is it relevant to a good running model A engine?

Seems to me there is a little wiggle room for getting a good running engine, specifically because the spark advance is manual, and not centrifugal, vacuum, or some other form of automatic adjustment.

eog



TDC
As said , too much rotation in the crank at TDC, Dimple is best.

And Its a Model A, it doesn't much care. Set the timing where you want. It'll probably run good.


An ohmmeter [or volt meter] is good for checking the points when setting the timing.

Set it with lever up at TDC.
Upon starting pull lever 1/2 to 2/3 down and go.
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Old 07-02-2022, 07:51 AM   #25
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Default Re: How in heck does this thing work? (Nu rex)

A trick learned from finding TDC on steam locomotives is to mark the driving wheel when the piston is part of the way up, say 3 inches from TDC, then rotate the driving wheel until the piston is descending at the same position and again mark the driving wheel. Half way between the two marks is TDC. TDC on a steam locomotive is needed to set the valve timing.

The same trick can be used on a Model A but will probably require the head to be off. The dimple in the cam gear is, as others have said, good enough.
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