Bullseye 2-Piece MTB Cranks (2nd Gen)

Roger Durham’s Bullseye cranks are legendary and his tubular steel 2-piece crank design has proven to be revolutionary. Why? Roger filed Patent Number 4,704,919 for the 2-piece crank design on March 18, 1986 and it was granted on November 10, 1987.

Fast forward to 2003 after the patent had expired and Shimano wasted no time in releasing their first 2-piece Hollowtech II cranks for their top end XTR groupset. Since then, the design has spread like wildfire and has become the dominant crank design in the industry.

GENERATIONS

There is some confusion about 1st, 2nd and 3rd generation 2-piece Bullseye cranks so let’s clear this up once and for all…

1st Gen
Released in 1984. Specifically intended for BMX use.  They are easy to identify because they only have a threaded mounting point on inside of the drive side arm which enables the direct attachment of one chainring (such as a Tuf-Neck) or a single spider/chainring combo. They were supplied with a Bullseye American bottom bracket. Decals are silver foil with red vertical ‘Bullseye’ lettering and attached facing forwards/backward on each arm. See our Bullseye 2-Piece BMX Cranks page for more details.

2nd Gen
Released in 1987. Specifically intended for MTB use. They have a built in 5 hole spider adapter for which either a triple alloy spider or a chainring (such as TA Specialities) could be attached. The axle is longer than 1st gen due to the extra clearance required on mountain bikes. They were supplied with a Bullseye MTB threaded bottom bracket or an optional Bullseye/Klein press-fit bottom bracket. Decals are either black or white vertical ‘Bullseye’ lettering printed onto clear vinyl and attached to the outside of each arm.

3rd Gen
They do not exist! Roger Durham confirmed there are only 1st and 2nd generation 2-piece cranks. Let’s preface this by saying that early 1st and 2nd Gen cranks had hollow axles and the only security mechanism to prevent the non-drive arm from slipping off the end of the axle was a small alloy locking key. Bullseye’s insurance company were not happy with the locking key alone and insisted on a rider weight limit for the cranks unless a better solution was implemented. The solution was the Bullseye Crank Keeper. This involved the axle on the non-drive side being capped and threaded so that a cinch bolt and alloy cap could be inserted from the same side to secure the crank arm to the axle.

The biggest gripe for Bullseye crank owners was not the minor risk of the crank arm falling off but the fact that play would develop during use due to the arm slipping on the splines. As Pace team rider and owner of a Pace RC100 from 1990-1997 Richard Thakeray said: “it didn’t have a good locking mechanism, like the modern Shimano,& kept working loose.” So the ability to be able to preload the bearings with the Bullseye Crank Keeper was the real highlight for Bullseye crank owners.

This minor enforced modification for new cranks does not substantiate a change in generation. Even more so as Roger would undertake the modification on earlier 2nd Gen cranks as well as 1st Gen cranks for anyone who wanted it. This would have been at some point after 1992 because Bullseye cranks were OEM on the Pace RC100 from 1988-1992 and none were supplied with Bullseye Crank Keepers.

The alternative solution for all Bullseye crank owners until then was the highly regarded IRD Crank Keeper. It is surprising that Roger Durham hadn’t taken it upon himself to address the preload issue himself much earlier.

CONSTRUCTION

Roger Durham opted for a tubular Cro-Mo steel construction due to its strength, rigidity and being lighter than traditional 3-piece aluminium equivalents at that time.

Each tubular arm is constructed from 2 matching pieces of tapered plate steel which is twice-bent and TIG welded to forn the box shape.

The narrow tapered end of each arm is mitre cut to receive standard 9/16″ 20 TPI pedal lug for drive and non-drive sides accordingly.

The drive side arm is then mitred so the axle and mounting plate with 5 holes is welded onto the inside of each arm to accept an alloy triple chainring spider.

The non-drive side is cut to receive a clamp containing 46 splines which match splines on the end of the axle. The clamp is then tightened with a 4mm allen bolt housing the small aluminium locking key. Roger filed Patent Number 4,728,218 for the locking key mechanism on May 7, 1986 and it was granted on March 1, 1988.

A selection of axle spacers and shims were supplied which fit between the cups and arms to enable the perfect chainline to be achieved. Rubber o-rings were also provided to take up any slack as there was no way to preload the bearings.

Length: 152, 157, 162, 167, 172, 178, 181, 184, 222mm
Axle: 2-piece
Colour: Black, White
Weight: 882g (178mm/110 BCD)
RRP: $264.99
Made: USA

BOTTOM BRACKET ISSUES

The Bullseye MTB threaded and Bullseye/Klein press-fit bottom brackets cups were of steel construction with ball bearings protected by a fibre board seal. This seal may be sufficient to keep out the elements in the California sunshine, but life expectancy is significantly reduced in wet and muddy United Kingdom. Roger Durham was aware of this issue! Replaceable double sealed (2RS) sealed cartridge bearings would have been a superior option and simplified the manufacturing process.

Finding a replacement Bullseye bottom bracket is near-impossible, but they are a necessity for period correct builds. However, if the priority is to be able to ride your cranks regularly and ensure they can be maintained well into the 21st century then you have three options available to replace your Bullseye MTB threaded bottom bracket:

22.2mm Bullseye to 24mm Shimano Hollowtech II Conversion Shims
This is a clunky solution but it works like a charm. You simply install a 1.8mm shim to fill the difference between the axle and the bearings of a Shimano Hollowtech II external bottom bracket. The only problem for the purist is that you are stuck with an incredibly ugly external bottom bracket which isn’t remotely vintage in appearance.

22.2mm Bullseye to 22mm Euro BB Conversion
Many Bullseye crank owners have machined 0.2mm from their axle in order to run a 22mm Euro BB. These bottom brackets are intended for BMX use and they are ideal for mountain bike use too. Unlike bottom bracket solutions (above), the Euro BB is seated within the bottom bracket shell and looks similar to an original Bullseye bottom bracket. And as 22mm BB’s are readily available you are not going to have a problem finding one.

22.2mm Bullseye Euro Bottom Bracket
The Bullseye Euro bottom bracket appeared in 2009 to the delight of 2nd generation Bullseye crank owners everywhere… and disappeared soon after. Not that it is a huge loss as the solution was nothing more than a Bullseye version of a Shimano Hollowtech II bottom bracket with their own 1.8mm conversion shims. The bearings installed as standard were MR2437 measuring 24 x 37 x 7mm i.e. the same size as the 6805 2RS bearings installed on Hollowtech II cranks.

REPOP CRANKS

There was a lot of chatter in 2012 when NOS Bullseye cranks started appearing on ebay. The problem is that they didn’t look as if they had been stored for 30+ years… and they weren’t. They were repop cranks newly produced by Bullseye and sold as NOS. This behaviour wasn’t limited to cranks either… but the subject is way too big for this page.