The 54.4 mm stroke RG cranks project started as a simple hack to allow
mounting Their cylinders but it quickly turned into a complete
re-engineering of every detail including aspects that were probably
not even taken into consideration in the original design. In fact,
the original design is more than 20 years old and aimed at a production
bike ("cheap") while all you see in the following (except pictures marked "OLD")
is based on the state-of-the-art stuff currently used by
As a result, the new cranks are not just a longer stroke version of the original
ones but a totally new design with plenty of new features aimed at improving both
reliability, performances, easy of manutaining and spare parts availability.
Even the 50.6 mm stroke version of these cranks should not be viewed as just a
replacement part but considered as a significant upgrade. Here you see a comparison
at a glance between the new and the old ones:
while in the following you'll find a more detaild explaination of some
of the new features, their main benefits and some old vs new comparison.
I don't have time to document everything plus I have an NDA with them and
can't tell their secrets, I just want you to know there are more features
and benefits than you'll find in this page.
And, we are going to go faster than Hayabusas ;-)
Seals and spacers
The stock seals had two lips plus four rubber teeth in the front.
The two lips were probably supposed to last more miles while
the rubber teeth serve as built-in spacers to keep some distance from the bearing
(which is necessary because in the RG the seal is on the "wrong"
side of the bearing):
These old seals are difficult to find, plus the two lips put a limit on the rotational
speed they can do, plus they were too thick for the new cranks.
The new design uses standard high speed seals easier to find
(high speed = single lip),
plus custom spacers made in ergal (an aluminium light alloy):
In case you are concerned about the reduced clearance between seal and bearing, do not,
as the absence of the second lip compensates for it in excess
(that is, the seal should be even better lubed than before
though the assebly is more compact).
They didn't want me to purchase the original replacement parts
as They use bearings with different specs, plus the new crank
design uses one extra kind of bearing (three kinds total, instead of two)
that had to be self made in any case.
So we took a dozen of Their bearings, disassembled them and had
them machined. Then, reassembled everything. Here you can see the three
different kind of bearings: the pinned-grooved (known as NP),
the just pinned (known as P), and the new one, which I named "P05":
P05 has the pin in a different position (necessary to make the new crank
compatible with the stock crankcase). It was discussed for months; I took
every possible care in the design to ensure the bearing is as safe a
the stock one and the pin mounting is even more stable. Bearings have
a very hard surface; to make holes in them wasn't easy at all.
Above you can see the "central group" with bearings, spacers and seals in place:
isn't it nice? ;-)
Even the bearing pins were discussed for months.
We considered different solutions and we purchsed
several different types until, just before reassembling the bearings,
we found pins that are the same as stock RG ones
(so called "coiled spring pins", but "standard duty". Later on, I finally
found the non-standard sized "heavy duty" coiled spring pins as used originally
Pins we used in bearings type "P" and "NP" are exactly same diameter and lenght
as stock RG ones, while model "P05" uses both a different
diameter and a different lenght.
I believe the pictures speak for themselves.
These rods are the result of years of testing
in the most severe racing conditions and can be abused
more than you could ever dream.
Their normal usage is at 14-15000 RPM with tons of HP on them,
but they're often overrevved up to 17-18 K RPM with no damage.
Here you also see the silver-plated shims with dimples for oil retaintion
(of course there are also nice roller bearings, but I didn't take a picture).
Then, the rod seats in the cranks, the clearances, the big pin tolerance...
everything up to the piston is exactly either as per Their specification
or Their standard parts. No need to reinvent the wheel.
And remember, these rods were born for a 54.4 mm stroke.
In case you'd want them on a 50.6 mm stroke crank (less solicitations
due to alternate forces) you could run them even faster!
The standard method of aligning the RG cranks was like in the left picture.
According to the gammalist knowledge, there was no special tool for doing it,
and the result relied on the operator art skill.
I was a bit scared by this as I'm not an artist and could not do it precisely
The new cranks have a precise reference for alignement that, if used in combination
with a straight and sharp point, allow everybody to get the cranks aligned with a minimal
error. The alignement reference (call it a "scratch") is now made at the opposite side
(180 degrees) than the rod as the rod area is thin and highly solicited and must be
more than perfect. Even a scratch in that area could compromise its safety and lead
to a fatigue stress crack in the long term. The scratch made at 180 degrees is perfectly
safe (there is nothing there) and the mounting procedure is the same except you have
to count the gear teeth in the opposite direction.
I had the pick-up notches built in two variants: stock 26-11 degrees and
the modified 30-18 degrees you see in the picture. The idea behing it is
to get a more precise advance where you need it, provided you have a
mappable (programmable) ignition. I'll post an explanation of this
as soon as I have time to write it.
Of course, if you want pick-up notches different than 26-11 or 30-18
it's a relatively minor problem, though for cost reasons it would still
be better to make the cranks all the same.
The new cranks shoulder has a shape more favourable to the intake air flow.
There are no more edges and jumps and it blends to the case intake port nicely.
I spent a few sleepless nights to redesign the intake port keeping a balance
between contrasting requirements (maximizing the section area, having it
as straight as possible, having a curvature with the derivatives under control,
taking away as less material as possible from the cases, not repositioning
the carburators too low, making the cranks as safe as possible in the rod area...)
The new shape corresponds to the last millimeters of the intake I've redesigned;
I mean to provide templates for working the intake port accordingly, but I am
optimistic this shape will in any case work better than stock cranks' one even
if you leave your intake port as it is now.
The new cranks have inserts in different materials to accomplish balancing
(the round objects you see press fitted into the big holes in the picture).
Balancing can be customized as needed by replacing the inserts with different ones
(different materials, empty inside, etc. etc.). I don't think anybody
has ever considered rebalancing the RG cranks when, for example, adopting
oversized pistons, however that's what you should do.
A 54.4 mm stroke crank running at 15000 rpm generates, due to the unbalanced
masses, about twice and a half the alternate forces on the bearings and the crankcase
than a 50.6 mm crank at 10000 RPM does.
An accurate balancing is critical for the safety of the whole.
Balancing of 2T cranks is usually only done statically, as they are normally symmetrical
and dynamic balancing is intrinsic.
As the RG cranks are not symmetrical (I posted a long article about this
on the gammalist, time ago), I had them also balanced dynamically that is, we put more weight
on the thinner flywheel and viceversa in order to compensate for it and reduce
(ideally, eliminate) the nasty side vibrations it could produce.
Crankcase free volume
The balancing holes also allow to tune crankcase compression ratio,
depending on what you put in them. In any case the crankcase
compression ratio is increased due to the higher volume of the
I do not want to discuss what compression ratio is better, I just say that
cloning Their bottom end as closely as possible is what will work better
together with Their top end. There are also other fluidodynamic
effects taken into account in the crank design that I can't tell,
but I am optimist they should provide better performances even in the
50.6 mm stroke / stock cylinders combination.
For those concerned about weight, these cranks weight more than
stock ones but also weight less than Theirs.
More precisely, they weight about half a pound less each,
that is, multiplied by 4, couple of punds less the whole assembly.
Last updated: 23 Apr 2009