Here's something to watch out for.

Situation: Random heavy blue smoke. Smokes on start-up, engine warms up and the smoke goes away. At various times the smoke will return, sometimes under acceleration, sometimes at cruise, sometimes at idle and some days not at all. It takes its spells with the exception of the smoking at the first start-up.

No problem, valve seals! Right? well, sort of. Did a compression test, it all checks fine 175 psi across the board. Good deal! I know the valves are all good and sealing.

Pull the valve cover off and check. Looks good. Compress and remove the #6 valve springs and find the seals are as brittle as glass. Okay then, now we are cooking. The valves are nice and tight in the guides. Replace the seals, move on down the row. Get to #1 cylinder, remove the intake seal. Hmm, that felt funny. Remove the exhaust seal AND the guide! Ahhhh, frick! Go back to the intake and give it a "wiggle" and sure enough, the guide comes right out! Frizzle-frick!

So anyway, I pull the head and here is what I have.

#1

Hmmm, seems to be something missing here.

#2

Oh yeah, THIS part! Notice the shiny area on the guide. This is from where it was sliding up and down in the receiving bore. Didn't affect the compression because the valve was still seating.

#3

What it's supposed to look like.

#4

This is the intake guide sliding into the exhaust receiver. Just for demonstration purpose. The exhaust guide is larger but it is also somewhere in orbit where I sent it after I discovered the problem!

#5

The intake valve. Notice the thick build up of carbon on the stem. It's normal to have a layer of carbon on the intake stem but this crap was about an eighth of an inch thick.

The head has other problems so I can't just replace the guides with "over size" guides which are available. Oh well.

Double-check your guides when you are replacing the seals.