My plugs become oil fouled after driving for a couple of hours. Took car to shop and they did a compression and leak down test. Said compression was 125 across the board, and leak down test didn't reveal any appreciable loss of compression. They seem to think I might just need new valve stem seals. Car is a 68 with a 200 cu in 6 cylinder 3-speed automatic. Does their diagnosis sound right?

 

Sounds about right to me. If the seals leak you will get oil on your plugs. Correct me if I am wrong, but I don't believe leaky valve stem seals affect compression.

 

I've read that the leak down test is the better test of the two for the particular problem I'm having. Guess I'll find out when they remove the head and get into the engine. Hope they're right. Would save a good deal of money compared to an engine rebuild.

 

Do you notice any blue smoke when you start it up? This is the typical sign of valve stem seal leaks. When the engine is sitting the seals will trickle a little oil down onto the valve and it will burn blue when you start it up.

As far as their testing goes, it sounds good to me. If it had been bad rings or cylinder walls it would have shown up as low compression on one of the cylinders. On the leak down test it would have shown as air blowing out the dipstick tube.

 

One question was it all of the plugs fouled or just a few of them?

 

I don't think you need to remove the head to change the valve seals....

IMO this would be a waste of time and effort.

 

i'd be too lazy as well

 

You can indeed replace the valve seals without removing the head. When you do it, however, you need to wiggle the valves to see how loose they are. If they are really loose, valve seals will not cure your problem. It will need valve guides.

There are other things that could cause oil burning problems such as a bad PCV valve or something else preventing crankcase ventilation.

 

There is blue smoke when first starting up, and sometimes while driving a puff or two will come out. All the plugs become fouled, some more than others.

 

ohhh i fully agree to the analysis that it could be the valve stems. it's a known problem with fords. they dry out and then oils sips past them. However i wouldn't pull the heads to change them.
If it's a machine shop, yes they'll ask you for the heads and will do the work. if it's a garage, they could do it with heads still installed.
There's two methods:
a) i never tried it just because I don't like the sound of it. might fail and the you will have to pull the heads. Turn cylinder to compression stroke TDC, so both valves closed, pressurize cylinder with aircompressor which is attached to plughole. when you have pressure under the valve it will not open and this way you can compress the spring to take the retaining plate off.
b) turn engine to BDC after intake stroke. shove rope through the plughole (leave a good bit hanging out). turn engine manually to compress (the rope will then be like solid material between piston and valves). now you can compress both springs. once changed, turn engine backwards to release rope. pull rope. do next cylinder.