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Hot honing or not?

General engine tech -- Drag Racing to Circle Track

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David Redszus
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Hot honing or not?

Post by David Redszus » Tue Mar 10, 2020 2:55 am

Hot honing or not?

Performance engines require tight ring to wall sealing to contain
blow-by gases and keep oil out of the combustion chamber.
In order to produce a cylinder bore with a minimum ovality and taper,
several things are required.

A deck plate is required;
a plate with bore holes sized to contact the gasket sealing ring, and large
enough to allow honing while bolted to the block. The material can
be aluminum or steel, either can be used. Since the E modulus of
aluminum is approx 1/3 that of steel, if an aluminum plate is used
it must be 3 times thicker than steel. In either case, it must not
allow plate compression, bending or flexing when bolted to the block,
so that only the gasket material will compress.

Fastening bolts should replicate
the material, size, thread, depth, and torque value of actual head bolts,
which cannot be used if they are too long or have a stepped shank.

A head gasket new or used
may be used as long as it is in good shape and not damaged. Especially,
the sealing ring areas must be intact.

As the bolts are tightened,
the cylinder bore will distort as a function of bolt tension or torque.
The distortion pattern is the result of gasket localized compression
loading, bolt location and number, and bolt torque tension in the block.

A dial bore indicator is used
to measure distortion; ovality, and taper. Measurements should be
taken in four clock positions and four bore heights; top ring turnaround,
oil ring bottom turnaround, mid stroke, and skirt area.

If measurements are plotted on a polar graph, it is easy to see the static
bore distortion resulting from clamping pressure.

At this point we have a good indication of bore ovality and taper distortion
due to clamping forces.
But if the engine is actually run, temperature and material differences
will produce quasi-static friction related movement at the sealing surface.

The materials used for the head and block and difference in temperature
will cause an expansion of the head while clamped to the block.
Several possibilities now exist:
an iron block with an iron head
an iron block with an aluminum head
an aluminum block with an aluminum head
each combination will produce a different distortion result.

The coefficient of thermal expansion of aluminum is approx double that
of iron. Therefore, an aluminum head on an iron block will expand more
than would an iron head, even if they were at the same temperature.
But they do not operate at the same temperature--the head will become
much hotter than the block and will expand more than the block.

The most expansion is experienced with an aluminum head and iron
block; the least with an iron head on an iron block or aluminum head
on an aluminum block.

The differences in head and block temperatures cause an expansion
enlargement of the head and a resulting bore distortion primarily
along the crankshaft axis.

If the engine is run at operating temperature for a few hours and
allowed to cool, it will shrink back to normal size, but the contraction
will compress the bore along the crank axis and distort the bore at a
right angle to the crank center line. It will cause an enlargement of
the bore perpendicular to the crank.

When the head and block are allowed to cool, a new and greater bore
distortion will result. If we loosen the bolts, the bore assumes a new
and different bore shape. If the bolts are then retightened--a new and
different bore distorted shape is obtained.

The resulting cylinder distortion during any particular engine run is a
superposition of several distortion patterns having different origins.

The first, is the stress resulting from the first tightening down of the
cylinder head the so-called static clamping condition.

The second, is the thermally related quasi-static movement between
the head and the block. The resulting oval distortion is either in the
direction of the crankshaft axis or at right angles to it depending
on the operating conditions.

The third, is a possible reduction in clamping force caused by thermal
deformation of components during operation.

The fourth, is a dynamic change in clamping conditions produced by
the gas forces. Combustion gas forces in the direction of engine vertical
axis will lead to a dynamic loading and unloading of the clamped
components. This is very difficult to measure but can be visualized
by over torqueing the bolts.

All of these give rise to cylinder distortions which together make up
total cylinder distortion during operation.

The initial clamping distortion is stable and remains constant during
the whole life of the engine. That means that distortion measurements
after the first tightening in the cold static condition and the reduction
of these distortions are especially significant.

Since the thermal bore distortion is due to head expansion and friction
at the sealing surface, the head and block surfaces should be machined
as smooth as possible.

Different gasket makers use different designs in the attempt to minimize
bore distortion; consider testing alternate gasket manufacturers products.

Bores will distort.
Therefore the use of rings that are conformable to the distorted bore
shape will minimize leakage, reduce wear, and improve sealing.

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Re: Hot honing or not?

Post by swampbuggy » Tue Mar 10, 2020 6:59 am

Interesting read David. Who figured all of this out ? Will Grade 8 bolts replicate ARP head studs for the honing process accurately enough ? Mark H.

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Re: Hot honing or not?

Post by bobmc » Tue Mar 10, 2020 9:05 am

how do thicker deck and cylinder wall race blocks compare distortionwise? there must be people on here who have checked this? back in the day it was claimed that starting a build with a used engine block was superior to new ones because stresses had worked out, this was before race blocks were available

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Re: Hot honing or not?

Post by David Redszus » Tue Mar 10, 2020 12:23 pm

swampbuggy wrote:
Tue Mar 10, 2020 6:59 am
Interesting read David. Who figured all of this out ? Will Grade 8 bolts replicate ARP head studs for the honing process accurately enough ? Mark H.
The grade of the bolt is useful but inadequate. Consider bolt length, thread pitch, tensile, thread friction, and bolt stretch at final torque value. Compare those variables to original head bolt specs.

With regard to the use of studs, I do not have sufficient research data upon which to render an engineering opinion.
This might be a question better directed to the stud manufacturer such as ARP. Remember, bigger and stronger is
not always better. But it does sell more hard parts.

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Re: Hot honing or not?

Post by David Redszus » Tue Mar 10, 2020 12:32 pm

bobmc wrote:
Tue Mar 10, 2020 9:05 am
how do thicker deck and cylinder wall race blocks compare distortionwise? there must be people on here who have checked this? back in the day it was claimed that starting a build with a used engine block was superior to new ones because stresses had worked out, this was before race blocks were available
It seems reasonable to think that more robust deck and wall materials will result in less distortion. Unless...a higher clamping force is specified, which might well be the case since more robust materials were required by design.

When a block is cast, it forms internal stresses as it cools. These stresses, when relieved, will change the
dimensions of the casting. If a casting is stress relieved before machining, less dimensional flex will result.
But machining also introduces stresses to the casting. Which are seldom relieved before assembly.

A running engine will stress relieve itself due to vibrations and thermal cycles. It will also change size by itself.

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Re: Hot honing or not?

Post by modok » Tue Mar 10, 2020 8:03 pm

I believe there IS some truth in "seasoned" parts simply because.....
blocks and heads are subjected to different temps and forces in actual running, and there isn't any better way to simulate that than actually doing it.
Some of the distortion will be "re-set" when you re-machine it, but also some of it won't.

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Re: Hot honing or not?

Post by digger » Thu Mar 12, 2020 8:44 pm

i don't agree on some of the points in OP as it seems like it is saying for a given engine the torque plate can be either steel or alloy. it must be the same modulus as the head material otherwise the local deformations are different and simply using a thinner plate if using steel is not equivalent. In addition the block and deck plate both deform as a system, its not just the gasket compressing.

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Re: Hot honing or not?

Post by David Redszus » Thu Mar 12, 2020 10:47 pm

digger wrote:
Thu Mar 12, 2020 8:44 pm
i don't agree on some of the points in OP as it seems like it is saying for a given engine the torque plate can be either steel or alloy. it must be the same modulus as the head material otherwise the local deformations are different and simply using a thinner plate if using steel is not equivalent. In addition the block and deck plate both deform as a system, its not just the gasket compressing.
The deck plate can indeed be made of aluminum or steel. What really matters is that the deck plate does not
deform under clamping load. If alternative materials are used, thickness must be adjusted to provide the same
compression. In either case, the deck plate must contact the armor ring of the gasket as does the cylinder head.

The gasket will deform under compression but not uniformly. The use of pressure indicating film will show
local pressure zones.

Another test is to measure bore distortion with and without a gasket. Without a gasket, the bore will deform
very little, if at all.

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Re: Hot honing or not?

Post by modok » Fri Mar 13, 2020 7:50 pm

It could be aluminum or steel and have a similar amount of flex.... depending on the thickness of the plate and the diameter of the spacers used.
Same material as the head makes sense, but does not HAVE to be.
There may be practical reasons to go the other way, lets see if I can imagine some......
If the bolt holes are VERY close to the bore them maybe steel/iron would do better, because a deck plate has to have a piston size hole in it while a head of course does not.

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Re: Hot honing or not?

Post by MadBill » Sun Mar 15, 2020 10:58 pm

David Redszus wrote:
Thu Mar 12, 2020 10:47 pm
... Without a gasket, the bore will deform
very little, if at all.
Many years back I had a friend build me a torque plate. He expressed total skepticism re the concept, but not long after, rebuilt an unmolested 40,000 mile 455 Buick engine. When he pulled the heads he found still visible hone marks everywhere except for a shiny stripe in line with each head bolt. It made a believer of him.
This kind of localized distortion might be confined to thin wall castings with maxed-out bore diameters but would not be affected by the head gasket.
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Re: Hot honing or not?

Post by RevTheory » Mon Mar 16, 2020 9:38 am

So in an iron block/aluminum head combo, do we run a few dyno pulls, let it cool completely, loosen and retorque the heads or leave it be?

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Re: Hot honing or not?

Post by David Redszus » Mon Mar 16, 2020 11:59 am

RevTheory wrote:
Mon Mar 16, 2020 9:38 am
So in an iron block/aluminum head combo, do we run a few dyno pulls, let it cool completely, loosen and retorque the heads or leave it be?
I would call the head gasket manufacturer and follow their recommendations.

Some gaskets require re-torque , some do not.

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Re: Hot honing or not?

Post by MadBill » Tue Mar 17, 2020 12:50 am

I suspect that some gaskets advertised as "no re-torque required" would benefit from the process but it's a hard sell to a flat rate mechanic, so they say "not needed" and cross their fingers.
I can't see how a cold "back off a half turn and re-torque" could possibly hurt. I re-did my aluminum BBC about a week after installing the heads with Fel Pros (never fired) and got ~ 30° more rotation on all the fasteners.
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Re: Hot honing or not?

Post by Cubic_Cleveland » Tue Mar 17, 2020 2:24 am

MadBill wrote:
Tue Mar 17, 2020 12:50 am
I suspect that some gaskets advertised as "no re-torque required" would benefit from the process but it's a hard sell to a flat rate mechanic, so they say "not needed" and cross their fingers.
I can't see how a cold "back off a half turn and re-torque" could possibly hurt. I re-did my aluminum BBC about a week after installing the heads with Fel Pros (never fired) and got ~ 30° more rotation on all the fasteners.
MLS or composite Bill? Also did you tension the fasteners to final torque once (following manufacturers recommendations), or back them off and re-tension when you first assembled the engine?

I have found similar to you with new MLS gaskets when re-tensioning the fasteners when first assembling the engine. Seems like the first go round compresses the gasket and the second go round tensions the fastener properly. Don’t seem to notice as much of a difference with composite gaskets. Also burnishing the thread/spot face does play a part too I think..

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Re: Hot honing or not?

Post by Jeff Lee » Tue Mar 17, 2020 6:09 am

David Redszus wrote:
Thu Mar 12, 2020 10:47 pm
digger wrote:
Thu Mar 12, 2020 8:44 pm
i don't agree on some of the points in OP as it seems like it is saying for a given engine the torque plate can be either steel or alloy. it must be the same modulus as the head material otherwise the local deformations are different and simply using a thinner plate if using steel is not equivalent. In addition the block and deck plate both deform as a system, its not just the gasket compressing.
The deck plate can indeed be made of aluminum or steel. What really matters is that the deck plate does not
deform under clamping load. If alternative materials are used, thickness must be adjusted to provide the same
compression. In either case, the deck plate must contact the armor ring of the gasket as does the cylinder head.

The gasket will deform under compression but not uniformly. The use of pressure indicating film will show
local pressure zones.

Another test is to measure bore distortion with and without a gasket. Without a gasket, the bore will deform
very little, if at all.
If that is true, then I would think one would adjust their deck height / compression height to allow for the thinnest head gasket possible. Agree?
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