Several weeks back after a food stop while on a short road trip, the wife's 240 would start but not idle. It only stayed running with the accelerator depressed. It didn't run well even then. But I was able to limp the thing into a local shop and they did a compression test. They found no compression on one cylinder - I think #1. I ended up having the car towed to my own mechanic. Once things were checked out and the head removed, he reported that the head was trashed - as I understood it, one of the valve seats on the cylinder in question had somehow come loose and jammed the valve open. Hence no compression.

This was a replacement head installed by yet another mechanic some 14K miles earlier. It came off a shelf at a parts house. So no real idea of what had/had not been done to it. After only 3K miles I noted that an exhaust manifold stud on this thing had snapped already. So I purchased genuine Volvo studs and nuts and had the same mechanic replace them all. I figured that the studs were either old at the time of rebuild and not replaced or replaced with crap parts. So this head felt questionable early on, I guess.

I have looked at some of my Volvo books and I do see specs for the diameter dimension of the place in the casting where the seats are inserted. So maybe new seats were installed (who knows?) into locations that were out of spec allowing the seat to come loose? Or do seats come in various sizes and perhaps the wrong size was installed?

I guess it doesn't matter now since the car is getting yet another head rebuilt. Obviously, not the same head. But at least this is being done by a machine shop known and used by our usual mechanic who told me the old one was toast. And that shop rejected the first head he gave them so I have at least some comfort in knowing there is some level of quality control at this machine shop. But I still find it odd that a valve seat could come loose and move so far as to permit the valve to be jammed open like that.

Has anyone seen anything like this before? Thanks!

Never had this happen on a redblock before. I did have this happen on an old air cooled VW years ago. For that, it happened on the number 3 cylinder which tended to run hotter than the others due to the placement of the oil cooler.

Has your engine been overheated lately that may have contributed to this?

As an ex-VW mechanic back in the old days, I do recall numerous issues with #3. But never saw this happen. Of course, back then we could avoid buying off-the-shelf heads if we wanted and I always encouraged that.

I don't feel there was anything really unusual happening. Oil, coolant, etc were fine. We were on a short road trip to visit some friends. And it was the height of a pretty warm summer here in the Pacific Northwest.

Hmmm.

Not on a car but I friend has a head and piston that have been beat to death when a valve seat came loose. A spectacular failure. I have never heard of an original seat falling out of a Volvo head. I think the mode of failure is that the seat comes loose, falls out of position and the valve tries to drive it back into the recess at an angle.

Valve seats do come in various sizes. A good machine shop does not have trouble installing new seats in an aluminum head. But obviously things can go wrong. I bought a rebuilt tractor head and none of the valves would seal. The rebuilder did a poor job of setting up their seat cutter said they guy who fixed it. There are probably a lot of other ways to do a poor job.

Greg