Derbi Day

Today was a busy day getting all my derbi junk together.

Tony hooked it up with pretty much all the plastics, controls and other bits from the revolution, the complete revolution motor (which someone managed to strip in one of the swingarm bolts and cut off the head, extracted it wrong and drilled a new hole at an angle to hold it together, wonderful!), the revolution wheels with new 2.75 Pirelli ML75, Rev. shocks, the messy pyramid reed motor (missing clutch, variator, cylinder and head), and a ducati cdi stator and flywheel. Oh yea, also a spare new revolution crankshaft. So yea, quite the collection.

First order of business was comparing fitment of the revolution motor in the c5 frame. Obviously its going to take some work but its not too far. A fellow down in the LA area put a Flat-reed motor on his rd50 (same frame) and basically had to modify the kickstand/motor holder and add an upper bar to support the upper/front bolts on the case. I’ll be doing much of the same. The rear holes in the mount will need to be slightly modified but beyond that it should all fit very well.

Here is the frame with the original piston port and another with the start motor. Kickstart lines up perfectly!

To keep everything simple to work on I will have to drill out the stud holes in the cylinder and head to fit the funny c5 mini-studs and bolts. All easy. Much of this will be on hold until school is up in may. So yea, just getting excited about what is to come.

To keep things complicated I’m going to be putting together another derbi with the help of Matt who has a really spiffy green Variant frame. We are going to build it mostly as a loaner for friends or us when all our stuff is broken. The setup will be simple, piston port bottom, stock cylinder bored out to 60cc, homeot 4p, milled flat reed head, tjt, malossi clutch springs, 20×30 gearing, 19phbg, revolution mags, and so on.

Tom had this cylinder on his Variant a few years ago and hit a hair under 50 with an estoril with a janky header. So optimized it ought to be a pretty rad bike that is decently reliable and quick. I’m going to try and get most of it together tomorrow, but I gotta switch a water pump on the diesel first.

Lastly, here is the nasty pyramid reed. Crank actually turns pretty well but it sure is crusty.


2 Comments so far
Leave a comment

What piston do you get for a overbore derbi pp cylinder? Weisco?

Comment by Responsible Jon

i wanna say that is correct but I’m not sure. There were no markings on the piston, lame. The cylinder was bored out to 60cc.

Comment by zack

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