Big Bore question

[T. Cotten]

I just purchased a 93in stroker in a 76 FLH. ( My 1st) I had to take off the rear head of due to a blown head gasket. I'm having the head repaired now but being my first stroker, I was wondering if the pushrods are adjusted the same as a 74 ci motor. Also does someone have headbolt torque specs on a stroker? Thanks.

Have you reassembled yet, OWG?

Which manifold design do you have, and does it mate up to the installed stroker head spigots?

You don't want to go through this twice...

...Cotten
PS:

Pushrod adjustment is the same. Headbolt torque is same as stock. No need to overthink it. Stroker just means trouble, not special.

We do need to think about whether you have stock pushrods or not, OWG; Have you stock hydraulics (on the right), or have they been replaced with solids, or some "performance" assemblies?

LIFTERS.jpg
(That's when it gets a little more tricky, but still no reason to resent strokers...)

[T. Cotten]

I actually asked that question back then.
The answer I was given was:

"We did it to allow movement during engine growth for expansion and contraction."

I was shown motor growth where they had dial indicators set up measuring the height changes of the engine from ambient temperature to operating temperature. This affected the manifold fitment on a V twin design engine. They still build manifolds that allow this growth today on 2023 models as we know.

Doesn't that raise the question, Duke,...

How did the seventy years of American v-twins that came before that, do so gloriously with rigid brass ferrules?

....Cotten
PS: You were half-right with 'fuel', as today's P4gas swells common O-rings, leading to the dreaded manifold leak, meaning more air, thus heat damage:

P4ORING1.jpg

ORING.jpg

The bands suffered more, by my experience, decades ago.

....Cotten

[dukekleman]

I actually asked that question back then.
The answer I was given was:

"We did it to allow movement during engine growth for expansion and contraction."

I was shown motor growth where they had dial indicators set up measuring the height changes of the engine from ambient temperature to operating temperature. This affected the manifold fitment on a V twin design engine. They still build manifolds that allow this growth today on 2023 models as we know.

[BigLakeBob]

images.jpg

[T. Cotten]

In order to achieve gasket sealing longevity, I highly recommend that you re-torque your gaskets early and often until you noticed them holding torque and settling has stopped.
Otherwise you will have problems later...

Really Duke...

How do some Folks get away without a retorque (as prudent as that may be?)

Tain't the fuel, Duke.

Its too much air.

....Cotten
PS: Why did the MOCO bother to redesign something that worked for over three decades?

SHOVMANI.jpg

[dukekleman]

Cotton I explained in my first post exactly what I ve found that causes a head gasket to fail. One head gasket or two head gaskets, doesn't matter. Those items I listed apply.

No dancing on my end. Just conversation on each topic of change that has been brought up. My thought was that I was helping, maybe I'm not???

[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

[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]

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]

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]

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 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]

...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'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]

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.)