Burnt intake valves?!?!

[realgonekatt]

I removed the head from my 46' today to replace the gasket (small leak) and found that the two intake valves closest to the carb (middle intake runner) are terribly pitted and burnt on top. The faces and seats look alright and fortunately I have an old tobacco can full of valves from a 230" (I love how easy they are to change on this motor)

So, my question is, If the heat riser is stuck open, could it cause this condition? I have yet to drive this car so I have no other symptoms to go by.

She does idle well though. Should I just plan on pulling off the manifolds?

I was hoping this engine would scoot by till I finished my 230" But I dont wanna burn it up either:confused:

[greg g]

could be they were just adjusted to tight, check the lash on the ones your are intalling keeping in mind the looser is better. Also if you valve is open try tunining it all the way clockwise and clamping it there. Even if you sacrifice a set of olde vice grips, clamping them on so their weight holds the flap closed and the exhaust flowing throughthe exhaust manifold.

[realgonekatt]

The "flap" wont budge one way or the other. I suspect that it hasnt since the carter administration:rolleyes: I think ill just pull the manifolds and take it from there. Is the heat riser controlled by a thermostatic spring type of deal? Seems problematic? I was just looking at langdons kit for running coolant to the intake manifold with a little plate adaptor, like a modern intake manifold. Anyone tried it out? Also, that offy intake they have is kinda growing on me. I cannot however, see shelling out 350 clams on their exhaust setup (looks **** though)

[tjustice]

I removed my heatriser plate and made a plate out of some 409 stainless. This plate is more or less permenantly mounted between the exaust and intake. I placed the gasket on the exaust manifold side to prevent leaks. Haven't driven in any extreme cold weather but so far she cranks and runs like a top.

[greg g]

That is how I have mine rigged but the flap is still in there welded on the hot position, the ends of the pivot are aslo welded closed, Never had an issue.

The default position is the one which direct exhaust into the intake, thats why they rust there, the bimetallic spring works against the counter weight when hot. So if the spring faisl, the counter weight just falls into the cold positioin then it rusts there.

[TodFitch]

That is how I have mine rigged but the flap is still in there welded on the hot position, the ends of the pivot are aslo welded closed, Never had an issue.

The default position is the one which direct exhaust into the intake, thats why they rust there, the bimetallic spring works against the counter weight when hot. So if the spring faisl, the counter weight just falls into the cold positioin then it rusts there.

Did they change that over the years? I'm out of state at the moment so I can't check my car or my books. But I recall the weight pulling the flap to the hot position and the thermostatic spring moving it to the cold. When the spring warms up and loses tension then the weight overcomes the spring and pulls the flap to the hot position.

Also the pivot is off center on the flap such that high flow in the exhaust opens (moves toward hot position) when the engine gunned.

So if the spring breaks I'd expect the weight to pull the flap to the warm position to rust in place.

Maybe they reversed things over the years but I don't recall the 46-48 service manual being very different than the 1930s one in that area.

[greg g]

I'll have to check the extra manifold inthe garage, but the 3 or 4 I have had off over the years the spring was gone on most of them, and they were in the position which fed exhaust gas to the intake. On the one that was free when you reved it it went to the horizontal position and then clunked back to the vertical forcing the exhaust up into the intak