<VV> 61 Loadside update and questions

[corvairs]

Here we disagree Bob - Comments in text -

BobHelt at aol.com wrote:
> EM engines in stock form already don't have enough area there. That is why 
> the 1965 and later engines all use an increased gasket surface. 
We know the gasket diameter was increased because of head gasket 
problems. But we also know that most head gasket problems were actually 
caused by lack of understanding regarding torque patterns and ratings. 
In fact, the factory made a number of changes in a wild scatter gun 
approach to try and solve this problem, including telling people to 
torque the heads to 67 ft lbs (!) in the 1969 tech bulliten.

> Jugs bored 40 
> over are already  marginal in sealing surface and to even consider going larger 
> is a major mistake in my opinion.
>
> In addition, I would be very concerned about the roundness of these jugs. Any 
> jug already overbored and subjected to this kind of heat has got to be 
> distorted.
I have advised that people, looking for more hp in early motors (also 
1964) go to a full .060 over. I have never seen nor have I ever 
experienced unusual head gasket or distortion problems with .040 or .060 
over in these motors.
>  Why would you want to even consider reusing these jugs?
>   
Now, that's another matter, as the engine in question had obviously been 
severely overheated. I wouldn't reuse much of any of the engine.
> If I were you I would toss all of these jugs and set an 0.030 overbore limit 
> on any EM engine.
>   
Well, it's a free country, but the only difference between 61-64 
cylinder barrels and  65-69  (actually very late 64's too) is that only 
the very top of the barrel (where it enters into the head) is of an 
"inferior" crossection. The rest of the barrel is no more affected by 
distortion that it would be on a 65-9. This area is also held captive by 
the cylinder head which makes any possible distortion much less possible.

Now that's all theoretical assumption. From a practical standpoint, 
we've bored and honed nearly 10,000 Corvair cylinder barrels and here 
are our observations.

1) In boring and honing thousands of barrels , barrels that are 
distorted signifigantly are less that 5% of the total we see. And 95% of 
those distorted barrels are earlies (1960-63). This doesn't just involve 
distortion but also castings voids. Sometime in 1962 or 63 GM upgraded 
this process for  casting the barrels. This seems to have reduced the 
distortion problem to virtually nil regardless of the overbore size.

2) We see no correlation between year and overbore size and distortion 
rate. In the rare cases where we do see distortion it almost always 
applies to ALL barrels in a set. This indicates to me that the problem 
is not because of design but because of specific severe abuse. I would 
be much more concerned with a set of .020 barrels coming out of a sand 
dragster than a set of 1960 barrels bored .040 over. Additionally, of 
the distorted barrels we've seen nearly all are still at standard bore size.

As for me, if I were to rebuild a 1960-64 motor /I/ would  bore out to 
.060, use copper head gaskets and observe a proper head pattern and 
torque of 35 ft lbs. I would not expect any problems. 

Lon
www.corvairunderground.com


> Regards,
> Bob Helt
>
>
>   
> Hi Jamie,