anyone know of a machine shop that has a torque plate that fits a vw block?
when head bolts are tightened down into a block the block distorts where the head bolts are. the rings ride on the block distortion and cylinder pressure blows past the rings.
a torque plate simulates the head installed on the block, if a machine shop uses a torque plate when the block is honed, the plate is torqued down the cylinder walls distort and the honing machine cuts the off the distorted part of the cylinder walls to a perfect cylindrical shape instead of a cylinder that is distorted where the head bolts are causing the cylinder to bulge inward.
try an internet search like torque plate chevy or torque plate ford and you will get info like this randomly selected blog, they are all about the same.
blog:
Guys, hope I can add something here. I currently design pistons & rings for diesel engines, and am responsible for the honing finish on our engines. I used to be responsible for the block/head/head gasket area.
Trumps, I agree with you 100% on some points. A torque plate is not needed during the boring operation, factory or aftermarket. I have done some honing with both a Sunnen CK-10 and a Rottler HP5a hone and have seen the difference a torque plate can make. As much as .0015" out of round difference!!!
First thing is block design: how many head bolts per cylinder; i.e. what is the "pattern". Early small Chevy's are five bolts per, small Fords are four bolts per cylinder. Our 6.0L diesel is four bolts per, due to cost, space for injectors & valvetrain, etc. The biggest problem with a four bolt head pattern, other than available clamp load for head gaskets, is that the fourth order distortion created by the bolt pattern around the bore is the most difficult for the piston rings to conform to. 2nd, 3rd, fifth and sixth order distortion has much less effect on the rings ability to seal.
Second, look at where the head bolt threads are in relation to the top of the bore, and how far they are from the edge of the bore, and what type of head gasket is used. With our MLS head gaskets, the bore does distort nicely. Also, with the head bolt threads at the top of the block, the head bolt loads will pull the top of the bore out or round, right at the top ring turn around area. If the threads are half-way down the bore, torque plate honing may not have as much benefit.
EricR, I think you would need to put the dial bore gage in the corners where the head bolts pull the cylinder walls. A better 'look' would be to hone the bore some, then install the torque plate, then re-hone some and you will see dark spots where the bore is pulled away. I have done this before.
Rich, if the block was just bored and not honed, it should have about .005" left for final sizing & finishing with the hone. If it was honed, you may end up increasing the skirt clearance too much, but that all depends on the piston selection.
In a production enviroment, as well as building a race engine, the cylinder bores need to have a circularity spec, a distance between centers, and a perpindicularity to the main saddles and head decks. The head bolts distortion of the bore is well within the finish sizing, so boring with a torque plate is not necessary. Trumps, 100% agreement on that one.
Honing is an actual finish sizing operation, not just a surface finish operation. Usually an overbore will go to within .005" of final and leave the rest for honing.
On honing finish, plateau is a much mis-used term. It refers to a surface finish with a negative skew, creating valleys for sub-surface oil retention and using a second and maybe a third brush step to remove the peaks and create a bearing surface for the rings to ride on. Do a google search on Abbott-Firestone curve and plateau honing, also Taylor-Hobson has lots of info on their website.
http://www.taylor-hobson.comTrumps, I know that some gas engine manufacturers are actually moving away from plateau honing and moving to a peak hone, an overall smoother surface after run-in which should give better oil consumption over time.... or at least through the warranty period.
Well, I don't think I can say anymore...
more blog:
http://i7.photobucket.com/albums/y276/CNCBLOCKS/TORQUEPLATEHONING001.jpgThis is a pic of a 454 block that has come in for some work as it only has about 3200 miles on it since the rebuild and it was making some lower end noises. We line honed it and squared and decked it flat and bored it and we blued up the 2 center cylinders installed the gasket and torque plate and went in for 6 strokes on each cylinder as you can see the results and look at the piston as it has blowby right to the oil controll rings as we could measure .003 distortion on the cylinders.
I am posting this as Gary from NY say there is no differance using a plate with what I have seen so far over the years I am a believer. I have done blocks this way and gone trade shows and guys are amazed at what a torque plate does to a cylinder and on the after market blocks the distortion is minimal compared to the OEM stuff.
http://i7.photobucket.com/albums/y276/CNCBLOCKS/TORQUEPLATEHONING001.jpgThis is a pic of a 454 block that has come in for some work as it only has about 3200 miles on it since the rebuild and it was making some lower end noises. We line honed it and squared and decked it flat and bored it and we blued up the 2 center cylinders installed the gasket and torque plate and went in for 6 strokes on each cylinder as you can see the results and look at the piston as it has blowby right to the oil controll rings as we could measure .003 distortion on the cylinders.
I am posting this as Gary from NY say there is no differance using a plate with what I have seen so far over the years I am a believer. I have done blocks this way and gone trade shows and guys are amazed at what a torque plate does to a cylinder and on the after market blocks the distortion is minimal compared to the OEM stuff.
http://i7.photobucket.com/albums/y276/CNCBLOCKS/TORQUEPLATEHONING001.jpghttp://i7.photobucket.com/albums/y276/CNCBLOCKS/TORQUEPLATEHONING002.jpghttp://i7.photobucket.com/albums/y276/CNCBLOCKS/TORQUEPLATEHONING002.jpg
