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Old 09-11-2019, 06:28 PM
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Serious miss

sbc in a '37 Chevy. Not a radical motor but healthy. Has a miss that seems like one plug isn't firing. All new plugs/wires. Checked compression and all cylinders are between 150-160. Took vc off and watched all rockers opening and closing valves properly.
Mallory igniter distributor with the Pertronix electronic system that has been in there about 12-15 years.Flame thrower coil recommended for the Mallory. Never a problem till this year. Wondering if it is time to replace the dist with a newer model. I'm limited on the size of the dist because of the firewall thus the reason for the Mallory in the first place.
Any ideas are more then welcome.

Jim

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Old 09-12-2019, 12:03 AM
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What would I do? I'd go to the closest boneyard and buy a used points distributor for a Gen I SBC. I'd stop at the closest NAPA Auto Parts store and buy a new set of points, condenser, rotor and cap. Tell the counter guy they're for a '70 350 Corvette. I'd set the points at 0.019", install the distributor and run the wires. Install a resistor wire from the switch to the coil to reduce voltage to the points. If the miss is gone, replace part or all of your present ignition system. Roll the "Vette" distributor up in a clean towel and stow it in the '37 for another time when you or a fellow rodder needs help. If the miss is still there, then it's either plugs or wires (yeah, I've seen brand new stuff that was bogus) or another part of the ignition system, like maybe a ballast resistor.
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abrasv (09-12-2019)
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Old 09-12-2019, 07:30 AM
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Does one plug show a missfire?
Sure the firing order of wires is correct, you can swap 5 and 7 and it will runs pretty good, just missfires.
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abrasv (09-12-2019)
 
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Old 09-12-2019, 08:49 AM
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Quote:
Originally Posted by abrasv View Post
sbc in a '37 Chevy. Not a radical motor but healthy. Has a miss that seems like one plug isn't firing. All new plugs/wires. Checked compression and all cylinders are between 150-160. Took vc off and watched all rockers opening and closing valves properly.
Mallory igniter distributor with the Pertronix electronic system that has been in there about 12-15 years.Flame thrower coil recommended for the Mallory. Never a problem till this year. Wondering if it is time to replace the dist with a newer model. I'm limited on the size of the dist because of the firewall thus the reason for the Mallory in the first place.
Any ideas are more then welcome.

Jim
That's a very old system as Pertronix electronics go, they usually need component replacement by 3 or 4 years of use.

With your tune up I would have expected a new cap and rotor also, have you looked inside the cap for terminal corrosion and carbon tracks that highvoltage makes when it arcs to ground or to other terminals? Also any condensation or water or oil or fuel for that matter accumulating somewhere inside the cap or housing. Oil gets in by way of a failed shaft seal or bushing, fuel by way of a tear in the vacuum advance diaphragm.

For a small cap HEI I'm currently experimenting with a ProComp/Speedmaster 7000 series with the HEI module in an external doghouse. Interesting little fellow using a customized HEI module to fit in the dog house as it requires a different terminal configuration from GM style module. The cap and rotor are patterened off of Ford points distributor with external spring clips for retention. Since I retired earlier this year I sure don't burn up miles like I used to at a couple hundred a day, so this grand experiment has been installed for 6 months and that essentially spring and summer so it's not been through the wet and cold of winter yet nor garnered many miles so I don't have enough time on the system to make a broad recomendation but so far it is trouble free. This is on a pretty healthy 350 stuffed in an S15 so I'm dealing with your similar problem of no space and all the irritations of a big cam, high compression, loose converter, and tall street gearing in a mix of city traffic and interstate running that is increasingly becomming city street driving on a super slab highway. Getting to dreaming of moving to someplace like Ely, Nevada where it's about 300 miles in all directions to anywhere as in Reno, Salt Lake City, or 'Vegas. Only the reality of 3 heart surgeries and a pacemaker plus the lack of a Home Depot and my wife's resistance prevent this move. I'm taking the hog out today for some mountain time. It seems the entire world is moving here, it's changed Seattle from quaint and quirky little, big city to Manhatten west, just sucks.

Bogie

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abrasv (09-12-2019)
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Old 09-12-2019, 10:35 AM
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No sign of a misfire and all wires are correct. Hitting a swap meet this Sunday in STL and will pick up a different dist. there to try.
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Old 09-12-2019, 11:28 AM
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Toss the Mallory parts and the old PerTronix stuff and install a PerTronix Stock Look distributor. Use a new AC Delco Restoration coil and bypass the coil from the ignition switch to the PerTronix module with red power wire.

The 12v power supply for the PerTronix module will be taken from the ignition switch 12v on/off position. The stock AC Delco coil will be fine and it will fit your coil bracket.

The PerTronix module will provide high coil saturation time from idle to 10,000 RPM or more. No more high speed miss due to point bounce and reduced coil saturation (dwell).

The reason why a PerTronix module begins to fail is because it was installed in a worn out distributor with a point plate that is not level and wobbles and excessive clearance between the drive gear and the distributor housing. My PerTronix Stock Look distributor had .015” thrust clearance right out of the box. The distributor gear to housing thrust clearance should be from .010” to .020”, especially when the distributor equipped with a magnetic “Hall Effect” ignition system instead of the sloppy conventional points and condenser.
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abrasv (09-12-2019)
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Old 09-12-2019, 12:18 PM
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Quote:
Originally Posted by MouseFink View Post
Toss the Mallory parts and the old PerTronix stuff and install a PerTronix Stock Look distributor. Use a new AC Delco Restoration coil and bypass the coil from the ignition switch to the PerTronix module with red power wire.

The 12v power supply for the PerTronix module will be taken from the ignition switch 12v on/off position. The stock AC Delco coil will be fine and it will fit your coil bracket.

The PerTronix module will provide high coil saturation time from idle to 10,000 RPM or more. No more high speed miss due to point bounce and reduced coil saturation (dwell).

The reason why a PerTronix module begins to fail is because it was installed in a worn out distributor with a point plate that is not level and wobbles and excessive clearance between the drive gear and the distributor housing. My PerTronix Stock Look distributor had .015” thrust clearance right out of the box. The distributor gear to housing thrust clearance should be from .010” to .020”, especially when the distributor equipped with a magnetic “Hall Effect” ignition system instead of the sloppy conventional points and condenser.
Liked what I read about this unit so placed the order. Will have it Sunday.
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Old 09-13-2019, 07:44 AM
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New distributor is okay but honestly you never isolated the problem from the information provided. You say the ignition wires and plugs are new and that it sounds like one cylinder is missing. After checking the cap and rotor, I would have pulled the plugs for a look to verify that none were cracked from installation and ohm'd the ignition wires. A quick check if you have headers is a sprinkle of water near the exhaust port on each cylinder or a infrared heat gun if you have one. That will tell you if a cylinder is cooler than the others. If the new distributor fixes the issue then winner, winner, chicken dinner!
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