The Stovebolt Site Forums The Shop Area Engine Shop torque plates

There has been some discussion about using torque plates when boring these engines, for the same reasons as using torque plates when boring any engine. However, who has one? None of the shops I know of have them...When I put that ungodly expensive 12 port on, I want it just right....

Depending on what you are doing(modifying) and core shift it's worth the effort to use one. Contact CNCdude over on
www.hotrodinlines.com and/or a couple of guys on Inliners, Tom Lowe or Larry from Florida.

Boring the block with a torque plate installed is a total waste of time. Use the plate during the finish honing process, and leave the bore 2-3 thousandths under your desired finish diameter with the final pass with the boring bar. Be sure to have the same torque specification AND depth of thread engagement you expect to have with the head installed. On our race engines, it was possible to measure a star-shaped pattern with a dial bore gauge after installing and torqueing the plate prior to honing. We made our own torque plates using a piece of 1 1/4" steel plate and a Bridgeport mill and a surface grinder. Use the head gasket as a pattern for laying out the cylinder spacing and bolt hole arrangement if you decide to make your own plate.
Jerry

thank you Jerry, I wasn't completely sure exactly about the correct care and feeding of a torque plate.

Torque plates pull the cylinder walls out of shape just like a head does when torqued down. Its not much, but enough to pull the cylinder wall out of round a tiny bit. For the normal everyday engine, you will see no difference in performance or wear. It really depends on the block design and how much material is around the bores on weather or not a torque plate will do much. We hardly see any difference on the V8 Pontiac's dad I build due to the blocks thick deck. The inline engines are fairly heavy blocks with small bores so who knows. Core shift (wall thickness) can make a big difference, but that requires a sonic test of each bore to determine where the core shifted to.

If you find a plate or make one, use it during boring and honing, my local shop will do it both ways, hone only or both bore and hone, they recommend both. Sometimes honing doesn't get all the distortion removed. They also charge extra to use a plate due to man hours of torquing and the extra handling.

With a large hole saw, drill press, plenty of cutting oil, and a surface grinder, a fellow can make one pretty easy. If you can find a flat cold rolled 1 1/2" or thicker piece of steel plate, you may not even need a surface grinder. The bore holes just need to be bigger then the final bore size so the tooling will pass though with out hitting. Be sure to use the same head gasket type for assembly as you do for boring, and be sure to lube and torque the head bolts the same. Any deviation from boring to assembly can change the cylinder walls making the torque plate useless.

I would assume you want to skim cut the block deck before boring so the torque plate will set flat. On the other hand, you don't cut the deck surface of the block till you test assemble the engine so deck height can be measured using the final pistons and rods. A good shop can adjust the deck side to side as well as front to back to insure its flat and square to the bores. A true deck assures each bore has the same compression and quench area.

Joe

Good points, Joe, and it looks like our race engine building procedures are pretty similar. We always start out with a line bore, and take all the rest of the reference measurements off the crankshaft centerline. We do a skim cut on the deck before boring, then bore and hone the cylinders. Equalize rod lengths, do a +/-1/10 gram weight matching, and make a final deck cut to establish piston-to-deck distance. Build it up with more clearance everywhere than a 100,000-mile street engine!

Then, if the engine lasts 1,000 laps on a 1/4-mlie dirt track, it's a real oldtimer. Doing race engine tricks on a street engine is just plain stupid!
Jerry

spending all this time and money on these old antique, obsolete vehicles is pretty stupid too, but it keeps me out of jail.

Point taken- - - -at least we're not doing something really dumb like playing golf! If I manage to get lucky and hit a ball a long way, isn't somebody else supposed to chase it?

I draw the line at drag racing- - - -spending mega-bucks and dozens of hours to build something that usually destroys itself in one pass down the strip- - - -even I am not that dumb! A good round track engine usually lasts a few hundred miles!
Jerry

I made a few sets for some race engine builders and learned a lot in the process helping me design mine from 2" 1018 steel. Having .0001" bore gauges available for measurement with and without it mounted I observed out of round up to about .002". Most definetly will be using it on my future builds. PM me if you want to borrow it.

Curt, how far down the bore does the distortion go? How does the hone cut only the high spots and not follow the bore, that I never figured out. A bore tool would cut right through and leave a round hole, just not sure about a hone, guess I never paid attention to machine hone.

Joe

There are several types of "hones". The ones most shade tree mechanics are familiar with are actually "glaze breakers", spring-loaded carborundum stones that do follow the cylinder shape. Those are only good for cutting through the mirror polish on the surface of a cylinder so new rings can seat. They're useless for finishing a rebored cylinder. Another service tool for re-ring jobs is the "button" hone with dozens of individual abrasive balls on flexible shanks. These are also only good for deglazing the cylinder walls.

The rigid hone used for final cylinder finishing after reboring is set to a specific diameter, and cuts only the high spots. After several passes with accurate measurements in between, the cylinder is left perfectly round, smoother than the boring cutter can accomplish, and with a cross-hatch scratch pattern that aids in the wear-in process necessary for new piston rings to achieve a perfect seal with the cylinder walls. It is virtually impossible to machine a cylinder smooth enough with a cutting tool to allow ring seating to happen, so the final 2-3 thousandths of an inch are removed with the hone. The torque plate lets the cylinder assume the shape it will have with the cylinder head bolted down before the final honing is accomplished.
Jerry

Joe, it's also a good idea for the machinist rough honing the block to stop about .003"-.004" from where he will change over to the finer stones and install the torque plate, then he can take the last few thousands of material out of the bores with the rougher grit stones before he changes to the finishing stones. As it does pull the cylinders inward at the bolts, its almost like spinning a round peg in a square hole and is harsh on the stones until it removes the high spots. And it can easily damage the smoother stones if its out of round too much. The depth of the distortion in the bores varies with the design of the block and the thread depth engagement of the head bolts/studs. But it usually the first couple of inches below the deck surface.

Looks like the question posed to me has pretty much been answered. I will add that the high performance boring tools I use for blow out preventers and hydraulic cylinders have capabilities not found in automotive machine shops so only leaving a few tenths of a thou for cross hatching is my preferred method.

Very good information guys, I am always glad to hear what others are doing and why they do the way they do. Next time I am over at the machinist, I am going to look over the bore / hone machine. Its been 23 years since I was a machine tool operator for the DOD, but I still find machining very interesting. I spend a lot of time on youtube watching machining video's, what can be done now is just amazing!

Joe

Yes Joe, it's amazing. The center of the job shop when I was
active was the Bridgeport and most average machinists could
only hold a tolerance of a mil or two on an old mill. A really
good machinist could work down to the tenths with a well
maintained machine but at that level your getting into an area
where temperature becomes a factor in dimensioning, especially
as the part you're working on grows in size.
The CNC mills, lathes and machining centers of today can hold
those close tolerances in a controlled environment, typically
68°F or 20°C if using NIST as the standard. I'm not a CNC
programmer but I believe my nephew who is, has told me there
is temperature compensation built into the programs now. This
would account for the reason they can hold such tight
tolerance's even when there are deviations in shop temperature.
Curt is more qualified to comment on that than I am.

Denny Graham
Sandwich, IL