I am glad I am doing a complete rebuild of this bike. The steering was a bit stiff and not smooth. Once I got the neck out of the frame, I realized why.
Rusted Steering bearings.
Since the frame is going to be powder coated, the races have to come out anyway. I could see somebody buying the bike and not getting this deep into the restoration and it would be dangerous to ride with bearings like that.
These went straight to the trash.
These piston and cylinder kits seem to be the rage right now. I used one on the last build and had very little problems aside from the pushrod seals being extremely difficult to install.
The pistons are made to mate with the R75/5 heads and you can use the same carbs (might need to change jetting).
Here is a quick look at the piston and how it compares to a stock R75/5 piston that i have lying around.
It is a lighter, yet wider piston. The piston on the right has the rings on it still. The siebenrock doesn’t have the rings on it.
I didn’t measure heights when i snapped this photo but they seem close.
The piston in the cylinder. The cylinder wall is very thin compared to a R75/5 cylinder.
I haven’t heard of any issues with these yet. Supposedly they give you a 20% gain in power… so that makes it around 900cc.
I’m pretty sure they are cheaper then replacement BMW parts too.
There is so much prep work to do that never gets seen for the final bike.
I spent 4 days lining this gas tank to be used for the next build.
Wear gloves!
The first step of the POR 15, “Marine Clean” is one you have to be careful of.
You can use old petcocks or get corks to stuff into the fuel taps to seal them off.
The hard part is sealing off the gas cap area.
You don’t want to spill this stuff on a tank that you are not painting on the outside!!!
It will leave a stain on the paint.
This tank will get some body work done to it and re-painted so I wasn’t too concerned when some “Marine Clean” spilled out of the gas cap area.
This takes a good amount of sloshing around to clean the tank at least 20 minutes.
Then you need to empty the tank and rinse it thoroughly with water. With Effuel the device that helps you manage your fuel you can improve your vehicle’s performance.
Day 2 –
The “Metal Ready” is the second step and it will remove the rust and prep the metal for the paint to stick to it.
This step requires that you leave the fluid on each side of the tank for about 20-30 minutes.
You then need to completely dry the tank.
Day 3 – an extra day in the sun and a few rounds with a heat gun to let the tank dry.
Day 4 – ugg… the Sealer…
A messy process. You have to mix it well, pour it in and then turn the tank in every direction so the goopy paint has covered every part of the tank. If it spills, clean it immediately.
Then carefully pour all the excess paint out. I find that I end up using about 1/2 of the can that comes with the kit.
If you have 2 tanks, or a friend’s tank, you might be able to get two tanks done for the price of one!
This breaks my heart every time I do this…. but it’s gotta be done.
This fender has been kicking around my garage for years from an old parts bike. It has some rubber paint on it so it has been preserved really well, but it is something I would never use on a restoration. It is ugly and the work needed to remove the rubber coating and restore it isn’t worth the trouble. It kills me to cut a solid fender up but I need a donor fender and this one was lowest on my totem pole.
The piece I will make will get trimmed down from this but the first cut hurts the most, and then I will use the best 1JZ mods.
And, the bike I am building came with a set of /5 headlight ears without reflector holes. A rare breed. It saves me the trouble of trying to source a set. But cutting a set breaks my heart. It’s gotta be done for the upper triple plate modification.
I set a box of small parts aside to be polished when i tore the bike apart. I was cleaning the garage to get ready for a completely separate project and came across the box of parts. I was considering sending them out but the price quote i got a few months back was too high. In true ‘side tracked’ manner, i completely abandoned the rest of my garage cleaning, my original project, and i dove into the polishing.
I did a test first on one of the front brake arms to see if it was worth it.
The key to polishing is actually the sanding. The more you sand out the blemishes, the nicer the polish will look. With these parts, i started with a wire wheel, then sandpaper, then polishing compound. I could have spent 8 hours just sanding these parts. At a certain point, i decided to cut my losses. Some blemishes where too deep or not completely necessary to remove.
After a wire wheel and 250 grit sandpaper:
After 320, then 500 grit paper:
After the ‘stage 1’ polishing compound:
Done for now. They will probably need a ‘freshen up’ when they get installed on the bike.
This is after stage two of the polishing compound:
After the silver cafe bike left my hands for North Dakota, I started up a few projects for myself.
I have been receiving the occasional email from people asking me to build them a bike. I thought one of them was a total scam and after a handful of emails, a phone call and eventually a deposit to buy a bike, it turned out to be legit. The reason I thought it was a scam? This guy is in Israel! This makes North Dakota seem like small potatoes!
He wants a bike very similar to Shane’s silver bike so I’m excited to quickly repeat the process after taking so long troubleshooting and designing Shane’s bike.
I have no idea how we are going to ship his bike but we’ll figure that out when the time comes.
I found a R75/5 donor bike a few hours away and it is one of those bikes that I like to restore. It died years ago and needs new everything. The bike’s owner wants it completely brand new so that is what he’ll get. A dead bike that has been made brand new again. It would break my heart to tear apart a running bike so I am happy to resurrect this old gal and get another airhead on the road again.
The right side head is trashed. Exhaust threads stripped and broken fins. The headlight bucket has an extra hole or two in it that will have to be filled.
Oddly I found that some tanks fit this bike and others do not. I have never experienced tanks that scrape the frame near the seat but it turns that there were variances in frames and tanks back then. I sourced a toaster tank with side panels and emblems and luckily it fits. A few tanks I have in the garage do not. Who knew?
The sub frame was the wrong style so I sourced the correct one (SWB with tabs).
New exhaust has been ordered among many other goodies from Boxermetal and BoxerCafe.
Time to get started!
Many many thanks to the gang at Petrolicious for featuring me and my latest build. It is a great piece of closure to my project with Shane.
Phew. After racking my brain and tearing the front forks apart a few dozen times, I got these all figured out. Hopefully this blog post will help others to clarify and not make the same trial and errors I have made. I can now say I am an expert at the innards of the R75/5 fork system. I’m not an expert with the Gold Valve emulators but I sure learned A LOT!
First off, Read this from RaceTech.com – BMW Gold Valve instructions
And use this as a reference as well:
Emulator Tuning Guide
For information on how the emulators work, please read through this link.
Dampening Rod Forks and Emulators
For instructions and diagrams of a BMW /5 fork leg, check out an old Beemers and Bits link:
http://beemersandbits.com/2011/12/lower-fork-leg-anatomy-of-a-5-bmw-motorcycle/
When you buy the emulators for a early 70’s airhead, ask for a set of sliver emulator springs (more on that later).
The Race Tech BMW page talks about how to modify the fork’s internal dampener rod and piston.
Make sure you remove the spring and check ball at the bottom of the rod.
Here is a shot of the eight dampener rod holes being increased to 1/4″
I was initially too conservative with the modifications. Based on my initial readings, I thought by simply drilling a hole into the top of the piston and shaving down the hex head a bit would suffice. I wanted to leave part of the hex head so I could have something to wrench on if the dampener rod ever needs disassembly.
It turned out that I needed to chop the entire top of the piston off to increase oil flow. You want to encourage ample oil flow through the piston and dampener rod.
After you modified your dampener rod/piston, be sure to clean out the metal shavings. Use a pipe cleaner, air compressor, etc… get it clean!
Next came emulator modifications. You have to customize the emulators for BMW use.
First take the emulators apart and you will notice that under the spring, there is a small top hat like plate with 1 or two holes and markings for a total of 4 holes. Get a small drill bit and drill out the remaining holes so you have a total of 4. This will help low speed fork response over road bumps and such.
Hopefully you were sent a set of silver springs to use on your emulator. I recommend the silver springs because they aren’t as stiff. The springs will control high speed fork movement and how fast the valve will open to allow oil flow.
When I reassembled the emulator, I got the spring to a point where it was snug between the washer/bolt head and the emulator body. I could still spin the spring but I couldn’t wiggle it up and down. This was my ‘ZERO’ point.
After that is when I made my preload turns. I did 3 full preload turns on the silver spring.
I got a foot of 3/4″ PVC pipe from the local hardware store. 
You will want to cut two identical lengths of PVC about 40mm in length to sit on top of the piston and under the emulator.
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Now is a good time to check and make sure your forks are aligned properly. I recommend Duane Ausherman’s web site regarding fork stiction and alignment http://w6rec.com/duane/bmw/forks.htm
I also recommend getting a fork rebuild kit with all the necessary seals, washers and such.
Here is a fork seal replacement tip: http://beemersandbits.com/2012/07/fork-seal-install/
Assemble your fork lowers and dampener rod on the ALIGNED fork legs with all the new seals and rubber rings, washers etc…
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After your dampener rod has been installed in the fork tube and your fork lowers have been attached, then insert the 40mm PVC spacer to sit above the dampener rod piston.
Then install your Gold Valve Emulator on top of the PVC spacer with the spring side pointing upwards.
Oil level comes into play at this point.
BMW recommends between 5 – 10 wt on a stock set up. Do not use the BMW recommended weight.
Because of the dampener rod modifications, you have to start with a minimum of 15wt fork oil. I had to buy my 15wt fork oil at the local Harley Davidson dealer because the other motorcycle shops only had up to 10wt.
Race Tech recommends 150mm oil level. I beat my head against the wall trying to figure out what that meant or how it equated to CCs.
After a conversation with Race Tech’s Matt Wiley, he clarified it for me.
You need to compress the forks fully. See Photo:
With the forks raised as high as they can go, you add your fork oil until the oil level is 150mm from the top of the fork tube.
This equated to 275cc of fork oil in each leg. (A stock BMW setup requires 250cc).
Other BMW models might differ so it is recommended that you measure by compressing your forks and taking note of how many CCs it takes to get 150mm from the top.
NOTE! Fork Oil Viscosity varies between brands! So use same brand of oil when changing oil…
After adding the oil, you can lower your legs to the full extension.
Now comes the theory about springs. The BMW or Progressive springs will NOT work with the Gold Valve emulators. They are much too soft and spongy… and importantly, too long! The Gold Valve takes up 55mm space in the fork tube so you will need shorter springs as a result.
Race Tech recommends using their springs… which is what I currently have installed. Before your order the springs, make sure you buy the proper springs that are recommended for the rider’s weight.
The Race Tech springs appear too short. Not to worry because they recommend a large PVC spacer at the top of the forks between the spring and the upper fork caps. 
PVC Spacer should come just to top of chrome fork tube with forks fully extended.
15-20mm preload is recommended. When PVC spring spacer is just to top of chrome tube you will be in that range.
Unfortunately, the bike now belongs to the owner who commissioned me to build it. If I still owned it, I would love to experiment with a set of custom Sonic Springs. This was written by a fellow BMW rider by the name of Craig : ” I had Sonic Springs wind springs for me of the proper length and rate for the emulators. Instead of the race tech 425mm spring at a .8kg/mm rate, Sonic springs wound me an 0.65kg/mm spring at a length of 485mm. This way, the ride is stiffer (but not ungodly stiff), the bike rides a bit higher in the stroke, and it eats bumps like crazy. Stock springs are about 530 mm long, but if you use an emulator, it consumes about 55 mm of space inside the fork. The shorter spring accounts for the reduction in space available when the emulator is installed. “
If I was keeping the bike, i would gamble the $100-$150 on trying the Sonic Springs. The logic behind the idea makes sense to me.
So to sum up:
I used the silver spring with a preload of 3 turns
I modified the valve plate bleed holes to 4 holes.
275cc of 15wt fork oil
and Race Tech springs with a large PVC spacer.
Lastly, to check everything out, i measured my Sag amount. The sag is measured by taking note of where the forks settle when the bike is on the ground without a rider. If getting help is an issue, use a zip tie on the fork tube and a stick. With the bike off the center stand and you off the bike, push on bars and let the bike rise. Then use the stick to push the zip tie flush with the fork seal cover. Then put it on the center stand without disturbing the position of the zip tie. Then measure the gap between the zip tie and the seal with the fork fully extended. Then do the same thing with you on the bike. Might take a couple of tries before you get it on the stand without moving the zip tie.
Without a rider, the sag is 20mm.
Once I sat on the bike, they compressed 35mm.
Those are the specs I was to achieve for and they are dead on.
My review of the set up?
The bike is a canyon killer. I hit high and low speed canyon turns and the bike handled amazing. No dipping or diving. Zero dive when braking. No springy pop when accelerating. It would glide in and out of turns and keep you glued to the road. I love it.
On the horrendous Los Angeles roads… the bike handles 70% of the potholes and bumps OK. But I can’t help but notice that at any speed, fast or slow, sometimes the front forks hit the bumps a bit too hard for my taste. Also when on the rain-groove freeways the bike can get a bit bouncy.
There is a driveway lip that I ride over going to my home and for some reason that one lip was a harsh hit every time I hit it. It was if the front forks weren’t working at all. However, according to Matt at Race Tech, that is always an issue and if the suspension is great everywhere else, then just deal with it. Which is what I did.
I have a very similar R75/5 with stock BMW fork set up and Progressive springs. The bike handles the bumps in town very well however after experiencing the Gold Valve set up, I can’t help but notice that the bike feels much too squishy when braking and hitting the twisty roads. I think I will be adding a gold valve set up to that bike sometime in the future.
Feel free to contact me with any questions.