DELIMA - MOTOR MISSING on 3 & 4

[nicklm]

We recently took our 1926 Touring into the Safety Harbor 4th of July parade. Car ran great about 10 miles there and nearly back. Best the car had run for years with new plugs, timer, one rod replacement, head gasket, starter and oil change.
After the failure of #3 and #4 cylinders to run the car was brought home by flat bed, AAA. It was running great and no skipping or falter, just quit running on 2 cylinders. We have worked on it between my company work and rather warm Florida heat only to NOT discover the problem. This is what we found:
1. All cylinders have nearly equal pressure, apx. 50 pounds. (No blown head gasket.)
2. All cylinders have strong spark at the plugs. Only 1 & 2 make a difference when grounded, 3 & 4
nothing when grounded.
3. Removed the intake manifold to check for leak. No leak and no blockage from carburetor to block.
Reinstalled. No difference - 3 & 4 still not working.
4. Cleaned and inspected the new, New Day timer with still strong spark on all cylinders.
5. The original coil box attached to motor at water port. All seems normal there, I think.
6. Changed positions of plugs and coils with no difference.
7. Discussed with several here and cannot find a solution yet.
Please offer anything you can think of to solve this problem. Car had never run as strong just before this failure. I have owned it since early 1960's. Usually great power with higher compression head.
Thanks for any and all suggestions.
Nick






































no difference

[Philip]

I have the same issue I think it is weak fire that does not fire the plug under
Compression. I'm going to try a distributor

[RVA23T]

I have the same issue I think it is weak fire that does not fire the plug under
Compression. I'm going to try a distributor

Why not look at the plugs then?
Swap the Suspect plugs, one at a time to a position that works or try new plugs.
I don't see where a distributor is going to make a defective plug that will not fire under compression work any better than a defective plug that will not fire under compression.

[paulgriesse]

I`d suspect a timer problem.....Its possible you might be getting a strong spark at the 3 & 4 plugs while in a static (not running) position , but if their not firing while running this could be due to a timer brush problem or the timer not centered properly on the timer cover. Use the centering tool and maybe try a differant timer? Good Luck! an interesting problem......

[Mark Gregush]

Check the lifter/valve gap. Cold engine might have enough clearance that valve seals but when heated up, that gap closes up because of expansion not allowing the valve to fully seat.
The OP said they moved the coils and plugs around and the issue did not change. I would rule plugs out. What it could also be is, there could be an open in the primary winding that lets the coil(s) work when cold but as they get hotter no longer function as they should.
Have the coils been rebuilt or tested or have you checked them in any way?

[TRDxB2]

Did you check for continuity in the wires - commutator to coils & then coils to plugs?

[TXGOAT2]

Make certain the plug and timer wires are in the proper order. Be sure the timer wires don't have any insulation issues that could cause shorts, either to ground or to one another. Be sure that the plug wires are not touching one another or anything else, so far as is possible. Do not bundle them together neatly. Be sure the plug wires are metal-cored, and not radio suppression type.

Problems with coil box insulation are common, and not always visible upon inspection.

Problems with coil "button" to coil box contacts are also common.

Coils can buzz merrily and throw impressive sparks and still be so far out of proper adjustment that the engine will run very poorly.

A number of things can cause coils to go out of adjustment or otherwise malfunction, including loose adjustment hardware or issues with points or condensers.

[TXGOAT2]

Was the head retorqued properly?

[speedytinc]

Look in 3 & 4 thru the spark plug holes looking for full opening & closing of the valves.
If something seems a bit off, pull the valve cover & look @ valve gap & lifter trouble.

These symptoms mirror a case of defective lifters.
A few defectives were sprinkled among good ones.
The heads were to thick & resized after heat treat. The heads wore away losing lift.
Anyway its a simple enough thing to rule out.

[Scott_Conger]

1. Before any swapping, cleaning or fooling around... what did the plugs look like RIGHT AFTER the breakdown?
2. after the car starts and only runs on two cylinders, can you smell raw fuel in 3 & 4 when the plugs are removed?
3. after the car starts and only runs on two cylinders (with perfectly clean plugs installed) what do the 3 & 4 plugs look like when removed?
4. when running on 2 cylinders, will turning the mixture knob 1/2 turn richer and then 1/2 turn leaner than normal affect the car in a positive way?

oily
dry black soot
tan
white

immediately following the breakdown, which plug was which (above condidions)?

other than a blown head gasket which you do not have, there are very few things (only 1 actually) which has a direct combined effect on 3 & 4 simultaneously, and that is fuel failure due to vacuum leak resulting in a bolixed up mixture. You cannot detect a vacuum leak at the intake manifold by removing it and unless you know what or how it failed, new gaskets are not a guarantee of success - it only takes a single aborted installation involving a slight torque and subsequent removal to align again to have dinged the seal to where it will not work correctly when everything is aligned (the copper 3 in 1 with gland rings are the worst for this)

[nicklm]

Thank you all for replies. I think I have looked at most all that have been suggested and I have:
Examined all plugs and changed positions, looked at sparking outside of the cylinders and for the most part seem same as normal. Plugs stayed clean.
Changed positions of all coils with same results. 3 and 4 not working.
Cleaned and checked the new, New Day Timer. Will go carefully thru the wiring next. Replace the timer.
Checked operations of the Pistons and valves thru the sparkplug hole.
None of the wires seemed to be sparking where not supposed to in nighttime observation.
I will try to go over each operation of and continuity of the wiring, timer, coil box, coils, and plugs to see if there is an electrical problem. All seemed ok before but it doesn't mean I haven't missed something. (Obviously I have or it would be fixed.)
The failure was immediate for the both cylinders, not gradual nor intermittent. (Same bridge you may remember, Scott, that may have bad karma.)
The head was off less than 500 miles ago when a tech seminar group replaced a rod that was loosing the babbited rod bearing. Then a new timer and plugs were installed followed by a rebuilt starter from Langs.
I know I am repeating the same story and I really appreciate any and all responses.
Thanks,
Nick

[Scott_Conger]

Good luck, Nick

that's a head-scratcher

In any event, with clean plugs and an immediate failure like that, it sounds all but certain to be electrical - and to that end, being that it is the next in the fault-chain to affect two coils simultaneously, I'd sure slap the old timer on there for a quick check

I once had a single cylinder go bad and it was a failed solder joint on the timer/coilbox loom down at the timer. I realize your plugs still fire out on top of the head, but wonder if there is wiring damage which has introduced resistance in the wire? Wouldn't hurt to put an Ohm meter on each of 4 wires and give them a healthy jiggle. Since the timer was replaced recently also perhaps screws on the timer lugs worked loose?

[DanTreace]

Examined all plugs and changed positions, looked at sparking outside of the cylinders and for the most part seem same as normal. Plugs stayed clean.
Changed positions of all coils with same results. 3 and 4 not working.
Cleaned and checked the new, New Day Timer. Will go carefully thru the wiring next. Replace the timer.

So you have normal (observed) sparking when lying spark plugs 1,2,3,4, on the cylinder head, with switch on BAT, and hand cranking over to have each plug fire in proper order 1-2-4-3 in air lying on the cylinder head?

Then either some plugs are leaking at the higher compression of running motor, or some coils aren't capable of firing at such higher compression, or very low DC current to the coils.

[Norman Kling]

Two additional things to check. !. Intake manifold leak allowing a lean mixture on two adjacent cylinders. Even with a good spark it would not fire because too lean . 2. arcing in wood of the coil box. If the wood has gotten wet, it could cause a spark to burn a carbon path into the wood. It might be enough spark to cause the plugs to spark out of the car, but the higher compression causes the spark to jump the wood. You might be able to find that kind of problem by looking under the hood after dark with the engine running. If you see any sparks it is arcing.
Norm

[Moxie26]

Remove spark plugs three and four, with an analog meter check for continuity from spark plug terminal to the center electrode. If the needle does not move, it indicates a bad plug.

[paulgriesse]

Any progress/solution on your #3 & #4 cly. problems?