PG Turbos?? Re: <VV> Re: TURBO BENT VANES

[Tony Underwood]

At 12:37 PM 9/11/2007, kenpepke at juno.com wrote:
>TONY SAID (IN PART):
>but I've not seen heads blow off, ever.
>
>Now I will agree I have never seen a head 'blown off' but on 68 and 69 engines
>and a number of times on other year cars also.
>
>I have had several occasions to put 'heli-colis' in the block when the threads
>started to fail.  It is easy to tell it has happened by the merry 
>little psst, psst,
>psst coming from the engine compartment.  I believe most refer to 
>that situation
>as a 'blown head gasket. They don't have to move very far for that 
>to happen but,
>it is possible;e to see where the threads are pulling out of the 
>crankcase.  Perhaps,
>after that there will not be enough cylinder pressure to harm anything :-{
>
>Ken



Interestingly enough, the leaky head gaskets I've seen weren't on the 
turbo cars, but usually on early model base engines like 80 and 84 hp 
variants.   The late-late engines evidently had some head gasket 
issues somewhere, hence the change in torque sequence GM outlined for 
the '69s which was supposed to cinch the head up 
tighter...   although of the '69s here and the others I've seen, no 
leaky head gasket issues have been evident.

There's one other thing, which makes me wonder if perhaps some of the 
gasket issues in these instances were caused by overheating which 
would swell the aluminum in the head and cause excessive tightening 
against the gaskets.   If it's bad enough, the head can actually 
soften and cause extrusion of metal around the gasket and into the 
chamber.   I saw enough of this sort of thing in a '69 140 engine to 
cause the extruded metal to actually contact the piston crown, 
causing what sounded a lot like a wrist pin knock when it was 
actually the piston hitting this extruded bead of aluminum.

The gasket had actually sunk down into the metal which was supposed 
to be the flat and thus the highest part of the chamber, only now 
this "rolled up" bead of aluminum was now sticking up like a fence 
inside the perimeter of the head gaskets with a peened surface 
indicative of where the piston crown had been hitting it.   The 
pistons also showed evidence around the edges of the crowns where 
they'd been striking these knurled beads of metal.   Interestingly 
enough, this particular engine hadn't shown any evidence of a head 
gasket leak, just the noise...  but I bet if it had run much longer 
the gaskets would have been spitting.

By the way, this 140 (after carving out the knurled bead around the 
gasket surface and reassembling with new gaskets) later on spit out a 
valve seat.   I'd hoped it would stay together, but after having been 
that hot it wasn't a good bet.

I saw this sort of thing in the original heads that came off my 180 
turbo engine as well.   Dropped a seat, pulled it down and saw that 
same knurled-up bead of extruded aluminum which evidently had 
resulted from overheating, likely the same reason it spit out the 
seat.   No head gasket leaks in that engine either.

In fact, most head gasket leaks I've seen have been in early engines 
with the narrower head gaskets.  But this is still only my own 
observations and certainly not any indication of the real world.


tony..