Beware new distributor cams!

Kurt in NJ said:
Original Ford shafts are concentric to .0001 or less and the surface was ground.
I would expect the cams to have similar tolerances
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Does anyone have a copy of the original Ford blueprint for the cam?

In fact, I think I have heard that the B cam profile is better, so I'd really like to see that one.

I'd like to compare a new reproduction cam to the original drawing.
 
Jim/GA said:
Does anyone have a copy of the original Ford blueprint for the cam?

In fact, I think I have heard that the B cam profile is better, so I'd really like to see that one.

I'd like to compare a new reproduction cam to the original drawing.
Click to expand...

The A and B cam drawings are not online, but you can look at the drawing for the 1941 Ford GP cam (Ford's version of the Jeep), which is extremely similar. Tolerance is .002" across the lobes.
 
That the 'B' distributor cam offers a hotter spark is another Model A wives' tail.

What the 'B' cam does provide a 'softer exit' for closing the points allowing them to last longer. Compare their profiles.

$.02
 
So the question is....where does one go to get a "good" cam? I have what is apparently one of the "questionable" cams. Two of the four lobes are the same and two are way off. Is there a reliable source? If so, who? Thanks.
 
There must be some grubby old original distributors out there. Check for a cam you can polish up and use that. :)
 
jb-ob said:
That the 'B' distributor cam offers a hotter spark is another Model A wives' tail.

What the 'B' cam does provide a 'softer exit' for closing the points allowing them to last longer. Compare their profiles.

$.02
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It does create a hotter spark by increasing dwell, but only at very high rpms, somewhere in the 2500-3000 range. The B engine operates in this range but the A engine doesn’t. That’s why they redesigned the cam.
 
jb-ob said:
Alex, Check in with Mike Keating on that.
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I talked to Mike. He said his testing showed that the A cam profile would not fail to saturate the coil until somewhere past 7000 rpm, so the dwell can't be the reason for the change. He suspects that the B profile slightly reduced wear on the phenolic cam followers used at the time.

He also noted that the B profile has a disadvantage: the extra dwell leads to more heat buildup in the coil. For epoxy coils in particular, more heat can damage the wire insulation over time.

Mike said that if someone was using a modern point arm, which use long-lasting plastic rather than phenolic cam followers, they would get more benefits from sticking with the A cam.
 
Alex,

Thanks for reaching out to Mike and listing his comments 'A' vs 'B' distributor cam.

(Appreciate the interruption as Mike usually speaks way above my pay grade !)

jb
 
I have not been able to determine by your posts whether or not the discrepant distributor cam is a current event or a thing of the past. Which is ti?
 
Bob, I have just bought a car that the previous owner had for 5 years. He told me that he had recently rebuilt the distributor. Since everything looked new I am assuming that it is less than a year old. I would say my problem is a recent one.
 
Ayers1 said:
Bob, I have just bought a car that the previous owner had for 5 years. He told me that he had recently rebuilt the distributor. Since everything looked new I am assuming that it is less than a year old. I would say my problem is a recent one.
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I received a horrible dizzy cam from a club member who claims to have bought it just this year. But it could have come from ebay for all I know.
 
Re: Beware new distributor cams and many other kinds of REPRO parts.

THIS HAPPENS EVERY DAY ...

Some guy whether from USA or China finds some parts and puts them up for sale on Amazon or Ebay.

Many of these parts are defective seconds OR cheap Reproduction parts made by a company that does not have any idea what the parts are used for. They just clone the parts (defects and all) and keep on selling them!


Also many of these parts end up in the trunk of some body's car and are of the same "Quality" and end up sold at swap meets.

Just because they sold them last week does not mean they are any good.

There are many repro junk companies making junk parts.

Float valves are famous for the same junk parts problem.
 
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