Boyesen link Honda CR500

Found a few at Thumpertalk:

http://www.thumpertalk.com/topic/1141707-anyone-remember-the-boyesen-li…

Here ye go

Is it a gimmick or would it be worth trying to replicate on a project bike?

No, not a gimmick - all reports on it , it did it's designed task of minimizing / eliminating drive train and braking forces from the rear suspension.

But, with even a cursory look, you can see the added complication / parts = expense of such a design. And that, is the killer hit to such engineering being taken up by manufacturers. That, and the "Not Designed Here" ethos most large companies have with regard to 'others' designs. Eyvind Boyesen had quite a few patents, some of which he Did sell / get royalties from major manufacturers, but not the Boyesen Link.

You've got a picture as your avatar of Roger DeCoster on the original Ribi Quadrilateral forked RN500 - so I assume you appreciate 'different' engineering approaches. As you'd know, Honda did buy the rights to that, and went further with it, but just think of the expense of building the single shock, aluminium version last seen (just recently another bloke on this site put another nice picture up of it) from Honda. At a conservative estimate, that has at least 18 pivot points, and however many individual seals and bearings. Imagine keep track of all of those parts / pivot points, when the average bloke doesn't attend to telescopic fork maintenance with diligence, or maintain their rear linkage as it should be maintained. A Telescopic fork is an engineering abomination, but hell, they work very well, after all these years.

Making a Boyesen Link rear end? - well, if you are an accomplished fabricator, and can contend with the maths / geometric intricacies of it, go ahead. I've an (American) acquaintance that, purportedly had access to a Boyesen Link bike, who intended to copy it, but I've not heard a 'peep' from him on it's progress, for a while now.. I suspect he might have finally cottoned on to it not being a simple / easy thing to do. But, I do hope to one day, suddenly get an Email from him showing his finished project

I used a far simpler device on my 500 - the AMP Torque Eliminator - for many years - well, up until only a few months ago. So I have been a 'fan' of Chain Torque reduction. It worked well, but, like all things, it had it's advantages, it had it's disadvantages . All 'things' do. I've finally weaned myself off it now - it was noisy, old (I was getting quite fearful of the idler sprockets shattering) and, added weight. It is / was Fantastic for controlling a 500s rear end in the terrain I ride in under acceleration, but problematic with not being able to use the chain torque for 'boosting' over things. Even an old 'sit down' rider likes to clear things with a blap of the throttle - the lack of chain torque made it a bit 'different' to do so. It's taken me a while to re-adapt to a 'normal' rear end Though, that 'normal' rear end, is a PDS / Ohlins TTX conversion on the 500.

Adding cost or complexity of design cant be used as an argument. We might have thought that in 1997 about manufacturers building a racing 4 stroke engine.

Cost from the complexity - simple as that.

Four Strokes? There was a rule that the Japanese finally cottoned onto that allowed far higher capacity 4Ts to be raced against 2Ts.- well, at least in the US. Husaberg had done very well, before 98, in an equivalency class racing era.

The major factories had Superbike / Sports Bike engines so far in advance of the XR /TT/ DR level engines they had at the time, that they easily transferred that tech from. Hell, even the latest 4T dirt bike engines are far behind production Superbike / Sports Bike engines in tech and innovation. Everyone's having kittens about the slight stacking of the KTM gearboxes - most Superbikes/ Sports Bike have had properly stacked gearboxes for well over a decade. .And that's just the tip of the iceberg in how basic our latest 4ts are compared to them.

There's a strong, and valid arguement, that the concentration of 4t only development by the majority of manufacturers, presented a significant savings for them over having 2t development 'streams. being run at the same time. Yamaha have remained the same for well over a decade in terms of the 2 2t units they make, KTM sucked dry their 2 engine units for near 2 decades with relatively minimal change, to finally, bring out the 2 new 2t units they have now. Bravo to them for that, but it's been a long time waiting.

Perhaps if there were rules at the time of the Boyesen Link , that held back , well, regressed suspension in the rear to non gas charged , twinshock designs, and with Forks ( in the case of something like the Ribi Quadrilateral) to 35 /38mm damper rod designs, both the Boyesen Link Rear end, and, things like the Ribi Quadrilateral would be with us now. It's a pretty valid comparison to the allowing of 250fs up against 125 2ts, and 540fs, then 450fs up against 2502ts.

Don't ever get me wrong - the Boyesen Link rear end was undoubtedly very, Very good, but more expensive than what manufacturers had then, and, well, even now. Here's an example for you with my own production experience : frames I made in the early / mid 90s, where I used Rose Jointed Rod Ends at a key pivot point, to have easy / fine adjustability. The only units that could take the loads, and last well, were $200 a pair, at my cost. It was a serious cost of production for me, and, when a few drongos fitted the readily available rod ends that cost around $20 a pair, despite specific warnings not to do so, they broke, destroying frames / swingarms / shocks. The wankers, of course, tried screaming 'warranty; at me. They sure as hell didn't get it. I went to solid mounts, that saved me a lot of money, made the final product lower in price, whilst I increased my profit margin.

Thank you to ted722 and vmx3 for putting up the link and pictures of Jo Jo Kellers CR500 - great to see it still exists.

It's 2.30am here in OZ, after a Long day of machining and welding, I'm off to bed.

If someone else has not gone into it in the next few days, I might go into it.

But, really, it's not hard to see what is going on. 

Effectively, a 'floating' swingarm main pivot, that, through the various arcs, would / could / may maintain a consistent main SA pivot to Countershaft relationship, to keep chain torque effects on the suspension in check / consistent / non existent. Depending on what the designer did with the geometries. 

Look to the lowest horizontal link - that attaches to a bell crank ( though, I might have missed another link or 'bar')  that drives the shock. Much like a 'normal' pull rod that is hard affixed to a std frame.

But, that link / arm,  besides pivoting on the main frame, is connected to that travelling upright, with the other horizontal link above, with the swingarm pivot attached to that upright, so, thus the 'floating' main swingarm pivot. 

It's a "6 Bar" suspension design - as against the "2 Bar" rear end on the twin shock Husky pictured beside JoJo's CR500.

There are so many permutations to what you could do with pivot points, 'bar' lengths, Arcs, you could produce a wonder, or, a nightmare.

Well, I guess I "went into it". Though, far from thoroughly - no doubt someone will have a go at / dispute what I've written.

At the 1986 250GP at UnaF**k'ndilla, Bob Hannah rode a Suzuki RM250 with a Boyesen rear end, to win the event.  You can find a short MXA article by Jody from October 15, 2021 that shows 2 pictures of  Bobs bike. And, pictures of another 2 variations of it. All were Very different to the one on JoJo's CR.

And now, I'm off to bed.