<VV> 61 Loadside update and questions

[Frank DuVal]

Hi Bob,

You seem amazed that 600 degree head temp didn't instanly destroy the 
motor. My however inaccurate 64 Spyder temp gage has seen 600 a couple 
of times (light/buzzer on also), and will typically run at 550 at umm 
excessive speeds on I-95 in the summer for an hour or so at a time. I 
only had trouble with valve seats, not rings/cylinders. (145 cu in motor)

Jack Dempsy at Hot Air Enterprises always bore his cylinders .040. Now, 
maybe he did mostly lates, but I was discussing an early motor at the 
time (propsed 64 Spyder rebuild, 164 cu in, still not done 20 years 
later...).

So, have you seen many head gasket failures with .060 barrels, or are 
you predicting failure? Most head gasket failures I have seen in my 
limited work was on standard sized early engines. I can see the concern 
but I have a fresh set of .040 jugs to go on a 64 A/C 110 motor and the 
surface width looks slim, but still larger than the big bore gaskets 
that will mate to it. I also have used the big bore copper gaskets on 
most all rebuilds going back to the early 80s. Back then it was to use 
the thicker gaskets to lower compression for less knocking. No head 
gasket failures that I know of, and the sealing area is very small.

Even SBC blocks distort with temperature changes. A friend builds race 
motors and just built a hot water recirculation system to hot/wet hone 
his blocks to get the size right at operating temperature. But, the ones 
honed at room temperature still run and last a long time.

Frank DuVal

BobHelt at aol.com wrote:

>Hello Lon,
>We haven't hear much from you lately. Nice to kinow that you're still around 
>and kicking. Well, you certainly entitled to your opinions, but much of what 
>you are referencing just isn't backed up by the facts (as opposed to opinions). 
>
>
>Please see below for more on this subject.
>Regards,
>Bob Helt
>
>
>In a message dated 11/24/08 2:05:42 PM Pacific Standard Time, 
>corvairs at pacifier.com writes:
>
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>>>Jugs bored 40 
>>>over are already  marginal in sealing surface and to even consider going 
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>>larger 
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>>>is a major mistake in my opinion.
>>>
>>>In addition, I would be very concerned about the roundness of these jugs. 
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>>Any 
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>>>jug already overbored and subjected to this kind of heat has got to be 
>>>distorted.
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>>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.
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>
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>
>Good for you, but very dangerous. An EM jug bored out 0.060 has a knife edge 
>biting into the gasket. This causes two concerns, one that the knife edge just 
>isn't a good enough contact area to hold back the combustion process. (again, 
>if this was so great, why did customers have gasket failures and why did Chev 
>go to the larger area in 1965?) Second, 35 lb-ft torque on this knife edge 
>tends to cut into the gasket and cold flow the aluminum in the head right below 
>the gasket. This cutting and cold flow cause an increase in clearance whis 
>relieves the head torque and sets up the cylinder for future head gaskle 
>failures.
>
>Just take a look that the knife edge that a 60 over EM cylinder presents to 
>the gasket and you will convince yourself. Why would you want to use such 
>suspect components anyhow?
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>Since you still are not convinced, please perform this simple bench 
>experiment. Take a newly bored cylinder and place it on the work bench. Then place an 
>inside micrometer across the bore, opening the micrometer until it just 
>supports itself across the bore.
>
>Now, without disturbing the micrometer, place your hands outside the cylinder 
>90 degrees  from the direction of the micrometer and squeeze the cylinder 
>between your hands. You will find out that the little pressure from your hands 
>will distort the cylinder and allow the micrometer to fall out of the cylinder 
>where you placed it.
>
>So you see that overbored cylinders can easily distort. Ray Sedman has stated 
>that cylinders are often at 0.002 in out of round after reboring on his 
>excellent equipment and that it is necessary to use a torque plate to insure 
>roundness. Even then with a perfectly round cylinder it is impossible to know what 
>happens when the engine comes up to temperature.
>
>
>As for the rest of your comments, it sounds like you are trying to justify 
>your business and processes. Maybe you turn out error free products, and maybe 
>not. But even if you do, you are operating in a very risky area overboring EM 
>cylinders so much in my opinion. Maybe your success has mostly been just luck.
>
>I still would recommend to everyone concerned that they limit their EM 
>overboring to 0.030 in. And for Jamie, that he NOT reuse these cylinder. Maybe they 
>will work just great. But if they don't, then it's another rebuild. Why take a 
>chance? 600 degrees he said!!!!
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>>> 
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>>2) We see no correlation between year and overbore size and distortion 
>>rate. 
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>So you are saying that despite thinner cylinder walls from boring, the 
>cylinders remain just as rugged and distortion free as before!  Bull-ony. Do you 
>expect anyone to believe that?
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>>Lon
>>www.corvairunderground.com
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>Bob Helt
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