Torque plate twist 1

[lugnuts67]

Just a question.
I was wondering if an aluminum torque plate should be used if you are going to use aluminum heads - I know they don't but should they?
It seems that if the torque plate is to simulate the distortion of the block when the head is properly torqued down so that the cylinder is as true as possible during operation, you should use a material that is going to simulate that distortion as closely as possible. You do not have to go to an metalurgical expert to know that aluminum has different properties - tensile strength, elastic limits, fracture limits, yeild strengths, compressive strength, hardness, thermal properties, etc. It just seems that you may over distort the block with a more rigid steel torque plate. Some may say that the difference is nominal but some used to say the same thing about using a plate while honeing years ago. Granted you will still be duplicating any distortion of the block at the bolting points internally.

Just for instance. It the plate distorts the block .0001 over the entire deck length, is it possible that the aluminum being less rigid and softer would only distort it .00005 because the aluminum abosorbed the rest? with this theoritical situation you will hone it with twice the distortion and when you put your aluminum heads on you have over compensated.

To go even further, should you use a head gasket of the same material with the torque plate?

Or am I just over thinking?

Hmmm....

 

[sreid]

The torque plate is used because the head bolt tension distorts the cylinder walls. This is, I believe, a local effect and the torque plate material probably makes little difference.

 

[ivymike]

the torque plate material probably makes little difference

Depends on how round you want the walls to be, and under what conditions. The torque plate design (material, thicknesses at various locations, etc) and gasket design (a gasket or simulated gasket is often used to get the load distribution closer to reality) can be critical if you want very little assembly distortion.

Some people have used FEA-derived torque plate designs to allow "honing out" of some amount of (assembly+thermal) distortion.

 

[patprimmer]

A torque plate cannot truly represent a cylinder head as for one, it needs a bog hole in the top to allow entry of the hone.

ivymike's suggestions help, but it is a lot of trouble.

A very simple jig can reproduce the distortion created by the tension in the threads of the head bolts where the bolt holes expand into the bores. I think all other distortions are to dependant on constantly varying conditions to be of any real world value

Regards

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[SMOKEY44211]

If you really want to get it dead on, hone it .001" smaller then your intended finished diameter. Clamp on head(s) with the same fasteners and gaskets you intend to use. Install main caps without crank. Circulate water or oil (I like water better. Tough to get all the oil out afterwards) at around 200 deg. through coolant system. Use stones designed for honing blind hole cylinders. Hone from the crank side and you'll have a round hole with all the mechanical and thermodynamic stresses in place.-----Phil

 

[patprimmer]

How do you simulate cylinder pressures on compression and firing strokes.

How do you simulate charge temperature effects before and after firing.

How do you simulate piston thrust against the sides of the bore.

How do you simulate crank loads on the caps and webs.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[lugnuts67]

I guess another question would be, why are torque plates typically made of steel?
Aluminum would be much lighter and easier to move around. The question of oxidizing then comes up but would it not be a factor with steel as well? Both would need to be surface trued from time to time because of corrosion. Anodized aluminum would last longer though or even a composite with steel inserts.
If that is a major concern, why not make them of stainless? Or if it is just the distortion at the bolting points, why use such a thick steel plate or even a plate at all? Just torque bolts in place with collars on them.
My original take was that the plates simulate the distortion of the block when the head is bolted on by providing a rigid point with which to cause similar core shift. That core shift distorts the cylinders either out of round or the overall center of the cylinder by a small amount (less on siamesed bores). Then the machining is done. If this is accurate, then a less rigid plate will cause less overall distortion core-wise but the same point distortion where bolting is concerned.
Does this really matter? Most likely not. It probably will not cause any measureable increase in cylinder pressure but has me curious non-the-less.

 

[Fabrico]

Good question, but that just leads to why a plate at all? Why not just a spacer and bolt in each hole? Would it make a difference? Who really knows when it might?

I hate to mention popular opinion, but it sure is popular. What is known is that they are widely used and more builders are using heat while final honing blocks.

 

[SMOKEY44211]

A couple of years back I had a long disscussion with a fellow named Tim Mears from Sunnen prods. about this subject. Sunnen had just come out with thier "hot honing" technique and related hardware. This was the result of a combined effort with a high profile custom engine builder involving a BBC. Seems the aluminum version was off about 50hp. vs the cast iron counterpart. The obvious wieght savings of the aluminum was desired and they were trying to bring the power #'s closer cast iron version. One of the interesting things that they did was the method of measurement. Rather then a typical dial bore guage diameter measure they measured the radius from a fixed location. The result was they were able to reduce assembled bore distortion by using a torque plate with passages in it to allow heated oil to flow through it and circulating the heated oil through the block also. They were able to pick up about 35 hp on the aluminum version. At the time this method had not been tried on the iron block so he didn't know if there was anything or how much to be gained. I asked if they had tried the method I described earlier in this thread and he reported they hadn't. In response to patprimmer, I don't think you can reproduce statically any of the dynamics you listed. I would think the initial design of the block would be such that it would be robust enough that distortion from the forces would be kept to a minimum.---------Phil

 

[Majik]

Phil is right. This information has been incorporated into Sunnen's "Bore Distortion" Seminars that they do at regional trade shows. The one I went to was about a 2.5 hr long dump on what seemed to be everything sunnen knew about distortion that a semi-engineering crowd could handle. Interesting things I've learned about it were that a home made torque plate did not always help with distortion. (by home made I mean head gasket pattern cut out of steel or aluminum) In about 50% of the cases it actually created distortion in areas where it didn't exist or amplified it to almost 2x it's ammount. I have no reason to believe he was like making stuff up but he never went right out and said "hey cheap home made torque plates can actually screw this up". He did use the time to hustle Sunnen "engineered torque plates" so whether it was hype or not, he had the graphs showing the tweaked bores with basic plates. The older the engine the worse it was. Again the aluminum block bbc was all sorted out in this seminar. the tool I believe was called an incometer because a dial bore gauge has no centerline so distortion can not be measured with it. The jist of the conversation was if you were a serious SBC dude. You needed a hot hone machine and one of their engineered torque plates. Without these you were just guessing. I believe their plates were made out of aluminum as well. If they didn't make an engineered torque plate for your application and/or you don't specialize in just one block then you were kinda SOL.

 

[speeddemon79]

Having worked for the big 3 on many of engine programs, i can tell you what i have done for them.
1. The material of the plate is always the same as the head. I have never had a problem with either aluminum or steel plate oxidizing because when used, the plates are flooded with oil.
2. Thickness of the plate, well this is the thickness from the deck surface of the head to surface the stud washer or bolt flange rest on on the head.
3. The combustion chamber can be removed on the plate for honing access because the combustion chamber provides little or no structural support on the actual head. FEA shows this when analysis cylinder pressures.
4. A production style head gasket is used between the plate and the block. The gaskets are either made with an approximately .020" larger cylinder bore or, depending on tolerancing, a gasket on the high side.
5. As for running warm oil or coolant through the block and plate during honing, well what you gain from this process is usually out weighed by the cost of the process.

All of these points are for production style engines. But these same processes were and are used on high performance production engines, i.e. LS7, Viper, Ford GT, 6.1 Hemi, etc.

Just my 2 cents.

 

[patprimmer]

I think exotic honing techniques are mainly used for race engine preparation.

I also think that race applications severely stress the components and do distort things. Anything really robust is generally considered to heavy.

speeddemon79

An opinion backed up by date and logic. Sincere thanks for your input.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

Also an opinion not based on someone else's sales pitch to sell some very overpriced gadgets is a nice touch.

Call me cynical, but data supporting sales that generate huge profits always brings validity into question in my mind. Health issues and tobacco companies come to mind.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ivymike]

Diesel manufacturers are also potentially interested in exotic honing techniques (for production). Why? With the 2007 on-hwy emissions regulations, they will all be using particulate filters. These DPFs have relatively painless ways of getting rid of soot (regeneration), but no really easy way to get rid of ash. Ash accumulation in the DPF is largely driven by oil consumption, and oil consumption can be significantly influenced by bore distortion and blow-by. The mfrs will choose a good balance of component technology and manufacturing technology to achieve a suitably DPF low ash service interval economically... in some cases that might include fancy honing techniques.