Dumb idea?? Making a torque plate from old cylinder head?

Hello:

I am restoring a 1970 GTO Judge and sometime next year will start building the engine. There is only one automotive machine shop around and they likely don't have a torque plate that fits my engine. If they don't, buying one is out of the question, they are $700US, but I have several old heads and a Bridgeport mill that I haven't got to use enough yet....

....so, I was wondering how successful I would be in making my own torque plate from an extra head I don't need, that I could lend to the machine shop when they bore/hone my block. My plan would be to clamp the old head to the table with the head gasket side down, and machine down the valve cover side until I get close to the head bolt bosses, then flip it over and drill/bore the combustion chambers until I have an open hole the same size as the bore + .090", for each cylinder.

I checked the BHJ website (THE maker of torque plates), and the plate they sell for Pontiacs is 1 3/4" thick cast iron with extension sleeves for the head bolts. My homemade torque plate would be somewhat thicker than this, maybe 3"??

Is this a good beginner project for my mill or a complete waste of time?

Thanks

Michael

If your not going for max H P skip the torque plate. they sure never used one at the factory.

I have seen this done before. They looked like a lot of work to me. For engines where no torque plates were available and they were desired, we made steel burnouts and bored the holes to final size.

+.090 may be to big for the holes. The gasket fire ring may fall inside the torque plate hole.

Proper use of a torque plate requires usage of a head gasket. This is extremely important on composition gaskets with fire rings and steel o-ringed heads used with either composition or copper head gaskets. Old style flat steel shim gaskets may not be so critical, I never tried them with and without to verify movement.

I'd consider it a waste of time for a street engine, or any engine that you're not looking to get the last bit of HP out of.

For that fact, I've yet to see anyone publish anything that actually proves a torque plate does anything positive.

Torque plates in general are suspect as they claim to emulate the engine in a 'bolted together' state. Yet torque plates don't resemble actual cylinder heads so it's fair to reason that whatever shape they distort the block to, it won't be the same as a real cylinder head.

Not to mention the fact that during the boring/honing process the block is at room temperature, not the 180+ degrees it runs at. What do we know about metal and heat?

If you have kids, take the cylinder heads you were going to use as torque plates and toss them off a high bridge into a river while the kids squeal in delight. That will be a far better use of your time.

Just a thought. Isn't the block going to change shape from the stress relieved by the machining process? Most metals do, depending on hard spots, cutting tool geometry and tip radius, and the type of machining. If nothing else take a trial cut on a junk block, bolt on the heads and gaskets, then take a dial bore gauge and check it out.

I've always considered torque plates a waste of time too. Now if the plate was 3" or 4" thick and stress relieved and ground flat and the block is decked before boring and honing then it might make a difference.

When you consider all the stresses an engine running has and the temps it works at I don't think torque plates do much good. Even racing engines get built after every race or two. The also don't build racing engines very tight either. They are for one race and that's all.

There's and old saying, "an engine runs best shortly before it blows up" and it's mostly because it's worn and loose and screams, then blows.

Torgue plate? Why. Consider the operating forces on an engine under load, how the block/cyl head moves around under unequal, temp gain due to varying load, etc. The engine when operating moves all over the place when measured in 0.0001" increments. It's supposed to. It's designed so these movements are not detremental.

I've checked out a dozen or so factory torque plates on my granite flat for a local speed shop. Few of them were actually flat. I milled them flat and checked again. Most were still warped after machining from internal stress resolution and I had to stress relieve and recut them. Is a torque plate stiffer than a cylinder head? Hell no. Measure one up and compare with an actual cylinder head. There's a big difference in their stiffness and behavior under bolt stress.

I pronounce torque plates to be a pointless refinement for street and amateur motor sports engine work. They were iinitially intended to impress the rubes but since its incetption the gadget has become instirutionalized. Sensible automotive machinists astually defend their use basing their defences on a few speed magazing articles written by the glib but unqualified.

The block itself is probably 20 times stiffer than the torque plate. Don't listen to me Mount a bunch of dialindicators on a block to register distortion/movement and bolt on a good head or a torque place. Point to point indicatoer reading in the crank caase should be in the tenths or less. In the bores there may be small differences but trivial when you consider the accommodation of the piston rings and piston to bore clearance.

Remember this: about 1/2 the expense of hot engine midification (ie blueprinting, high precision balance, trick lube oil systems, etc) are needless expenses having little effect on the engine's power output and operational reliability except if applied to professional racing engines where 1/10 of % improvement is a significant factor in race victory and an addition $10K is justified in securing it.

Torque plate is a good idea, I'm a firm believer in them. They do exactly what they are suppose to do. They mimic the stresses in the head bolt area to keep the bore round. They do work. I've seen it personally, proven it and made it repeatable.
We did a block that was bored and honed with a torque plate. The bore was .0025 out of round and tapered when the plate was removed. Bolted on a head and measured it from the bottom, bore was back to being round less than .0005 and taper was virtually gone.
They didn't use them from the factory because they really didn't need them, now the block is pushing 40 years old and had how many thermal cycles put to it.
Just my take on things.
Dave

here is my take

a torque plate is probably not necessary for 99% of engine's built, however having said that some more on the subject

jillions of engines are done without torque plates, run as far as anyothers, win as many races and all that,

boring and honing without a torque plate simply means it will take a bit longer to break in the rings to the bore. but they will break in together with reasonable care.

the bolts will distort the cylinders, and in some engine's worse than others.

the venerable small block chevy can easily be distorted by simply applying hand pressure across the bore sufficient enough to get an inside mic to fall out of the bore. i have seen it done, and have done it myself because i didn't believe what i was seeing.

now i know i can put maybe a hundred lbs of squeeze across a cylinder bore with my bare hands before my eyes pop out, but it doesn't even take that much effort to distort the cylinder the needed
half thousands it takes to allow the internal mic to fall out of the bore.

we all know the stresses from torqued bolts are in the "tons"

in a perfect world i would use a torque plate if i had one available, if i didn't i wouldn't worry about making one or buying one.
just bore, hone, and clean, clean, clean ... then assemble and follow standard breaking procedures and you will be good to go.

i have seen many jobs that turned out inferior even when torque plates and every last machining detail was spot on perfect, just because of poor cleaning practice before assembly, and worse break in procedures,
just as conversely i have seen engine's built with substandard machining, use of bead hones, and all sorts of corners cut that performed much better because of the attention to detail when it comes to cleaning before assembly, and how the engine was broken in.

your judge came with a 455 there ought to be a machine shop somewhere that would likely loan, sell, or rent your shop their plates, so i would check around and see what is available. probably some shop out there with a set under about a half inch of dust doing nothing anyway.

i think i know of a set for the 348/409 chevies, that likely have not been used in nearly 40 years, and i bet he would part with them cheap. of course they won't fit your application, but you see my point.

bob g

I didn't stay at a Holiday Inn Express last night, but I used to run the NASCAR engine program at Cosworth Racing. We could and did measure the difference in power between different block honing techniques. It's more about the bolt induced distortion than the stiffness of the cylinder head, so your bored out cylinder head should work fine. Whether it makes any measurable difference in your engines performance depends on what state of tune you're looking for but it sure won't hurt. Have fun!

If it's just bolt distortion, how about some simple sleeves with the bolts through them? Maybe an inch in diameter and an inch long. Or even a stack of thick washers for that matter.

As for distorting cylinders with hand pressure ... ever seen a Porsche 928 block? OMG!

With respect and not wishing to offer anything but an observation as rebuttal:

if torque plates made a difference, any distortion resulting from the bolt tension wiuld be telegraphed by the wear pattern from the rings. I've seen teardowns of enging machines and bore prepped with and without torque plates and never saw anything but a faint shadow in the cylinder wall adjacent to the bolt locations. The rings clearly sealed regardless of refinements.

The bolt loading is only a small part of the function of a torque plate. The most distortion comes from the fire ring on the head gasket. The fire ring carries most of the load imparted by the torqued head bolts. This induces a very localized loading around the edge of the cylinder bore. The effects of this vary from one block design to another, but they are there. This is similar to the strap clamp and heel block set-up used in machine work.

Will a torque plate help a street engine get better gas mileage? Who cares? You're driving a Goat!

Are they as worthless as Addy proclaims? No, as he has completely ignored the effects of concentrated loading.

Would I go to the work necessary to make one for rebuilding the engine in my old muscle car? No.

In my opinion torque plates are anal mythology!
To assume that the plate will bring the distortion to the same point as the head AND that when torquing the head bolts they will return to the same exact point is wishful thinking. And do they re-use the same head bolt in the same hole everytime?
And then as mentioned throw in the 200-500* or so heat cycle (I'm guessing on temp) not to mention Nitro-Methane or Alcohol properties, add in Global Warming and some astrology!!

I am a Model Shop Machinist at an R&D facility for a major truck brake manufacturer. The air compressors that produce the air for heavy equipment brake systems are very similar to internal combustion engines. They have crankcases with pistons and valve heads. We do an enormous amount of testing before our products are released due to the liability exposure. We actually sandwich a torque plate in between the crankcase and the cyclinder head in order to spread out the load of the bolts because it is just as gbent has described. The greatest amount of material movement is seen in the area immediately surrounding the torqued bolts. But our torque plates STAY with the unit - they are not used only for machining. We actually do not use torque plates for machining. We use 3 point fixtures for machining. As moonlight, forrest, and others have said, I would machine without the torque plate.

Wow....I didn't realize I was dealing with snake oil here!! LOL!!

I personally do believe they make a difference, how much is debatable, but was trying to gauge how much work it would be to machine an old head into a torque plate vs. not using one at all, since there would be ALOT of metal requiring removal to convert the head.

So if the consensus is they aren't that important, I may not bother...BUT:

If someone wanted to do this, what would be the best method to open of the chamber area to be a large hole? I am guessing that the first operation would be to mill the valve cover area parallel to the head gasket area, then flip it over, find the centre of the cylinder (likely using a gasket as a template to account for core shift), then drill a big hole though the head then open it up with a boring bar to the correct diameter?

Lets hear some machining talk on how you might do this rather than if it is worth it, as the machining steps involved interest me.

Thanks

Just remember when rebuilding an engine you are trying to build in some longevity also. Sure, you can do the cheese-bag overhaul, will it run, yes, will it run well, probably, but, for how long before it starts smoking a little, rattles when you first start it, starts using a bit of oil????
If your rebuilder is worth his/her salt you will have a better engine than Detroit could ever build in a production setting. Those HP/Torgue ratings from the factory are pipe dreams. They are theoretical and can only be achieved by doing everything possible correctly (by blueprinting) and then the rating can be met and probably be exceeded to a certain extent.
I can tell you stories about rebuilders in the area, some are good, some shouldn't own a pliers.
Find a good one, ask for references and talk to previous customers. Your looking to get the most bang for your hard earned dollar.
Again,
Just my observations
Dave

mrennie said:

Wow....I didn't realize I was dealing with snake oil here!! LOL!!

I personally do believe they make a difference, how much is debatable, but was trying to gauge how much work it would be to machine an old head into a torque plate vs. not using one at all, since there would be ALOT of metal requiring removal to convert the head.

So if the consensus is they aren't that important, I may not bother...BUT:

If someone wanted to do this, what would be the best method to open of the chamber area to be a large hole? I am guessing that the first operation would be to mill the valve cover area parallel to the head gasket area, then flip it over, find the centre of the cylinder (likely using a gasket as a template to account for core shift), then drill a big hole though the head then open it up with a boring bar to the correct diameter?

Lets hear some machining talk on how you might do this rather than if it is worth it, as the machining steps involved interest me.

Thanks

Click to expand...

Not snake oil in the least.
We made a torgue plate for a 426 Hemi using a head gasket as a template and cut it with a tracer torch a little undersize in the bore. Then drilled all the bolt holes and finished the bores to max oversize to cover all the bases.
Worked well except the flame finish in the bores were harder then the hobs of hell. Once we got through that is was really easy.
Dave

mrennie; You mentioned BHJ (The mfrs of torque plates), I've looked at their stuff too, just from reading their catologue, it seems that everything registers off of the cylinder head dowels. I think thats how you would locate your bore centers.
I run a blown big blockl chev, and I've had the same thoughts as you. I found a drawing of a BBC cyl head showing the bore spacing and dowel pin locations in a fel-pro head gasket set. I don't know where you'd find a drawing of your particular head but a fel-pro catalogue would be a good place to start.
I recently tried installing head bolts into a BBC block with sleeves under them and torqued to spec., had a dial bore guage in the hole before and after and could not measure any distortion with a .001 bore guage, though surely a .0001 guage would show some distortion. May also be different with a full torque plate C/W gasket.
Interesting experiment nonetheless.
I didn't bother with a torque plate for my application, my feeling is its too much trouble and expense for MAYBE a 4 or 5 hp gain.

mrennie said:

If someone wanted to do this, what would be the best method to open of the chamber area to be a large hole? I am guessing that the first operation would be to mill the valve cover area parallel to the head gasket area, then flip it over, find the centre of the cylinder (likely using a gasket as a template to account for core shift), then drill a big hole though the head then open it up with a boring bar to the correct diameter?

Lets hear some machining talk on how you might do this rather than if it is worth it, as the machining steps involved interest me.

Thanks

Click to expand...

I'd scribe the outline of the bore, either from a gasket as you described or from the block. Then I'd rough out the opening to within .060 or so of the scribed line with a 3/4" roughing end mill just by hand in X/Y steps, as deep per pass as the tool will accept. Then go back and bore the holes to finish size. After it relaxes for a week or more have it surfaced in a head surfacer.

I think drilling and breaking through the water jacket and ports would be a PITA unless you had some sort of Z-rougher and used the knee to feed it.

I think using the head is a good idea - theoretically it more closely approximates the loading produced by the real head than a block plate does.