Pin offset question.

[SuperMag]

In other threads it has been mentioned that pistons from other engines may work with the 300 with some alterations. This info is all well and good, but it does bring to my mind the question of piston pin offsets...

Does anyone know how the typical pin offsets on a V-8 motor compare to those on an I-6?

 

[xctasy]

They are the same. I think its 1/32 of an inch. If you put them in backwards, you'll get more power, and significantly more noise,( an old 1974 Cleveland 351 racer trick from Aussie).

The offset creates a two step vector change without over loading the gudgeon pin in one sharp step. I forget the impulse change at top dead centre at maximum torque, but it is tens of tons.

 

[SuperMag]

Thanks Deano... you do realize of course that if you ever try to leave this forum, we will kidnap you and put your brain in a jar for display in the tech pages...

Further searching turned up an interesting source... http://www.eng-tips.com/viewthread.cfm? ... 26&page=10

 

[Lazy JW]

The late Gene Berg wrote several good articles about wrist pin offset in VW pistons. Seems as though most of the aftermarket pistons made for the VW's have no offset. Gene claimed (and could demonstrate) that this had an adverse affect on longevity, as well as more noise.
Joe

 

[Anonymous]

If I may jump in with some Ford FE experience:

the truck versions of the FE (called the "FT" series) had slightly different pistons from the higher-performance FEs. The differences were: 4 rings instead of 3 for better oil control when pushing hard and distorting the piston and: less pin offset. The greater pin offset in the FE was done to reduce noise. The FT produced more low-end torque, like 21% more, despite the extra ring. It just rattled more, too....

 

[Fred]

The link talks a little about cylinder bores not being inline with the crank centerline. This is known as the De Saxe principle. Both the De Saxe principle and the offset piston pin are breifly discussed in the November 1951 Hop Up magazine page 4 (I have the book that is the first year repinted, book page number 148). According to the tech editor the offset crank has very small theoretical advantage (obviously not worth much because no one has used it in 50 years), but the offset piston pin has certain advantages in reducing piston slap and giving equal piston side thrust. If anyone wants to research it further, Cadillac originally wrote a paper on the offset piston pin subject that was published in the SAE Transactions for July 1949. I would be interested in reading it myself if I knew where to find that...