No spark to #4 - Problem Solved

[Brother A]

My A is running on 3 cylinders. Checked the spark to each plug and nothing at number 4.

Swapped plug wires - no change
Put in spare rotor - no change
Installed spare cap - no change

I'm stumped. Any and all suggestions would be welcome. Thanks

Steve

[ford1]

see if the dist cam lobe for #4 is worn, is it opening the points when the dist cam lobe gets to #4

[Franchise_24]

Originally Posted by Brother A

My A is running on 3 cylinders. Checked the spark to each plug and nothing at number 4.

Swapped plug wires - no change
Put in spare rotor - no change
Installed spare cap - no change

I'm stumped. Any and all suggestions would be welcome. Thanks

Steve

Did you try a different spark plug?

[rollingsculpture]

spark plug gap and gap at pointsv and double ck timing

[Barry B./ Ma.]

Could be a bad lead inside the distributor housing. I had that happen once.

[columbiA]

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Have you checked compression on # 4?Maybe burnt valve?Try another spark plug.

[Fred K-OR]

It would seem like you should change the spark plug and the distributor housing and thy that. Maybe one at a time. Also maybe to much play in your distributor shaft.

[Brother A]

Thanks guys. I did change the plug, checked the gap, re-timed the engine and checked the points gap. I rotated the cam and the points seemed to open equally on each lobe. This is a newly rebuilt H&M engine so I doubt it's a valve but I'll check the compression. I had the distributor apart to replace a bad lower plate. (I should mention that this is a "modern" dist.) and all the leads looked fine. My guess is that a bad lead would effect more than one cylinder consistently. Am I correct with that?

Please keep the ideas coming. Thanks

[Mike V. Florida]

What exactly do you mean "modern"? Just the upper plate or do you also have a "modern" cap with true plug wires coming out?

How and where exactly did you check for spark?

[Pete]

Is it an electronic distributor?
I had one with a cracked magnet. It would not fire on one cylinder no matter what till I replaced the magnet.

[Ron in Quincy]

About 85% of problems are electrical. Today I checked a problem one of the fellows was having: no fire to number 3 and 4, 1 & 2 was firing good. Checked the clearance between the rotor and contacts in the distributor body; 1 & 2 contacts had .025 clearance, 3 & 4 there was no clearance. filed the contacts on 3 & 4 until we had .025 clearance. The engine fired up and ran smooth.
The fellow said he had checked the clearance only on lobe 1 and assumed the other 3 were ok.

Ron

[Brother A]

Originally Posted by Mike V. Florida

What exactly do you mean "modern"? Just the upper plate or do you also have a "modern" cap with true plug wires coming out?

How and where exactly did you check for spark?

Mike,
It's a round distributor cap and the condenser is on the top plate. (I have a Simmons HC head on this motor and the traditional style distributor doesn't fit)

To check for spark I grounded my screwdriver to the head and touched the shaft to the plug wire. I see spark and notice a change in RPM at 1,2 and 3 but nothing at 4.

Ron,
I can't check the rotor to cap clearance on this type of cap. However, I thought changing the cap and rotor out with old spares that I had would cover the clearance issue.

[1931 flamingo]

Soooooo, what kind of a dist DO you have?? On mine a while back, new dist body from very reputable supplier, ck'd rotor to contact clrnc, each was way off, reinstalled orig body, perfect clrnc's on all 4 contacts. problem solved. new isn't always better.
Paul in CT

[Patrick L.]

OK, so it appears that you have a ' modern ' distributor with a one piece round cap ?? What style plug wires are you using?? ' modern ' or flat straps ??
It seems you could have 2 defective caps or a defective plug wire if using wires rather than straps.. Have you looked inside the caps for any cracks or carbon tracking ?? Sometimes carbon tracking can be removed with an eraser..

[Richard Lorenz]

I vote for bad distributor body. The number 4 spark sometimes jumps internally to the #3 plug.

[Brother A]

As usual, when I'm stumped it's usually something simple.

As I started putting my original cap back on this morning, I noticed that the cap moved when I pulled the #4 wire off. I grabbed the cap and noticed that I could move it without much effort. I bent the cap spring clips a bit to secure the cap more securely.... started her up and to my great relief it was purring like a kitten. I checked for spark on #4, just to be sure, and there it was. That will be the best 4th of July firework that I see this year. I took her out for a test ride and she climbed the most challenging hill on the way home like a race car.

My sincere thanks to all you Barners that chimed in. All those suggestion kept me focused on this.

Steve

[tbirdtbird]

Thx for the follow-up. we don't get it anywhere near enough to be able to help others

[Mike V. Florida]

As Tbirdtbird said, here the resolution was something not even suggested. Thanks for posing!!

[Brother A]

Originally Posted by Mike V. Florida

As Tbirdtbird said, here the resolution was something not even suggested. Thanks for posing!!

Actually, you guys helped a lot. Ron in Quincy's comment about measuring the gap between the rotor and the contacts in the distributor body was what came to mind when I noticed that the cap was loose. Even though that is not a measurement that I could take on this style distributor cap the same principle applied.