Distributor cam

George D

George D

Member
Hi, just got done restoring 30 coupe have 350 miles clicked off and all is well. When I rebuilt the distributor I replaced the points cam with a new B style cam that is said to give hotter spark because it increases dwell time. When putting together a travel kit of spare parts I included a condenser, points and coil as suggested. The coil on my car is an original and works well. Yesterday just for fun I changed the points cam back to stock and went for a ten mile sprint with my wife. The car ran great she asked what I had done because it seemed to run much smoother. I'm going to leave it this way my thoughts are that the increased dwell with the B cam may very well reduce miss fire and help with quicker starting but won't it also lead to more stress on the points, condenser and coil leading to less reliability? Any thoughts on this? Maybe I'm just over thinking it.
 
That's all I use with many miles and no problems.
 

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Some of the repro B cams are not machined very well and may be no better, or worse, than a stock A cam.
 
From what I have found with the distributor cams purchased from Sacramento Vintage Ford, Brattons, and Snyder's, the stock cams have more dwell time than the "B" cams. And, like you, have discovered that the car runs much better and gets better fuel economy on the stock distributor cams.
 
I think that all of the distributor cams that are now produced are the B profile. The B cams have an ocean wave profile. The model A dist. cam profile is more pronounced. With the A cam, its easier for me to tell when its on high cam, when prepairing to adjust the points. The B cam gives more dwell for hotter spark. Bill Stipe makes the best cam. Some other vendors sell a dist. cam that is rough and wears out the rubbing block on the points fairly quickly.

More than likely, the reason that it ran better after changing back to the previous cam is that you got the timing set better.
 
The B cam gives longer dwell time than the A cam. I compared them using a degree wheel. With a point gap of 20 mils (.020 inches), the A cam dwell was 32 degrees and the B cam was 43 degrees.
 
From A ... experience. I have seen many repro cams are not machined with true same lobes all around.. there is a big varience.. Use a degree wheel as mentioned or a caliper. Like ford said; GYP parts..
 
Right- the cam that looks like "ocean waves" is the one that works best. My catalog has it backwards, I thought that was the A cam. My sincere apologies for the mixup!

You MUST polish the cam before use, and also check that all 4 lobes provide exactly the same gap. You may ruin 1 or 2 before you get the hang of it and polish up a real good one, so buy a couple extras.
 
Or get one from Bill Stipe and no mods required. I don't know if this number still works 920-467-2895 . the part number is SMC 0033 This cam has 10 more degrees of dwell.
 
Can someone post or refer us to a photo so we can see the difference between the A and B cam? Also, when P.S. talks about polishing the cam, what type of procedure is being used and what are the items needed?
 
Increased dwell time will put a higher load on the coil and it will run hotter temperature. Don't know if that would effect the life of the coil significantly.
 
I would like to see these on a tester and a lab scope to really tell whats going on. Would make a nice post on the actual value etc.
I would do one at no charge if anyone would like to ship me the parts etc???
 
Here you go. Notice the A can has 8 distinct lines, while the B cam has 4 sharp lines.
 

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Tom Wesenberg said:
Here you go. Notice the A can has 8 distinct lines, while the B cam has 4 sharp lines.
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My thanks to Tom W. for posting the photo and explaining the difference between A and B. I have a whole bag full of discarded cams. I went through them trying to determine the difference. The "ocean wave" description didn't help me. The 4 and 8 lines better explain it. I found the difference in the collection I have, but thought the reverse was true.

Tom Endy
 

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Thanks for the photos Tom & Tom. Does anyone know the proper way on how to clean up these old cams so they will not chew up the points block?
 
leo said:
Thanks for the photos Tom & Tom. Does anyone know the proper way on how to clean up these old cams so they will not chew up the points block?
Click to expand...

I've polished them with fine crocus cloth, then keep them lubricated with cam grease. I smear a light coat over the whole cam, so it doesn't rust anywhere on the outside surface.

As Richard mentioned, I've also found about 32 for the A and 43 degrees of dwell for the B cams.
 
Tom, have mercy, what is crocus cloth and is it sold in grades like sandpaper?
 
leo said:
Tom, have mercy, what is crocus cloth and is it sold in grades like sandpaper?
Click to expand...

You might find it on a long roll about 1" wide at an auto parts store. I think I bought my roll at a swap meet years ago. It's a redish color fine grit. No reason a fine sandpaper wouldn't work also, but with the cloth backing, the crocus cloth lasts much longer.
 
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