Mopar (Piston Wrist-Pin Off-Set)

[69 Cuda 440]

Getting the understanding of 'Wrist-Pin Off-Sets' in Stock Mopar Pistons.

Left Bank {Driver Side}...................{ 1, 3, 5, 7}
Right Bank {Passenger Side}............{ 2, 4, 6, 8 }

 

[Mrmopartech]

What is your question? mrmopartech

 

[moper]

I don't believe any of the existing new "stock replacement" pistons have an offset. They haven't in decades. There was little benefit from it and it meant piston manufacturers, warehouses, and shops had to stock twice as many numbers so it was discontinued. That was going out of style when I was in parts in the late 80s.

 

[69 Cuda 440]

Just adding a little 'early performance tip' information.

The 'Factory Pistons' were built with an 'Off-Set Wrist-Pin' to help prevent
piston slap during cold starts.

But, as 'MOPER' stated, after-market Pistons were machined with a 'Center-Positioned' Wrist-Pin.

Back in the day, reversing the Stock Factory Cast Pistons (left-bank to right-bank and right-bank to left-bank)
was supposed to be 'The Trick', for less friction and higher RPM's.

 

[moper]

In my early days I screwed up and ordered and sent a set of 8 of the same side and got yelled at for it - and then told they were "not doin' that anymore but look closer next time!"

As your scan notes (J&E) some guys still do it when rules are strict and every little bit counts.

 

[69 Cuda 440]

If memory serves correctly,

Back-In-The-Day.....

Both 'JE Pistons' and 'Forged-True Pistons' had '0' Off-Set in their Forged Pistons.

Even TRW #L2222N Forged Pistons were machined with '0' Off-Set.

The 'general theory' was, that the 'less friction' between the piston and cylinder wall
resulted in an increase in approximately 200 RPMS, and 15 More Horsepower in engines
with the 'Factory Cast Pistons'.

 

[moe7404]

if i remember right, the offset was to fix piston slap noise. in 1964 the racers running the 273 engine would reverse the pistons to get little more torque. never knew if it did. i really had to dig deep in to my brain for that one.

 

[69 Cuda 440]

Pistons on the 'Left Bank'.......{1,3,5,7) came from the factory with the
'Wrist-Pin' slightly 'off-set' towards the top of the block (towards the lifter valley).

Pistons on the 'Right Bank'......{2,4,6,8} came from the factory with the
'Wrist-Pin' slightly 'off-set' towards the outer edge of the block.

This was 'only' with Factory Cast Pistons, to help prevent 'piston-slap' during
cold starts.

Reversing the Factory Pistons would help reduce friction.

After-market forged pistons were machined without the 'off-set'.