Davpmars

I have a 68 corvette with a big block. I took out my spark plugs on the right bank. I found that one plug had hard oil deposits built up.

I am guessing it is the valve seals. Can I fix this without removing the head? If so, how do I go about doing that?

Could this be something else?

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SH-60B

If you have an air compressor use a leakdown tester or some other adapter to use compressed air to hold the valves closed while you remove the springs

Davpmars

Could this problem be caused by something else besides a bad valve seal?

530planeman

How many miles on the plug ? also could go to a colder heat range plug for now and yes you can change the seal with proper tools and knowledge
Wes

Davpmars

There are only a few thousand miles but I believe the plugs date back to about 2008.

Once I get the valve seal out, will there be an easy way for me to confirm that the seal was bad?

530planeman

The seal will most likely be very hard and brake into if it even has one at all left most of them with age break up into pieces .You have to be really careful with the air pressure holding the valve closed as valve may drop into cylinder .Old school people use the close line method like me

SH-60B

A couple other things come to mind, rings or intake gasket.

ddawson

Mine was the intake gasket. When who ever installed it did a bad job and oil was getting sucked in to the intake track.

mortgageguy

Are you getting smoke on cold start up?

cv67

Leakdown test for sure as mentioned above
If all cks out change the seals....and drive it hard once in awhile
I would not put a colder plug in
Those are awful wet

REELAV8R

Is it only that cylinder? If anything a hotter plug is going to be more foul resistant not colder.
It could be any of the so far mentioned items. Valve guide seal is the easiest to start with.
Use rope or close line in the cylinder to hold the valve up. Air is a pain.

Jebbysan

You do not know how many leaky intake gaskets I have replaced in my time. Leak from the bottom will certainly foul plugs.....and run like crap.
My bet is on those as it is just one side.
A leaky intake will make a vacuum gauge needle bounce.......check it out and see if it is suspicious.

Jebby

jersey68l36

If the oil fouled plug is in the back, #8, it could be a valve stem seal. If you do decide to replace the seal(s) you could get an idea if the guide is worn by wiggling the valve stem while the spring is removed. The valve has to be off it's seat and just be careful to not accidently drop the valve in the mtr. 3X on use of a rope to keep the valve in-place.

For now install a heat range one step hotter plug, fire it up and check vacuum. bouncing needle=leaking intake gasket.

mikem350

Check for spark at the plug (misfire). Might be a bad wire.

spedaleden

I would do a leak down test to see where the oil is coming from. If you can borrow a scope with camera you can look at cylinder and piston. If piston is clean around the edges then rings are bad, if piston is black all around rings are good. i just did this on my sons C5 and leak down test determined leaking from head. Pulled head and found bad valve guide on intake, leaking oil into number 2 cylinder, all other cylinders are fine.

Leak down tester was $70.00 and you need a air compressor

Here are pic what we saw on his LS1