<VV> Installation of engine pistons

Frank DuVal corvairduval at cox.net
Sat Oct 25 19:47:06 EDT 2014

To this and Mark's information, let me add.

Yes, the Corvair pistons are pin offset.

Yes, the rods are symmetrical and can be used with the numbers facing 
down or up. Even numbers can be on the odd side of the engine. But, 
always the notch has to face the front of the car, flywheel end on the 
Corvair engine.

And, I've never seen a Chevy inline 6 share crank journals with two 
connecting rods. The ones starting in the early 60s (not the stovebolts) 
have 7 main bearings, one between every rod journal, plus the two ends.

Frank DuVal

On 10/25/2014 3:30 PM, BBRT via VirtualVairs wrote:
> Offset piston rods are used in pistons to reduce piston slap when 
> piston crosses top dead center (TDC).
>> From Google...
> Piston is generally offset to major thrust side of cylinder. The major 
> thrust side is the side of the cylinder wall the piston is pushed 
> against on the power stroke. The minor side is the side the piston 
> rides against as it pushes upward the compression stroke. The purpose 
> of the offset is to reduce the amount of piston slap as the piston is 
> forced from the minor to the major thrust side just after crosses TDC. 
> Then the piston is pushed up on the compression stroke it rocks 
> slightly so the lower skirt on the major thrust side contacts the 
> cylinder wall. As the piston crosses TDC that contact allows the rest 
> of the skirt to ease its way over to the major thrust side. Without 
> the tilt of the piston, the skirt would ride up the minor side, reach 
> TDC and be slammed agasint the other side by, to combustion pressure.
> Chuck S
> ----- Original Message ----- From: "MarK Durham via VirtualVairs" 
> <virtualvairs at corvair.org>
> To: "Jerry Brown" <air_cooled63 at yahoo.com>
> Cc: <virtualvairs at corvair.org>
> Sent: Saturday, October 25, 2014 3:10 PM
> Subject: Re: <VV> Installation of engine pistons
>> Jerry, always follow the tech manual for the engine. Even when it 
>> appears
>> that everything is symmetrical and balanced. How else are you going 
>> to tell
>> what you have down the road or while you are working? If you do your 
>> work
>> in a inconsistent way, there are more chances to make mistakes, forget
>> something, etc, and aligning the piston marks and rod position 
>> numbers help
>> to provide that consistent work we rely on to provide years of 
>> trouble free
>> motoring.
>> While I did assemble my engine 4 years ago, I did not check to see if 
>> there
>> was offset built into the location of the piston pin, or if the rods 
>> were
>> something else besides symmetrical. I have seen aircraft engines and
>> automotive engines were there were offsets in piston pin location to
>> compensate for say a piston leaning in a V-6 or V-8, or in a flat
>> configuration like aviation piston engines and Corvair motors are.
>> In short, follow the book!  :):)  If you don't, then you should not be
>> doing the work. You are bound to make mistakes.
>> Mark Durham
>> Hauser, Idaho
>> 62 Monza coupe Red/Red 4 speed
>> On Sat, Oct 25, 2014 at 11:46 AM, Jerry Brown via VirtualVairs <
>> virtualvairs at corvair.org> wrote:
>>> Through the years I have had several persons tell me that when 
>>> installing
>>> the pistons and rod to the crankshaft that it didn't matter if the 
>>> piston
>>> didn't face the fly wheel because each rod had it own journal to 
>>> ride on
>>> and didn't share a journal like some Chevy straight 6 cylinders.  I 
>>> know in
>>> the tech manual that it says the notch should face the flywheel.  Is 
>>> there
>>> something in the mathematics that the rod number should be up and 
>>> the notch
>>> facing the flywheel? I know some of you engine Gurus can help me on 
>>> this so
>>> I can be sure if the these people telling me it's ok to install a 
>>> piston
>>> backwards.   I have always followed the tech manuals instructions.  
>>> Jerry
>>> Brown

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