Category Archives: BMW R75/5 rebuild

BMW Black Gold – Update

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Well, the bike runs thanks to the help of a local BMW genius.
But it wasn’t without a bunch more setbacks.
After an hour or so of scratching our heads, we found out that the starter relay was bad. I had a real old ratty one to replace it with and despite all the rust, it worked.
The rear set bracket I made was pinching a bit and made shifting really tight. We had to make a new shift rod. We actually made one out of a R65 pushrod.
The front forks were really stiff which ended up being due to the high weight fork oil. I drained and checked for stiction, then added lighter oil and all is well.

I took it for a break-in ride and it rides and sounds amazing.
After the break in though, the idle was not setting properly. The old /5 carbs were nasty and saw a bit too much action in their day… and i think despite the rebuild, there is nothing you can do with worn parts.
I’ll be replacing the carbs soon so fingers crossed she’ll run a bit smoother. I hope to have it dialed in this weekend.

I still have some finishing touches to do as well. Almost to the finish line. Almost.

Here’s $60 of BMW’s texas tea:
Oil

Crankcase breather

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I had to put on my plumbing hat for this job.

I started by building a bracket to hold a breather filter above the transmission.

bracket

I then scoured my garage for all sorts of tubes, hose, fittings etc…
I was able to piece together a connection that ran from the crankcase breather outlet to the filter.
initialplumbing

Unfortunately, the angle of the crankcase breather outlet aims outwards towards the right side of the engine. I test fitted the custom starter cover before I added all the hoses but once the hoses were added, the starter cover wouldn’t fit. I tried shaving down the edge of the hose but it wasn’t going to work due to the angle of the breather. If I forced everything together, after time, the vibration of the the parts would have damaged the fiberglass starter cover.

Luckily, there is a later model breather that has the exact same footprint but the outlet aims upward. Uprightbreather

Then it was just a matter of connecting new hoses.
newSpout

I cut down a new BMW crankcase breather hose meant for this style breather.
I also made a trip to my local hardware store and found a brass elbow fitting to connect with the filter.

plumbing

I had a small tray fabricated out of aluminum. I placed it under the filter and connected it to the top of the transmission using the original air filter retaining bracket’s bolt hole.

I don’t anticipate any oil coming from the crankcase breather for many many many miles to come. But should the engine start to weep oil from the breather, it will get caught in the trough and not leak onto the transmission.
newPipes

It isn’t the prettiest plumbing job but it will work and luckily it will get covered up by the starter cover. If you want to get your plumbing work done then you must go for a professional plumber Toronto.

Exhaust hanger brackets made

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Fingers crossed this exhaust works. It is from a 1930’s R12 BMW. I had a larger inlet welded to mate with the R75 headers. I hope they do not restrict power in any way or make the tuning of the engine difficult.
The headers and mufflers connect OK and luckily the brackets on the mufflers line up pretty close to the exhaust hanger area on the R75/5 frame.
To connect the muffler to the frame, I had to make some custom brackets to attach the muffler.
I made a test set out of aluminum and everything worked out OK. My holes were slightly off but I corrected for that later.

aluminum

Here is the test fit.
testFit

I took my brackets and a pocket full of cash to a local welding and machine shop. He replicated my brackets with stainless steal and put the holes in the correct place as per my instructions.
Stainless steel should withstand the heat, elements and keep its shape. I worried that the aluminum brackets I made would not do any of the above.

stainless

Here is the bracket attached to the frame:
HangerHung

There isn’t much room to work with in there but with the right nuts and bolts, everything went to together just fine. HangerDone

One step closer to starting this baby up!

Gascap cork replacement

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Unfortunately, BMW only sells new chrome /5 style gascaps with the lock mechanism. I really like the smaller look of the non locking gascaps. I sourced a very good condition aluminum gas cap and unfortunately, the cork gasket is worn.

oldcork

Luckily, BMW does sell replacement gaskets. I happened to have one in my parts stash, brand new. What I needed to order was a new retaining pin and washer from BMW.
Removing the old one was difficult. I started by shaving the old pin head down with a dremel. By doing so, i was able to remove the old cork gasket and create a flat surface to align a drill bit to drill out the old pin.
disassembleCap

I then took the gas cap to my drill press and tried to center my drill-bit as best I could to drill out the old pin. Unfortunately, the drill bit took on the path of least resistance and did not center perfectly to drill out the old pin. And, the old pin’s metal was either extremely hard, or it got hardened from all the heat of the drill bits.
It was one of those jobs that took an hour longer then I had anticipated.
I eventually got it drilled out. Here it is with the new gasket, pin and washer:drilledout2

I used some JB weld in the old pin hole to fill the area where my drill bit went awry. I then drove in the new pin by tapping it down with a hammer.
She’s now ready for fuel.
Gascaplr

/5 BMW Speedometer Wiring

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Hopefully the following wiring photos can be of help to somebody.
I hope to add to this post once I am done.
Click on the photos for larger versions.

On my last /5 build, I adapted a /6 relay board to my /5. I cut off the terminals i did not need due to the simplicity (and less features) of a /5 vs /6. I also liked the idea of having the fuses easily accessible. Everything works great however in hind sight, I maybe went too far (did I complicate a simple /5 wiring scheme by adding the /6 board?) and perhaps I left the fuses too exposed where they could get knocked out. But I have over 3000k on the bike right now and no issues.
The gold resistors on the bottom of the headlight bucket are for the LED turn signals. Resistors are necessary to adapt the low current draw of the LED’s so the relays still work.
The large black box at the bottom is a /6 /7 and R100S style turn signal relay.
BlueWith6
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Here is my naked speedometer. I highly recommend painting the inside of the headlight bucket a bright color. It really helps for seeing inside there.
Labeled
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Here is the speedometer wired. It is hard to see some of the actual terminals/connections but this should be a nice short-cut for somebody who doesn’t want to read the wiring diagram.
Please note: My Red/Yellow wire going to the instrument lighting is also a gray/black wire in most wiring diagrams.
Wires
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UPDATEUPDATEUPDATE
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In hind sight, my /6 relay board wasn’t such a bad idea. I scoured electrical stores, auto stores and the internet for terminal relays and fuse blocks that would work for inside the headlight bucket.
I never really found the perfect solution. I was looking for a nice, compact 2 fuse relay. I also looked for a junction box that suited all the necessary connections.
I ended up using the terminal connector that came with the Rocky Point headlight key conversion (white junction on the right side of the photo).
I also used a CINCH 6 position terminal for wiring up the turn signals, brake light and other connections.

I decided to abandon the typical inline ceramic fuse holders that BMW supplies. The ceramic fuses aren’t readily available at your local auto parts store so I have planned to seek the help of experts from https://telluridetireandauto.com/. And I have also opted for something common like the rubber covered fuse holders carry a typical ATC fuses. BMW specifies an 8 AMP fuse. I went with a 7.5 and a 10 (because that is what i have in my garage). The 10 will be fine. The 7.5 vs 8 shouldn’t make a difference.

The Clymer manual did a great job for most of the wiring.
The other diagrams helped A LOT though. One diagram specified which wires connect to which pin on the turn signal flasher.
One thing that none of the diagrams specify is which terminal numbers on the relays connect to which wire. Yea, a bunch of wires plug into the starter relay, but which wires go to each pin/terminal?
Luckily I took a BUNCH of notes when I tore the bike apart. And luckily the old connections were correct.
Here are my resources:WiringDiagrams
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Here is the headlight bucket as tidy as can be (for now).
WiredHeadlight2
Another iphone quality photo of the headlight:
WiredHeadlight1

After some battery charging, and some testing, and pulling my hair out only to realize that the Rocky Point switch was labeled incorrectly (blue and yellow wires were mixed up and mislabeled). we are good to go!
I popped the headlight on and the bike is showing signs of life again!

HeadlightOnCloseup

HeadlightOn

UPDATE UPDATE – – – –

Here are the photos of the second silver bike’s headlight wiring.  It looks somewhat messy in the photo but take my word for it, it ended up being tidy.  I used a cut down /6 relay board and mounted it inside the headlight bucket.  HeadlightRelayBoard_IMG_4588
 HJeadlightWiring_IMG_4592

Custom Battery cables

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Due to relocating the battery I had to make some custom battery cables. One has to run from battery (located in the tail section of the seat) to the starter and the negative cable will most likely ground on the transmission near the shifter instead of at the speedometer cable.

I bought some #4 Welding cable. It is a nice and thick gauge wire, and flexible.
WeldingWire

I stripped the wire and found a few different sized terminals. This terminal end will connect to the battery.
terminal

Pre-Crimping. FWIW, this crimper is really heavy and cumbersome but works pretty good.
Crimper

Crimped:
Crimped

Cleaned up with Heat Shrink covering.
heatShrink

In addition to the positive wire that connects to the starter, I made a small positive lead to connect to the main harness positive lead. I used the same crimper and it came out great.
positive