Distributor rotor.

[wmws]

I have set the timing on my 28 Tudor. Points set at .018. If I advance the timing to about 3/4 down on the lever where I normally drive it the rotor has barely come to the pin in the distributor cap. It is right about at the leading edge of the pin maybe not even quite to the pin. At that point I am at about 23* advanced. I would think the rotor should be covering the pin. I tried posting a picture but don't seem to be computer literate enough to do it. If anyone can follow what I am saying do you have any advice. Thanks.

[Mitch//pa]

The spark advance lever moves the upper plate along with the points... It does not move the rotor....
A good improvement is to purchase the B profile cam for the points

[Tom Wesenberg]

Since the spark lever moves the upper plate 20 degrees, which is 40 crankshaft degrees, 3/4 of the way down would be 30 degrees advance. I always adjust the points to the recommended .020", which will make them open a bit sooner than .018", and this might get your rotor better lined up to the contact.

I read that some repro upper plates had the points located a bit off, and this could affect the rotor location when the points open to create the spark.

[wmws]

Tom, I think opening the points to .020 will make the problem worse. I think your last sentence is probably what is happening as I am using a modern point set. I may try my distributor with original points and see if that makes a difference. Thanks again

[tbirdtbird]

the rotor tip does NOT have to be in perfect alignment with the contact in the dizzy body.
If you play with things in order to accomplish this, you will be off somewhere else that is more important

[wmws]

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Yes tbirdbird but on mine the rotor tip has really not quite gotten to the contact in the Dizzy body when the points open. It is still probably .030 away.

[Tom Wesenberg]

Here is how it should be lined up when the timing pin drops into the cam dimple.
It the timing lever is at the top, then the points should be just ready to open.
I've heard some cams had the dimple drilled off location, but I've never had that happen.
The rotor turns CCW, so if I used .018" instead of .020" the rotor would be further past the contact when the spark occurs.
With the spark lever full down, the spark would occur when the leading edge of the rotor is by the contact.

[old31]

Originally Posted by Mitch//pa

The spark advance lever moves the upper plate along with the points... It does not move the rotor....
A good improvement is to purchase the B profile cam for the points

Pardon my stupidity but what is a B profile cam and what does it do?

[goodoldvic]

To old31, The dist cam with the "B" profile allows the points to stay closed longer to make a hotter spark, I think that's it. The vendors sell them and you can get one from Stipe Machine direct.

[old31]

Originally Posted by goodoldvic

To old31, The dist cam with the "B" profile allows the points to stay closed longer to make a hotter spark, I think that's it. The vendors sell them and you can get one from Stipe Machine direct.

Thanks.

[old31]

Is there a way just by looking at the cam to see if you have an A or B cam installed?

[d.j. moordigian]

In my youth I never saw "new" parts that were new,...just used parts that were new to
me. Now with that statement you should be very mindful of the "back lash" in the drive
for the distributor. If you have the 2 piece shafts that are worn, the drive that is driven
by the cam, there could be quite a bit of slop. Set the dist. cam with all the back lash
on the load side of the slop and see were you are...

[Tom Wesenberg]

Originally Posted by old31

Is there a way just by looking at the cam to see if you have an A or B cam installed?

Yes, the A cam has 8 vertical lines, while the B cam has only 4.

[old31]

Both A and B appear to have 14 vertical lines, or are these old eyes failing me.

[tbirdtbird]

not the serrations on the bottom...the sides of the lobes

[wmws]

I tried my original distributor and now the rotor lines up just as it should. As Tom said in post 3, the points rubbing block is not positioned quite right on the new distributor.

[old31]

Originally Posted by tbirdtbird

not the serrations on the bottom...the sides of the lobes

OK thanks.