BMW Restore 01

Written by Ron Roberts  |  Category: Cycles
 |  Hits: 3303  | Sunday, 02 February 2014 03:42

 Rebuilding the BMW Motorcycle

bmwframe13This is what I started with.   Actually, the bike was not in bad shape, and looking at it just sitting there you might be tempted to buy it without riding it, thinking it was in good shape for a used bike.  May I suggest that if you are looking to buy a used bike -- any used bike -- first make sure all of its features and functions work properly, and then take a test ride for several miles, not just around the block, to help you get a better idea of its condition and whether the asking price is inflated.

After a test ride of a few miles, I determined this bike had a few minor problems, but nothing I couldn't fix.   The motor needed some work, and there appeared to be some electrical work necessary as well, but those things, in themselves, were not enough to rule out this bike being a good buy -- it just meant that I knew some work needed doing, and that I needed to keep that in mind while negotiating the price.

After the deal was done I brought the the bike home, did a little work on it, and began riding it to sort out anything else that needed doing.  I thought those cylinders sticking out each side were ugly -- and I still do -- but after riding it awhile and realizing how comfortable it was compared to the Intercepter I had been riding, I just had to keep it.  I thought if I added a fairing it might help the looks of those ugly cylinders so I installed a Luftmeister fairing.  Wow!  After riding it a couple of months with the fairing I found it was great (especially in the Winter) but what I thought might be an alignment problem kept nagging at me, and I also noticed some cracks in the welds of the frame.   In the back of my mind, I was thinking more along the lines of a complete restoration so I would be comfortable taking this bike on some extended trips.    Believe me, you don't want to discover some drastic problem when you are a thousand miles from home;  Plus, I had thought about the possibility of a sidecar.    bmwframe1

I determined to first find the nagging alignment issue and go from there.   Sure enough, after inserting a five foot long pipe into the steering head to amplify any indication of a twist, I found the steering head was out of alignment and evidence of possible structural trouble with the cracked welds.   I straightened the steering head by using the five foot long pipe as a lever to pull the head into alignment then welded the cracks.  After it cooled and with all tension off there was still a very slight error, so I drilled a small hole in the opposite side downtube and welded it up so as it cooled it shrunk just enough to finish pulling the head into perfect alignment!   But after finding the cracked welds, I decided to completely tear the bike down and do a complete rebuild.  The cracked welds could have been due to age or possibly the bike had crashed in an accident at some point, and if so I wanted to fix all of the damage.  This photo is a close-up of the upper portion of the main frame showing new welds.  The serial number has been blacked out for privacy.  

Once the bike was completely dissassembled, I spent some time carefully looking at each part to check its integrity and alignment.  In this case I straightened the frame and ground out all old, cracked welds and rewelded all joints that were suspect.      

bmwframe2A common failure on the BMW /5 bikes is stripped threads on the center stand mounting bosses, and this bike was no exception.     I welded up the holes, then re-drilled and tapped them.  

In the left photo you see the main frame mounted on the lift with the sub-frame on the floor to the right.   

While I had the opportunity, I welded new bungs into the downtubes to accomodate bolting on a Luftmeister fairing support, which does away with the stock "hose clamp" type of mounting system.  

Much more firm and stable and a much more classy look as well!  

bmwframe3Here we have the sub-frame attached to the main frame, with the frame now in alignment, straight and true.  

All parts have been cleaned, sanded and are ready for priming and painting. 

After priming, I intend to spray it with several coats of gloss black, the original frame color, so it will look like new.  The finish color for the fenders, tank and other body parts will be the original maroon. 

But the important thing is not that once painted it will look like a new bike --  everyone will be able to see it's an old bike!   No, the most important thing is that the bike is going to be dependable, and it's going to be safe!  

bmwframe4I will be able to ride it any place I choose, near or far, and not have to worry about stability or structural failure.  Plus it will ride smoother, be easy to control and not "wear you out" in three or four hours.  

As you can see in this photo, the Main and Sub Frame (removed from Main Frame for painting) have been sanded, primed, washed, dried then painted.   

Notice the lack of paint on the coil mounts in the center of the top tube.   This is necessary for proper grounding of the coil.   As mentioned earlier, the gloss black color conforms to the original.   The Frame is now set aside and will wait for assembly after the other work is done.  

Remember, I said the motor needed some work?  Rather than just fix the symptoms I saw during the test ride, I decided to disassemble and thourghly inspect the inside of the motor as well.

bmwframe5I suspected either a burned piston or valve problem by the way the motor felt and sounded.   Sure enough I was right!

When tearing down and rebuilding any engine or motor, whether it be automobile, motorcycle, lawn mower, or whatever, one primary concern is cleanliness!   There have been too many instances where someone determined to "rebuild" an engine and was not careful about cleanliness.   The specific work was done properly, the correct parts were replaced and the "rebuild" completed.  But after awhile the engine again has trouble... maybe the same trouble or something different, and when disassembled foreign matter is found inside the engine.  

The motor has been cleaned and dis-assembly has begun.  But the area you are looking at is too filthy for an engine rebuild.   That will be undertaken in another part of my shop.

bmwframe6After moving to a different area I disassembled the engine.  The next few photos show some of the things I found.  

This photo shows the burned piston.   I did some preliminary cleaning in order to provide clear photographs, but the inside of this engine was pretty clean already.  After careful inspection and measuring, I determined I will not replace the piston rings as they are well within tolerance and show little wear.  

This piston, though, needs attention.  Besides the carbon build up, the seals on the push rods (which occupy the two holes to the left of the cylinder in this photo) need replacing and the piston needs to be cleaned, polished and inspected.

bmwframe7The photo on the right shows the cylinder head with the burned and "caked" valves in this engine.  

Extensive cleaning, lapping and polishing will be necessary.  You can also see evidence of a leaking gasket around some the passages and bolt holes in the top portion of this picture.

Pay attention to the center portion of this photo.  Of course, it becomes the top of the firing chamber in this cylinder, so obviously, there is a tremendous amount of heat generated when the fuel in the chamber is ignited.  You can easily see the "caking" on both the valves and the head itself.  

This needs to be addressed properly... not just a few swipes with a with a wire brush!

bmwframe8This photo is what I call a "half-way" photo.  There are some things done that you can't really see, but they were done.   Other things are partially done so as to show a "before and after" effect.  

For example:  You can't see the stem and valve seats in this photo, or that the top valve has been polished, checked for wear, and lapped to the seat after all cleaning and polishing.  But it was done.  

You can see that the valve on top has been cleaned and polished, and you can see that most of the "caking" has been removed from the area just to the right of the valves.  Before the job is complete, the head will be cleaned and polished and both valves will be completely cleaned, polished, inspected and lapped to the valve seats.   Then the entire head assembly will be thoroughly cleaned and kept for re-assembly after all else is done.

bmwframe9Another thing I noted on my test ride was that the starter did not always engage the flywheel properly.   Once the engine was dis-assembled, I saw why.  Certain areas on the flywheel had some teeth that had been knocked off or chipped.  Sometimes this can come from the starter being engaged while the motor is running!  

This photo shows some work done on the teeth of the flywheel where the starter engages.  The chipped or broken teeth were ground down to more readily accept the molten metal in the welding process.  

I used my wire welder to build up the damaged teeth, then carefully ground them to the proper size and shape with a small air-powered grinding wheel.   This is a tedious task, and most folks might just replace the flywheel assembly, but I enjoy doing these little things and it saves money that can be spent on other things.

bmwframe10These next photos are of the burned, scorched and scratched clutch parts.  When the clutch is bad the symptoms vary, but generally are poor acceleration due to the clutch slipping, rough gear changes when going either up or down through the gears, an odor that smells like burned bakelite, etc.   The sad thing is, in most instances, this is caused by the rider.  Letting the clutch hold you on a hill, or holding a slight pressure on the clutch lever while riding.  

The only solution for these problems is to either repair or replace the clutch assembly.  If either or both of the clutch plates are badly worn, the only solution is to replace them.  But in this instance the plates were not worn -- they were burned.  Replacement was not necessary, but repair was.  The second photo (below left) is really just a closer view of the burned plate.

bmwframe11bmwframe12You can see the scorched areas where there was slippage and overheating.  Fortunately, the plate did not warp, which could happen if it were to get too hot.  The photo on the right shows the same clutch plate still mounted on my lathe after it has been resurfaced.  Now that will work!  There were other minor repairs done, and a complete re-wiring of some parts of the wiring harness to eliminate the electrical problems, but all that remain now is a careful cleaning and re-assembly.  

completescbmwrearvwOnce all of the reassembly and painting was done I installed a few accesories, designed and built the side-car shown (see other build articles) and this is what you get!

The bike is exceptionally smooth and comfortable along with being reliable and safe.  Not bad at all!    

 

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Jon Roberts --- jdr@jdrsvp.com

 

 

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