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Discussion Starter · #1 · (Edited)
The bike I really admire and wanted is the BMW R51, which was based on the prewar model of the R5 - both are hard to find and even harder to pay for:(.
I scaled a drawing (photo) from the web and thought about how to convert my in pieces on the garage floor CX500D to something similar or as closed as possible.
Here is the drawing I used.
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I agonized for a long time over the conversion of a CX500 frame to a rear plunger suspension or something look a like.
Made countless card board mock ups of frame tubing as below.
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....and came to the conclusion, using the existing frame with shorter shocks would be best for me.

Here is the project in it's present stage.
I am hoping to end up with a vintage style bike may be with 40's like appearance (BMW..like).
Lots of modifications have been done so I fully expect a few problems. Land vehicle Motorcycle Vehicle Motor vehicle Automotive tire
 

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I like it, you are headed in the right direction.
Tell us about the front brake and the spoke wheels.
How about springer front forks?? Too much vintage style??.
 

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Discussion Starter · #4 · (Edited)
I like it, you are headed in the right direction.
Tell us about the front brake and the spoke wheels.
How about springer front forks?? Too much vintage style??.
Thanks, I considered a springer front end.
However, the involved modifications and cost would have been a bit too much for me.

The front wheel is from a 1972 CB350. The forks are 1972 CL350. Bought these parts on eBay for almost free.
The CB/ CL350 have the same fork tube diameter, wall thickness and spacing as the CX500. The forks are shorter but work since I lowered the bike anyway.
There is still sufficient travel - travel is not limited.

I refinished everything and used new fork tubes, springs and a short spacer to stiffen the front end a bit.
The wheel (18") received a new rim and new spokes. This was my first attempt on spoking a wheel.

My bike will be a lot lighter than stock and not that much heavier compared to a stock CB350.
Expecting a bit of tuning will be required.
 

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The drum brake has double cams, I think.

I hope it has the same "negative accelerating power" as a hydraulic brake with one rotor.

I recommend for the bowden control cable the thickness minimum 2,5mm.


Never drive faster than your guardian angel can fly. ;)
 

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Discussion Starter · #8 · (Edited)
The frame was cut just behind the upper shock attach points. The square frame tubes were closed using welded on steel plates and small fender mount extensions were welded on. I fabricated all these parts from mild steel.
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Decided to use a vintage BMW seat replica which I found on ebay.
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Fabricated the seat and seat spring mounting tubes and gussets from mild steel and had them welded to the frame. Here are a few pictures.
Used a file and a grinder to make these parts... wished I had a mill.
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Discussion Starter · #9 · (Edited)
Picture shows the rear seat spring mount being fitted to the frame.
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Fabricated the forward seat frame post (hinge point for the seat) and got it welded to the frame. It required a bit of time to get all the tube ends shaped to fit.
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The cross members should stiffen the frame enough to substitute for the missing frame parts.
Made a couple weld on gussets for rear fender mounting.
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Discussion Starter · #10 ·
Here is another view at the forward seat post. Could have probably used lighter tubing, but...that's what I had in the garage that day:D.
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Discussion Starter · #11 · (Edited)
Picture shows the rear fender mount frame extensions and the fender fit up with wood spacers on the rear wheel.
Fender is high enough to allow for full wheel travel.
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Discussion Starter · #12 ·
I spend a lot of time looking for a tank and finally decided on a 1998 VT1100 Honda tank that was for sale.
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The tank required new mounting provisions. Fabricated a forward mount post that was welded to the top of the frame tube.
The rear mount was integrated into the forward seat post. This is hard to see in the picture.
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Discussion Starter · #13 · (Edited)
Frame parts were blasted and powder coated at a local shop.
They did nice work.
Machine
Here is everything back. The kickstand won't be used since I lowered the bike.
 

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Discussion Starter · #14 · (Edited)
Found out that mounting the frame to the motor is a lot easier than mounting the motor to a roller frame. I could balance the frame with one hand and insert the bolts with the other hand - didn't even scratch it.:D
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By the way, don't forget to mount the coolant bottle first, it is hard to do with the motor installed.....
 

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Discussion Starter · #15 · (Edited)
Changed the steering stem bearings to tapered roller bearings. This is the second bike I have done this on and it was a lot quicker this time. The kit came with a thick and a thin spacer washer. However, I found a couple machining washers at a local hardware store that worked better and assured near full thread engagement on the top.
Used a couple O-rings on the top to form a dust cover. The dust cover on the bottom had to be opened up in the center to fit.
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Discussion Starter · #16 · (Edited)
I am going for the vintage look so I "needed" a mechanical drum brake setup for the front wheel. Doing some research, I found the CB/CL350's were made for a few years with drum brakes and used the same fork diameter and spacing. The forks are shorter, which will be helpful in lowering the bike in the front. I use shorter shocks in the rear. Found a CB/CL front wheel hub and forks on eBay.
Here are the parts ready for primer after cleaning and sanding.
 

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Discussion Starter · #17 · (Edited)
Next was spoking the hub to a new 18" rim. I am going with 18" in front and rear.
I have never spoked a wheel. Build a stand from some scrap wood an followed instructions from the world wide web.
Turned out to be easy after I got the spokes in the correct pattern on attempt two.
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Got it near round and true:D.
Mounted the tire the good old way by hand using tire irons. Could have had it done but not that night.
Here is my home made tire mounting stand- a board with a hole for the axle.
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Here is the finished wheel after mounting the vintage style Heidenau tire.
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Discussion Starter · #18 · (Edited)
Next was rebuilding the CB forks. Used new fork tubes, seals and aftermarket aluminum top fork nuts. Wasn't able to find stronger springs, so I used the stock springs with a short spacer. This is a bit of a gamble and might need final adjustment when driving.
The fork lowers were polished. Here are the forks as received with badly corroded fork tubes.
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Short PVC spacer as installed.
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and here is everything installed.
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Discussion Starter · #19 · (Edited)
Tank received welded on mounting gussets for rubber knee pads 1950's BMW style. I had to hand form these a bit to match the tank contour.
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I like the rubber knee pads:D.
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Really nice work....is that the bike you needed the engine for?

VC3
 
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