Beware new distributor cams!

Ayers1

Ayers1

Well-known member
I was trying to get my recently purchased car started yesterday and had issues with it firing. I pulled the distributor out to go through it even though it looked like it had all new parts. One thing I noticed was the cam had uneven lobes on it. It looked brand new with no wear on it. On 1 lobe the points opened to 25 thousands. Another was about 18, the other 2 opened up 10 or less. There was no wear/play in the distributor shaft. I have no idea where the previous owner got the cam but if you're having firing issues this is something else to check. Luckily I had a spare and swapped it out. Older one is definitely better!
 
No, I haven't checked that. I did check the gap after I installed a different camera and it was only 3-4 thousands off between the lobes. That could be the shaft. I'll have to check it. Thanks for the heads up!
 
This was a problem with repo distributor parts in the eighties. It would seem like condensors were failing one after another.
 
I remember when it seemed like you had to buy several condensers just to be sure you had a good one!
 
ModelA29 said:
Shaft runout, worn bushings, lots of variables.
Click to expand...


If you notice in my original post I noted that it appears to have been rebuilt and there was no shaft play side to side or up and down. All new bushings etc. I put either an original or a very old aftermarket cam in and the wide gap differences disappeared. I figured I could safely assume that the cam was at fault. I'm hoping it was a short run of a manufacturing defect and was found quickly. A 10 thousandth change between cylinders could definitely make a difference!
 
Make sure the rotor button base is not touching the points, this will do what you are describing.
Basically the rotor button is going on to far down on the shaft. I've found this on two New distributors.
 
Interesting Wick. I've never heard that. I threw the cam in my scrap metal barrel. I'll have to try and find it to see if that's what is going on. Thanks!
 
Wick said:
Make sure the rotor button base is not touching the points, this will do what you are describing.
Basically the rotor button is going on to far down on the shaft. I've found this on two New distributors.
Click to expand...

Very true. Happens during rebuilds.

This happens when folks do not check the position of the shaft (up/down) and put all of the (.015 and or .030) shims at the bottom of housing and no shims on top of housing.

The bottom of rotor rubs on top of points as rotor rotates:

1. Point gap changes as a result.

2. Points rapidly burn when movable point moves up and down with each revolution.
 
Last edited:
You guys really went deep. Nice. But still, some of the new distributor cams are garbage. I have seen one myself. It was pretty bad.
 
I wonder what original tolerance was on Ford made cams ? Couple of.001 ? If the diameter where the cam fits to is out of alignment with the bushings area , may cause an out of roundness too.
 
Original Ford shafts are concentric to .0001 or less and the surface was ground.
I would expect the cams to have similar tolerances
 
It still amazes me what can be learned in what I thought was a simple post! Thanks for sharing all of your information!
 
I went through 4 new cams before i got one that was ground correctly so reproduction cams are not consistant in production, most now come with a"B" profile spec,
Peter
 
You must log in or register to reply here.
Back
Top