NEVERL8

I will compression test all the cylinders again and publish the results. I may have this completed tonight.

I normally crank the engine for 3 seconds to get the compression. I do the exact same to each cylinder. Correct? Incorrect? Should I do this differently?

67-427ci

Bruce: Crank till the compression gauge hits its highest mark (not just 3 seconds). You also need to prop the throttle open at least 1/2 way for an accurate reading. Good luck.
Roy

GMJim

NEVERL8
Forgive me if I missed it in your post but what transmission is in this car?

NEVERL8

Muncie M20 with a 3:70 rear end.

DansYellow66

I would tend to agree with doing a leak down test, although even a weak, leaky cylinder should fire and it sounds like your cylinder probably isn't firing at all. I suspect if you short out this cylinder at idle you don't see any change in your rpm. The compression test appears to show that you don't have anything like a catastrophic failure. But you could have a broken ring or burned valve fouling the plug. It still should fire however. I had a very similar problem on my car after I restored it. And I agree that a totally missing cylinder can feel like vibration issue due to the cylinder not firing. I finally traced it to a broken plug wire (brand new repros). New Taylor wires fixed it. Good luck solving the mystery.

DansYellow66

duplicate post

1955 copper

Over the years I've seen bent plugs as you said , it's Carbon build-up on top of the piston ,also the oil ring may be stuck . "NOW I know you won't do this" , but install a colder plug so it don't extend deep into the cylinder and get hit again , then hold your RPM up to 2500 or 3000 while spraying water from a hose down the Carb for about one minute at a rate that JUST keeps the engine running a little ruff , then let it ideal for a while and again for one minute. The cold water will brake up the piston Carbon and loosen the oil ring.
If you can locate an old mechanic that knows about this have him do it.

NEVERL8

Here is the latest development from tonight's diagnosis.

I installed a new distributor cap, and a new plug in the #8 cylinder. Started the car and it ran like before with a vibration at 1500 RPM, getting more pronounced as the RPMs build past 2500 RPMs.

I shut off the car and proceeded to compression test all the cylinders.

#8 180 psi, the plug did not have time to foul but it was on its way
#6 175 psi
#4 185 psi
#2 180 psi

#7 185 psi
#5 180 psi
#3 185 psi
#1 180 psi

That's it for tonight. Damn hard getting to the left side plugs with all the AC stuff in the way.

Racer-rt

As far as the cam is concerned, if the exhaust valve were not opening or barely opening a very loud pop would be heard through the carb every time # 8 plug fires. (Its the combustion from # 8 entering the intake manifold when the intake valve opens) This is obviously not your problem.
I do like the intake gasket possibilities except that the vacuum leak caused by the intake gasket broken or out of place would give you a high and rough idle even on a fresh plug. A vacuum gauge should help out on that check.
The lack of any smoke also points to the possibility of the intake gasket allowing it oil.

rene-paul

Spray bottle with water or atf down the carb with eng running may decarbon the combustion chamber and possibly free up a stuck ring as Copper mentioned. I've done this. In the past there have been various combustion chamber cleaners marketed, not so anymore. Source of the carbon is my concern. Is it un/partially burnt fuel or oil fouling? Your compression is good. A leakdown test will add more data. Remember you are adding a metered amount of air into a closed combustion chamber, piston at tdc. The potential leak can have many paths.
Valve seating = air into exhaust manifold or intake. Piston rings = air into the oil pan. Valve guides can be a bit more difficult to diagnose.
IMHO I suspect an umbrella seal.
Keep us posted.
rene

Don SSDD

Is it using any oil on the dipstick? I'd vote for a valve seal- what kind do you have?

Or a ring problem (not likely with the compression numbers?).

If it is a valve seal, fouling a plug like that should see a lot of oil consumption. Like a litre in 300 miles or so.

If its getting spark, it should be burning fuel and fuel won't foul a plug like burning oil will. Thats oil. My 59 283 would burn oil 50 to one like a 2 stroke- it was worn out when I bought it and that is what one of the plugs looked like.

I think you need to pull the head. You seem to have eliminated everything else. I would at least remove the lifter on # 8 and check the valve seals there.

Don

NEVERL8

I do not see a lot of oil consumption, but then again I have only put 400 or so miles on the car since I bought it. I agree that it is oil, it is not unburnt fuel.

The question becomes where the oil coming from. I believe the car will need some surgery. Will it be outpatient (heads) or inpatient (bottom end). I will pull the heads but if it is the bottom end there is no friggin way I am getting into that.

67-427ci

This is an example of oil fouled plugs I had in my engine. It was using 1qt in 350 miles. Turned out to be a combination of oil being sucked in through the intake gasket (from the valley) and leaky valve seals. There was also some leakage from oil coming up some of the intake manifold bolts. I solved the problem by installing positive sealing valve seals (instead of the umbrella type), replacing the intake gasket (properly positioning it) and using sealer on the intake bolts.

My plugs were certainly not as fouled as yours. I thought I would offer a comparison. Good luck.
Roy

My plugs are not as fouled as yours and were still firing.


Here you can see the intake gasket was installed low (manifold is upside down) and oil was being sucked in.

mid-year crisis

NEVRL8, PLEASE don't be insulted, but..are you sure that you couldn't have mixed up #8 and another plug wire from the same bank?..all of the above being mentioned, it still sounds to me like it's possibly ignition related. Just because the cylinder is getting spark, doesn't mean it's getting it at the right time... just a thought..

67L36Driver

Do you have power brakes?

A leaky master cylinder w/power boster will suck brake fluid into the intake manifold. Vacum take off is at the top of the intake runner feeding #8 & #5. Most manifolds have the port biased to the pass side.

ghoastrider1

........................................ .......
I havent seen this done/talked about in years and years. Good on you mate. This does work sometimes.

ghoastrider1

Those are great compression figures. Bet its sucking oil from a manifold leak. Keep the "leak down" test in the back of your mind tho.

65 COUPEDEBLUE

Looking at pic's of #4,3,2,1,spark plugs it appears you have an oil problem. It looks like there are not any valve seals of any kind in this engine,or some very bad intake valve guides. #8 sounds like it passed a chunk of something that was not supposed to be there and it bent the electrode on the way by. Thats my $.02 worth. Dan.

ghoastrider1

Ihave seen this happen. usually you can see the break fluid level drop at a very fast rate. But tale-tale signs show up in the brake efficenticy rather quickly...no brakes.

Ben Lurkin

With the #8 plug installed; mark the top of the ceramic insulator with a permanent marker so you can reorient it once it is out. Your fouling is taking place mostly on one side of the plug. Once oriented; if the fouling is on the bottom of the plug it's your valve guides/seals or a manifold leak. If it is towards the top of the engine it's the rings.

-Lurkin