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1931 Buick 90 series


Bernie F
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Does anyone know how critical it is for the piston pins to be offset, on a 1931 Buick 90 series

Piston manufacture doesn't seem to think it matters.

Does anyone have experience in this?

E: Bernie  at  gail1946@hotmail.com

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Typically, the purpose of offsetting wrist pins is noise abatement.  If piston pins are not offset the piston may wobble in the bore causing clatter.  Most contemporary car engines, especially those with V configured engines, use offset wrist pins.  In a Buick straight 8 I doubt you could tell if pins were offset or not, the engine block castings are thick by today's standards, and the engine makes enough mechanical noise otherwise to mask piston wobble.  I only had trouble with this one time, and it was with a motorcycle.  I had a 1973 Moto-Guzzi 850cc Eldorado which featured a 90-degree V-twin engine and it rattled like hell every time you opened the throttle.  It was air cooled and had alloy cylinders with chrome bores.  I spent a lot of money replacing the cylinders and pistons to get rid of the noise and after the new pistons and cylinders were run just a few miles they cackled every time you opened the throttle.  I finally figured out the reason was the crank centerline and bore centerlines intersected right on center and the wrist pins were in the exact center of the piston.    

MC005 1973 Moto Guzzi 850 Eldorado.jpg

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No. I don't think it's relevant. Perhaps more than noise, the early engineers thought they could reduce the wear on the power side of the piston by offsetting the pin. It's splitting hairs, especially with modern clearances and lubricants. 

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I am pretty sure that the original pistons were cast iron or steel . Modern replacement pistons will be aluminum. Aluminum piston tend to grow with heat to close some clearances. This being said, I doubt that the pin offset will yield any significant engine noise reduction. Besides, there are plenty of other engine components that you will be hearing.

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I had high compression pistons built for our 90 series 10 years ago and they aren't offset.   Over 10k miles without a problem.    I had Ross Racing pistons build them.  They should be on file.   I sent them resin shaped slugs of the head and we rough calculated 6.5 to 1 ratio.  Much better than 4.5 to 1 and mileage almost doubled.  

 

Hastings rings is 40 minutes from my house and they were sold several years ago and have since gotten ride of a lot of the odd ball stuff that doesn't sell.  You used to drive up there and they would hook you up.  Now you get a catalog and if it's not in it then your SOL.  

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