The Stovebolt Site Forums The Shop Area Engine Shop Plugs fouled on one bank

Friend has a 54 Chevy panel with a 350 in it. Yesterday he was driving and everything was fine, then things turned south. He just made it home, plugs on one side are fouled, any thoughts as what might do this. Dave

Does he have dual exhausts? Crumpled pipe?

Ed

I don't know I will have to check.

Maybe the exhaust manifold heat valve (or whatever it is called) is stuck shut causing all exhaust on one side to be forced under the carb through the intake manifold carb heat path to the other side??

Or, intake manifold not sealing on one head and sucking oil/coolant into one bank.

Update, he has replace parts to no avail, today he ran it and it backfired through the carb, he noticed fire come from the carb base, he may have a vacuum leak.

Firing back up through the carb is pre-detonation of the fuel. All can be caused by excess fuel(running to rich), timing to far advanced and the intake valves aren't completely closed before spark, or an intake valve(s) not seating completely. Either way you have fuel igniting back up into the carb. Fouled plugs are a good indicator of running rich. What's he using for a carb?

It could have wiped a camshaft out, but usually things gradually go south when that happens and not all at once like you said. Fire coming out around the base is a sure sign the base gasket is bad and could be the root cause of the original issue.

homer 52 If gasoline flies back up out of the carburetor it may be stopped-up exhaust system,you know like that old schoolbus trick...potatoe up the tailpipe.

This has not been resolved yet, my friend has more ed parts on order, I will report on results, he has put a lot of money into this problem.

Quit shotgunning parts at the problem and do some diagnosis. Try pulling the intake manifold and look for a vacuum leak at the bottom of the ports on the side that's fouling the plugs. Have the heads been milled?
Jerry

I am not doing this Jerry, my friend is. I am just trying to get suggestions to help him.

As the saying goes.... Test, dont guess. Id check the timing chain to see if the chain jumed a tooth. Especially if it happened all at once. Do a compression check also. It will tell ya alot and not cost anything but time....

Compression check was all cylinders good and even, I think he said 145.

Good compression, plus fouled plugs on only one side screams "Vacuum Leak"! A milled head can expose the bottom of the intake passageways to the crankcase unless the intake is also milled to align the ports, and it ALWAYS happens on the bottom. Some NASCAR teams did that deliberately. The engine would run lousy and smoke during caution laps, then clear out and suck a little extra air past the restrictor plate at speed. One backfire can push the bottom of the intake gasket out and create a vacuum leak on an otherwise good-running engine if the gasket is just barely sealing before.
Jerry

Wouldn't a vacuum leak cause a lean condition?

Has he pulled the valve cover on that side. It may be the oil drain holes on the cyl. head may be plugged up letting oil get sucked down the intake valve guides.

George

Yes. According to the original post, it's barely running, which happened suddenly. Sucking air and oil through a leak between the intake and the head will oil foul plugs quickly, and make the engine run rough. Fuel fouling and sooty plugs from running rich, on only one bank is highly unlikely. Sooty plugs indicate a fuel problem. Black, oily deposits are a different can of worms. We simply don't have enough accurate information to do more than guess about this situation.
Jerry

I totally agree, he has shot gunned the process so much we really don't know what is going on. I will report on the final solution if there is one.

Not to mention, the lack of engine specifics dont help in any way of diagnosing this mysterious creature.

By the way what carb and intake are on this thing? Pics?

I know he changed carbs during this exercise plus lots more, not sure about the intake manifold. I have told you all I know.

Well it is running great right now. Long story shortened. He was convinced it was first spark, new distributor installed, then new wires, then he thought carburation and changed the carb. After sitting and talking with him ai guess I finally got him thinking about the intake gasket. When I stopped by his place yesterday he was putting the manifold in and installing the carb. He wanted to let the sealant setup in the valleys so we did not attempt a start. He said I think I am doing a lot of work for nothing! Today he called me and said it was running good. Called me a few minutes ago and thanked me for pushing me on the intake gasket. NOW, I want to thank all of you that contributed to this troubleshooting exercise! Dave

There's an old Winston Churchill quote- - - - - "The Americans can always be counted on to do the right thing, after they have exhausted all other possibilities!" The same can often be said of hotrodders!
Jerry

Jerry, I have dreamed up some ideas on how to check for an internal vacuum leak, how should you check without just replacing the gasket?

If you can block off any kind of crankcase vent system and figure out a way to adapt a vacuum gauge to a valve cover or an oil filler cap you'd probably be able to see at least some vacuum on the crankcase. One of the "smoke generators" used to find leaks in closed loop ventilating systems on newer emission controlled cars might be useful if a test procedure could be developed. If your buddy is dealing with a milled head and a poorly-fitting intake, installing new gaskets might only be a temporary fix until the vacuum distorts the new side gasket. If it was just a gasket installation mistake previously, he might have made a permanent fix this time.
Jerry

Jerry, as long as the engine will run could you use the unlit propane torch trick?

I'd be reluctant to put Propane into a crankcase- - - - -launching a set of valve covers into low earth orbit would be a distinct possibility. I've seen a severely flooded MOPAR 361 engine develop enough fumes in the crankcase to bulge the valve covers and oil pan when a spark plug finally dried out enough to fire. There was a hole burned in one piston, and the crankcase vapors exploded. I felt the breeze as the oil filler cap went past my left ear. We never found the filler cap, and my ears stopped ringing after about 15 minutes!
Jerry

One of my thoughts was to use my differential pressure tester I use to do compression testing on aircraft. The thought was to rotate the engine until an intake valve opens then block off the carb, add pressure to the cylinder and check the crankcase for pressure. The only thing is how much pressure would you dare put on it.

I'd try 1-2 PSI at most. The problem will be getting all the potential leak points in the crankcase plugged- - - -oil filler, PCV valve plumbing, etc. Putting smoke into the cylinder and watching an oil fill point might be more effective. Find a buddy who likes to vape, and let him huff some smoke into the spark plug hole! LOL! You could also loosen up the rocker arms to close all the intake valves and apply a little bit of pressure to the carburetor inlet, maybe with the blower side of a shop vacuum cleaner, or maybe a hair dryer with the heat turned off, and check for leakage at the oil fill cap.
Jerry

Good thoughts Jerry. I am just wondering if this is a permanent solution or it will be coming around again. Time will tell. Dave

Look at the thickness of the head casting where it meets the block below the spark plugs. An unmilled head will be approximately 1/4" thick there. If it's been milled enough to disrupt the head/intake fit and compromise the bottom of the intake ports, the thickness will be closer to 1/8". When I would angle mill heads 0.100" to turn a 76 CC combustiom chamber head into 60CC's, we also had to custom fit the intake to the heads to make the intake ports line up. Ray Charles could have caught my milled heads by simply running his fingers along the sides, but the tech inspectors were too dumb to do anything other than check casting numbers. If a head is milled straight down instead of angled toward the spark plug side, it only takes about 1/16" of head nilling (.0625") to start running into intake runner problems. Once heads are milled very far, the heads and a custom fitted intake need sto stay together as a matched set.
Jerry

I had a similar experience with an Ford inline six. Backfiring through the carb, fouled plugs, etc.

I thought the timing was off so I checked chain tension, Compression, etc. It turned out to be a faulty condenser in the dizzy.

An update here. My friend had continuing issues with this engine, he has now replaced the intake manifold. He told me the old one had evidence that someone did some metal removing and one side is not perfectly flat. He will hopefully drive down to Homer on Sunday for a show. This will test it.

I wish him the best of luck- - - -I'm pretty sure he's going to need it!
Jerry

Today he went Ninilchik to Homer and return and had no issues at all, he thinks he has it whipped . Dave