[Phil Spargo]

I was at my local book store and somehow came across this "rotor alignment" article.
When I install a distributor, I bring the piston up to TDC, drop the distributor in with the rotor pointing to #1 and rotate the cap to #1 wire. (post) Start it up and set the timing!
Now, saying that... I never even thought of the rotor be off, (in between TWO terminals) just as long as I could time it, I assumed everythings OK! And, has been as long as I can remember.
Is this rotor alignement valid??
In this article the guy has holes cut in a old cap to make sure that the rotor is dead on at TDC!
Please comment!
Phil

 

[Wally]

Well I do it the way you so, have done so for 30 or more years, started lots of motors using that method. I have also used the cut away cap method, works as well.

It's like ideas about how to make horsepower, there are as many as you can count, lots of them work, so take your pick.

 

[Riffers70]

cut-away cap method? Never heard of it. Sounds like you take a same type cap and cut it out so that you can see the rotor at #1 post. Can you elaborate a little more Wally?

Thanks,
Fred

 

[Gene McGill]

Maybe for an engine that you are trying to get an initial timing on, like when you accidently bump the engine over with the distributor out, or your placing the distributor in the engine for the first time. For your basic engine-already-runs-with-the-distributor-where-it-is-but-want-to-set/verify-the-timing-anyway job, it would be a waste of time.
IMHO, when it comes down to needing to do that, you're better off marking on the base of the distributor where your #1 wire lines up to, and lining the rotor with that mark, rather than trying to "see thru" the cap.

 

[Tom Mobley]

The alignment of the rotor tip to the spark plug wire contact in the cap at the instant of spark changes during engine operation. GM's typically line up perfect when the vacuum advance it halfway to full advance and mechanical advance is all in. Also, when assembling a Chevy dist it's possible to put the gear on backwards. There's a dimple on the side of the gear below the teeth, above one of the roll pin holes. This dimple must be aligned with the rotor tip. If the gear is installed backwards and there's no vacuum advance, the rotor tip can be physically closer to the #8 terminal than the #1 terminal when the spark happens. Bummer deal, man.

Personally, I can't imagine why they didn't make the gear teeth symmetrical to the roll pin holes.

Little-known stuff here. I think that who wrote that article was trying to show that this condition existed and could happen, not that he was running his car all the time with the hole in the cap.

Tom (seems like I remember seeing that article years ago somewhere....)

 

[283v8]

Seems someone can always find a real hard way to do a simple job.

------------------

 

[Tom Mobley]

Yup

 

[GaryR]

Phil,
Cutting the hole in an old cap so you can see the rotor tip and checking it with a timming light is just a check to see that everything ( like the drive gear as Tommob mentioned) is assembled correctly. It is not a method of setting the timming. Once you check it, you should never have to check it again.
As Tommob said it will only line up perfectly at one point in the vacuum advance curve. The mechanical advance will not affect the rotor alignment because the rotor mounting plate and the cam that controls the points (or elect. pick-up) are one unit and cannot get out of phase with each other.
I installed a magnetic pick-up in my Delco distributor to eliminate the points. The directions I got with the conversion were wrong, so I had the two wires from the pick-up switched. The car flattened out around 5500 RPM and lost power. Using an old cap showed that the coil was firing when the rotor was midway between cylinders. Modifing the vacuum advance rod moved the breaker plate to make everything line up. After I found out that the wires were crossed, and correcting them, I was able to go back to a standard vacuum advance unit. Now everything lines up correctly, and it doesn't loose power at high RPM.
It is worth checking to be sure you don't have any cheapo parts that are not made correctly, and that your distributor is assembled right.
GaryR

 

[Wally]

Lets us dispel a myth, that little deal about the gear. There is no wrong way to install the gear other than upside down! After market gears, like all the bronze gears, are not marked. So it stands to reason that it makes no difference which way it goes on. The gears are symmetrical, not asymmetrical.

Next the cut away cap was used to phase the rotor to the point cam. Lots of the early distributors had problems with that mickey weld/swedge on top of the shaft, not done correctly or loose. Not for timing, not for peeking at the rotor

 

[GregGillette]

What Ive read, and makes sense to me, is the stock dist. gear has the dimple oppisite of the rotor. The rotor itself is an extended weight. The dimple or small half drilled hole on the oppisite side of the gear keeps entire shaft balanced.

 

[Tom Mobley]

Wally, might want to check that. Look at a gear, you'll notice that the roll pin hole comes out between two teeth on one side and right on a tooth on the other. If it's put on backwards the rotor comes out indexed wrong. I agree that this doesn't change the relationship between the rotor and the point cam but it does change the relationship between the rotor and the body.

Tom

 

[Wally]

tommob, where is the index mark on my brand new bronze gear? I await your answer with great anticipation.