Maximizing Torque Plate Performance
While just bolting on a torque plate is enough to put you ahead of a standard production machine shop's bore quality, paying attention to the fine points can increase the degree of accuracy substantially. Fastener loads and type, as well as the lubricants and thread engagement, torque plate stiffness and surface finish, and even gasket type can all vary the bore distortion replicated by the torque plate. It is important to mimic the final engine assembly as closely as possible. Sunnen has done extensive research in this regard, with precision bore measurements showing that these factors can materially affect the final bore quality.
True bore distortion cannot be measured with a dial bore gauge since it only measures length without considering an axis. The Inner Contour Meter is a precision device that can map the actual bore shape. This is an important tool at Sunnen in developing tooling and techniques, which closely replicate an ideal cylindrical shape. With it isometric and radial plots of the bore are generated under various conditions, allowing comparative evaluation of the cylinder bores. This is useful in solving complex distortion simulation problems, and allows compensation or correction that can lead to a better finished product.
Distortion related to clamping...
Distortion related to clamping force on the gasket can be mapped by making a gasket from a special load-sensitive film. The color trace can show the deck torque loading of the actual cylinder head, providing a guide that can insure that the torque plate is indeed accurately replicating the head's loading. When the torque plate loading is a poor match for the actual cylinder head loading, the bores can be significantly distorted when the actual cylinder head is installed.
These two isometric maps of...
These two isometric maps of the cylinder bores show an exaggerated view of the change in bore distortion that can be influenced by cylinder head gasket type, comparing a standard fire-ring gasket to a Multi-Layered-Steel (MLS) gasket type...
...Notice how dramatically...
...Notice how dramatically the bore distortion changes at the upper portion of the bore with the variation in clamping loads imposed by the two different gasket types.
Here is an example of a pro...
Here is an example of a pro race engine's bore isometric, with what looks like a near perfect bore, with the torque plate installed...
...Isometric two shows how...
...Isometric two shows how far off the bore actually measured with the true cylinder head in place. A redesigned torque plate built specifically to match the cylinder head's clamping loads resulted in the cylinder shown in isometric three, and a gain of 25 hp, along with an extra 1 in-hg of pan vacuum...
...That's about a 2 percent...
...That's about a 2 percent gain in a high-end race application from getting the torque plate correct.
THERMALDISTORTION
So much attention is paid to mechanical distortion, and for good reason. However, a running engine is a dynamic system and subject to thermal loads when under operating conditions. Thermal distortion can be created by the heat of the coolant in the water jackets, taking a perfectly round and true bore out of shape. In situations demanding the ultimate in cylinder bore accuracy, a "hot-honing" process can improve the quality of the bores. Here, heated fluid is circulated through the block using a special torque plate equipped with water jackets. This system is yet another step in mimicking the engine under true operational conditions.
This is an example of the...
This is an example of the type of special torque plate developed for hot-honing. Inside fluid passages and transfer holes through the decks allow a temperature-controlled fluid to circulate through the blocks water jackets, much like coolant in a running engine. The design of these hot-honing plates is tedious, with a goal of closely simulating the clamping loads of a real head. Actually, it has been found that a cut-away and welded cylinder head makes a poor hot-honing torque plate because of the lost stiffness.
ACCHere we have a hot-honing...
ACCHere we have a hot-honing system rigged outside of the honing machine. The arrangement is fairly simple, consisting of the fluid unit, which contains the pump and a regulated temperature system.
With the hot-honing machine...
With the hot-honing machine in operation, the block is honed as usual, however, the thermal distortion created by the coolant temperature is compensated for in the honing process. This can be particularly acute in aluminum block engines.