head cracks

[Anonymous]

you may have read my posts on 'trials of the 200 learning curve'. I have had quite a time trying to get a 200ci I had rebuilt to run proper. After the intial rebuild, I burned two pistons (3 and 4) after about 14,000 miles which landed me back at the door of the rebuilder and I sunk another $800 to r/r the bottom end as the rebuilder claimed the head was good. On to the second rebuild now, couldn't get the engine to runn w/o a stumble, which eventually prompted me to remove the head (after a leakdown test) to discover I had an exhaust valve not sealing. Head back on, and I discovered that my exh manifold and pipe were running cherry red under sustained load. I have checked my timing advance, and dizzy, swapped dizzys and carbs (new 32/36 now jetted rich, and a ds II), checked cam timing, fuel pressure, vacuum, and just replaced the whole exhaust system. An old timer I once met warned me of the I-6 heads having a propensity to crack, sometimes between the intake and exhaust. I might add, the last time I had the head off, the rebuilder was curious about the carbon on the valves and pistons. I am running out of ideas, but am leaning to the exh/intake crack theory..... thoughts?

 

[Anonymous]

First thing, get a new Engine bulider.

If your head was cracked, you'd think you would be losing coolant (white smoke). Sounds carb related - mixture to lean? or a manifold leak?

 

[Anonymous]

well unfortunately I'm stuck with them if I need 'warranty work'. I was thinking of a crack specifically in port area, between an intake port and exhaust port, would cause exhaust to be forced under pressure back into the fuel mixture (assuming high heat and metal expansion) and thereby create a lean combustion scenario. I am certain I am not running a lean carb. If there's an intake leak between the carb and head, I can't identify it, and that's assuming its a condition re-created with 2 different carbs/spacers/gaskets.... no sucking sound.... no difference with w-d40 or propane tests.... david soCal

 

[Anonymous]

Ok, if your carb gasket(s) and vac. hoses are in good shape then a port crack sounds plausible. What sucks is you have to pull your exh. manifold. Get yourself an LED flashlight, they're brighter.
Do you have a thermactor sys or EGR?

 

[Anonymous]

Do you have a thermactor sys or EGR

I'm not sure what this refers to. There is a space below the carb that pulls manifold vac and is connected to a PCV valve towards the front of the rocker arm/valve cover. The oil fill is at the rear of the cover. I would guess this is Exhaust gas recirculatoin? What about valves or valve springs.... wrong valves? Any possibilities there?

 

[Anonymous]

Smog pump, Exhaust Gas Recirculation.
If you have an early six, probably not.

PCV - Positive Crankcase Recirculation, Reburns your crankcase vapors (blow-buy) is your PCV valve in good shape?

 

[Anonymous]

That could be 2 years old or so.....

 

[finnstanger]

I know that have minor crack between 3/4-cyl exhaust and intake, just below the carb. The head was recently rebuilt, but I could not get it idle evenly. I've been wondering if that crack has something to do with it. Before the rebuilt idle was fine. I could not see the crack when I took the head to be rebuilt. the machinist told me that the head was warped or possibly milled incorrectly earlier. They milled it even and the crack appeared when I installed the head. I'll replace the head anyway, but I'm going to run the old one to test the new driveline amd brakes.

 

[Anonymous]

seem's like we're building a theory? a crack opens and sucks exhaust as the engine heats... runs leaner.... cherry red exhaust. By the by, I forgot to mention, because I thought It was just my ignition switch, that my engine sometimes 'runs on' when I turn the key off. Perhaps excess carbon from exhasut in the mix is maintaining the ignition process after shut off? I suppose the only way to find out is to swap heads. Anything wrong with using a late 60's head on an 80's block as long as I use the matching pushrods?

 

[addo]

Nothing wrong with that setup proposed; you'll need the carb to suit but that's about it.

 

[Bort62]

okay, slow down a second.

If you were getting exhaust gas back into your intake, it does not make you run leaner. In fact, it will tend to cool the combustion process (IE EGR).

I'm not saying that a sufficiently large crack wouldnt cause problems - but its not going to cause you to run lean.

As far as the engine continuing to run after you shut it off - does it continue to run like normal or does it kinda sumble and fart for a few seconds and eventually stop?

If its the later - it's dieselling which can be caused by too much timing, or too high idle.

 

[Anonymous]

The engine continues to run like normal, with the exception that my voltage will drop for 14 to 8 or so. I should back up and say too, that my central concern is that my exhaust manifold gets red hot when under a heavy load. Thanks for breathing some sense into my desperate theories....

 

[Bort62]

If the engine continues to run like normal but your votlage drops - there is something weird in your wiring.

Fix that first before you go worring about this other problems.