I have a 68 390 with an exhaust bolt snapped off flush with the head -it's the top bolt of the number 7 cylinder (it was that way when I bought the truck). In an effort to find a way to get a hole drilled in the bolt to extract it, I pulled the valve cover and as I was looking at the springs, etc. I noticed that the valve cover gasket mating surface (on the intake manifold side) by one of the pushrods on the number 7 cylinder is blackened, like the paint has been burned off in a 2 to 3 inch area. Just below, on top of the head and down into the pushrod hole, I have a crusty, black deposit, kind of like cooked oil, or carbon build up. This doesn't exist anywhere else in this head, but does exist on the other side of the engine, by the number 2 cylinder. Do I have a couple of exhaust valves that aren't seating?

I'm also wondering if this isn't why the exhaust manifold on the driver's side is cracked between number 6 and number 7 cylinders. Could an exhaust valve not closing cause enough heat to warp the exhaust manifold to the point that it would break a bolt and crack the manifold? The other manifold is not cracked.

I suppose I could go buy a compression gauge, but at this point, I have the exhaust manifolds off, I cannot warm the engine up before doing the compression test.

If this is burned valves, I will probably go ahead and get the heads rebuilt, it just may take awhile before I can afford it.

 

I do not think you have a burned valve. The heat risers for the intake run from the #2 to #7 this has NO air running through it. It is designed to help worm engine and atomize fuel better when cold. I would guess the heat build up in the heat exchanger is cusing the burnt look. I would think it odd that valves on both sides of the engine were burnt in th esame spot, respectively, on the head. Just to much of a coiencedence IMHO.


Scotty

 

Not sure (it's been a while since I've been into one) but isn't this where the exhaust crossover to heat the intake runs? The gasket darkening/ oil crusting should be a normal condition for an engine with a few (many) miles. Not to worry. Probably NOT an indication of bad valves.
Even cold, a compression test will give you a good indication of engine condition.
The cracked manifold was probably caused by the broken bolt and resulting uneven pressure on the manifold. Cause of the broken bolt? Who knows! Previous owner? :+ Hard to say.
Just my $.02
Greg

'77 F-250 Camper Special 400ci driver
'76 F-250 Supercab 360ci current project
'71 Mach I 429CJ in storage
'79 F-150 for parts
HONK if you love peace and quiet!

 

Thanks guys! Glad to hear that I don't have to yank the heads just yet (at least for this problem). I had not considered the possibility of the exhaust heat ports... D'oh!