K100 restoration

In June 2005, I bought this K100rt as a winter project. The bike was looking pretty bad. It was rusty, dirty, the plastic and rubber parts were grey, and some of the body parts were missing. It was in need of a lot of TLC. This bike had less than 56,000 kms on the odometer, but considering that a lot of them had been replaced (sometimes twice) under warranty, it's impossible to tell the real mileage if you don't have the maintenance history of the bike.

Except for a noise in the back of the engine, the bike seemed to be in reasonably good mechanical shape.
I tried this bike for only 500ft to test the transmission and decided to have the owner to deliver it to my place. The tires were totally bold (You could see the cord on the back one) and under inflated. It was almost impossible to steer the bike at low speed. I didn't feel secure even for a short 10kms ride. Here are the first pictures taken after the delivery.

The next morning, I got up early and decided to clean the spider webs and quickly assess what was needed to restore it. I was flying to Europe at night and could buy some of the parts overseas.

This was how the bike looked after a 4 hours cleaning with the high pressure washer and a lot of elbow grease. Much better, but still rusty.

After a quick assessment, the parts needed to put the bike on the road and pass a safety inspection were tires, battery, brake fluid reservoir (Plastic was crumbling).
During my trip to France, I visited my old BMW dealer and bought an additional $300 worth of parts.

When I returned, I spent another week cleaning and replacing parts to have the bike ready for safety inspection. I also had to fight the tax man: Without seeing the bike, he gave it a value of $3000 and was claiming the taxes on this amount.

I went to RPM Cycle in Dartmouth to have the bike inspected and appraised. The result was an appraisal of $2000.

I decided to ride this bike during the fall to find anything wrong and be certain that it was worth rebuilding.
I replaced the oil in the transmission and engine, all filters and checked the splines on the transmission shaft. (I expected to have to rebuild them, but they were in perfect shape).

Other than the triple tees bearing that almost seized up on me (The grease was 20 years old and dried up. It was like a varnish on the rollers) and a break down on the highway caused by the EFI computer plug coming off the socket, the bike ran pretty smooth.

By the middle of December I had put 5,000kms on it and decided that it was time to take it into my basement for the winter.
I had a big problem: The bike was too wide to go through the door of my basement, and I couldn't remove the mirrors because they were seized by the rust. I had to strip the fairing off in the shed.

As I promised to give a K bike training to other K owners, until January I spent time cleaning all the corroded aluminum.
I used steel and brass brushes attached to the drill gun.

I also put apart the front brake system and found a lot of humidity in the calipers. Seals and pistons were in good shape. I removed all the electrical wiring. Every connection was marked to facilitate the reinstallation.
I also spent time to draw on a CAD software the whole electrical diagram and printed it in colour in a very large format: This is a lot easier to trace the wires than the small German black and white schematic found in the Clymer. If you like a copy, register with on the K100 newsgroup and you will be able to find it in the download section

The main wiring harness was removed from the bike. All the green tabs are masking tape with identification of the plugs. I left some on when I put the bike together. If I ever break down on the road (are you ever breaking down with a BMW???) it will be easier to follow the schematic and troubleshoot the problem. Later when the electrical harness was put back on the bike, every connection was coated with dielectric grease.

The first week end of January, 4 BMWONS members (Bruce, Bill, Amedee and Piet) came to see the dismantling of the bike.
After a couple of hours I had big piles of parts stored all over the workshop. I discovered that the frame had rust all over and was
in need of a full paint job. I was expecting only touch-up on the sides.

Removal of the power train....

The alternator is taken off after removing 3 screws.
Only 2 screws retains the starter

The whole back brake system is removed all together

Removing the suspension and the differential

The splines are looking good
If you ever need your splines rebuilt check this web site. He is doing a faboulous job: Bruno's Machine Shop and Repair
See also this link: result of lack of grease.......

A gentle tap on the wise grip and the drive shaft is off.
The swing arm should be in an horizontal position or the rubber boot on the gear box output shaft will be damaged.
(the drive shaft may hook on the boot)

The splines on the engine side of the drive shaft look good too

By removing these 3 screws, you get off the right swing arm shaft

Slacking the nut of the left side swing arm shaft

Removing the left side swing arm shaft - This is the
adjustment screw for the swing arm's bearings

Here is the right side swing arm shaft

If the swing arm bearings are stocked with dirt, pack some grease in the inside race, insert your right side shaft into the bearing
and with a good size hammer give a big tap on the shaft. The pressure applied on the grease will push the bearing out.

Removal of the gear box

Oops!!! I didn't tie the clutch lever to the gear box and the rubber boot on the clutch mechanism got destroyed.
($50 mistake)

Support the gear box to avoid bending the clutch push rod.

Inspection of the "small" splines (the one fitting on the clutch)
The rusty color is the color of the grease previously used.
It is very important to lubricate them otherwise you could be in for costly repair.

If you need to rebuild your gear box, here is the minimum part list needed:
You can buy industrial bearings and seals (I indicate all the dimensions)
K75 AND K100 gearbox are identical

A complete detail of parts with BMW numbers is available here

Removal of the clutch

The clutch is ready to be taken off

The alignment pins are giving a bit of rough time. Gently pry with
a screw driver to remove the plate.

After measurement, the clutch is put together in the order
that it was removed. (the 3 painted marks are 120 degrees from each other)

Time to remove the "big" nut on the output shaft.
Inserting a hammer handle in one of the 3 holes will lock the clutch in order to slack the nut.

Removal the front fork and brakes to get the frame off the engine

3 more screws and the engine is off
On a K bike, do you remove the engine or the frame?

Time for the engine inspection

Here is where the MNDhL@#! noise was coming from... The bearing on the alternator driver is bad..

Checking the inner parts of the engine. My worry was that the rivets on the output shaft were shot.
This is a disease of the 1985 K100 bikes. The 1985 has only 6 rivets when the 1986 has 12.
Lucky me!!! Everything looks perfect...

Caution: When re-installing the output shaft, put some loctite on the outer race of the bearings to avoid them to spin free in the crankcase.

Except...... One of the other problem of the output shaft is the tensioner spring between the absorber and the idle gear
The spring is supposed to remove the slack between the output shaft gear and the crankshaft. As you can see on the pictures, the hole for the retainer pin is wearing out at the point that the tension on the absorber gear is nul.
I have now seen 3 engines with less than 80,000kms having the same problem. The symptom is a gear noise that seems to come from the back of the cankshaft.

Removing the spring ring from the outside race of the bearing allow the use a regular puller.

separating the absorber from the idle gears

This is the $14.00 spring that has to be replaced

Timing Chain
One of the other problem on the K100 is the timing chain. Even if your engine has less than 80,000 kms, the timing chain may have to be replaced. Looking at the wear on the front engine cover can be a good indicator of a chain being in need of replacement.

The mark on the front cover (near the seal) indicates a lateral wear on the timing chain. The bow on a new chain is about 1" when the bow on a chain with 50,000kms + is 2" or more. The result is the chain rubbing again the front cover.

Oil/water pump

The water/oil pump is 21 years old. The seals are in bad shape and need to be replaced.
The mechanical side of the pumps are OK, but the rubber of the seals is rotten by the anti freeze

TGPI switch

The TGPI switch was not working properly and as a result, the gear digital display as well as the neutral's green light were not
functioning. I opened the switch and cleaned it. This is a minor common problem on the K bike. The switch is not water tight and
the contacts get corroded. This is easy to fix, and when reinstalling it, I generously coated the casing of the switch with silicone.
How to test your switch before removing and opening it? Check the following article on IBMWR:
http://www.ibmwr.org/ktech/trans-switch.shtml

Warning.... The 3 little pins (contacts) are spring loaded and they may fly away when you open the switch.
To avoid hunting for them if they fly away, work in a clean area. The best is to work in a contained area like a shoe box. This fix is very easy and doesn't require a lot of mechanical abilities.

Time to work on the cosmetic.
A lot of sanding and scrapping is required.
The frame was sanded to the bare metal and next to no filler was used on the body parts.
All the and nicks and stone chips were sanded to blend with the rest of the fiberglass

The workmate bench was the ideal support to sand the frame

The fairing was ready for painting, and I constructed an articulated support in order to facilitate the painting. See pictures further down.

The whole power train is put back together.

During the paint's prep time I put back the power train together. I replaced a lot of seals and cleaned all the aluminum parts.
For this project, I have used 8 metallic brushes to clean the aluminum.

The frame is finally painted and it's time to refit it on the power train.
The black epoxy paint looks really good.

It's finally looking like a motorcycle again!!!

When waiting for a set of original BMW grips, I installed a set of Kimpex heated grips (They are only $30)

Time to check with Wayne at the paint booth.. Whoaaaa... This is impressive!!!
It took me 3 weeks to select a color, but I am happy with the result.
Because of all the neon lights, and the flash of the camera, the pictures don't show the real colour of the bike.
It's a nice mid green metallic, but on the pictures it shows more teal.

I got some parts back and I rushed to do a "dry fit" on the bike. Again, none of the pictures show the real colour.
I have 8 neon tubs and 9 halogen spot lights in my workshop and it's so bright that some of the pictures were showing just a big glare.

This morning (Saturday February 11), I got up early and finished to reassemble all the body parts.
Yesterday, I got my new front tire and I am happy to be able to remove the block of wood from under the bike.
As soon as I get my water/oil pump seals, I will be able to start the engine and see if I solved the noise's problem
I am really confident that I isolated the problem because the bearing on the alternator shaft was not running smooth at all.

Today, a friend came to see the K100 and he is so impressed that he is considering a Beemer for his next bike.
I started the K75 for him (1986, 230,000kms and original engine),
She started right at the first pull of the starter. This is impressive for a bike that has not ran for over 2 months. The battery is
still fully charged. Thanks to the kill switch that isolate the battery.

Here is the K100 after a month and 1/2 of work.
She looks really classy and this is what you would expect for a 21 years old bike.

As a note of humour, here is the next generation of BMW fanatic.
My twin brother has a 1985 K100rt too and his son at 2 1/2 loves working on the bike.
He already knows that a ratchet needs a socket and an allen key is no mystery to him.
Smart kid but don't tell him.

Here is a picture of the twin brothers sharing info and knowledge of the K100 engine

November 2006:

This year, I had shared my riding between the K100 and the K75.
The 2 bikes were made on the same concept, but are radically different. The K100 is a lot more powerful and handles the best when you have a passenger. It's also a lot heavier than the K75. The K75 is lighter and a lot smoother. It's still my preferred bike for the twisty roads. During Spring and fall, the K100rt fairing is a big plus when the temperature is close to the freezing mark but during the summer it's like riding a steam engine. This is good if you don't have time to go to the sauna and want to lose weight. I solved some of the heat problems by recently installing an electric windshield from a K1100LT.

September 2007

The K100 is here in it's final version with the K1100 electric windshield. Since I restored this bike, I rode it for almost 20,000 kms without any problems
The K75 has a "Sprint" fairing. This fairing was originally produced in England for the K100 but fit very well the K75. The company has stopped producing this model, but they still have parts in stock.

October 2012: Here is the latest addition to the K farm (Another 1985 K100).
I just got this bike in Jacksonville (Florida)
I will spend the winter working on it.