What Is a Torque Plate & Should You Use One?
Updated: Oct 16, 2021
Using a torque plate while honing out the cylinder bores to make room for a larger bore piston, such as from 81mm to 81.5mm, may be preferable if you're rebuilding an engine and need to make room for a larger bore piston.
But what really is the benefit of using a torque plate compared to not using one? I explain that below.
Table of Contents:
What Is a Torque Plate?
An engine block torque plate is a plate that may be tightened down against the engine block during the machining process.
It is intended to simulate the stresses and distortion that the cylinder head would exert during the assembly process of the motor.
Essentially, a torque plate allows you to hone and machine an engine block as if it was fully assembled.
It should be torqued onto the block in the same pattern and with the same torque specifications that you will be using when you complete the final assembly of the engine.
A torque plate should also be torqued down using the head studs or bolts that you want to use to build your engine.
Most of the time, a pre-built torque block would be constructed of the same material as the OEM cylinder head, such as cast iron or aluminium, to ensure compatibility and correct distortion.
Benefits of Using a Torque Plate
Some distortion occurs whenever you increase tension of the cylinder head onto a block.
As a result of this slight distortion, the cylinders will move somewhat and will not be as round as they were when the engine was bored and polished originally.
When you machine and hone the block while using a torque plate, the block will maintain its distortion when it is machined and when the motor is fully built with the cylinder head installed you'll have a precisely straight cylinder bore.
When a torque plate is used in the machining of an engine, not only is the ring seal improved, but the engine also wears more evenly.
This not only enables the motor to produce more power, but it also allows it to operate for a longer period of time.
Using a torque plate helps increase power and reliability.
It may also decrease blow-by and oil usage.
Closed Deck vs Open Deck
Long ago, it was believed that torque plates were only essential for usage on closed deck blocks, where the cylinder walls were in direct contact with the block throughout its length and depth.
This assumption has since been proven incorrect, though.
Open deck design blocks are usually constructed in such a way that the cylinder liners are free floating, with the exception of the area at the bottom of the block.
Theoretically, the torqueing of the heads on their respective blocks would produce little to no distortion as a result, and therefore, a torque plate was not required.
Machinists began testing open deck design blocks using torque plates and observed distortion in the design blocks, but there was not as much distortion as in a closed deck design block.
Therefore, it is suggested to use torque plates on both open and closed deck engine blocks.
Should You Buy One or Make One?
Usually the price of a pre-made torque plate varies between $300 and $750, sometimes more or less, but there is a way to get a torque plate cheaper than this.
You can actually make a torque plate from a scrapped cylinder head by machining out the correct sized bores for allowing a honing machine through.
The price of a scrapped head is usually around $50 and the price to machine out the cylinder head can be between $100 and $200, possibly more or less depending on the size of the engine.
Therefore, the price of making a custom torque plate from a scrapped cylinder head is less than buying a pre-made one.
It may also be beneficial to use a custom made torque plate from a scrapped head of the same model due to the same internal structures and composition as the actual cylinder head you would be using.
Using a custom made torque plate from an actual cylinder head may allow for more precise simulation of the stresses and distortion.