My spark plugs

[Lawrence S.]

Guys these are the plugs that I recently removed from my 67 L36 M20. These plugs have approximately 2500 miles on them except for plugs 3, 5, and 8. Those plugs have around 1,000 miles on them and these cylinders seem to be giving me the most trouble. The engine has 66K miles on it and as far as I know has never been rebuilt. The owner of 40 years whom I bought the car from said the engine had never been rebuilt. These plugs are R44xls and I recently installed R45xls in the car. It runs so much better but I am guessing the car would had run regardless if I put in 44's or 45's because of the attached being so fouled. Does it look like I have oil ring issues from the looks of the plugs? I know the valve stems or valve seals are shot. Could that problem cause this much fouling? The carb is recently rebuilt by Eric Jackson.

Thanks

Lawrence

[Duke W.]

Re: My spark plugs

Are the black deposits wet/greasy or dry?

What's your typical driving profile? Trip length? Engine run time? Ambient temperature range?

Do you drive it like and old lady or like Corvettes were meant to be driven? (Sorry, but I have to ask.)

Does the engine run smooth and strong with a stable idle at about 600?

What is the rate of oil consumption - miles/quart?

How long have you owned the car and how many miles have you accumulated?

Has the engine had a recent compression or leakdown check?

Duke

[Lawrence S.]

Re: My spark plugs

Are the black deposits wet/greasy or dry? Mostly dry and sooty

What's your typical driving profile? Cruising with some mild acceleration maybe up to 5K rpms bursts Trip length?No more than 25 miles each outing....usually. Engine run t30 minutes then turn it off, and get back in it again for another 30 minutes. ten miles each way...driving to work. Ambient temperature range? Car generally runs at about 170 ish. I need to check that with my infrared gun.

Does the engine run strong smooth with a stable idle at about 600 I would say the idle is stable, but seems rich to me. I have adjusted the air/fuel mix per the specs. I used a vacuum gauge to solve for max manifold vacuum.

Has the engine had a recent compression or leakdown check? Here is the compression test results 1, 184 pounds, 2, 174, 3, 184, 4, 160, 5, 185, 6, 169, 7 179, 8, 179. I have not done a leakdown test. I don't know how.

Thanks Duke

Lawrence

Duke

[Timothy B.]

Re: My spark plugs

Lawrence,

From what you report I think the engine is fine, don't tear into a motor that's never been apart with 66000 miles with compression figures like what you posted above.

It's hard to see the plugs in your picture but if they are sooty that indicates a rich condition or ignition problems. How old are the spark plug wires, take some time to check ohms on the wires to see if they are bad. Poor voltage to the plugs can cause problems like you report and then when plugs get dirty the motor misfires, plugs get blamed but it's the ignition that's the real problem.

IMO, a good plug wire will have approx 3000 ohm/ft. and maybe a little less. Does the car have a points ignition and where is the timing set. Did the carburetor adjust OK at hot idle using the A/F emulsion screws, make sure you do that idle adjustment with a hot engine or you could end up setting it richer than necessary.

[Lawrence S.]

Re: My spark plugs

Timothy,

The plug wires are new dated, versions that nobody likes. I may should consider changing them out to a better quality but not correct for judging. The points, cap and condenser were all replaced when the wires were replaced.

I will recheck the a/f mixtures with a hot engine.

Thanks,

Lawrence

[Edward B.]

Re: My spark plugs

No offense meant, but I just can't understand avoiding a better product because it is "not correct for judging," especially when what you are using may make your car run poorly thereby decreasing the chances that you will drive it even to a show. Put in the better wires and enjoy the car. End of my $.02.

[Lawrence S.]

Re: My spark plugs

No offense taken, and can't disagree. I need to look for the better wires with the shielding.

[Edward J.]

Re: My spark plugs

Larry, just looking at the tips of the spark plugs indicate a rich running engine. likely some sort of carb. issue. air fuel mixture adjustment is some to look at and also make sure the choke is functioning properly, not staying on to long of a period of time. should be fully open after 3 to 5 minutes depending on outside temp, colder it is longer it will stay on.

along with the other posts, timing and advance curve.

[Stephen L.]

Re: My spark plugs

You can "rebuild" your shielded wires with some "Packard 440 wiring. Its been available on EBay in bulk. Use some paint thinner to remove the nomenclature on the wires where it shows. Napa has new end terminals and a tool to crimp them onto the wires. If your original GM shielding is in decent shape use that, as it has a different weave than the aftermarket stuff.

[Timothy B.]

Re: My spark plugs

Lawrence,

The NAPA premium house brand spark plug wire is made by Belden Cable Co, I installed these wires on my 67 and they are a nice wire set. The spark plug boots are black, distributor boots are orange and the wire color (7mm) is blue but you can't see any of that. They ohm out at approx < 3000ohms/ft.

Also, you report in post #1 problem with plugs #3-5 and 8 which could also be a fuel distribution problem in the stock cast manifold. Do you have a functioning heat riser valve, this heat is a important aid vaporizing the fuel load so make sure this is working properly.

Soot on plugs (carbon) is what's left behind by unburned fuel that has not been properly vaporized. On a stock motor we have the benefit of manifold vacuum and heat to turn the emulsified liquid gas into vapor for good combustion so the heat is important especially with a cast iron manifold. I know these heat risers can be a issue in the hot summer with the ethonal gas but that's another discussion.

[Duke W.]

Re: My spark plugs

Are the black deposits wet/greasy or dry? Mostly dry and sooty

What's your typical driving profile? Cruising with some mild acceleration maybe up to 5K rpms bursts Trip length?No more than 25 miles each outing....usually. Engine run t30 minutes then turn it off, and get back in it again for another 30 minutes. ten miles each way...driving to work. Ambient temperature range? Car generally runs at about 170 ish. I need to check that with my infrared gun.

Does the engine run strong smooth with a stable idle at about 600 I would say the idle is stable, but seems rich to me. I have adjusted the air/fuel mix per the specs. I used a vacuum gauge to solve for max manifold vacuum.

Has the engine had a recent compression or leakdown check? Here is the compression test results 1, 184 pounds, 2, 174, 3, 184, 4, 160, 5, 185, 6, 169, 7 179, 8, 179. I have not done a leakdown test. I don't know how.

Thanks Duke

Lawrence

Your description of the plugs indicates an overly rich mixture rather than excess oil consumption.

You are driving the car long enough and sporting enough to get it fully warmed up, so short trips or "granny driving" are not an issue.

Your #4 compression reading is just outside the 20 psi acceptable variation, but I don't think this indicates a major internal issue. It could be a sticky ring. Make sure you are using CJ-4 oil as its heavy detergent load can help free sticky rings.

What was you vacuum reading at idle speed? Please state as xx"@xxx. How many turns out from the seat are the idle mixture screws?

Does it have the original Holley? Check the choke valve and linkage to be sure they are free. The choke should fully close when stone cold after depressing the throttle to the floor and releasing. Immediately after startup the choke valve should open part way (check that the choke vacuum break diaphragm holds vacuum) and then fully open as the engine warms up to full operating temperature. All the measurements and adjustment procedures are in the CSM, and you should be able to check/adjust everything without removing the carb from the engine.

Also check that the VAC holds vacuum. I'd also like to know the stamped numbers on the mounting bracket. I believe your engine has full time vacuum advance so total idle advance should be the sum of initial plus full vacuum advance. Numbers please if you have them.

As stated those repro plug wires could be an issue, but if they are you would probably feel misfires at idle or under load.

It's great that you have an original, low miles engine. It should have a lot of service life left and likely just needs some checking and adjusting/optimizing of the ignition and fuel systems and regular "Italian tuneups". In particular, elastometic materials like the diaphragms in the VAC and choke vacuum break and valve guide seals don't last forever, and they may be 47 years old.

You didn't tell us the rate of oil consumption. If you don't know you should start checking and documenting. The best way to check the oil is when the engine is hot and the car is on a level surface, such as when you bring it home to the garage. Remove the dipstick, wipe it down and lay it aside for a several minutes. This will allow oil in the tube to drain down so you get a clear readings. Insert the dipstick and record the reading. A good time to do this is also at the gas station. Remove/wipe the dipstick first thing then measure after you have finished refueling.

Cold readings after the car has sat for a week may be noticeably higher.

Duke

[Lawrence S.]

Re: My spark plugs

Thanks for the replies guys. My heat riser is new, but it was a repro. The carb is correct for the carb and rebuilt, i.e. correct list and stock. But I have not checked to confirm the choke is completely open when the car warms up?

Duke, you have given me a lot to look into and will do so when the weather warms up. We are in a deep freeze here in NC. I will pull out the CSM and check things out.

Thanks again

Lawrence

[Richard M.]

Re: My spark plugs

Interesting and great diagnosis info from the crew.....

I've realized lately while diagnosing some engine problems on a '60 283 I have here that I needed to learn more about "Reading Spark Plugs". These documents helped me identify certain issues I was having and taught me some "refresher" lessons. It's amazing what spark plug reading can tell you about engine condition.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

http://www.aa1car.com/library/sprkplg2.htm

In particular, see the section regarding fouling here:

http://www.aa1car.com/library/spark_plug_fouling.htm

Also Lawrence, it may be wise to get the true facts about your engine specs/tune data here....

http://gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Corvette/1967-Chevrolet-Corvette.pdf

......because the CSM data is sometimes wrong.

Rich
p.s. I'd also think your valve seals are overdue for changing. I recently replaced them in my '59(not since a 1995 rebuild) and my smokey condition ceased and plugs no longer getting "oil" fouled.

[Scott O.]

Re: My spark plugs

Additional questions for you
Does the oil smell like gas. If you take a few drop and rub between your thumb and forefinger , does it feel like there is gas diluting it? (Take a drop of new oil and try for reference) old time mechanics will know what I mean.
Also monitoring oil level for several weeks, does it seem like oil level is increasing.
all of the above would also indicate fuel mixture issues - Float level, Choke stuck closed, Heat riser etc
good luck
Scott