BMW 70’s Era Tire sizes and their equivalents

I’m posting this so I have my own record of it. I always have to look it up and this is a great place to store my ‘notes’.

Typically, tire sizes for a R75/5 R90/6 R90s R100S, etc will have a:

3.25 x 19 Front
4.00 x 18 Rear

The metric metric equivalents would be 90/90-19 for the front and 100/90-18 or possibly 110/90-18 for the rear.

Check out

Just an update… I have 3 bikes in the works but they have been taking longer then expected.  I’m trying to customize many features vs buying the available parts out there.
And, I’ve been busy over at helping to develop some Airhead aftermarket parts that look good, and function, for customizing these old BMW’s.

Recent additions are rear sets, and top clamps…  more ideas to come!!

Black Rear Sets for 1970's BMW motorcycles

Black Rear Sets for 1970’s BMW motorcycles



BMW Airhead Clutch and Flywheel Removal on the Cheap

It’s been about 5 years since i have pulled a flywheel and a clutch from an airhead engine. I do remember the process being slightly ‘dangerous’ in that if you don’t remove the clutch properly, the force of it could cause harm to yourself or your motorcycle.  I don’t have the BMW ‘special’ tools at my disposal to do so safely… so i figured i would make my own. Total cost – $10 from my local Ace Hardware store (which happens to have the best spare bolt, nut, screw selection i’ve ever seen).
No need for the BMW Special tools.

Clutch Removal

You will need to purchase three M8 x 1.00 thread (fine thread) bolts about 2 inches long.
i also purchased a small piece of aluminum tubing that fits around the bolt:

M8 x 1.00 bolts and aluminum tubing. Bolts cost $1.50 each(damn pricey metric fine thread bolts)and tube was $2.20


The first step is to remove every other bolt on the clutch disk that secures it to the flywheel:

I cut the aluminum tubing into three sections about 3/4 inch.
Then screwed in the 2 inch long bolts with the tubing on it into those every other holes:

Bolts with spacers on them

The reason for the bolts with the spacers is to safely alleviate the pressure into a ‘second’ stage.  When you remove the three remaining ‘factory’ bolts, the disk’s pressure releases itself outward, safely, onto the spacers:

Clutch pressure now lessened and on the bolts with the spacers.

Now it is simply a matter of removing the remaining 3 bolts, evenly, until the clutch disk is released.

If your bike has these spacers, Keep them! Some clutch disks don't.

Clutch bits, friction plate, etc...

Flywheel Removal:
To remove the flywheel, you have to prevent the engine from turning while removing the flywheel bolts that secure it to the crank shaft.
Also, without securing the flywheel, you can also run a risk of knocking the inner thrust washer (around the camshaft) off the pegs within the inside of the engine block. SERIOUS damage could occur within your engine case if that happens.

BMW recommends a ‘special tool’ but it is merely a device that locks the flywheel in place.
I made my own from a piece of steel for $2.00.

12" piece of steel.

After some quick cutting and drilling, I have my very own version of the ‘special tool’.
Use the original flywheel bolts, and finger tighten them as much as you can and you are now free to use a nice breaker bar, a 17mm socket(i think) and crank out those flywheel bolts.
Some suggest using a center punch and making a small score on the crank shaft and another on the flywheel so you can put the flywheel back in the exact same position and your TopDeadCenter mark is still accurate.  Using a permanent marker might do the trick for a short term solution.

Piece of steel, cut and drilled out to prevent the flywheel from moving.

That’s it!  Now that the flywheel is removed, time to send it off to get lightened!
Another note while the flywheel is out… some people put white paint on the timing marks so you can see them better when timing. Just a tip….

Oh… and remember to THROW AWAY the 5  flywheel bolts. They are torque specific bolts and once they are torqued to spec, the can’t be used again. If so, they may wiggle back out and cause some SERIOUS damage.

For more info on clutches and flywheels, look here:
Measure your clutch parts –

Northwoods airheads sells a $4 crankshaft blocking bolt to prevent the crankshaft from moving forward when removing the clutch / flywheel.
it is located here.

Broken clutch cable – repair on the road

The other day i had to work on location about 35 miles from my home (typically i work 2 miles away from home).  In order to beat the insane traffic at that hour, i loaded up the saddle bags on my ’77 R100s and beat the 2 hour stop and go car traffic by 1.25 hours. Lane Splitting in California is awesome.
After a hard day’s work in the hot and windy ‘central valley’ i got in my bike to shoot home. While at the stop sign about to pull into traffic i pull the clutch to get in first gear and then.. SNAP!  Broken Clutch Cable. 35 miles from home. If you need truck repair parts, check
I immediately shut the bike off and pushed it to the side of the road.
Luckily i have a fairly complete tool kit hiding under the seat chock full of basic wrenches, sockets, tape, rags, etc…
I took photos after i view publisher site for details and started to take everything apart and replaced it with a NEW BMW Clutch cable. The previous clutch cable wasn’t BMW. Motobins in the UK sold it to me and from the day i got it, i was suspicious and contacted them about it.  They assured me it was better then BMW’s… i think after 20,000 miles, a BMW cable would still function.  Motobins sold me some crappy pipes about 8 years ago too.  I’m NEVER using them again for motorcycle parts.
Here is my roadside repair:

It seems the very end of the clutch cable’s ‘catch’ piece gave out. That separate piece should be at the very end of the cable. Then the entire cable’s end fits inside the large round cylinder.

With no other option, i had to think of a solution or wait hours to get home via tow truck or friend with a pickup. I managed to wedge the broken piece of the cable into the Cylinder aka ‘nipple holder’. And yes, that is what BMW calls it.

The cable’s end is usually contained inside the cylinder but since the end was broken off, i had to think of something else. I ended up wedging the cylinder as far into the handle as i could. This meant that i lost about a half an inch of Clutch Cable length.  It took some effort trying to get the other end of the cable to connect to the clutch arm. 

Clutch Handle back in place with wedged cylinder and cable end sticking half way out.

Luckily i have a roll of electrical tape in my tool kit. I was able to tightly wrap around the cable’s end and the clutch handle. Phew. Temporary fix.

Funny thing happened on the freeway on the way home.  I was lane splitting through 15mph traffic on the freeway and recognized a classic ’59 teal Chevy pick-up truck.  It happened to be a great friend of mine.  I pulled along side and told him the story (while riding down the freeway). He said he’d throw the bike in the back. Talk about luck! But i decided to press my luck and I declined the offer… only to have the clutch cable’s cylinder fall out of the handle after we split ways.  I called him up and we went to my house to get a ramp and straps… but by that time he got there, i did the repair again and this time i wrapped the electrical tape even tighter and it was enough to get me home.
No more non-‘BMW’ parts unless they are a proven upgrade!