Torque plate

[TurboTom]

OK here is the scoop. Block was honed with the plate and roundness and taper were within .0001". I measured the bores after removing the T/P, and things are not so good.
#1 and 6 holes did not distort as bad as 2345. There is not much of a pattern but the bore size moved around from .0005" to .001" around and down the bore. Before the plate was removed you could stick the bore guage in about any where you wanted and get readings within .0001". Now it is all over the place. Bottom line is the torque plate (or the head) stresses the block alot more than you would think. Even 3/4 ways down the bore there were differences.
Here is a pic of the great hone job. By the way I am running Diamond forged pistons from Hesco and installed them at .0051" clearance.

[03GC]

Thanks for the info Tom

If I am getting this correct , you are saying the bores are still round within .0005 to .001 after the plate is removed? I would think that would be OK on a "less than maximum effort" build such as a daily driver.

Sounds like a 4.0 block is fairly stout. I have heard of other blocks moving .002 to.003 after the plate is removed.

Thanks again for checking it out

Paul

[IrnGynt]

I came across this in my Mopar Jeep Engines book in the 4.0 section (I believe it's the 1st edition):

Honing Plates

Contrary to popular belief, there is no magic to building a fast, high horsepower racing engine. Unfortunately, racers love magic, especially related to the engine. Racers don't like to believe the first statement. Okay, we'll play! We'll take a honing plate and call it Merlin. Properly used, what Merlin does for the engine is magic!

For the serious all-out race engine, the use of honing plates (Merlins) is strongly recommended, almost mandatory. By properly using the honing plate, torquing the main caps, and honing the bores straight (round with no taper), you can ensure that the cylinder bores will remain straight and round with the "throttle open." This is the most important aspect of basic engine building because if the cylinder bores aren't straight and round at WOT, the engine won't make any horsepower.

Honing plates should be made of 1" to 1.5" thick steel plate. with a honing plate of this size, which is held on by cap screws, (sometimes actual head bolts can be used with hardened washers), the screws should be torqued to the same specification as the standard head bolts.

The thickness of the honing plate and installation torques are very important; but, of equal importance, and an item often overlooked, is the depth of thread engagement. After the cylinder head bolt holes have been cleaned and a bottoming tap run down each bolt hole, each cylinder head bolt should be turned all the way in and then backed off one turn for proper thread depth. This depth is approximately 3/4" of actual thread engagement. Compare this actual depth to the length of the bolt that protruded from the bottom of the head with the bolt inserted in its proper location. It should be the same. If not, then the longer one must be corrected to the shorter one. It is best to check each bolt separately. With the honing plate properly installed, all the engine builder has to do is make the bores straight and round with no taper. It must be magic that engines honed with a honing plate make more power. Merlin did it!

Honing Plate Tool

A special billet steel torque plate tool designed to hone Jeep 4.0L blocks straight and round. Very accurate for precision engine building. Required for high output, high rpm engines.

P4529201 Honing Plate Tool. (In-Line 6 cyl. only.)

Honing Plate Thread Engagement

The honing plate should be held onto the block with cap screws of the same thread length as the actual head bolts. This sounds easy enough, but how do you get the two to be the same? Since the head distortion is what you are trying to match, the first step starts with the head after machining. The head bolts with washers, if they are to be used with the head on final assembly , are inserted into the head and the length of bolt protruding out the bottom of the head is measured. We'll assume that this measurement is .895". The bolts that are going to be used with the honing plate are inserted into the plate. The amount that sticks out of the bottom of the plate has to be adjusted to .895". If the first pass yielded 1.200" length, then hardened washers can be installed under the bolt head. The hardened washers are about .100". So, in the example, three hardened washers would be used to get the correct length.

[Alex22]

First off, Thanks for the data Tom.

A few comments on the article. It says that the benefits of using a torque plate are only when the engine is at WOT. I don't see how WOT would make much of a difference. The purpose of a torque plate is to stress the block the same way a cylinder head would stress it. When the block is honed with a plate the bores will be out of round when the plate is removed, and then when the head is installed and torqued down the bore will be round.

The goal is to get as close as possible to conditions within a running engine. When we use torque plates (most are BHJ and made from a cast chunk like the one in TurboTom's picture) we use a head gasket and use head bolts with steel sleeves to make up the difference in under head length.