Technical My new mallory paperweight

After 20,000+ miles my $50 estate sale Mallory bit the dust. After about 50% in depth, serious, technical diagnosis and 50% throwing parts at a horrible misfire/no spark issue on my 8BA, I finally discovered my distributor cam had 4 lobes considerably less "lobey". A variation of around 8 thousandths between my best and worst lobe made adjusting my points across all eight cylinders an impossibility. I installed my spare distributor and we're off again but here's my question, is my old distributor just a fancy paperweight now? I looked online and couldn't seem to find replacement distributor cams, are they serviceable? The cam has a part number stamped right on it. What's my next step if I want to make this distributor usable again?

 

Make a lamp

 

What vintage is it? Is it the old two piece cap variety? I'm figuring that an eight lobe cam off of almost any other Mallory dual point of similar vintage would be interchangeable.

 

Are the lobes worn or is the shaft bent? Most of my customers think they have wear when the real issue is that the shaft is pushed off to one side, allowing more point lift on one side, less on the opposite. They're pretty soft so straightening shafts is a normal part of tuning distributors. The cam itself is case hardened, so anything rubbing on it shouldn't leave marks.

 

or possibly worn bushing in the housing where the shaft runs . it would be an easy check and fix

 

Just thinking out loud, but I’d agree with the two posts above. Only other thing is it would have been drilled off center and been like that from day one.

I’ve never heard of one or two, etc distributor cam lobes going flat

 

How did you measure the lobes? Did you put a dial indicator against the lobes as you rotated it, or did you use a micrometer/dial caliper and measure the diameter across two lobes, or some other way?

What and how you measured may play a part in the readings you got.


IF, the lobes are actually "worn" that much or manufactured that poorly...... you could try using a hard honing stone and removing metal from the higher lobes to make them all more consistant. Not the best idea,,,,,but its not any good like it is.

 

I removed one of the ground posts going through the body of the distributor and stuck the dial indicator through the hole in the body, touching the cam, and then turned the distributor measuring that way

 

i guess i could put the dial indicator on the shaft above the cam where the rotor attaches and check for any variance.

 

When the distributor was still in the engine i checked for excessive play in the shaft and the bushings still felt nice and tight to me. No movement from side to side or anything of that nature and negligible movement up and down. How would you check the bushings?

 

Bushings could be good but if the shaft is bent just slightly above the top bushing it would make the distributor cam wobble in relation to the point plate

 

While rotating and watching the dial indicator, watch the base diameter, not the lobe diameter. If the base diameter is not steady, then something is bent and wobbly.

 

You should be able to tell if there is any shaft movement by using the dial indicator set up you mentioned and simply using your hand to try to move the distributor shaft. Expect a little movement due to the clearance between the shaft and the bushing. Maybe .001/.002

As for the distributor shaft being bent, that same set up with the dial indicator against the shaft should tell you if it has any bend in it.

If both of those tests are fine, you could use a drill to spin the distributor. Put a little dykem blue or permanent marker on the shortest lobe. Then rotate the distributor cam and put a fine file or a fine honing stone in a place where you can lightly touch the lobes as it spins. When you start to remove the dykem blue on the low lobe, all your lobes should be the same height. Then the question is whether the flat spots are low enough to let the points close. Probably be ok.

 

I’ll be darn, I’ve never noticed that screw plug before, but never had an AM distributor, I assume aftermarket? My ‘59 Chevy 235 had a flip up cap like a generator does. Think that’s the only distributor I had that could take oil like that.

 

Some of the for truck 6 OHV distributors came with an oil port w/flip up cap. Kind of a mini Plews fitting..
The 1974 F-100 300"6 I bought new had a distributor with an oil cup/port..

 

i have a screw like that, never knew thats what that was for. How do you oil yours? just a couple drops of 80/90 or what?

 

10w30