Big Bore question

[T. Cotten]

While we continue to ignore where the fuse gets lit most often, Folks,...

A few observations on head gasket surfaces:
The headbolt inserts I remember on Shovels were recessed, however the heads were still not 'flat'. I have no pics from the era, but a light grind on a flat surface often displayed low spots over both intake and exhaust ports. Metal moves.
(I preferred to grind them flat, rather than machine, as it took the least time (expense), and removed the least material.)

Pans certainly suffer from 'pulled' inserts, and I feel decades of duty were enough, although over-torquing made things worse:
SRTGRND2.jpg

Even this Chief cylinder deck shows a depression over both exhaust and intake ports:

warpage.jpg

deckwarp.jpg
The exhaust was detectable with the feeler gauge, but only a light grind illustrated the intake warpage.

Inspection must be diligent; Any stone unturned hides something that will bite you.

....Cotten

[dukekleman]

Spot face machining head bolt inserts. One a Panhead the other a Shovelhead. See images...
Panhead Cylinder head.pngShovelhead Cylinder head.png
The RA finished I use on these is for a conventional head gasket. The photo below shows the RA for a MLS head gasket...
Twin Cam cylinder head MLS RA.jpgTwin Cam cylinder head.pngCylinder head surfacing.png

[T. Cotten]

I really don't know the mil-profile my stones produce, Duke!

But its sharp and bright enough to grab a composite gasket; What is "MLS"?

Once again, I preferred to grind because it was much faster, easier for me, and removed minimal stock, thus keeping compression pretty much the same. I stopped spot-facing when I realized it just gave the inserts somewhere to go.

If I can return to stressing for fitting to the pistons,
Here is an inverted Chief cylinder (which distort far, far less than an HD) where you can see the dark patch where the stone hasn't touched where the bore wall is pulled outward, by the fastener-stress of the base stud right next to it:
distort.jpg

At .070" and over over-bores, I have observed HD spigots distort both inward and outward a full thou and a half. If not stressed as if installed while honed, the spigots will rub the piston skirts at a normal clearance.

....Cotten

[dukekleman]

MLS (Multi-layer steel) is a layered riveted gasket with integrated embossments and coated in a mil layer of Viton. In order for them to work as engineered (Seal and Transfer Heat) correctly for prolonged mileage, they require a different surface finish. The Japanese manufactures have used them in the motorcycle world far before the American manufactures. What I noted is that as aftermarket companies started using them for Harley Davidsons, they were torqueing them wrong. The Japanese have a different torque procedure than say Cometic...
The first company introducing them that I recall was Branded "Motor factory" from a company called Chrome Specialties. Now you see them branded/produced by others...Also the American bike manufactures (Harley Davidson, Indian and Victory) have used them in OEM production for years now. These are not to be confused with SLS and AFM...
On HD series engines that I bore and hone often, I've built into my torque plate an adjustable lower plate for the spigot area. "Panting" or "Belling" as some call it is a major problem just as Cotton pointed out. There is an art to honing cylinders correctly and a science to the honing oil formulation used taught to me by my friends Doug Coffee and Joe Mondello. I must give credit where credit's due...
I measure a lot of new cylinders for Harley Davidson's! Most do not come close to passing standards set.
The spigot area is often a issue and starts by having patience during the boring process. To much tooling pressure starts to mess it up prior to honing which only gets worse from stone pressure. Hone stroke, Over stroke, Dwell and Stone Pressure experience is key to proper X & Y axis's measurements in the end.
I like to use a infrared temperature gun to monitor the heat created by the friction of honing. The heat definitely effects cylinder measurements!
Last note on cylinder spigots, When it comes to Big Bore/and or stroker motors, one must be careful to bore the crankcases correctly for the oversized spigots I've seen them to tight and cause piston skirt issues due to expansion restrictions under growth. Also the crank case fasteners can contact the spigot and cause distortion.
Fastener Stress: Cylinder structural integrity is huge and I've seen fasteners cause distortion to cylinder bores just as you pointed out in the image above. This should not be overlooked and adds to the importance of torque plating with gaskets being used in the final build.

[T. Cotten]

So these modern gaskets, Duke,..

If they transfer heat better, wouldn't that take it to the cylinders?

....Cotten
PS: My 1993-vintage Sunnen honing oil has aged nicely!

[dukekleman]

The upper portion of the cylinder bore is exposed to the most heat due to flame front and PPR after ignition. The cast iron cylinder doesn't dissipate heat as well as the aluminum cylinder head as we know. Giving the heat a pathway to dissipate from the cast iron into the aluminum via the gasket and RA surface area is looked at as an advantage/advancement.
Thermo imaging cameras show a very interesting picture of heat distribution through colored imagery and numbers

[T. Cotten]

The upper portion of the cylinder bore is exposed to the most heat due to flame front and PPR after ignition. The cast iron cylinder doesn't dissipate heat as well as the aluminum cylinder head as we know. Giving the heat a pathway to dissipate from the cast iron into the aluminum via the gasket and RA surface area is looked at as an advantage/advancement.
Thermo imaging cameras show a very interesting picture of heat distribution through colored imagery and numbers

Please show the imagery, Duke!

The head is always hotter (or you hope so...), so it cannot suck heat from the cylinder.

A conductive gasket can only let it go the other way.

....Cotten
PS: I do remember some thermal pics of modern twins that registered the front head hottest, just as I suspected.

But why, if it gets the most wind?

PPS: What's PPR?

Thanks in advance!

(I haven't even searched RA yet.)

[dukekleman]

I'm not quite sure how I'd get the thermo-image screen information onto this forum. It would have to be video'd and then???
Anyhow, Yep the head is always hotter being it's location and function. Harley Davidson has obviously made material changes in the cylinder head for this reason. Knucklehead to Panhead for example. Also as we know the number of Aluminum cooling fins and the size of cooling fins have increased over the years. Eventually circulating motor oil or Glycol coolant around the exhaust valve seats to help cool that particular area of the cylinder head. Thermo imagery shows all these hot areas. Allowing the transfer of heat through head gasket material verse isolating the two has shown advantages, not disadvantages. Shortening pathways for heat travel to cooling fins and not being a stop gate or diode of sorts for you electrical minds.
Cylinder temperature balancing act is an art form on these V twin motors. Never has it been easier (EFI technology) yet harder (Regulations) on these air cooled V twins. When I write ECM calibrations I can get very creative with today's ECM. The vintage V twin is more difficult and feels like your hands are tied when you want to give the motor what it wants and needs but can't...

[T. Cotten]

...Yep the head is always hotter being it's location and function...

Please explain, Duke!

We know HD was aware of something when their OHV got soo much more finnage on the front, but the function is the same as the rear, and location in the wind is not a good thing?

And you lost me at coolants.
With all practical respect to our fossils, I still find it hard to buy soaking heat to the cylinders.
(I can see a practical advantage however, if the motor was so small and utilitarian to where a more uniform cylinder and head would be more reliable, but not for an OHV.)

...Shortening pathways for heat travel to cooling fins and not being a stop gate or diode of sorts for you electrical minds...

Uh oh.

Can you screen-shot your thermo reading to illustrate this phenomenon, if possible? I may still not understand, but would like to.

Otherwise, I stll gotta believe heat goes where it ain't.

....Cotten

[dukekleman]

I can sure try to capture a screenshot for you next time I have one in the Dyno room. Currently I have Milwaukee 8's series in the room as well as in line... I did just wrap up a 59' build for a friend. If I get a slot to fit it in I'll do that.
Heat, yes it has many pathways with in the confinements of the combustion chamber.
I'll list a few areas heat absorbs/travels for consideration:
Some blends in vaporization, some travels through the porcelain path in the spark plug, some into the piston dome, some through the combustion chamber ceiling and into the cooling fins, some through the piston rings and into the cylinder wall cross hatch escaping in the oil film while the rest absorbs into the iron liner out to the cooling fins and some into energy. Mean while, depending on camshaft profile numbers, some is blown out the pipe.
It has many pathways, if we identify a particular problem area, we can change things to our advantage.
Let me give one example of this. Say the piston rings were glazing. That's a sign of to much oil retention in our cross hatch combined with the heat. We can change this by increasing our angle and lessening the RVK number.
Or say our combustion chamber temperatures are to high. We can lower them by changing our exhaust cam timing events in turn changing the center line, lobe separation angle and evacuating the exhaust gases from the chamber more efficiently. I truly hope this helps.

[T. Cotten]

I can sure try to capture a screenshot for you next time I have one in the Dyno room. Currently I have Milwaukee 8's series in the room as well as in line... I did just wrap up a 59' build for a friend. If I get a slot to fit it in I'll do that.
Heat, yes it has many pathways with in the confinements of the combustion chamber.
I'll list a few areas heat absorbs/travels for consideration:
Some blends in vaporization, some travels through the porcelain path in the spark plug, some into the piston dome, some through the combustion chamber ceiling and into the cooling fins, some through the piston rings and into the cylinder wall cross hatch escaping in the oil film while the rest absorbs into the iron liner out to the cooling fins and some into energy. Mean while, depending on camshaft profile numbers, some is blown out the pipe.
It has many pathways, if we identify a particular problem area, we can change things to our advantage.
Let me give one example of this. Say the piston rings were glazing. That's a sign of to much oil retention in our cross hatch combined with the heat. We can change this by increasing our angle and lessening the RVK number.
Or say our combustion chamber temperatures are to high. We can lower them by changing our exhaust cam timing events in turn changing the center line, lobe separation angle and evacuating the exhaust gases from the chamber more efficiently. I truly hope this helps.

Please Duke,

Although there are conceivably infinite things that can happen in our fossil-design motors, they still managed historical success.
And worse yet, they remained legendary for many decades, in spite of field repairs.

To get enough heat to blow a head gasket, you need too much combustion.

Its easier than it sounds.

....Cotten
PS: It should be taken for granted that by the time a head gasket has been heat-compromised, there is usually collateral damage. But the head gasket didn't light the fuse.

[dukekleman]

I'll just say that heat is an obvious natural component in that area of the engine. It's my experience that the common ( Not all) root cause of head gasket failures come down to loss of torque retention. Torque loss for various reasons I listed early on in the postings.
The natural component of heat in a combustion chamber then the flame front goes to work destroying the head gasket during power and exhaust strokes. These are common reasons I've seen for head gasket failures.
A little lesser common head gasket failure comes from engines that are far from stock. Those motors can have issues that go deeper due to modifications. These modifications need to be developed on the motorcycle carefully for long term success.
Ignition calibration and carburetion calibration need to be developed. This should be done in a controlled environment, a chassis Dyno room. This way AFR, Timing, Leak observation and HEAT can be monitored. Any discrepancies seen and the motorcycle can be shutdown, adjustments made and then proceed again.
With stock "like" engines , This isn't such a concern. You can follow the calibration specifications published by the engineers whom originally created them.

[T. Cotten]

The loss of 'torque retention', Duke,

Is the result of heat, not the initial cause of it; Once the fuse is lit, heat begets more heat.

Combustion is fuel and air, and the heat produced depends upon their ratio.

When one head burns, why not the other?

....Cotten

[dukekleman]

The loss of 'torque retention', Duke,

Is the result of heat, not the initial cause of it; Once the fuse is lit, heat begets more heat.

Combustion is fuel and air, and the heat produced depends upon their ratio.

When one head burns, why not the other?

....Cotten

Overall Combustion seen at the end of the "loop" (Exhaust Stream) is indeed Fuel and Air entered , but we can't forget about the type of fuel purchased at the pump (Its Octane and Burn speed does vary) and of course the ignition time we gave it to burn/occur at a specific RPM.

[T. Cotten]

Fuel, Duke?

That still doesn't explain why only one head blows, when they both see the same fuel.

(Certainly fuel additives can indirectly be a contributing factor, especially for Shovels, but its not how they burn that does it.)

You are dancing all around the elephant in the room.

....Cotten