wrong rotor position

[Synchro909]

I once had the timing on one of my cars go out of adjustment as I took off from the lights. Like the OP, the rotor was pointing half way between the contacts and the car was backfiring so badly it sounded like WW3. After much head scratching and resetting, I found that the rotor button was faulty. The little protrusion inside it that is supposed to locate in the notch in the cam was barely there. It had been made that way, not broken. It was so small that the rotor was free to move on the cam with very little resistance. I am still surprised that it stayed put for as long as it did.

[alexiskai]

Originally Posted by john charlton

My suspicion is that the cam is not tight on the shaft . With the distributer seated and secure see if you can rotate the rotor by hand . It should not rotate only slack in the drive shaft/camshaft connection . If you can move it the plain washer under the cam could be missing (this is NOT a lock washer) or the maybe repro cam screw is too long and bottomed out. Remove the cam and check the underside it should have clearly defined grooves which help it to lock to the distributor shaft . Take out all the spark plugs so you can rotate the engine easily and use the gizmo on the timing cover to find TDC no 1 . Use Robs picture and rotate the rotor so it is EXACTLY the same as the pic tighten the cam screw use the " New Rex" cam wrench so the cam does not move when you tighten . Put the gizmo and the plugs back and it will run like a champ . The Rob picture is the key you cant go wrong (trust me !!!) As long as the points widest open on any lobe adjust to 18 thou or credit card or thereabouts .When you tighten the screw take out any anticlockwise lash gently .

John in Suffolk County England ..

This is mostly good advice, but I will say that in my experience, using the Nu-Rex wrench with the Nu-Rex upper plate produces slightly different timing than using it with the stock plate. The Nu-Rex plate puts the points at a slightly different angle. If you time it using a light/multimeter, you will end up with the cam in a slightly different place. I only use the Nu-Wrench with stock plates.

[nkaminar]

As usual, Synchro has probably hit the nail. Try turning the rotor back and forth.

[Y-Blockhead]

Originally Posted by alexiskai

OK, the Nu-Rex upper plate is pretty easy to time visually with a B distributor cam. At TDC, looking down from the top, the upper edge of the cam slot should align with the lower edge of the rubbing block as illustrated with red lines in the attached photo. This will position the points just barely closed and they'll open in the next instant as the rotor turns CCW.

This advice applies only to the Nu-Rex upper plate, the stock plate looks different.

I agree with all you are saying but at what point gap do you use? The gap (or dwell) has to be the same every time you set it up this way or the timing will be off. The wider .022" gap the points will open sooner, advancing the timing. Closer gap .018" retards timing.

One thing people often over look is changing the point gap will also change the timing (if nothing else has changed).

[Bob C]

To me the last two pictures look correct, the points are just ready to open.

[alexiskai]

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Originally Posted by Y-Blockhead

I agree with all you are saying but at what point gap do you use? The gap (or dwell) has to be the same every time you set it up this way or the timing will be off. The wider .022" gap the points will open sooner, advancing the timing. Closer gap .018" retards timing.

One thing people often over look is changing the point gap will also change the timing (if nothing else has changed).

I believe it was .020 when I took these photos. This was part of an experiment I did to test timing via multimeter and the Nu-Wrench on both the stock and Nu-Rex upper plates. I had two distributors and did both at the same time and took pictures of the results. That's where I found that the Nu-Wrench did a very good job mimicking the timing you would get from the more tedious multimeter method – but only on the stock plate.

[redmodelt]

RE the washer under the cam, all the original A distributors I have taken apart have a thin special lock washer under them, the replacement "B" style use an off the shelf lock washer.

[Benson]

Addition to post #27.

Look in the Green parts book.

Original distributor cams had two washers one thin lock washer and one thin flat washer.

I found that if the thin washer is missing that the original screws will bottom out and allow cam to move thus the timing will change.

Repro screws might be longer which would make it worse if used with original washers.

I did not look that close.

Recently repro lock washers are about twice as thick as original lock washers.

Because they are so thick you must loosen them much more that originals to make adjustments to the distributor cam.