Mallory Maxfire

[Rootbeer Roadster]

My roadster has about 12,000 miles on it. While driving last week it jerked suddenly just once and then ran normally. I was going about 45 or so. About ten minutes later I heard a few muffled pops coming from the pipes and then another hard jerk. Like before it smoothed out and I drove home for another 45 minute without any problem. I suspect ignition. How many miles should I get before needing to replace the cap and rotor on my Mallory Maxfire distributor? Is there something else I should look at?

[johnnybgoode]

I had similar symptoms a couple of years ago and it turned out to be my Crane electronic distributor. The module had gone bad. Unfortunately that Crane distributor has been discontinued so I ended up buying a new MSD which has worked fine ever since. My problem happened when the car was hot, would run fine for the first few minutes. The tach would also bounce around when this was happening which helped identify it was the distributor. Not saying this is your problem but it sounds similar. It's hard to test for this kind of intermittent problem. Scott

[Rootbeer Roadster]

Thanks for the reply. I’ll keep an eye on the tach if it happens again. If it’s the distributor it would be the second one. The first time got me a ride in a tow truck. Bucket list checked.

[Rdone585]

I moved from Tampa in 2008, curious if I ever met you. Lived in Lutz east of hwy 41. I met 3 people that had just started a build in the year before we moved.
It's likely a firing problem but when you say it jerks suddenly I think of other things that have happened to me over the years. Suspect are the wires, plugs, distributor cap, distributor, connections to the ignition module, or power / grounds to the ignition module. It cold also be bad gas. Just in case check your dip stick to make sure you don't see metal particles in the oil. When you're attempting to diagnose try to figure out if it's a firing problem or something else. Check the plug wires to make sure there are no cracks or burned sections. You could check each plug for proper gap and rich / lean conditions.

[Rootbeer Roadster]

I moved from Tampa in 2008, curious if I ever met you. Lived in Lutz east of hwy 41. I met 3 people that had just started a build in the year before we moved.
It's likely a firing problem but when you say it jerks suddenly I think of other things that have happened to me over the years. Suspect are the wires, plugs, distributor cap, distributor, connections to the ignition module, or power / grounds to the ignition module. It cold also be bad gas. Just in case check your dip stick to make sure you don't see metal particles in the oil. When you're attempting to diagnose try to figure out if it's a firing problem or something else. Check the plug wires to make sure there are no cracks or burned sections. You could check each plug for proper gap and rich / lean conditions.

I believe we met. I met you at your house just off US41 about a mile north of the apex of Florida and Nebraska. You gave me a ride and encouraged me to join the Deep South Cobra Club.

To keep things confusing I drove the car for about an hour this morning and it ran great.

[Rdone585]

I thought so, too much of this seemed familiar. Glad to know your "on the road". Have you checked your distributor? Is it filled with black dust? If so, (wear a mask) and blow it out every now and then. My engine builder told me these distributors with spark advance curves will cause the caps to deteriorate, especially around town driving with low RPMs. If I remember correctly the dust mostly comes from the button at the top center of the cap. He tried to get the new motor he built for me to run smooth with a fixed advance setting, but since I also wanted it to be a street car on occasion it wouldn't behave itself enough to be street-able. So, he restored the spark advance settings and I keep an extra cap and rotor around just in case. I do have to blow out the cap every now and then and each time before taking it to the track. When my builder saw mine after I blew my motor a few years ago, he said if it hadn't have blown then (block where the main bearings connect exploded), it would have had problems soon because of the poor condition of my cap (about 8 years old and numerous track events). I'm still a little concerned about your statement that you felt a jerk, can you describe it with more detail? Did the exhaust just go "pow" from miss fire, or did it actually upset the track of the car?

[Rootbeer Roadster]

I haven’t removed the cap in a very long time. Something I need to do. My original question was a general time frame when the cap and rotor needs to be replaced. Trying to figure out routine maintenance. The pops from the pipes were muffled unlike a loud backfire. The jerks are hard to describe. It’s all engine related like the engine died briefly and then caught. I can’t feel the deceleration as much as the hard acceleration when it catches. I’ll check the items you mentioned. Is there a better more reliable distributor if I go that way. I do want something with a rev limiter.

[Rdone585]

The rev limiter is usually in the ignition system, unless it's an "all in one system" where the ignition is included in the distributor. So, yes with the Mallory Maxfire it's inside that unit. Most builds I've seen have a MSD distributor in the engine, a coil mounted to one side of the engine on the wheel well panels, and a MSD ignition box that is typically mounted on the firewall. But the MSD systems aren't without their failures either.