The Birth of the “EVER SLEEVE™” — A New Step Forward for ICBM™
Discover how iB’s revolutionary EVER SLEEVE™ technology transforms the way aluminum sleeves are fitted—allowing perfectly finished ICBM®™ cylinders without thermal distortion.
First of all, please understand that the finished ICBM®™ cylinders equipped with the new EVER SLEEVE™technology are identical in performance and precision to all the ICBM®™ cylinders we have produced so far.
There is, however, one important difference in the manufacturing process.
In the new method, the aluminum-plated sleeve is completely finished—including final honing—before being inserted into the cylinder block at room temperature, after which the surface machining (such as deck-face finishing) is performed.
At first glance, this may look like nothing more than a change in process order. But in conventional practice—whether the sleeve is made of cast iron or aluminum—no one inserts a sleeve that has already been finished to its final inner diameter.
Why not? Because when the sleeve is press-fitted by heat (so-called shrink fitting), it inevitably deforms as it cools and contracts.
For this reason, the final inner-diameter finishing has always been done after the sleeve was press-fitted, to ensure the required precision of the cylinder.
When a cast-iron sleeve is fitted into an aluminum cylinder block, heat-shrink fitting is the only realistic method available.
(Exceptions exist, such as some two-stroke engines with cast-in sleeves.)
Even after iB succeeded in developing aluminum-plated ICBM®™ sleeves, we continued to use shrink fitting as the most reliable insertion method.
Then came an unexpected discovery.
While working on many ICBM®™ cylinders, we sometimes had to remove the sleeves.
In cases where both the sleeve and the block were aluminum, we found that even a very small interference fit could cause the two parts to bond together so tightly that they could not be separated.
And from this experience came a remarkable realization:
“An aluminum sleeve, even with zero interference, does not move inside an aluminum cylinder block.”
Why?
Because the heat of an internal-combustion engine originates inside the cylinder bore, while the cylinder block itself—whether air-cooled or water-cooled—is constantly being cooled.
Since both components are aluminum, their thermal expansion rates are identical.
Therefore, in operation, the heated sleeve expands slightly while the cooled block does not, causing the sleeve to cling tightly to the block and behave as one solid piece.
In retrospect, it is a simple and obvious truth.
Yet it is something that no traditional engine-machining professional would ever consider when dealing with cast-iron sleeves, nor would an OEM manufacturer ever need to know while producing directly-plated aluminum cylinders.
This was a unique discovery that only became apparent after machining large numbers of aluminum-plated ICBM®™ sleeves—and it proved to be one of the greatest advantages of using aluminum for both the sleeve and the block.
The Path to EVER SLEEVE™
Once we realized that a zero-interference fit was possible, new possibilities opened up.
It meant that the sleeve could be inserted at room temperature, without any heat-shrink process—and that, because there was no thermal contraction afterward, the sleeve would not deform.
In other words, contrary to all established machining practice, it became possible to insert a sleeve that had already been honed to its final precision, with absolutely no problem.
In the world of engine machining—whether diesel, gasoline, or motorcycle—this was unheard of.
A process where you could simply say:
“The sleeve is already finished to final spec—just insert it and you’re done.”
was truly revolutionary.
To hold the loosely-fitted sleeve in place during engine assembly, we developed a stopper ring, and this new method was successfully granted a Japanese patent (international patents not yet obtained).
Such a process is impossible with a cast-iron sleeve, since cast iron and aluminum have expansion rates that differ by roughly a factor of two.
As explained in our previous post, even with a conventional interference fit, a cast-iron sleeve will actually move slightly inside the block during operation.
A “zero-fit” is simply unthinkable in that case.
But with aluminum sleeves, these problems disappear completely—and more than that, we realized that we could now sell the sleeves as fully finished products under the name EVER SLEEVE™.
Toward Wider Adoption
At iB, we decided to embrace this new possibility.
Through repeated testing and fine adjustments of the fitting clearance, we succeeded in producing the EVER SLEEVE™ with no technical issues whatsoever.
With EVER SLEEVE™, even workshops outside of iB—such as engine rebuilders or machining shops capable of boring and resizing cylinder-barrel holes—will be able to assemble complete aluminum-plated cylinders by themselves.
This will allow far more enthusiasts and professionals to experience the benefits of aluminum-plated sleeves.
We at iB hope that as many riders and engine builders as possible can enjoy their machines in perfect running condition.
That is, and always will be, our mission.
