Spark problem, oa-331(FIXED)

[Stretch44875]

The M108 is running on 3 cylinders at the moment. Did a compression check and all but one cylinder is 120 psi, the other is 70, but firing. Check spark and 3 cylinders are dead, 1, 2, and 6.

So I install new plugs, change wires, clean distributor, clean points and set. Still three dead cylinders.

If I pull the wire on a dead cylinder and install a plug outside of the hole, I get spark.

I swapped plugs with one that was in a good cylinder, same problem.

Any way the plug hole wouldn't be grounded?

No matter what I do or swap, the same 3 cylinders don't fire.

Dennis

 

[Barrman]

RE: Spark problem, oa-331

This is going to sound silly, but spark plugs that spark in open air and under compression, don't always spark under partial compression. Ever seen a spark plug test stand? They are sealed boxes that you pressurize. Most plugs will spark with no pressure, but as you turn up the psi, most will go out at some point and then start sparking again the higher it gets.

I have one in my class and will have to look on Friday what the "green" section of the psi gauge is.

I would suggest cleaning the plugs, pouring oil in the cylinder and then firing it up. If you have bad rings, the oil will seal it off and probably give you all 6 firing and a bunch of smoke. Until the oil burns away that is.

 

[JasonS]

RE: Spark problem, oa-331

Compression takes more voltage to fire. What color is the spark? Fat blue or orange/ yellow?

 

[Stretch44875]

RE: Spark problem, oa-331

Yep, I knew that one... already traded plugs between holes with the same results. All the hole's have 120 psi. One cly that sparks and runs has 70 psi.

All the plugs are new.

Just checked the lobe for the points, it was okay.

Managed to get one more to fire, just missing 1 and 6 now.

Blue spark. Not as fat as I would like, but I'm used to newer stuff.

Dennis

 

[Stretch44875]

RE: Spark problem, oa-331

Got all them to fire temporailry. Left the cap loose, and by lifting it a little, had spark. Going to space the cap up a little and see what happens.

Well that didn't work. Up to one dead cyl, the front one. No more time to mess with...

Next step is new cap, rotor and wires. Anyone have some they want to sell?

Dennis

 

[acetomatoco]

RE: Spark problem, oa-331

Those old REOs, like the 6602s in the 5 tons only like to run flat out....any idling will foul the plugs in short order. I would suggest you change the inner dist cap and the resistor and the condensor and then take it out for a against the governor ride loaded for a few miles and you should see some improvement. They run best when the manifold is glowing red. Also, you an advance the spark timing a little as the original spec is for 68 octane MoGas. I have a new OEM inner cap for $20 plus $5 for priority mail. rampartsllc@aol.com

 

[Barrman]

RE: Spark problem, oa-331

I am glad to read that about revving and manifold heat ACE. I drove my 1952 M35 legally down the road for the first time yesterday. I soon found out that revving it was the only way to get any speed and that my manifold was 500-600 degrees after a 5 mile drive. Now I just need to find a tach so I can not fear while running through the gears.

The more I drove mine, the better it ran. I am convinced that was because it has done not much besides idle for the last year or so.

On your cap problem. Is the vent line actually venting the distributor? If not, you could be building pressure inside the cap which will take up more energy to jump the gap between rotor and cap leaving not much for the plug gap.

 

[Stretch44875]

RE: Spark problem, oa-331

Got it fixed! Found a new distribuator at the swap meet, and it cured it all. Runs MUCH better, hitting on all cylinders. Bumps around some at idle, but sounds like the idle is a little rich. Need to set the timing yet... Very happy to have it running better, going to try it on the road soon.

Thanks for the advice guys!
Dennis