I've just run my 406 v/Vortec heads for the first time.  About 5 minutes after start-up I heard a very loud, continuous, sound like an air-horn you'd carry on a boat.  I shut the motor down thinking I had spun a bearing (the engine was running fine otherwise).  I discovered a spark-plug wire melting on a header tube.  I wire tied it out of the way and started the engine again.  It fired right up and ran fine.  After 15 minutes of good running the sound started again.  I shut the motor down again but it had been running fine with good oil pressure (~50 psi) and right in the middle of the temp. range.

Is it possible something in the cooling system could make a noise like this?  It really does sound like an air horn.  Very loud.  I'm nervous about starting the motor up again.

If I did, in fact, spin a bearing what would it sound like?  Would it not make noise until the engine got hot?

Baffled,

OM Gang

Is it possible it's the fan clutch?  I've been racking my brain this evening trying to figure it out.  There was no knocking or ticking sounds of any kind coming from the engine.  It was running perfectly right around 1550 rpm.

Still baffled,

OM Gang

I had the same thing happen to me when I first started my last motor.  On my motor it was a huge vacuum leak......there was a chunk of gasket stuck to the bottom of the carberator that I didn't see before I put it on.  Once I scraped off the old gasket the noise was gone........Good luck  

I thought about a vacuum leak too but I've checked everything out.  I've heard vacuum leaks before - everything from a low hissing sound to a high-pitched whistle.  The sound I heard was exactly like an air-horn.  Hopefully I get it figured out this afternoon.

OM Gang

Is this built on a 400 block? Almost a self answering question.

Did you dril the 6 holes in each head to allow upper cylinder steam to escape into the cooling system?

Bogie

Yes 'Bogie, I did have the steam holes drilled in the Vortec heads by the machine shop that did the short block.  This is the 406 Impersonator motor I've been working on/posting about since February.  I'm going to give it another go this evening when I get home.  I'll pick up a new fan clutch to take home with me in case it turns out to be the problem.  It kind of make's sense that the engine will run fine for a while before the noise starts, i.e. it take's a while for the clutch to reach the temp. at which it begins to function.  I hope that's it.

OM Gang

I removed the oil filter and cut it open for inspection.  I didn't find anything in the element.  The oil from the filter contained the grayish swirls from the assembly lube and some very fine metalic paticles that settled out to the bottom of the drain pan.  On a brand new engine that has just run for the 20 minute break-in period is this normal?  If I had a bearing fail would I expect to see more evidence, i.e. larger metal particlels or flakes in the filter?

I installed a new filter and ran the engine again for 15 minutes last night.  It fired right up and ran fine.  It did not make the 'air-horn' sound again.  I am contemplating taking the truck out for a test drive - at this point I'm not sure what I have to lose.

OM Gang

Your oil filter sounds fine. You're right to consider a metal part failure would show chips or flakes. Very fine "grist" looking something like metallic paint pigment is normal, mostly from the rings seating on the honed bore surface.

I looked at the steam vent hole as a possibility on these heads as I had a friend that put to gether a Vortec headed 406 and forgot that little item. On startup everything sounded normal after about 20 minutes the steam began to escape into the cooling system with loud (did I say LOUD) sounds eminating from the return hose and radiator. I mean you jumped first and sought an answer later kind of sound.

Inside the engine room you can look for belt missalignment, if the engine uses a thermactor pump when these fail the sound is impressive. Or a power steering pump running on empty. Bearings in the water pump or alternator. Wrong rotation water pump or fan (serpentine pump/fan mixed for Vbelt drive or conversly, but these usually result in overheating pretty quickly. (I had this a few weeks ago on a 350 I converted from serpintine back to V-belts, the Hayden fan was for Serpintine, I didn't see that on the package. Took the truck out, it made a loud roar that started about 2000 RPM, drove it about 2 miles, back in the shop I noticed that no air was flowing over the engine and when standing in front you could feel hot air being blown out the grill. Oh, that's weird? Shut it off pulled the shroud and found half the blade to hub rivets were missing from the fan and the pitch was in the wrong direction. Still fighting with the parts store. A great reminder to BS less when getting parts and pay more attention to the parts.)  Of course the ever present air leak. The damper rotating against a piece of structure.

Where you can't see a badly missaligned thrust bearing eating the crankshaft. A bearing spinning in its bore. Starter hanging up on the ring gear. Ring gear hitting something inside the bellhousing which could also be the starter gear which insufficient depth clearance to the ring gear or protuding into the ring gear's path and being hit on its end.

If a clutch a bad throw-out bearing or missing or dry pilot bushing. For an automatic a torque converter that's not fully seated putting heavy side loads on the tranny pump and or crank thrust bearing.

Anyway some things that come to mind.

Bogie