Distributor Shaft End Play? - 460 Ford Forum
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post #1 of 5 (permalink) Old 09-22-2019, 05:33 PM Thread Starter
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Distributor Shaft End Play?

I fired up the 460 in the jetboat yesterday, and she was backfiring through the carb, running very rough. I checked timing, it was 40-60* at idle! She would die quickly if dropped to <30*.
Pulled the cap; it and the rotor are pretty chewed up, the rotor more-so than the cap. The rotor coil pickup tab is crushed into the rotor body. the end of the rotor arm is very chewed up. Obviously riding very high in the cap. The cap has some wear at the top of the contacts, the plastic has some shearing/wear.
This must have happened recently; I started it once a few months ago for 10-15sec, was getting it ready to finally get it in the water this year.

There is approx 1/8" vertical play in the distributor shaft, no perceptible side play. Dist is a Prestolite IBM-7025s (NOS a few years ago, limited hours on it) with a Pertronix 91582 Ignitor II conversion kit. Have several seasons with this converted dizzy and have had no problems.

Wondering how the rotor tab would get so crushed and how the rotor would contact the cap interior if the shaft is drawn downwards.

Also curious about the vertical end play. Is that something that is a precursor to major failure, or a normal amount of play?

1978 Glastron/Carlson CV23; 466ci/Berk
1997 Newmar Mountain Aire 3757; 460ci
1964 Falcon 'vert; 260ci, 351w 4v heads, C4, etc
2000 Big Dog Bulldog; 107" S&S, Shorty G, Bassani, etc
1999 Tahoe
2004 Saab 95 Aero
1980 Bradley GTE
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post #2 of 5 (permalink) Old 09-22-2019, 07:07 PM Thread Starter
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I rechecked the rotor fit to see if that could be an issue. I bent the coil contact tab back where it should be; the rotor seems to sit down in the Pertronix spacer at the correct height, and the fit seems pretty tight on the dizzy shaft. Installing the cap did not push the coil tab back into the rotor body.
I've ordered new cap & rotor, will see how it works before spending a wad of $$ on a new marine distributor. If the end play is an issue, I'll have a new dizzy on the way.

1978 Glastron/Carlson CV23; 466ci/Berk
1997 Newmar Mountain Aire 3757; 460ci
1964 Falcon 'vert; 260ci, 351w 4v heads, C4, etc
2000 Big Dog Bulldog; 107" S&S, Shorty G, Bassani, etc
1999 Tahoe
2004 Saab 95 Aero
1980 Bradley GTE
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post #3 of 5 (permalink) Old 09-23-2019, 11:46 AM
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Cool

End play is typically about .040" give or take. .125" seems excessive.

Is there any garbage inside the distributor to indicate damage?



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post #4 of 5 (permalink) Old 09-23-2019, 06:56 PM Thread Starter
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Scotty,

No debris inside other than the rectangular plastic piece that covers the rotor arm and some plastic/nylon shards from the tip of the rotor.
The only similar distributor reference I have is the one on my 64 Falcon vert. It has roughly the same axial play, maybe a bit less. As far as I know it is the original Falcon dizzy; I've had her since 1985 and have never replaced it.

I'm going to order another Prestolite dizzy, see if it has less end play. It's cheap insurance!

1978 Glastron/Carlson CV23; 466ci/Berk
1997 Newmar Mountain Aire 3757; 460ci
1964 Falcon 'vert; 260ci, 351w 4v heads, C4, etc
2000 Big Dog Bulldog; 107" S&S, Shorty G, Bassani, etc
1999 Tahoe
2004 Saab 95 Aero
1980 Bradley GTE
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post #5 of 5 (permalink) Old 09-24-2019, 07:24 AM
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We have found that the pertronix instructions say to use a ford rotor. They mean it. Using an aftermarket rotor caused the same issue on a 351C, the OD of the bottom of the rotor does not let it seat properly in the pertronox module and holds it up too high.
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