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By skygazer - 12 Years Ago
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I've been running a Mallory Unilite 3838701 (mechanical only, tach drive) for the last 18 months. It was a cheap way to get my '55 bird running again, along with a used "B" manifold and 4160 carb. The car ran very strong, including a delightful 1000 mile round trip excursion to the CTCI regional with my son. Couldn't be happier with the performance. I have about 5K mi on the rebuilt motor now.
Well, Sunday the car started acting up... it idled low and rough, and would start coughing if I gave it over half throttle under load. It just wasn't making power! Got were I needed to go, and smelled burning plastic... the tach cable was melting to the battery heat shield! The engine compartment was remarkably hot. I immediately figured it was a spark advance issue.
After I got home, I checked the timing... it was extremely erratic! It seemed to shift around while I was watching... at first I though my timing light was screwed up. When I pulled the cap and the rotor, I found that the base plate under the advance mechanism could move back and forth a little, maybe 10-15 degrees. Bummer... I'm hoping that a roll pin didn't back out or shear off, and is now in the bottom of my oil pan (or worse)! I won't have time to pull the dizzy for another week or so. It could be a simple fix... but I kind of doubt it.
Anyone else have mechanical problems with the Unilite 3838701? Perhaps they are so cheap on Amazon for a reason?
In the meantime, I picked up a '57 Mercury dual-point tach drive dizzy on eBay. I have actually been considering this for a while now, and this was a "good excuse" to pull the trigger. Vacuum advance is probably a good thing on a street machine.
I'll update this thread when I figure out what went wrong with the Mallory.
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By Ted - 12 Years Ago
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While I’ve had extremely good luck with the Mallory Unilite modules either with conversion kits or as a complete Mallory distributor, there have been a number of people around me that have had continual problems with the modules failing. I’ve tracked many of those failures down to poor grounds, bad connections, and voltage surges. So with that in mind, if the module is failing or has quit completely, then double check all the wiring on the car for good connections and insure that the engine is adequately grounded to the frame and/or battery before firing up a new module.
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By skygazer - 12 Years Ago
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Electronics seem to be fine. The advance weight base plate seems to be loose on the shaft. Will pull the distributor this weekend and take a look.
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By skygazer - 12 Years Ago
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Finally pulled the distributor. The rolled pin had started to slip out of the hole on the distributor drive gear, causing it to be a little loose on the shaft. The pin shattered when I tapped it out with a drift. A new rolled pin (or "spring pin" in the NAPA catalog) cost 23 cents. The car is running strong once again.
I suspect there are a few little bits of the original rolled pin in my oil pan or oil filter right now.
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By skygazer - 11 Years Ago
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Sorry to reanimate such an old thread, but I just pulled the Mallory Unilite to replace it with a re-curved stock '57 dizzy/pertronix. Guess what... the rolled pin on the Mallory broke AGAIN!
Distributor Shaft Shattered Pin
I'm wondering if anyone else has had this kind of problem. The gear seems a little loose on the shaft without the pin... maybe 2-3 thousandths. That may induce enough of a 'rattle' when the engine is running that it causes stress fractures in the pin.
I replaced the pin again, but I won't use the Unilite in the engine again unless I absolutely have to! |
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By Ted - 11 Years Ago
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Are you running a spur gear oil pump? If so, these have been known to induce some erratic shock loads on the distributor when the gears are not meshing correctly. With the distributor out of the engine and an engine priming tool in place, the oil pump can be turned over by hand with the intent of checking that the pump does turn over smoothly and without any binding.
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By skygazer - 11 Years Ago
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Thanks, Ted. Yes, I have the regular spur gear pump. I'll check the rotation next time I have the dizzy out... seems like a wise thing to do. If the pump ingested some broken pin fragments (ugh!) then it could certainly cause some erratic loading on the drive shaft.
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By rick55 - 11 Years Ago
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I have had similar issues with a Cleveland 351 Distributor in the last. Kept snapping the roll pins. In desperation I used a high speed drill as the securing pin. That shattered as well. The problem was the oil pump pressure was too high and the pump was binding.
The roll pin should not rattle loose in the gear. They are a very tight fit normally. I would check that you are using the correct pin. Maybe you can fit a bigger pin.
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