cylinder head rebuild

[richn]

I want to update everyone on the problem with Z. (1971 240Z 250K miles 150K since engine rebuild.)

The problem ws that I was throwing the #3 intake cylinder rocker arm off the engines every so often.

I had to take the head off to find the root cause. The valve seat on #3 was loose, drop down out of it location and would stick somtimes, jamming the valve and kicking the rocker off.

Go figure, it takes 150K and 30 years for a valve seat to come loose.

The solution was easy new seats and a valve job (the seats were all origional).

It runs good now.

Any opinions on why the seat came loose now?

Rich Nedinsky

San Jose, CA

[jmortensen]

Sounds like a bad rebuild.

I had a bad rebuild experience myself just a couple years ago. Was on my Toyota 22RE engine. I didn't have time to do it myself, so I bought a remanned engine. After I got it installed I couldn't seem to get the valves to stop making noise. Kept messing with it for about a week, then finally got frustrated and dropped it off at a local shop. They pulled the head and called me. The valve seat AND the valve guide were LOOSE and the valve seat was following the valve up and down. No wonder it was so noisy!!! You could push the guide back and forth in and out of the head with your fingers. Took it back to the place that remanned it and they said "Oh no problem, give me a sec, we'll take it out back and stake those suckers back in tight." I told em "Uh, no you won't. You'll give me a head that was put together right." So they did.

Crappy machinists are out there... beware.

[richn]

Bad machining that took 30 years to happen?

Rich

[Arne]

This was an original intake seat, right? So it was a bronze seat that probably was mostly worn out. As it got thinner I suspect that it finally got too thin to take the abuse and pounded itself loose.

[madkaw]

Just had my head rebuilt and had the same exact circumstances. The valve would stick open and dislodge the rocker. When the machinist started removing seats, two of them basically fell out and the motor only had 100k original.