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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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Re: Hot honing or not?

Post by David Redszus » Tue Mar 17, 2020 1:21 pm

Jeff Lee wrote:
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?
If we were to replace a head gasket with pressure indicating film, we would notice that the head does
not contact the block surface uniformly. Consequently, a gasket with some compression is necessary to
provide uniform sealing.

Solid, soft copper gaskets were sometimes used with turbo engines. But a used gasket could not be reused
since it had work hardened from previous compression.

Head gasket technology is a subject that requires professional insight from a gasket engineer at FelPro.
My guy has retired some time ago.

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Re: Hot honing or not?

Post by MadBill » Wed Mar 18, 2020 1:20 am

Cubic_Cleveland wrote:
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..
0.039" Fel Pro composite, # 1017. I brought the fasteners up to spec in three steps and stopped. A week later I backed them off one at a time and re-torqued. These nuts and studs have been joined/separated many times over the years.
Felix, qui potuit rerum cognscere causas.

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Re: Hot honing or not?

Post by David Redszus » Wed Mar 18, 2020 12:16 pm

Clamped surfaces lose clamping force over time, even if never run.

FelPro makes gaskets of several materials for the same engine. It would be nice to know the advantages
and disadvantages of each material or design.

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Re: Hot honing or not?

Post by Cubic_Cleveland » Wed Mar 18, 2020 7:50 pm

MadBill wrote:
Wed Mar 18, 2020 1:20 am
Cubic_Cleveland wrote:
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..
0.039" Fel Pro composite, # 1017. I brought the fasteners up to spec in three steps and stopped. A week later I backed them off one at a time and re-torqued. These nuts and studs have been joined/separated many times over the years.
Very interesting Bill, thanks! I’ll have to try it on the next engine I assemble and can hold onto for a few weeks.

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Re: Hot honing or not?

Post by oldjohnno » Thu Mar 19, 2020 3:42 am

How round is round enough? I guess that's going to mainly depend on the conformability of the ring but at what point do we say "that'll do" and move on to a more productive use of time? Should we be willing to accept a tenth, five tenths, a thou? It's generally accepted that there are advantages to holding down roundness tolerances but on the other hand I bet we've all dealt with engines that didn't leak down particularly well or maybe had some significant blowby yet still maintained their power output. There must be some point at which the ring ceases to care about minor deviations because they are within its range of conformability.
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Re: Hot honing or not?

Post by David Redszus » Thu Mar 19, 2020 9:44 pm

oldjohnno wrote:
Thu Mar 19, 2020 3:42 am
How round is round enough? I guess that's going to mainly depend on the conformability of the ring but at what point do we say "that'll do" and move on to a more productive use of time? Should we be willing to accept a tenth, five tenths, a thou? It's generally accepted that there are advantages to holding down roundness tolerances but on the other hand I bet we've all dealt with engines that didn't leak down particularly well or maybe had some significant blowby yet still maintained their power output. There must be some point at which the ring ceases to care about minor deviations because they are within its range of conformability.
We are all aware that bolting a head to a block will cause ovality distortion; which may be first, second or third order
in shape.
Some also know that the heating and cooling of head and block further distorts the bore shape.

Some are aware that pistons are not round but oval in shape. And that ovality changes with inertial forces and
gas pressure.

So now we have a situation of an unknown oval bore fitted with an unknown oval piston.

How does one determine clearance between two ovals?

If the distorted bore shape can be kept as round as a circle, a piston can also be made nearly circular. Then almost
any ring could be used and we could run very tight piston to wall clearances.

As it is now, modern engines run interference clearances, allowed by piston skirt flex.

So, if you can reduce ovality, perhaps under 0.0002", you can run tighter piston and ring clearances.
Perhaps with leakage values of under 0.5%.

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