Why We Built a Billet H2 Cylinder

Why We Built a Billet H2 Cylinder – and What It Means for ICBM™

The Crazy Idea Behind a Legendary Engine

Kawasaki’s H2 Mach 750 is more than just an old motorcycle.
For many of us, it’s a symbol of a wild era – brutal acceleration, straight-line speed, and a kind of beautiful “madness” that will probably never be repeated.

But in 2025, H2 cylinders are no longer something you can simply order new.

What we see on the bench today are:

• Cylinders with cracks
• Blocks that have already been over-bored to their limits
• Scars from past overheating and seizures

And yet, H2 owners still say things like:

“I just want to feel this engine pull one more time.”
“If I can, I want to ride this H2 for another 10 or 20 years.”

That kind of attachment to an engine is exactly why Inoue Boring exists.

From “Consumable Part” to “Future-Proof Component”

As an engine machining shop, I kept asking myself:

“Can we stop treating H2 cylinders as consumable parts
and start building them as components that can survive into the future?”

The natural extension of that question was this:

What if we made a brand-new H2 cylinder from a solid block of aluminum?

Not repaired.
Not sleeved in the conventional way.
But completely re-engineered and machined from billet, then plated and finished with our latest know-how.

That idea became the starting point of our billet H2 cylinder project.

A Project That Makes No Business Sense (On Paper)

Let’s be honest:
From a pure business perspective, this project makes almost no sense.

The current price for a complete set is 1,320,000 yen (about USD 8,000+ depending on the exchange rate).

Even I look at that number and think:

“Yes… that’s expensive.” (laughs)

But we didn’t start this project because it would be easy to sell.
We did it because we wanted to prove something:

• If we redesign the H2 cylinder from scratch with today’s materials and machining technology,
• How far can we push reliability and smooth power delivery?
• How strong, how durable, and how enjoyable can this old two-stroke become?

In other words, this was our way of answering the question:

“What does it mean to truly ‘preserve’ a legendary engine for the next decades?”

Built on the Foundations of ICBM™

This billet H2 cylinder is not a random one-off experiment.
It stands directly on top of the technology we have been developing for years with ICBM™.

The same core elements are there:

• Precision-machined aluminum sleeves
• Advanced NiSiC plating and honing techniques
• Detailed understanding of port shapes, clearances, and thermal behavior

For a long time, we have been using these techniques to restore and upgrade worn-out aluminum cylinders with ICBM™ sleeves and plating.

Then one day the question naturally came:

“If we can do this with sleeves…
what happens if we design and machine the entire cylinder from scratch
using the same philosophy?”

The billet H2 project is our answer to that question.

You could say:

“The billet H2 cylinder is ICBM™ taken to its logical extreme.”

The First Unit: Built for One Owner, But Aimed at Many

So far, only one owner has purchased and installed this billet H2 cylinder.
It is, in every sense, a very special and luxurious piece.

But for us, this first unit is not the end goal.
It’s the beginning of a longer journey:

• How can we reduce the cost through smarter design and production?
• How can we make this level of reliability more accessible to more H2 owners?
• How can the lessons learned here feed back into “normal” ICBM™ cylinders for other models?

Our dream is simple:

To give H2 and other legendary engines
a real chance to survive another few decades on real roads,
not just in museums.

The billet H2 cylinder is the “flag on the hill” that shows how far we are willing to go.

What This Means for You as an H2 Owner

If you own an H2 or other Kawasaki triple, you might not need a full billet cylinder set.

But you might be thinking:

• “My cylinder is already at its last over-size.”
• “The bores are tired, but I don’t want to give up on this engine.”
• “If I rebuild it, I want it done in a way that truly lasts.”

That’s exactly where ICBM™ comes in.

ICBM™ is our way of turning tired aluminum cylinders into strong, stable, long-life components, using:

• Machined aluminum sleeves
• NiSiC plating with exceptional wear resistance
• Carefully controlled clearances for both performance and longevity

The billet H2 cylinder is a kind of “showcase” of what this technology can do
when we remove the usual limits.

ICBM™ is how we bring that same philosophy into a more accessible, real-world form.

Looking Ahead

This article is just the first part of the story.

In future posts, we’ll go deeper into:

• The internal design of the billet H2 cylinder
• The machining process and challenges
• How this project influenced our thinking about ICBM™ for other engines

If you ride an H2, an H1, or any other classic two-stroke and you’re wondering:

“Is my engine really at the end of its life?”

we’d like you to know:

“There may be more options than you think.”

Our mission at Inoue Boring is simple:

To keep legendary engines alive and enjoyable – not just for us,
but for the next generation of riders as well.

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