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Suggestions when buiding a conversion

Posted: Sun Feb 06, 2022 12:04 pm
by vechorik1373
I built myself a conversion side car rig 10 years or so ago. This wasn't the first conversion that I built, but this is the last one that I will ever put together. The idea was, when I got too old to ride a solo bike, I would have something that would run down the interstate at highway speeds, and there would be no danger of dropping the bike because I could no longer center stand a BMW.

Anyway, here is some of the things that I did, that I want to pass on to anyone that is interested in building a conversion, that make life easier. You may, or may not want to do all of this, but this is what I did. For reasons unknown to me, the photo rotated when I attached it. When you click on the photos they turn right-side up.

1. I welded on tabs to the frame, between he backbone tube and the lower tube so I cold mount the dual lead Dyna coil solidly to the frame. I drilled two holes, on each side , at the top of the timing gear cover, where the engine harness entered the engine, and used plug wire grommets from a /2 in the cover. I then routed the plug wires along sides of the starter, and drilled two more holes, and used two more /2 grommets, to bring the plug wires out through the engine case, as you can see. I did this, so there would be no danger of the plug wires being pinched between the frame and the gas tank. It made a very clean installation.

2. Because there is virtually no room for the rubber air scoop on top of the starter cover, I cut out of 1/4 thick rubber, a blanking off "grommet". I cut it out, approximately 1/4 of an inch larger than the actual hole, and cut a slit all the way around the perimeter, so it would pop into the hole. I drilled LOTS of holes in the back of both filter box covers, (like an R90S has) so the engine could breathe through those holes.

3. I welded a plate to the upper backbone of the frame, to mount the solid state voltage regulator. and starter relay, as you can see. The Dyna III ignition brains are mounted to the lower frame member.

4. You can see on the down tubes of the Earles Fork, that I carefully removed the curved brace and re welded it to the down tubes (If your going to do this, have the swing arm mounted in place before you weld the brace back on!)

Just to be different, I Used R12 bar end levers, ( I had to reduce the diameter of the part that goes up into the handlebars, to get them to fit, because these bars are 22mm and prewar bars are 25 mm) Of course, doing this also required drilling holes in the handlebars to bring the clutch a brake cables out of the handles bars, just like an R12.
I converted the R12 spark advance lever into a choke for the Delorto R90S carbs. I used a throttle cable splitter from a later BMW to make the connection to the choke slides. Since I'm old, and don't like low bars anymore , I used handlebar risers for a R25/2 and made spacers out of stainless steel on the lathe, and polished them to look like chrome. This brought the side car bars up higher, which made it more comfortable to me.

This bike has a 1973 R75/5 engine, and a 4 speed gearbox, with later 1984 only 900 cc /6 heads, cylinders, and pistons. I made out of aluminum, on the lathe, two internally tapered intake manifolds, that I heat shrunk on the inlet spigots of the /6 heads, in order to mount the 38 mm R90S carbs to the 32 mm intake ports.

Because I wanted a backup method of starting the bike, I removed the "T" shaped /5 kick start lever, and replaced it with a Stainless Steel /2 kick start lever. The /5 lever would hit the foot peg, reducing the travel but the /2 lever clears the foot peg, so you get a complete stroke when using it.

I used /6 Stainless steel header pipes, so I could cut the off the turn up at the end, and weld in tubing to make the pipes go straight back, and used R69S mufflers so they would mount in the "correct" position.
I used a stock /5 headlight bucket, in the stock /2 fork ears, and when I had the /5 speedo restored, I had them calibrate it to a solo 25/8 slash 2 rear end. And the speedo is accurate! And it has the tachometer built in.

I used a later /7 deep sump oil pan, and used a passive Breil oil cooler between the pan and block, so I have a 4 1/2 quart oil capacity. I installed a VDO oil temp sending unit into the back of the Breil oil cooler and mounted the temp gauge in a home made brass "can" mounted on the handle bars.

The side car that I used is a repop Steib S500. I converted the running lights in the Cobra handle into directional lights, added a Eber tail/brake light to the rear of the fender, and added an automotive Hella driving light to the frame in front of the fender. I wired it using a relay, so when I flip the lights to high beam the driving light comes on. Not shown in the photos, in order to add all this extra wiring, and to add interior lights in the nose and trunk of the side car, and mount a GPS on the upper sidecar attachment arm, I used a military Amphol waterproof, panel mount connector with multiple pins for all these extra circuits. That is mounted in a plate, welded on the frame, just behind the rear upper s/c mount on the frame.

Do you like my "naked Lady" cast bronze valve covers? :lol:

Re: Suggestions when buiding a conversion

Posted: Mon Feb 14, 2022 3:18 pm
by olebmw
Thanks for the suggestions and posting the pictures. I've been thinking for some time about building another conv.
and correcting all the mistakes I made the first time and put the original matching # engine back in the donor frame.