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Deck height and stack-up
At top dead centre the distance from the crankshaft centreline to the piston crown is the sum of the crank radius, the rod and the piston's compression height. Compared with the block deck height it gives the piston-to-deck clearance. Enter the measurements and we solve the clearance, or the deck height a desired clearance requires.
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Piston-to-deck clearance
0,80 mm
A positive clearance means the piston crown sits below the deck at top dead centre, a negative one that the piston goes above the deck. Measure the actual clearance during assembly.
How the calculation works
The stack height at top dead centre is the crank radius (half the stroke) plus the rod length centre to centre plus the piston's compression height, that is the distance from piston pin to piston crown. It is how high the piston crown sits measured from the crankshaft centreline. The difference between the block deck height and that stack height is the piston-to-deck clearance.
A positive clearance means the piston crown sits just below the deck at top dead centre, a negative one that the piston pokes up above the deck. The clearance is one of the factors behind squish and compression. Reverse it and choose a desired clearance instead, and you get the deck height the block needs. The figures are theoretical, the real clearance depends on the head gasket thickness and how the block actually measures.
Example
With a 144 mm rod, 30 mm compression height and 86 mm stroke the stack height is 217,0 mm. A block deck height of 217,8 mm then gives a piston-to-deck clearance of 0,80 mm.
Stack-up at top dead centre
| Part | Contribution to the stack height |
|---|---|
| Crank radius | Half the stroke |
| Rod | Length centre to centre |
| Compression height | Piston pin to piston crown |
| Piston-to-deck clearance | Block deck height minus the sum above |
The head gasket thickness is not included here, but affects squish and compression during assembly.
Common questions about deck height and stack-up
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