OK, since a while, my yellow '68 seems to burn some oil on 2 cylinders. The car runs fine but uses a little bit of oil (about 1 qt every 500 miles or so but the car does NOT smoke at all except sometimes at start up)
Every 3000 miles or so, I have to change 2 of the plugs as they are oil fouled. All the other 6 plugs look PERFECT. I haven't done a pressure test yet, but I assume that there are issues with the rings on those 2 cylinders. I wonder if it could also be a issue with the valve seals?
How can I determine if it's a problem with the valve seals or with the rings? If it's the rings, I wonder if just having the pistons re-ringed could solve that problem??

 

do a compression test on the 2 cylinders and then squirt some oil in them and redo the compression test. if it increses it's the rings, if it's the same then it's the valves. if it smokes on start up them it's most likely the valve seals

 

Simply you do a compression test per cylinder, and keep track of all readings. Give each cylinder several seconds, and record each cylinder 3 times. If you have a cylinder reading lower than the rest, squirt a tiny bit of oil into that cylinder and see if the readings increase.

Next, get the adapter needed for a leak down test, which pressurizes the chamber and you read the loss of pressure. If a cylinder loses pressure faster than the rest, it could either be the rings, or the valves may have wear or are not seating properly.

Compare the cylinder pressure results to the leak down results, and see if you have any cylinders with one or both negative results, and those will hopefully correspond with the fouling plugs.

If the compression checks out, and you get some funny results from the leak down test, start the engine, and using a water spray bottle, squirt a bit of water mist into the carb every few seconds.

You should see a pretty good amount of soot and carbon blow out the exhaust.

As I said, if you have bad compression in one or more of the cylinders and the leak down test matches those cylinders then you may have some bad ring seals.

 

How do I sqirt oil on the cylinders? Through the spark plug hole?

 

Yep, you can use an old syringe or an old turkey baster or something along those lines if you don't have an oil bottle with a squirt tube.

 

Thanks! I'll try that this weekend..

 

I would check the intake gasket and see if the gasket is misaligned allowing oil to be sucked into the cylinders from the lifter valley

 

Thanks! I haven't even thought about a issue with the intake gasket.. I'll check that too!
So far, the yellow '68 has been trouble free except for a minor electrical issue.. Drove over 15k miles with the car and other than oil consumption and that little electrical problems, I had no issues.

 

500 miles and it's using 1 quart, but fouls a couple of plugs. I'd bet it's valve guides..

 

The misaligned intake gasket is a common problem, and usually results in one cylinder or more getting wet and fouling the plug.

Many years ago After I got my rebuilt 350ci back from the machine shop they told me the oil consumption problem I had was misaligned intake gasket

 

Compression testing is a waste of time unless you are buying a used car with 150K miles and you want to know the general health

Leak down testing will actually tell you what's up with your rings or valves.

 

Maybe I should just pull off the heads and have them checked when I pull off the intake.. It's a lot easier to have the heads fixed than to pull out the pistons.. I know that it can be done but I really don't like to pull out pistons with the engine in the car.. Very messy job...

 

The engine actually has less than 20k miles.. It has had oil on those 2 plugs since it had about 5000 miles on it...
What kind of thing do I need to do the leak down test? Who has it? Is it just an additional part for my pressure tester?

 

look up how to do "leak down testing".

Oliver, I accomplished the ultimate old farmer trick down at the race shop. I could not get one of my rear slicks to seat against the rim. I dorked with it with the boss. He did not have a air belt that you put around the middle to squease it against the rim.

So I ask him if he had ever seen the flammable gas inside the tire trick to blow it against the rim? I gave it a shot of hot start and threw a match at it.

Instant seating

 

I'll look it up..

Hey, I'd like to see a video of someone performing the trick with the flamable gas and the tire

 

From my experience, usually if the plugs are wet with oil, particularly on the threads of the plugs, its usually oil seals. Especially if you are getting some smoke on start up.

BUT....on my 71 350 car, it was the same situation as yours, about 40k miles on a budget rebuild that occured 20 yrs ago, it had started smoking pretty bad on start up and eventually was smoking at a dead idle and even on the highway. EVERYONE told me it was rings. I decided to take the easy approach and change the oil seals first. So I did that and the smoking instantly stopped and the plugs stayed dry. I have put about 5k miles on it and to this day, doesn't smoke at all, not matter how long it sits between start ups.

HOWEVER, it does burn oil, it also seems to use about a qt every 1000 miles or so.... There is some evidence its burning on the plugs, only on 2 really. They are just a tad more black/damp then the others. I also assume its the rings. I replaced the intake/gaskets the same time I put valve seals in so I am pretty sure they are sealed up.

I have never done a compression check or leak down test on it but I am sure its got some wear. 145k miles on the original cylinders so....


Good luck on yours, just remember things are not always as they seem.

 

I'd be happy with a quart every 1000 miles.. Many '01 Z06's burned just as much

 

Guys,
Compression testing is for the purpose of determining compression sealing. It sounds like the issue here is an oil consumption problem as opposed to a compression sealing issue.

Oil consumption is normally controlled two ways.
1) The oil ring assemblies press against the cylinder walls and scrape away the excess oil not needed to lubricate the two compression rings above it. The oil rings can lose their tension over time and/or the drain back holes in the pistons can become clogged and restrict the flow of oil back into the crankcase.

2) The valve guide seals allow for a controlled amount of oil to lubricate the valve guides and valve stems. Over time the valve guide clearance increases which causes the valve stem to wear against the valve seal causing increased oil flow. The valve seals themselves also become brittle and hard with age and therefore do not conform to the valve stem as they should.

I would investigate the valve sealing issue first. If you have an open plenum intake you could remove the carburetor and use a borescope to peer into the intake port of the heads. If the seals are leaking the stems will likely be wet with oil and there will be a significant build up of carbon on the back of the valve as compared to the cylinders that are not consuming oil. The intake gasket could be leaking, if in doubt pull the intake inspect the gasket contact.

If the diagnosis is leaking valve seals the task is not that difficult even with the heads on. There are several methods however I will describe the one that is easiest for most DIY owners.

1) Purchase about four feet of 3/8 soft cotton rope.

2) Remove the valve covers, rocker arms and push rods. I recommend keeping the parts in some sort of order so they can go back into their original locations.

3) Remove the spark plugs.

4) Rotate crankshaft so you can stuff the cylinder with about three feet of the cotton rope. Rotate the crankshaft back up so the rope fills the void between the top of the piston and the bottom of the valves.

5) Using an on car valve spring compressor (rentable or purchasable at most parts jobbers) compress the valve springs to allow removal of the valve keepers (two small split locks that like to fall inside the engine if you let them) and the valve spring retainer. If you find the valve retainer does not move remove the valve spring compressor and with a socket that fits the OD of the retainer smack the socket to loosen the retainer from the keepers. This is why I use large diameter soft cotton rope as it cushions the valve so we do not have any valve bending.

6) Remove the old valve seals from the valves. The valve seals could be of three varieties. A simple "O" ring looking affair just above the valve retainer area, an umbrella seal (most common) or PC seals. PC seals lock tightly over the valve guides.

7) After removing the valve seals rotate the piston back down in the bore slightly to allow the valves to just unseat from the heads. Take each valve and move it in line with the normal movement of the valve train. The valve stem to guide clearance us usually .002 or less, practically no visible movement. Excessive clearance equals excessive oil consumption and new seals are only a stop gap measure. If excessive clearance is not the issue rotate the piston back up to seat the valves.

8) Install new valve seals. If your heads use PC seals be sure to use the supplied sleeve in the seal kit to insure you do not nick the sealing surface when installing the seals. I usually coat the seals in oil.

9) Reassemble the spring, retainer and keepers (remember they like to fall in the engine). Once the retainers are locked into place rotate the piston slightly downward to allow some clearance between the valve head and the rope and smack the valve stem to seat the keepers into the retainer.

10) Remove the rope reinstall the spark plug and move to the next cylinder. I would recommend doing all eight as you are already there.

Good luck,

Stormin

 

Great info - thanks!!

 

Just bought a spring compressor on Ebay...

http://cgi.ebay.com/ebaymotors/ws/eB...243287764&rd=1

Hopefully it'll get here before the weekend, so I can work on the engine..