One of the common questions about the 426 Hemi is its pistons, rings and wrist pins. Let’s examine, what size pistons are in a 426 Hemi?
426 Hemi pistons are made to fit the 4.250″ bore size. They weigh 841-845 grams and have an overall length of 4.060 in. The wrist pin size is 1.0310″-1.0312″ diameter, 3.395″-3.405″ long and weigh 204 grams.
Continue reading below for more specifications about the engine’s pistons, rings and wrist pins.
426 Hemi Piston Size: Bore Size, Length and Specs
The pistons are made of forged aluminum and tin plated. Their overall length is 4.060″ and have a dome height of .537″and dome volume of 88.3 cc’s.
The dome volume of 88.3 cc’s results in a 10.25:1 compression ratio. The race Hemi has a dome volume of 102 cc’s and gives the engine a 12.5:1 ratio.
The pistons are made to fit the bore size 4.250″
|426 Hemi Pistons|
|Piston Material||Forged Aluminum (Tin Plated)|
|Weight (Std through .040″ oversize)||841-845 grams|
|Dome Volume||88.3 ccs|
|Rings||3 Total (2 compression/1 Oil)|
|Wrist Pin Type||Full Floating|
|Wrist Pin Diameter||1.0310″-1.0312″|
|Wrist Pin Length||3.395″-3.405″|
|Wrist Pin Weight||204 Grams|
The pistons have intake and exhaust valve reliefs on the sides of the dome. This is to provide clearance for the engine valves and avoid having the piston contact the valves.
The pistons are domed so they can fill the combustion chamber which is also domed. This is to provide better combustion and compression ratio.
426 Hemi Piston Rings
The pistons have three rings. The top two piston rings are compression rings and the bottom one is an oil ring.
The oil ring is made of three pieces. It has chrome plated rails with a stainless steel expander/spacer.
The compression ring thickness is 5/16 in. and the oil ring 3/16 in. The compression ring groove depth is .220″ and the oil ring groove depth is .186″
426 Hemi Wrist Pin Size
What is the diameter of a 426 Hemi wrist pin? The wrist pin diameter is 1.0310″-1.0312″ and is 3.395″-3.405″ in length. The wrist pins weigh 204 grams and are full floating.
The wrist pin bushing bore diameter is 1.0314″-1.0317″.
Wrist Pin and Pistons
The wrist pin is what goes through and connects the small end of the connecting rods to the piston.
There is a pin opening on each side of the piston. The pin is pressed through the piston opening and the rod at the same time. The pin is held in with a circular retainer.
The photo below shows some rod, pin and piston assemblies. 426 Race Hemi on the left with the big bolt:
Someone I know recently called me because he came across old, original wrist pins measuring 1.09″. The Race Hemi had a 1.09″ diameter wrist pin.
Check out one of my latest articles, 426 Hemi Rod Journal Size.
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Check out more Mopar engine wrist pin and piston articles:
For the past 40 years, I’ve been studying and researching Mopar Hemi, pistons and engines like the 426 Hemi. I’ve assembled engine parts, pistons, read books, articles, magazines, watched videos, attended seminars and spoken to other Mopar experts.
Read More Mopar Hemi Spec Articles
- Google books: How to Rebuild and Modify Chrysler Hemi Engines
- Google Books: Chrysler Engines 1922-1998
- Wikipedia: Chrysler Hemi engine