Beginning in about 1981, Boyesen Engineering began developing prototype linkage systems for motocross bikes with the idea of eliminating "Chain Torque" and during the subsequent years, there was an enormous amount of testing and fabrication which was performed on each of the major manufacturers dirt bikes.
After the bulk of this testing concluded with the major brands which included Honda, Yamaha, Kawasaki, Suzuki and KTM, Bob Hannah climbed aboard and rode a production based model Suzuki RM 250 equipped with the "Boyesen Link" designed to eliminate chain torque to a victorious win at the USGP held at Unadilla Motorsports in 1986.
Incredibly enough, we were able to spot Hurricane Hannah's former link bike as these bikes were also referred to as, which was on display at a Florida Vintage Motocross (FLVMX) race which we were attending, as it was brought out by one of the founders of the "Legends and Heroes of Motocross" tour which is traveling the country and happened to be at Lake City Motocross (LCMX) in Lake City Florida while we were attending, at which time we were able to take some pictures of this, and that combined with the excellent assistance we received from Dag Boyesen of Boyesen Engineering, we are able to present Bob Hannah's former race winning link bike to you with some details that you should find interesting.
Combined with the Notes Below, The Following Picture will give you an idea of how exotic this "Production Based" link bike that Bob Hannah Rode to Victory in the 1986 USGP at Unadilla Motorsports was.
Referencing the numbered items above, the following information should prove enlightening with even more information surrounding the bike below the numbered list.
- Focusing on the area which is somewhat under the carburetor, you'll see where the engine cases were extensively modified to provide a location for the linkage arm to mount, as well as you should note that there were additional mounts added to the frame in this area as part of the upper linkage mounting arrangement.
- This shock absorber (damper) was modified in ways such as changing the length and valving to accommodate and work properly in unison with the Boyesen Link system which Bob Hannah rode to a victory in 1986 at the USGP at Unadilla.
- Shows the bottom supporting section of the sub-frame where it was originally non-removable on a stock 1986 RM 250 but the folks at Boyesen modified the sub-frame of this bike as well so as to allow removal of the sub-frame for easier servicing of the bike.
- This illustrates where the swingarm of the 1986 RM250 was modified for fitment of the Boyesen Link.
- Here you can see the heart of the Boyesen Link system and upon closer inspection you can see some of the truly impressive custom fabrication which can be seen in the welds and overall construction of the unit and can also be seen clearly in the right side picture of this setup.
- Shows the very bottom mounting area of the Boyesen Link linkage used on Bob Hannah's 1986 USGP winning machine and the picture above clearly shows where there was some serious fabrication work performed as you can see just by where the bottom frame rail was cut and modified extensively to create a necessary pivot point for the Boyesen Link to attach.
In addition to the points outlined above, you'll likely also notice what you should recognize as the Boyesen "RAD Valve" but what was most interesting about this particular unit was that in 1986 the "RAD Valve" had not yet been placed into production, and this unit was a hand made piece built specifically for Bob Hannah's RM 250 which he piloted to victory at the 1986 USGP at Unadilla ahead of Johnny O' Mara after what has been rumored of Bob Hannah pushing the O' Show so hard that the "Hurricane" caused O' Mara to run out of gas on the last lap handing the win to Bob Hannah aboard this RM 250.
Now considering all the modifications to this bike you may be left wondering how this bike could be referred to as a "Production Bike" and we wondered the same thing, so we asked Dag Boyesen at Boyesen Engineering and after posing the question of: We've heard talk about Bob Hannah winning on this bike and that he was the only one to win a USGP on a "Production" bike, but is that accurate? Is a bike considered "Production" with an exotic rear suspension such as that? At which Dag Boyesen commented: "I would say that it was a production based bike. Started as a stock RM250, bought from a dealership and modified."
Then we just wanted to find out directly from the people who designed this setup what the true benefits of using this setup were, so again, we went back to Dag Boyesen and asked him: Could you tell us the benefit(s) of this setup? We heard it was something to do with constant chain tension but are not certain on that. At which Dag Boyesen Replied: " The system eliminated chain torque. The chain could be set with tension because the distance between the countershaft and rear axle never changed. In stock form the shock dampening had to be firm enough to offset the chain torque. The Boyesen Link eliminates the "squatting" from the chain torque and allows for much improved traction and feel over acceleration bumps."
And finally... We wondered why this was discontinued: So, Again we asked Dag Boyesen; Why was it abandoned? At Which Dag Boyesen replied: " All major manufacturers tested the system and saw and acknowledged the benefits. The cost to retool and manufacture this is what was always the negative from the decision makers."
And with that the rest is history but you may enjoy some of these pictures of Bob Hannah's former Unadilla USGP winning bike...
Additional Pictures of Bob Hannah's 1986 Unadilla USGP Winning Machine
Click Thumbnails to View Larger Image
From RH Side
If you're interested in more motocross history don't miss our brief introduction to the History of Motocross, followed by an excellent resource presented by the AMA motorcycle hall of fame.