Charley B

I had some exhaust work done on the Euro last week and the tech, using a stethoscope, said he could detect a small leak where the pipe attaches to the manifold on the passenger side. I can't hear any leak so I told him to leave it alone.

The question is, could a small leak at that point possibly cause any damage in an overhead cam set up?

ZEUS+

No, damage to the exhaust valves can happen from a major leak at the head. Running an engine with no manifold would damage valves, not a minor leak downstream.

Dennis Wilson

A leaking exhaust valve can let unburnt combustion gases into the exhaust header which can detonate and cause a leak, but not the other way around. Did the tech do a compression test on that cylinder?

Dennis

123quattro

Don't worry about it. It won't hurt anything. Tons of cars on the road have leaking exhaust manifolds.

dr bob

Charley--

That's a gasketed connection, easy enough to replace the gaskets and probably the bolts/hardware at the same time.

For those playing at home, the concern is that cold air will be drawn back to the valves on shutdown, risking warpage of the valves. There are urban legends associated with this, mostly with folks who ran engines hard enough to glow the valves with no exhaust at all. If it's a leak too small to hear, I wouldn't give the valve damage issue a second thought.

Dennis Wilson

Bob,

The concern about the cold air was very real. Prior to the incorporation of catyltic convertors and valves designed for hotter running, Detroit auto makers placed temp controlled valves on the exhausts to slow the cool down. With today cats and better engineered valves, it shouldn't be a problem.

Dennis

ZEUS+

Ford used sodium filled valves.

dr bob

The temp-controlled valve in the exhaust was there to speed warm-up of the intake manifold. One valve only, mounted on the right side almost exclusively. In the middle of each head was a port to allow exhaust gas to pass to the other head through a passage under the middle of the intake manifold plenum. Partially block one exhaust when cold, and more warm exhaust gas would flow through the manifold passage. When the manifold was cold, fuel that had been atomized in the carburetor would condense out on the walls of the plenum and the runners; Heating that section meant that the engine could be weaned off the choke earlier, and would have better cold driveability within minutes of cold start.

It had absolutely nothing to do with keeping cold air off the exhaust valves.

Dennis Wilson

Bob,

Guess I should have been more specific on my time line. I was specifically refering to the old Ford Y blocks (made until 63) that had the passenger side exhaust wrap around the front of the engine, go into the drivers side manifold, then exit through a valve to the exhaust. My pet peeve was that the valve was spring loaded and would often freeze up and stall the engine. IIRC the Plymouth flat head engine (made until 59) had the valve just before entering the exhaust also. You are right in that the later V-8's with automatic chokes only used it for heating the manifold.

Dennis

dr bob

OK, now I know what you were referring to. It's easy to date our knowledge when we can think back to 292/312 V8's and remember how the little spring-loaded exhaust flapper valve worked. But can't remember what we had for lunch yesterday. I can't remember the last time my memory was good...

6.0-928S

Yeah, & the valve heads would pop off over 8500 rpm. Ask me how I know!
Wassup Zues!

Hammer

Dennis Wilson

Bob,

What's memory? You can't be as old as I am (61 and counting). Actually, it wasn't that long ago that I gave away my 63 Ford 1/2 ton pickup with the 292. BTW I hated working on that engine when it was warm. There was plenty of room to put the exhaust underneath.

Dennis