Distributor Cam Backlash ?

marc hildebrant

marc hildebrant

Well-known member
Group,

I'm confused over the cam rotation direction for setting the timing. In the Early Ford Service Bulletin, the method to set the timing location to where it "just" opens, is to rotate the cam CCW and then stop at this point.

In a later Ford Service Bulletin, the method, similar to that in Les Andrews Book, is to rotate CCW till you are open/on the lobe and then approach the trip point in a CW direction. This method is to "eliminate the backlash".

But......

If the distributor rotates CCW in normal operation, shouldn't you approach the trip point CCW ?

Marc
 
Viewed from the top, the dizzy shaft goes Anti-Clockwise, or CCW. So, if you physically twist the shaft in the opposite direction, or CW you will be compressing backlash to zero, just as if the cam gear was turning it while running, PUSHING the shaft CCW. With the timing pin/ cam gear at zero, and the top lock screw for the points cam set so there is some friction required to twist the cam on the shaft, twist the point cam CLOCKWISE to take out the backlash while setting.
 
On youtube, there is a video in two parts of Les Andrews giving a presentation to a club meeting on timing the Model A . Very worthwhile !

Search on "Model A timing Les Andrews ".
 

THIS ALL STARTED because the little 8-32 x 1/4" screw in the upper plate stripped out at the 'points' end. So the offending hole [ho] was tapped out to 10-32 brass and ground to length under the upper plate.


Marco Tahtaras..."That is probably a safe bet for most folks as most tend to over advance it when driving. However I've always taught people to set the timing at TDC as I do. If the light comes on at two clicks you are at approximately 8 degrees ATDC."

I watched your video and followed your directions to the letter! And you know what? It's never run so well. Points set to 0.018", close as possible.

The The main things to be sure of is get that pin in the timing gear!
1~Full retard, I used a rubber band to hold it in place, set that rotor edge and pick up point edge exactly as shown for a close timing in need of fine tuning later.
2~I used a multimeter for continuity. Two to three clicks down and it goes silent. Full 'up' it 'whines' again. That's where I tightened up the cam screw. And checked after tightening. It takes a few tries to fine tune those two to three clicks in.

The other thing I did before I had it running well was to take a Sharpie black permanent marker and 'paint' the entire dia of the dist. cam.

After she ran poorly because the timing was off for about 2 minutes I took the cam and looked very hard at the start-stop ink marks left on the cam by the point block. The cam looks very even and symmetrically true to me.
__________________
http://www.abarnyard.com/


Same question. TIMING...OK. No 'wiggly' shafts or worn out parts.
This is from 1999 Marco Tahtaras' site. Model 'A' Ignition Timing- Make it Right.
I paraphrase...

~Points I set for 0.018 with the point block on the distributor cam's high lift area.
~0.018 increases dwell and coil saturation time. 0.020 decreases these.
~0.018 retards timing. 0.020 advances timing when adjusting the dist cam later on.
~The timing pin is in the detente.
~#1 is at TDC.
~Rotor points to #1 firing.
~Test: Upper plate travel is full swing. From notch to notch of dist body.
~20 degrees total advance.
~Timing rod is the correct length and throw.
~She' in full retard. All the way up.
~Rotor's trailing edge [she turns CCW] is flush with the #1 spark pick-up leading edge in dist when retarded.
~Rotor's leading edge is flush with the #1 spark pick-up trailing edge when advanced.
~Test: Full advance/retard is 20 deg, all the way down or up to achieve the above movements. For get about dwell meter readings.
~The points MUST always be adjusted prior to the ignition timing!

Setting the timing;
~Full retard, lever up.
~Loosen cam screw and rotate cam CW as close as possible to opening points.
~Begin tightening the cam screw this removes backlash. Do not open points!
~This takes some doing...till it's right. And tight.
~Turning cam screw CW you feel no movement.
~The SLIGHTEST movement CCW of the tightened cam screw spark's the points with key 'on'.
~Slightest means...you can't see it move but you can 'feel' it move and induce a spark.
~Slightest movement; sparks the points, Turns test light off, Breaks Continuity on a meter, whatever is used to test timing.
~If points won't spark. Setting is too tight and too advanced. Points aren't closing.
~If too much cam movement before points spark, too far retarded.
~Key 'off', dist body on, rotor on, check for 0.025 gap, top-O-dist on and snapped down.
~See how she runs. skip.

Thanks to both Mr. Tahtaras and Mr. Andrews

Again Control Key held down, tap + key to enlarge print.

Hold Control down and tap - to go back smaller.

Timing1of4.jpg


Timing2of4.jpg


Timing3of4.jpg


Timing4of4.jpg
 
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Group,

Well, I have to say that just when I "think" that I know what to do, something happens to change it !

Here is my confusion...in the Les Andrews video, the last step is to rotate the cam CCW to the "just opening point" and then tighten the cam screw CW. This is the procedure in the early Ford Service notices.

In the Les Andrews book and the method I used , you rotate the cam CCW to the points open position on the flat and then CW till it just closes.
While holding the cam in position, lock down the cam screw.

One method takes out backlash, the other doesn't.

What is the method to use ?

Marc
 
I timed both my engines using the Les method. Removed the backlash and when the retard lever is pulled down about 2 clicks the light lites. They both fire up right away, run great, and run about 1/2 way down on the retard lever when running down the road at 30 to 35 MPH. That seems to be the sweet spot. Never ran either one at 50 so would be guessing about how far to advance the lever at that speed. sometimes you have to expeirment a couple of times but it is fairly easy. You will get it right.
 
zzlegend said:
I timed both my engines using the Les method. Removed the backlash and when the retard lever is pulled down about 2 clicks the light lites.
Click to expand...

That is probably a safe bet for most folks as most tend to over advance it when driving. However I've always taught people to set the timing at TDC as I do. If the light comes on at two clicks you are at approximately 8 degrees ATDC.
 
Group,

While spreading manure (gardening), I think that I now see the answer !

It's the tightening of the cam SCREW in the CW direction that eliminates the backlash. I had falsely assumed that the ROTATION of the cam itself eliminated the backlash. That would occur only if you had a slight drag on the cam as you rotated it CW.

The other difference of opinion is with regard to just WHAT the timing should be at full retard in the car. Les A. seems to want a small amount, while Marco wants none at full retard...i.e. 0 degree's at full retard in the car.

Did I get this correct ?

Marc
 
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Marco Tahtaras said:
That is probably a safe bet for most folks as most tend to over advance it when driving. However I've always taught people to set the timing at TDC as I do. If the light comes on at two clicks you are at approximately 8 degrees ATDC.
Click to expand...

Point well taken Marcos. Thank you, Mark.
 
marc hildebrant said:
Group,

While spreading manure (gardening), I think that I now see the answer !

It's the tightening of the cam SCREW in the CW direction that eliminates the backlash. I had falsely assumed that the ROTATION of the cam itself eliminated the backlash. That would occur only if you had a slight drag on the cam as you rotated it CW.

The other difference of opinion is with regard to just WHAT the timing should be at full retard in the car. Les A. seems to want a small amount, while Marco wants none at full retard...i.e. 0 degree's at full retard in the car.

Did I get this correct ?

Marc

Marc
Click to expand...

Marc,

As I see it the clockwise rotation of the cam and the CW rotation of the screw as it is tightened go hand in hand, and you do indeed want a little drag on the cam so it does pull out all the backlash.

Note that Marco's opinion has the advantage of agreeing with Ford Service Bulletins 210 and 346:


IGNITION TIMING

1. Fully retard spark lever.

Joe
 
marc hildebrant said:
Group,

While spreading manure (gardening), I think that I now see the answer !

It's the tightening of the cam SCREW in the CW direction that eliminates the backlash. I had falsely assumed that the ROTATION of the cam itself eliminated the backlash. That would occur only if you had a slight drag on the cam as you rotated it CW.

The other difference of opinion is with regard to just WHAT the timing should be at full retard in the car. Les A. seems to want a small amount, while Marco wants none at full retard...i.e. 0 degree's at full retard in the car.

Did I get this correct ?

Marc

Marc
Click to expand...

Marc. That is what i read into that. I think Marcos has a valid point, but i also think you need to try it both ways and see what you think. It is fairly simple to time one of these so not much effort would be wasted. I might even try the Marcos method and find it is better. Good luck and keep us posted. Mark.
 
Isn't the total distributor advance 20 degrees, rather than the 25 degrees cited near the start of this thread? The difference between the leading and trailing edges of the rotor blade is 20 degrees. The "A" was designed to have a total advance of 40 degrees of crankshaft rotation which is 20 degrees of distributor rotation.
 
ursus said:
Isn't the total distributor advance 20 degrees, rather than the 25 degrees cited near the start of this thread? The difference between the leading and trailing edges of the rotor blade is 20 degrees. The "A" was designed to have a total advance of 40 degrees of crankshaft rotation which is 20 degrees of distributor rotation.
Click to expand...

Yep. Skip must have had a fat finger that day.

Joe
 
Opps FNG here.
Sorry all. Not 'fat fingers', fat head!
I went back and corrected 25 deg advance to 20 deg advance if anyone printed any of this please make the corrections.

skipster.
 
Group,

I settled on the method by Marco where it's "just ready to break" at TDC and full retard.

Car drives good and I'll stay with this for now.

Marc
 
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