Question about head work Options

[anthony]

My second 914 is a project car runs great but it's annoyingly smokey - like if it had to pass smog I'd guess that there's no way that it would. It puts out noticeable amounts of smoke at idle and gives the visible poof on downshifts.

Well, everybody told me that it was due to worn valve guides. Would it be advisable to pull the heads and have new ones put in? Is this even feasable or do you have to go all out and have a valve job too?

[meursault]

Well, yeah, you've got to pull the heads to replace the valve guides. If your valve guides are worn, then the valves and seats are going to be worn too. Basically, the valve guides have gone oblong so the valve starts to seat itself in different places.

Yes, you'll need a valve job. the guides are replaced by drilling them out. Heat up the head, freeze the guides, air hammer the cold, contracted guides into the hot, expanded heads, and hone the guides. Then grind the seats and valves and lap them.

You might need to resurface the heads as well. Blackened areas on the head where the cylinder is supposed to seal up to it will tell you if this work is needed as well.

Obviously, a competent machine shop needs to do this work. They might also alert you to other problems with your heads once they're off the motor, like oh, cracking by the spark plugs. All this work obviously needs to be done while you've got the heads off the motor. No way around it. You'll be pretty miserable if you don't do some of the work and try to reassemble the motor after just replacing the valve guides; the smoking may go away, but you won't have the compression numbers you want, and so forth.

While you're at it, you may just want to hone the cylinders and re-ring the pistons. If you have to resurface the head, you might have to pull the cylinders to add shims anyway....

Hope this isn't too much doom and gloom. Good luck.