TO35 head rebuild failure (so far) Please Help

Well, I started the process, and my friend said "Since you have it open, let's put in new valves for all cylinders." Never should have listened to him, but I did. In the process I reused those little buttons on the tops of the valve stems - which according to other posts on this forum may not be necessary any more. Don't know if that made a difference or not. I also discovered that the original valves in the weak cylinder didn't look all that bad. Neither did the seats, which gave me pause for a second. Not sure if that's indicative of something else, or just a red herring.

Buttoned it back up, torqued the head up to 30, then 60, and on the first pass up to 90 I stripped a head nut - one of the old crusty ones outside the valve cover. I replaced the stud and nut after waiting a few weeks for the parts, and left the whole thing torqued to 84 for an initial test. I gapped the valves at .015 and now my compression is between 45 and 65 on all four - although the original cylinder is now one of the high values. That's my first question: what's the proper torque for the Z134 engine?

This also brings up my second question: What am I missing that caused such a precipitous drop on compression?

I lapped the valves, but did not actually regrind the seats. However, I did get a nice matte ring on the valves and the seats also looked appropriately polished. Haven't had a problem with this in the past, using an identical technique.

I didn't blow any bubbles (a la a warped head leaking coolant) and all of the valve springs appeared to have good tension. I didn't actually check the compression resistance of the springs, however.

I did leave it torqued to 60 for about 3 weeks without any coolant in the engine and missing one head stud, but I don't think that would be enough to allow any corrosion of the head or block, which would then allow air to sneak past the gasket. I did not check this, however.

Those are about the only things I can think of which would cause such a dramatic drop in the compression, although I'm not necessarily the brightest bulb on the christmas tree at times.

So, I'm flummoxed. Any and all thoughts are greatly appreciated.

Thank you for your time,
Max

I have heard that lapping valves was more along the lines of "fine-tuning" or "finishing" the mating of the seat and valve, not as good as grinding the seat to correct a significant difference in the mating surface. I have long complained about poor quality replacement parts. I would not be shocked to hear your replacement valves had different face angles, or different stem lengths than the originals. I don't think any amount of lapping would compensate for something like that.
I personally hate messing with valves, seems like unless you do a whole rebuild with guides, seats, valves, springs, the works... it is hard to get a good job. If the compression doesn't build after running it, and you decide to tear it back open again, tell your friend the head needs to go to a shop to check for warping and grind the seats. Around here, that is about $50 at the machine shop + the cost for your beer. Let us know your next move, and how things turn out. Good Luck

I also was disappointed at the initial apparent lack of compression - but I ran the old girl anyway. A few months later the starter switch was playing up, so I decided to start her on the handle - lined it all up and gave my usual half-hearted pull (which would normally have spun it over nicely).

I nearly did myself an injury - running the engine had bedded in the valves nicely, and boy, was there compression now!!

Moral: Don't panic yet, run it for a while and see what happens after it has all bedded in.

As to torque values, sorry I can't help.

The contact test told you that you had good valve seating.

The springs wouldn't die overnight if weak spring pressure was suspected as they were good enough for your initial readings.

But if your replacement valves STEMS WERE TOO LONG, the springs could not be as springy.

Since you said what you did and did what you did, with a final reading where all cylinders are perculating evenly it says you got everything pretty much where it belongs. So what's wrong is affecting all cylinders equally, and a full set of soft springs (via longer stems) would surely do that.

Don't know what else it could be including head gasket torque/leaking.

Check your valve stem length.

Mark