Engine miss

[Kahuna]

Guys
I have a 1939 Ford that I'm working on in an attempt to remove a slight miss that occurs at all engine speeds. So far this is what I've done:

1) rebuilt carb--no change

2) replaced all eight plugs--no change

3) ran a compression test-
results:

Cylinder #

1) 85
2) 85
3) 88
4) 87
5) 82
6) 85
7) 80
8) 85

4) Helmet distributor, 12 volts along with coil

Converted to electronic and tested OK on machine to 5000 rpm- no change

5) replaced plug wires- no change

Next area I will address is the distributor end caps, as I've seen a problem there before with carbon tracking and cracks.

What I'm wondering is about cylinder #7 being a bit low at 80#?
I wonder if I could have a sticking valve that didn't show up during cranking test?
Would this be something that Marvel Mystery Oil might help? I've never used the stuff, but the engine hasn't had anything major done to it in over 47 years.
Just thought I'd ask

Thanks for any thoughts/experience.
If the distributor caps don't fix it, I'll just start drinking..But,
I'll check back in if that fixes it.
Thanks
Jim

[BUBBAS IGNITION]

Whose helmet electronic system are you using and whats the primary resistance of the 12 volt ignition coil????

[Kahuna]

I convert them myself and a friend has the testing machine.
The coil is an original type that I bought some time ago from Macs. (now discontinued)
I use a Mopar ballast resistor,
I have this ignition on both of my cars and they run well. I use the Helmet type with the 11A advance on one and the 68 internals on the other.

Just as an added note, (you have to be old to recognize the name),
I also have a couple of coils rewound to 12 volts by the late and great George Pounden.

[G.M.]

Take it for a drive to get warmed up. In high gear slow down to 8 or 10 MPH. Press the gas pedal slowly and see how the speed picks up. If is stumbles that can be a sign of sticking valves. Drizzle MMO down both sides of the carb as it is running, Pour at least a pint of MMO in the gas tank. Drive about 10 miles and try the slow pick up test again. G.M.

[Kahuna]

Thanks George
I've never used the MMO. Where can I find it?
Napa?
Thanks
Jim

[51504bat]

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Originally Posted by Kahuna

Thanks George
I've never used the MMO. Where can I find it?
Napa?
Thanks
Jim

Marvel Mystery Oil. Napa should have it. If not Wally World has it or almost any parts store.

[B-O-B]

I buy it @ Wally World in the gallon size & I have seen the gallon size @ O'Reilly. If you can't find it try some sea-foam. I even used atf on a f-500 223 I had. It took a qt tho & didn't have to worry about mosquitoes for a while.

[Kahuna]

B-O-B
Did whatever you used work?
Unstick the valves?

[Kahuna]

OK
I replaced the inner distributor caps. No change.
It's gotta be a sticking valve.
I'll try the MMO and see what happens
Thanks to all. I'll report back maybe tomorrow
Jim

[Capt Kirk]

Wont a vacuum test pretty much identify a sticking valve?

[Kahuna]

Hey Capt
I don't know why I didn't think of that. I'll give that a go and see what it looks like.
Thanks
Jim

[ford38v8]

Jim, your definition of "a slight miss"... One cylinder constant miss, or an intermittent or occasional miss? I've been cruising along at 70+ mph, and get a single miss, 8 to 12 ? minutes apart. At that speed, a single miss is kinda jolting! Haven't a clue as to the cause, either!

[Capt Kirk]

It'll identify a lot of other things too. Hope that helps to find your problem.

[ford38v8]

Kirk, Wouldn't his compression test show that as well?

[Capt Kirk]

Ford38. I'm no expert on these flatheads but have an opinion based on my experience with other engines. When taking a compression test, I've been taught to crank till you attain the highest reading. If that happens in 2 revolutions or 12...it doesn't matter. If a valve is sticking, it might not be sticking every revolution. You might get a full compression reading after a longer period of cranking. A vacuum test reveals real-time what the engine is doing. Now, if a valve was burnt or never closing all the way...then yes, it would show on a compression test. A leak-down test is a good thing too. A 5 minute test with a vacuum gauge will reveal a lot.

[B-O-B]

Originally Posted by Kahuna

B-O-B
Did whatever you used work?
Unstick the valves?

Yes it did. The truck sat for long periods & I would not remember to fire it up once in a while. This s*** they call motor fuel can get them sticky pretty quick so I use sea-foam or MMO + marine grade sta-bil with every fill up.

[Kahuna]

Follow up
I think I have found the problem.
I've been using some neat old spark plug connectors. After changing the plug wires with no change to the miss condition, I noticed one of the plug connector felt a bit funny. Upon closer inspection (meaning putting my glasses on), I found that one connector had a loose internal screw (they screw onto the plug wires), and it was somehow broken.
I replaced it and it seems to have cured the problem.
I'll know for sure tomorrow when I have the opportunity to actually drive the car.
Funny how the smallest of items can create havoc on my old brain.
I'll report back tomorrow one way or another.
Thanks again, everyone
Jim

[adileo]

Jim congrats! I know it feels gr8 to resolve a nagging issue. I've had many and this forum has helped on most

[Kahuna]

Hi Andy
Yes, all, it now drives like it should. Makes me happy. I had to wait for it to cool down here, as it was 97 degrees today.
Jim

[36tbird]

Geez, Jim, seeing as how you followed me around in Austin a couple of months back when I had one plug loose with it missing intermittently, I would have thought you would have recognized a plug/wiring issue right away.