Keep fouling number 3 and 8 plugs

[Lawrence S.]

I have fouled number 3 and 8 plugs too often in my 67 L-36. I have adjusted the carb to what I feel like is in spec. I have replaced the plug wires, even though I have used the original dated code repro style. I am running stock points, coil etc. The car is basically an original car with 66k miles on the engine. Not sure what the next step I should take to remedy this problem. I guess I could install a Pertronix system. Have had good luck with this in my 67 L-79. Any ideas on what I should do next?

Thanks Guys,

Lawrence

[Joe R.]

Re: Keep fouling number 3 and 8 plugs

Lawrence,

A 67 with 66K miles on it surely has some valve stem seals that have gone away. Probably the intakes are sucking a little oil down the guide. I wouldn't panic but employ a mechanic to change ALL the seals on the valve stems. The springs will have to be removed to accomplish this task so a mechanic that is familiar with this problem would be the best to use. There are several designs used but as I say follow the advise of a recommended local mechanic.

JR

[Lawrence S.]

Re: Keep fouling number 3 and 8 plugs

I agree Joe. I can get a little puff of smoke on start up on occasion. Some of the plugs are oily, sooty and look pretty bad. I was hoping a hotter plug other than the 44xl will help burn this off. I will move towards new valve stem seals.

[Wayne W.]

Re: Keep fouling number 3 and 8 plugs

You need to install new plugs and run the car for a while, but not long enough for them to foul. Then pull them to see whats going on. After it is fouled it is hard to tell exactly whats going on. If you have a build up of hard material on the tips, it is likely the valve guides and seals. The seals on these cars don't often fail. They are simple o rings inside the spring retainer cap. Not much chance of that failing, but the guides do get worn and since the design allows a considerable amount of oil down the valve stem, it causes problems. When you do the seals, replace the original ones and add bonnet seals on the intake valves. That will solve the problem.

[Gene M.]

Re: Keep fouling number 3 and 8 plugs

If you have worn guides replacing only seals is only a band aid. Guides and valve job go a long way for a better running engine. Check the rocker arm and tip wear while you are in there.

[Duke W.]

Re: Keep fouling number 3 and 8 plugs

I agree Joe. I can get a little puff of smoke on start up on occasion. Some of the plugs are oily, sooty and look pretty bad. I was hoping a hotter plug other than the 44xl will help burn this off. I will move towards new valve stem seals.

Those plugs are not hot enough for normal road use. Install AC heat range 5 or equivalent. Also, get a handle on the actual rate of oil consumption before you start changing parts. Excess oil consumption in a couple of cylinders is not that big a deal as long as it doesn't foul the plugs to the point of misfire.

Duke

[Michael H.]

Re: Keep fouling number 3 and 8 plugs

I have fouled number 3 and 8 plugs too often in my 67 L-36. I have adjusted the carb to what I feel like is in spec. I have replaced the plug wires, even though I have used the original dated code repro style. I am running stock points, coil etc. The car is basically an original car with 66k miles on the engine. Not sure what the next step I should take to remedy this problem. I guess I could install a Pertronix system. Have had good luck with this in my 67 L-79. Any ideas on what I should do next?

Thanks Guys,

Lawrence

Lawrence

If your 66 has the original valve stem seals, it's very likely that this is your problem. The original design seal was nothing more than a rubbery umbrella on the valve stem. After many years of heat, the seals actually crumble and fall off the valve, or at least leak badly.
The later design from GM was a new valve spring retainer with a seal included. Or, I suppose you could use an aftermarket seal that is similar to original production.

Changing seals on a big block isn't a difficult task if you have the necessary tools and compressed air available.

As far as spark plugs go, if the engine is in decent shape, you shouldn't need anything hotter than the original recommended 43 heat range. If it runs a bit rich or uses a little oil, a 44 would be ok. I wouldn't go any higher on the heat range though. The original recommended spark plug was a 43N. These engines ran ok with 43N's when new and that was a time when fuel still contained lead.

Since today's fuel is lead free, there's no reason to automatically use hotter plugs to cover up a different problem.

I've had the same set of AC R43N plugs in my 66 425 HP 427 car for about the last seven years with no issues.

[Ken A.]

Re: Keep fouling number 3 and 8 plugs

43N's were a whole lot different back in 66, but they were still bad. GM back then recommended Champion N65Y, a race plug used on Chrysler Hemi's for any HP BB. Today I would recommend something comparable to 45N. If you have set of R43N's, a RESISTOR plug, that still hit a redline, then I'm amazed.

[Michael H.]

Re: Keep fouling number 3 and 8 plugs

43N's were a whole lot different back in 66, but they were still bad. GM back then recommended Champion N65Y, a race plug used on Chrysler Hemi's for any HP BB. Today I would recommend something comparable to 45N. If you have set of R43N's, a RESISTOR plug, that still hit a redline, then I'm amazed.

If someone can't keep a big block running properly with 43 heat range spark plugs, with today's gasoline, there's something wrong. I've owned a LOT of big blocks over the decades and driven them all over the country without fouling 43's.

If the engine is huffing oil or running rich, like we used to do back in the 60's, of course 43's won't live long. Back then, a speed secret (that didn't work) was to increase the size of the main jets by a few numbers. Spark plugs wouldn't survive but everyone was convinced that engines needed a lot more fuel to be fast.

I rebuilt the engine in my 66 425 HP in 1984, just in time to participate in the NCRS Copper Mtn Colorado road tour. The entire round trip from Illinois was over 4500 miles and the engine never missed a beat. In fact, that same set of plugs was still in the engine for another 4,000 miles without issue.

I still drive the same 66 to local car events and I probably have 5,000 miles on the 43's that have been in it since I left Illinois and drove it down here to Florida.

[Joe R.]

Re: Keep fouling number 3 and 8 plugs

If someone can't keep a big block running properly with 43 heat range spark plugs, with today's gasoline, there's something wrong. I've owned a LOT of big blocks over the decades and driven them all over the country without fouling 43's.

If the engine is huffing oil or running rich, like we used to do back in the 60's, of course 43's won't live long. Back then, a speed secret (that didn't work) was to increase the size of the main jets by a few numbers. Spark plugs wouldn't survive but everyone was convinced that engines needed a lot more fuel to be fast.

I rebuilt the engine in my 66 425 HP in 1984, just in time to participate in the NCRS Copper Mtn Colorado road tour. The entire round trip from Illinois was over 4500 miles and the engine never missed a beat. In fact, that same set of plugs was still in the engine for another 4,000 miles without issue.

I still drive the same 66 to local car events and I probably have 5,000 miles on the 43's that have been in it since I left Illinois and drove it down here to Florida.

Michael,

Do you still have a tool box with valve spring tool, several springs, several black umbrella seals and a couple of push rods??? Brings back a few memories doesn't it???

JR

[Lawrence S.]

Re: Keep fouling number 3 and 8 plugs

I know I will foul 43's if I am fouling 44's. Again it is just two cylinder's that are fouling and it looks like oil and soot on the plugs. Not excessive carbon build up. The plugs in the other cylinders for the most part look like they are operating correctly. The color is a light tan for the most part.
If I wanted to run number 5's in number 3 and 8 cylinder is this an issue to run a hotter plug in a few cylinders? I can't see how it would be a problem?? But I am not sure. What do y'all think?

[Michael H.]

Re: Keep fouling number 3 and 8 plugs

I know I will foul 43's if I am fouling 44's. Again it is just two cylinder's that are fouling and it looks like oil and soot on the plugs. Not excessive carbon build up. The plugs in the other cylinders for the most part look like they are operating correctly. The color is a light tan for the most part.
If I wanted to run number 5's in number 3 and 8 cylinder is this an issue to run a hotter plug in a few cylinders? I can't see how it would be a problem?? But I am not sure. What do y'all think?

Lawrence

Yes, you can run a hotter plug in the cyl's that are fouling the plugs. It won't hurt anything.

Eventually, though, cyl's that use excessive amounts of oil tend to detonate a bit because of red hot chunks of carbon in the combustion chamber and on the spark plug itself. Detonation isn't a good thing. It will eventually damage the piston and/or break the top piston ring.

I would try replacing the valve seals, at least those on the affected cyl's. As I mentioned, this is a very common problem on older big blocks.

[Duke W.]

Re: Keep fouling number 3 and 8 plugs

That should do no harm, BUT...

Many big block owners have reported fouling with the OE AC heat range 3 plugs, and those who followed the recommendation to use AC heat range 5 or equivalent report good results and usually no more fouling. Check the archives.

The same applies to small blocks. Since the OE AC heat range 4 is no longer produced the parts books all call out heat range 3. That was the heat range I used to do road racing track events back in the sixties!

Most vintage Corvettes don't get run very hard. The proper heat range has nothing to do with the engine's peak power, but the average power it delivers in normal driving. These high power engines in light cars rarely see more than 10-20 percent sustained load, and if higher it's only for a few seconds.

The factory heat range recommendation was conservative on the cold side. Why, I don't know, but long time owners figured out decades ago that a hotter plug for normal road driving lasts a lot longer than the OE recommended heat range.

Duke

[Lawrence S.]

Re: Keep fouling number 3 and 8 plugs

Thanks guys I really appreciate the feedback. I have AC 44XLS plugs in the engine now. So I will change out the plugs in number 3 and 8 cylinders to AC 5. I am guessing this is the heat range 5 we have been discussing. I don't see where I can buy a 45XLS at Napa, Advance or Autozone. They just have the "5".

Lawrence

[Duke W.]

Re: Keep fouling number 3 and 8 plugs

In the AC nomenclature system:

4 = 14 mm thread

The following digit is the heat range and higher is hotter. The letter suffixes denote other geometry features.

I think R45XLS is a common plug. R = resistor, and I don't think AC plugs are currently available in non-resistor types that were OE prior to '69,

Duke