The Cafe Racer Project

Im getting ready to head off to Africa and so I've been finishing off a couple of Projects that have been "on the back burner". The big one is the Café-Racer motorbike restoration/renovation.

The bike is a 1972 BMW R75.
I had left it with my machinist friend Mark for the winter so that he could do a suspension modification and a couple of other minor fixes over the winter whenever he got the time... And he has now completed the work and last weekend I went out to his place and collected the bike

First thing to do of course is to check out the changes to the bike... Mark is always so professional in his work that I hardly need to worry about the quality or soundness of design but he often modifies the way a "fix" is built compared to how I might have described my desires.... Its always for good reasons and this time its no exception... he called me a while back to discuss some slight changes and we agree over the phone on alternate solutions, but this is the fist time I get to see what the end product of his labours looks like.

... and I have to say I think it looks very nice :)

So here are a couple of pictures of the "work in progress":

The rear suspension "brace/stirrup" while being fabricated

The gear shift linkage (had to modify it so it would not get hit by the kick-start pedal.

This is how the new rear shock installation looks now that its completed.And here is what the finished bike now looks like with the "mono-shock" rear suspension:

 

Now the rear-end of the bike looks nice and clean... like a racer should :)

So the bike now looks just how I wanted it to and there is virtually nothing else I would do to it.
But there is a bit of a hitch with that new rear suspension in that it is excessively "stiff".
Now I thought Id figured out a design and chosen a shock absorber that should mean this would not have been a problem, but it turned out during the build that I had overlooked a critical factor... Mark figured it out and told me what was going on and we have a solution but Im yet to fix it.
The problem is that the old suspension had only three inches of travel in it... The replacement shock I found was in a "direct" suspension application without the usual rear suspension linkage that complicates things, and was on a bike of approximately the same size ( a Kawasaki Ninja 650r) so I thought I would be OK... but, the Kawasaki had a rear suspension travel of about 5 inches...

Now because of that, in order to make the shock work over its full range of travel without having the BMW's rear suspension travel increased (which would likely play havoc with the rear drive-shaft gears), Mark had to adjust the "angles" of the build...
The net result of it all is that the new rear suspension is overly stiff... And the best solution seems to be to change the shock spring for one of about 2/3 of the stiffness (its that 3" to 5" ratio from the differences in the suspension travel).
So, I will need to source a new rear spring, but that can wait till I get back from Africa I think.
In the mean time Im really happy with my motorbike and don't plan to do any other modifications too it any time soon :)

Thanks Mark for another great job on the fabrication work :))