I see on another thread that you finally got the crank pulley off. I'm still a little curious though as to what the original problem was. Maybe I missed it somewhere along the line. Timing chain skipped a tooth or two and bent a valve ? Hoping for a happy resolution.

 

The not so good news is that it looks to be a valve seat is displaced. (broken?) The picture using a cheap probe is not great, but I now have an idea of what to expect if or when I pull the head. If I shine a flashlight down the sparkplug hole I can see light around the valve. Does anyone have an opinion of if this damage can be repaired, or should I just look for another engine? My hot rod buddy's all say to pull it and install a Chevy small block. But I don't care for that suggestion. For one thing it would be very difficult to smog in California, and for another it would not increase the value of the car to offset the cost.
Oh well, first world problems I guess.

 

[QUOTE=Lanny;2623704]The not so good news is that it looks to be a valve seat is displaced. (broken?) The picture using a cheap probe is not great, but I now have an idea of what to expect if or when I pull the head. If I shine a flashlight down the sparkplug hole I can see light around the valve. Does anyone have an opinion of if this damage can be repaired, or should I just look for another engine? My hot rod buddy's all say to pull it and install a Chevy small block. But I don't care for that suggestion. For one thing it would be very difficult to smog in California, and for another it would not increase the value of the car to offset the cost.
Oh well, first world problems I guess.

Stick the endoscope down the sparkplug hole and examine the piston top. Hopefully, there are no gouges. You'll probably find the damage is minimal then.

Valve seat is interference fit so one option is clean up the combustion chamber and reinstall new seat and then they can peen it in place for insurance. I have an MG TD head someone machined only one exhaust seat and installed an insert with a gap. They peened all around the insert and didn't touch the other three chambers, having learned their lesson. I wasn't aware of it until I pulled that engine with 20,000+ miles on it with supercharger, and never had any compression loss with it.

Machine shop might opt to remachine and stick in a larger insert for better integrity.

You might look around and find a used head to slap on or steal one off your XKR engine if you don't mind cannibalizing it. If you elect the latter, pull the valve cover off the XKR bank and see if the VVT solenoid will work with it.

 

Pull the head off and take it to a machine shop and have one seat replaced if the piston is OK . Strip the camshaft off and the valves to reduce your costs or just buy another head. A Chevy will not integrate with the electronics.

 

^^What they said.
You need to get a proper look at the piston crown.

If the piston is OK, then IMO the worst you're into is a replacement head.

 

Well I finally have a clear look at the damage that caused all the trouble. It looks like the valve seat insert came loose in the number 5 cylinder intake valve. I have never seen this type of failure before. Has anyone else? It makes me wonder if this was a repair not done correctly.
I don't think that the piston is really damaged , just some carbon knocked off the crown. The bores look good, the chains and guides look good. So I will probably just buy a used head and put it back together. Thanks to everyone who helped me though this. I want to mention a YouTube video by a gentleman named Dale Huxford that proved to be extremely helpful. I hope nobody on this forum has to do this job, but if you do, watch the video.

 

engine overheated at some point or just bad luck. press fit varies a lot, some of them take overheating like a champ others do a dodge and drop seats

get a used head these will never be right without a full set of 16 and a valve job

 

To be 100% sure I would clean off the block surface ..bring the affected piston to TDC ,put a rule across and measure the gap between rule and top of piston. Repeat on another cylinder . If your damaged cylinder has a bigger gap it may have bent a con rod but I think you can replace with the sump pan off . ie take off bearing cap ..push out piston replace and re fit with new bearing shell.
Lets hope no damage.

 

I still think it has something to do with my using the engine on compression to travel downhill for several miles. It could be a coincidence ,but I don't think so. I imagine it was marginal and the increased vacuum sucked the seat out of the head. But, it doesn't matter now.

 

Your valve seat was going to fail irregardless of the engine vacuum.

the pounding of the valve head on the seat x millions of cycles is the real hurdle that the seat has to endure, not a few inches of vacuum for a few minutes.

most likely, the car has overheated at some time in the past. This is the precipitating cause of loosening a valve seat. The seats are installed with the head heated up and the seats cold. This alone locks the seat into place, generally for the life of the engine.

As you say, it’s water under the bridge now. But it would be nice to have a definitive engine forensic autopsy to pin down the actual chain of events. But only F-1 teams can justify that type of expenditure.

Z

 

I am almost ready to start to button this thing back up. I bought a used replacement head and of course a new gasket set. I used the retainer bars to locate and secure the camshafts. I inserted the positioning tool in the flex plate to insure the crankshaft didn't move. I have watched the excellent youtube videos put up by O&DR Modurol. But I am still not 100% sure about the VVT system. The instructions seem to say to be sure that the cam is in the retarded position before tightening down the sprockets . As you know, there are no keyways, no locating device at all to insure the cam is in the right time. Same with the crankshaft gear. So it all depends on everything being in just the right place before you tighten the gears down. My question is," how do I know if the VVT is in the retarded position or not? Someone mentioned that the VVT has a spring that tends to rotate it to that position. If so, I should be ok because I did nothing to move it from where it "wanted" to be. But is there anything I can do to be sure before I button this thing back up?

 

There's some flats on the cam's rough shaft casting between lobes you can grip with a wrench and confirm the shaft springs clockwise with a wrench (as you look from the front bumper) and springs counterclockwise, retarded when released.

Pay close attention to your short chain tensioner between the two cams. It should be springing UP on B bank and DOWN on A bank, opposites.

Anyone confirm that or correct me?