The Ford Barn

Ohc Joe · 01-18-2025, 08:56 PM

So wired up the 36 really quick to hear her run before I move on to front end stuff..
Turned over for awhile
Couple times back n forth and nothing
No spark
Remove distributor cap and rotor was broke in half
37 block with crab style cap N rotor all new parts from CG ford parts in Escondido cali
I installed the pertronix unit in there
It's all the way in and spring ring is in there rotor went in smooth no issues
Just strange
Thought I'd post to see if any thoughts or past stories..
Thanks guys
Let me look for the pics

flatjack9 · 01-18-2025, 10:17 PM

Wrong rotor? The 42 and the 46 to 48 are slightly different even though they look the same. One is slightly bigger.

Ohc Joe · 01-18-2025, 10:29 PM

Shoot ok I'll have to look at that

cas3 · 01-18-2025, 10:36 PM

Also, cap is a tight fit to keep out moisture...be sure its seated proper

Lawson Cox · 01-19-2025, 02:01 AM

When installing a new rotor be sure everything clears properly. Spin it over in your hand and make certain everything clears before installing it on the engine. Don't ask me how I know that.

Terry,OH · 01-19-2025, 07:11 AM

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Some of the crabs caps slightly interfere with the rotor usually just one maybe two of the terminals. Rotate the distributor with the rotor and cap in place to find interference before installing the distributor. Slightly file the terminals that the rotor hits removing only enough for clearance. Don't file the rotor.

cadillac512 · 01-19-2025, 09:04 AM

Joe, unfortunately this has become more common. Current rotors/caps can have clearance problems that break rotors. The latest one I worked on had the rotor touching all the cap terminals and I had to file .020" off the rotor contact to make it work.

Drbrown · 01-19-2025, 11:35 AM

Sounds like the rotor, or more rarely the cap, where not on proper or as suggested the rotor may not have been the correct part. The fellows here who rebuild crab (and other) distributors usually check the clearance between the rotor tip and the terminals inside the cap and file-down the rotor tip if to little. Too much clearance and it inhibits the transmission of the spark. Adding a side remark, my '47 came with a pentronix unit and it failed. Spent a lot of money replacing them twice. They always failed when I was far from home. They kept failing and the experts couldn't trace the faults except to note that the failures were probably due to under and over voltage situations. I had the distributor rebuilt back to using points instead an no problems. Like they say "points will always get you home" .... maybe not always but "Usually'.

Ohc Joe · 01-19-2025, 01:07 PM

Good morning guys wow that's crazy I was thinking maybe the housing on the petronics unit might be a little too thick where the rotor slides over I will look into all of that I ordered a cap and rotor I'll keep you guys posted thank you

Ohc Joe · 01-30-2025, 04:41 PM

well got new rotor removed distributor
turned rotor by hand with cap installed and it’s definitely hitting
so sanded contacts inside cap a bit also rotor back n forth till she spun freely
installed it all back and she fired up for the first time in along time
now the radiator madness happens
hopefully tomorrow
thanks guys

Terry,OH · 01-31-2025, 07:38 AM

There are tight tolerance to maintain between the rotor and the cap terminals. If the rotor touches one or two cap terminals file them so there is clearance, file the rotor and you increase the gap between all the cap terminals.

01-18-2025, 10:17 PM	#2
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,600	Re: Crab distributor rotor broke????? Wrong rotor? The 42 and the 46 to 48 are slightly different even though they look the same. One is slightly bigger.

01-18-2025, 10:29 PM	#3
Ohc Joe Senior Member Join Date: Nov 2021 Posts: 114	Re: Crab distributor rotor broke????? Shoot ok I'll have to look at that

01-18-2025, 10:36 PM	#4
cas3 Senior Member Join Date: Jan 2011 Location: Beverly Kansas Posts: 5,301	Re: Crab distributor rotor broke????? Also, cap is a tight fit to keep out moisture...be sure its seated proper

01-19-2025, 02:01 AM	#5
Lawson Cox Senior Member Join Date: May 2010 Location: Above the gnat line in Georgia Posts: 7,082	Re: Crab distributor rotor broke????? When installing a new rotor be sure everything clears properly. Spin it over in your hand and make certain everything clears before installing it on the engine. Don't ask me how I know that. __________________ Life is like a roll of toilet paper. The closer to the end, the faster it goes. It is better to be seen, than viewed. "We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm".

01-19-2025, 07:11 AM	#6
Terry,OH Senior Member Join Date: May 2010 Posts: 5,187	Re: Crab distributor rotor broke????? Sponsored Links (Register now to hide all advertisements) Some of the crabs caps slightly interfere with the rotor usually just one maybe two of the terminals. Rotate the distributor with the rotor and cap in place to find interference before installing the distributor. Slightly file the terminals that the rotor hits removing only enough for clearance. Don't file the rotor.

01-19-2025, 09:04 AM	#7
cadillac512 Senior Member Join Date: Apr 2019 Location: Kansas Posts: 1,172	Re: Crab distributor rotor broke????? Joe, unfortunately this has become more common. Current rotors/caps can have clearance problems that break rotors. The latest one I worked on had the rotor touching all the cap terminals and I had to file .020" off the rotor contact to make it work. __________________ "It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302

01-19-2025, 11:35 AM	#8
Drbrown Senior Member Join Date: Oct 2013 Location: Glens Falls NY Posts: 1,355	Re: Crab distributor rotor broke????? Sounds like the rotor, or more rarely the cap, where not on proper or as suggested the rotor may not have been the correct part. The fellows here who rebuild crab (and other) distributors usually check the clearance between the rotor tip and the terminals inside the cap and file-down the rotor tip if to little. Too much clearance and it inhibits the transmission of the spark. Adding a side remark, my '47 came with a pentronix unit and it failed. Spent a lot of money replacing them twice. They always failed when I was far from home. They kept failing and the experts couldn't trace the faults except to note that the failures were probably due to under and over voltage situations. I had the distributor rebuilt back to using points instead an no problems. Like they say "points will always get you home" .... maybe not always but "Usually'. Last edited by Drbrown; 01-19-2025 at 11:46 AM.

01-19-2025, 01:07 PM	#9
Ohc Joe Senior Member Join Date: Nov 2021 Posts: 114	Re: Crab distributor rotor broke????? Good morning guys wow that's crazy I was thinking maybe the housing on the petronics unit might be a little too thick where the rotor slides over I will look into all of that I ordered a cap and rotor I'll keep you guys posted thank you

01-30-2025, 04:41 PM	#10
Ohc Joe Senior Member Join Date: Nov 2021 Posts: 114	Re: Crab distributor rotor broke????? well got new rotor removed distributor turned rotor by hand with cap installed and it’s definitely hitting so sanded contacts inside cap a bit also rotor back n forth till she spun freely installed it all back and she fired up for the first time in along time now the radiator madness happens hopefully tomorrow thanks guys

01-31-2025, 07:38 AM	#11
Terry,OH Senior Member Join Date: May 2010 Posts: 5,187	Re: Crab distributor rotor broke????? There are tight tolerance to maintain between the rotor and the cap terminals. If the rotor touches one or two cap terminals file them so there is clearance, file the rotor and you increase the gap between all the cap terminals.