patrick22309

I have broken valve springs before and had the same type of symptoms. Intake valve bent and valve stuck open. I would agree, a compression test is in order.

TomZ

Wouldn't the valvetrain be making a noise with the broken valve spring? I would think so.

Budman

Tom,

FWIW, I had a valvespring break on a 406 that I was running in a Camaro that I used to own many years ago. I do not recall hearing any valve noise (i.e. clicking or tapping) when it happened. It just suddenly started missing badly - vacuum gauge was bouncing all over the place. I wasn't seeing any kind of smoke out the exhaust either. I suspect that the hydraulic lifter took up the slack when it happened. Intake valve was not closing all the way after the spring broke, hence the miss and vacuum readings.

Good luck with it.

patrick22309

Each time my valve springs broke, they still kept the valve high enough probably because the piston beat it there so the lifter stayed in place not poping out. I had no valve train noise and plenty of oil to the top side of the motor.

TomZ

Well, I'm hoping and praying that it's a valve spring.

TomZ

OK folks... some interesting test results and some even more interesting finds.

Did the compression test.

#1 10 PSI
#2 190 PSI
#3 190 PSI
#4 190 PSI
#5 190 PSI
#6 185 PSI
#7 195 PSI
#8 195 PSI

So... out come the tools and a half hour later off comes the port cylinder head. Water falls into the cylinders, all cylinders hold water.... noticed this while trying to get the head out of the bilge. I quickly turned over the head thinking that I was going to see a burned exhaust valve. Nope. So I go back to the half cracked open block and I look carefully again. Nothing out of the ordinary except that the #1 piston is a tad bit blacker than the rest, but even that appears within the normal range. I spent a good ten minutes looking over that hole to find the problem. The head gasket was good (perfect graphite/stainless gasket) and I saw absolutely no signs at all of any problems in the bore. I thought that if a piston was bad or whatever, you'd see something to indicate it. So... back to the head. Looking... looking... looking... all the exhaust valves are good, nice and tan. The intakes are good, lightly tan... ooops!!! #1 is not tan and is slightly blue in color and not only that... it looks like a valve out of my dad's 410 CID elephant motor (as in this looks like it was made for a hemispherical combustion chamber). The valve is no where near flat and looks like it got sucked into the head! WTF??? It was still moving in the guide because I was able turn the motor and watch the valvetrain work. There was no sign of heat on the rockers either (no burned oil, everything clean).

So, looks like the intake valve either burned or the seat broke or something. My wife is complaining about me working on it so I'm going to leave the cylinder head disassembly to sometime over the weekend. I'll know more about the condition of my head sometime on Sunday probably. I have never seen this before, ever. I've worked on a lot of stuff, built engines left and right, and taken apart some pretty well grenaded ones and have never come across a melted intake valve.

At least is wasn't in the short block.

Any ideas or thoughts??

Gearhead99

Sounds like it got HOT. Do you have an intake leak at the #1 cylinder?? I'd be checking the others too.

TomZ

The other three on that head are perfect and cylinder pressure is good all across the board with exception to that one cylinder. I'm thinking that since the plug was loose, additional air was allowed to get into the cylinder which created a lean condition?.?

Blueman

I had a big block truck that a friend helped on a tune up and a few days later developed a miss. guess what, loose pulgs that was what probably caused your problem. Little things can be such a big pain in the A--.

TomZ

Actually, after looking at it again in daylight, it seems that it may just been a bad valve (thanks Manley!). The valve was no a blue color and what I was seeing was a trick of the flashlight. I really can't see why the valve failed other than heat (which now doesn't seem to be the case). The back side of the valve is OK and appears normal. The combustion chamber appears normal as well.

I'm debating about whether I should send the head out to be checked or if I should just order another valve and lap it back in there. The seat looks like it has a groove in it at the deepest edge where the port necks down into the port. I know that the valve does not normally sit there. Should I try to polish that out or will it need a new seat (these heads do not use a removable seat as they are created in the iron by an electronic process... I'm worried about having it messed with). If I go my way, I can have it back together in the time it will take for the parts to come in. If I send the head out, I may be waiting until God only knows when (anyone that I want to deal with is beyond backed up right now).

Thanks!