1 reply [Last post]
spuds's picture
Joined: 11/17/2016
Posts: 1


Will not open by saying I've been lurking here for ages, 'cuz I haven't.

Kinda caught the "fix up that old bike" bug over the past year when I bought an early 70's Suzuki 500 cc 2 stroke, that I build into a not-bad-looking (if I say so myself...) "garage-built" cafe racer, using just the skills and basic tools I had.

Had always thought too of having an older boxer twin based cafe bike too. A couple of weeks ago I picked up a mid 70's empty R /5-/6 frame. It needs to be cleaned up a bit, but it appears solid. The more "sane" approach would likely to have found a more complete "barn find" bike and go from there, but what matters most to me in the build is to end up with something built around that boxer engine. So, tacking on (for example) different forks, tank, solo seat, clipons/rearsets, electrics etc would be totally OK---and for $80 for a frame, why not grab it and potentially use it as a starting point?

That all said, and as I also passively keep a bit of an eye out for an alternative starting point, .......Help!!!!!!!! Questions 1 and 2 of a thousand:

1. With the frame's VIN, my local dealer identified it as suitable for anything from an R60/5 to a R90/6 engine. Would love to use an early 70's airhead if I could find one, but there are also good reasons to look for something perhaps newer too. Without getting into all kinds of crazy fabrication/modification - are there other boxer engines that will bolt right into that /5-/6 frame?

2. IF not (and that would be totally OK!)----can a slightly later rear mag wheel (either the cast 3 spoke or the 4 spoke "Y" rim) be made to work somehow with any /5 or /6 generation motors (---without going to the moon and back!!)? Would it be a matter of cobbling together driveshaft/swingarm bits to make the transition? Is it even possible?

Many, many thanks

khittner's picture
VBMWMO #8223
Joined: 02/15/2012
Posts: 371
So, I'm guessing that your

So, I'm guessing that your "mid-70s /5-/6 frame" must be either a /6 or a later, long-wheelbase /5 frame. I think that any 600, 750,800, 900, or 1000cc airhead engine made up until the end of airhead production will fit in that frame without customization. I'd be less confident in a 450 or 650cc engine from the R45 (exceeding rare in the U.S.) or the R65 being a drop-in fit, but someone who knows those engines better than I may say that they do.

BMW's 3-spoke cast wheels were used on the later monoshock K-bikes. The 4-spoke airhead "Y" rims (rear wheels, anyway) were made for use on the later ('85-'95) monoshock airheads. Neither of these types of cast rear wheels were designed for the earlier twin-shock final drive units, swingarms, or frames. To go to a monoshock on the back, with the frame you have in hand, will take some fabrication of a shock mount on the right side of the main frame hoop, as well as sourcing a monoshock swingarm and final drive. Others have asked about this surgery; I don't know what their outcomes have been.



Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.