Category Archives: BMW

BMW R850R Side Stand Switch

On the “oilhead” model BMW’s there is an interlock switch so that you are unable to pull away with the side-stand in the down position, you cannot even start the engine when it’s in the down position.

This is done by having a switch that is operated by the sidestand, a BMW special incorporating a micro-switch.

On my R850R this switch had gone permanently open circuit, so I could neither start or run the bike.

On visiting my local BMW emporium for a replacement I found that it was “Not Currently Available”, while it is still a listed spare there were none available, not even in Germany, not only that but they’re grossly overpriced for what they are, according to the dealer the current price is just over £110 !!.

Fortunately it is a simple matter to bypass the switch, so I was not left with an inoperative bike but to do this I had to bypass a safety system, not the best of ideas!.

So, nothing ventured nothing gained, I removed the switch to have a look at it.

Interlock switch

The interlock switch

As expected it was not meant for servicing but when I had a good look I could see how it had been assembled.

There were a couple of moulded tabs and a steel locating pin so first step was the pin.

Switch peg

The metal locating pin half-way out

I gripped this pin with a pair of pliers and it came straight out with a twist and a pull. I then pried the tabs back a little and ran blade round in the joint  between the parts of the assembly.

It took a bit of fiddling what with having to pry and split at the same time but the two halves soon came apart.

Split housing

The opened housing

Now I could see how it worked, there was a plastic cam bearing onto a micro-switch.

In bits

The switch components

The micro-switch body was deeper than the standard one but since it had the wiring loom coming direct of it rather than having the more normal terminals this is probably why.

Anyway, because the standard switch is shorter it can easily be fitted into the available space and it can then be fixed in place.

So I now needed a suitable switch and the obvious place to try round here was the local branch of MAPLINS.

A look on their website confirmed that they had a range of micro-switches, all in the C.O.(Change Over) format, that is that rather than their being simply either N.O.(Normally Open) or N.C.(Normally Closed) their connections were switched from one state to the other.

This meant that I had no worry as to which was the correct conformation for the job, it was just a case of finding which one would fit best into the casing so it was off to the local branch.

Button switch

Plunger type micro-switch

Once there I soon found a snag, the switch plunger on the new switch did not touch the cam.

It turns out that the standard “offset” on a micro-switch plunger is 1.2mm and BMW in their ineffable wisdom have elected to use a non-standard switch.

Idea is presumably to force the purchase of their dedicated (and expensive) switch but however there is a way round this snag, there is an alternative switch has an operating lever.


Basic lever type micro-switch

This lever that can readily be bent into a suitable shape using round-nosed pliers, so I got one of those switches at a price of £2:29, that’s just not quite 1/50th of the price of the BMW part.

lever modified

The lever bent to shape

Once I had the lever bent into the requisite shape I found that the plastic housing round the cam was fouling on the base of the lever and this was preventing the new switch from going fully “home” into position in the housing, but a little careful easing with a router bit in the Dremel soon got round this.

switch in place

Lever switch installed in housing

Now the switch had to be fixed in position. The original had located with pegs on its sides that located into recesses in the housing but the new switch body had a pair of mounting holes rather and these were just under 3 mm in diameter.

These holes however lined up nicely with the recesses in the housing so it was just a case of opening these through to take the appropriate countersunk head bolts.

Assembled unit

Finished job with screws in place

I’ve committed the heresy here of using the old 6BA size for this, simply because I had some in stock along with having the appropriate tap, rather than having to buy in metric machine screws and taps.

All that was left to do was connect the wires to the switch and close up the housing, test the whole assembly and then, once it was found to be working, refit it to the bike.

Job Done!

Transplant Surgery

When I started this blog it was to cover the rebuild of my M100 Panther. Well this bike has now been back on the road since the turn of the year and now that most of the initial snags seem to have been sorted out there’s not been a lot to say lately
Once I have a few more miles under her belt I intend to fit a sidecar so I’ll be covering that but for now all that’s happening is that I’m racking up some miles on her..
SO – – – I’m going to broaden things out and take in the happenings with other bikes as well, and the first is a problem that appeared out on the road last Saturday on the R850R BMW.


The Patient

Standing at traffic lights and suddenly the tick-over went all to pot, pulled away but obviously only one cylinder working properly, although both were firing.
On checking things over I found that one end of the return spring on the right hand injector’s butterfly valve had broken off.
Since I always have some Viney bands with me (rubber bands cut from an old inner tube) I was able to codge things up so I could ride home.
I went to the local BMW emporium on Monday only to find that the spring was not listed as a spare! Delightful!.
Fortunately I have a spare injector body, a known wear point is the butterfly shaft on the right side and I’d taken the chance of getting a good used one when I saw it a couple of years ago. As the body fitted is showing signs of this  wear now is the time for this to be fitted, HOWEVER, there are two O-rings involved so rather than re-use the ones currently on the bike I ordered up a new set, “delivery due on Wednesday”.

Throttle Body

Replacement Body

In the meantime I gave the cable adjuster a good dose of penetrating oil so it had a couple of days to soak.
Once I’d picked up the parts it was time to start so first thing was to disconnect the injector body from the fuel line and the electrics.
For the electrics it’s just push in the wire clip towards the body and the connection pops apart, you’d never think it had been undisturbed for the last 12 years!. A touch of silicone grease on re-assembly will help keep it this way.

To detach the fuel line meant pulling out the spring retaining clip and then pull the connector off the injector, this was a bit stiff, probably through the O-ring having swollen a bit from contact with our modern ersatz petrol.

Fuel line removal

Removing the fuel feed line. “D” is the spring clip.

With these clear I now had easy access to the throttle cable so a 10mm spanner on the lock-nut and the adjuster was free and unscrewed from its mount.
Then having slackened the clamping screws at either end of the tube to the air-filter that tube was slid back into the air-filter housing.
All that was left then was to slack off the clamp screw at the cylinder head and the body came free, except for the throttle cable at the pulley sheaves but this was easily dealt with with the body free.

Cable removal

Removing cable from pulley sheaves

As I had decided to use the known quantity of the old injector this then had to be swapped into the new body, the removal of two Allen screws saw the injector come free.

Before I fitted the new body however I took the opportunity to remove and clean the pilot needle valve (No.2 on the picture below). This controls tick-over and tends to get gunged up so it should really be removed and cleaned every major service.


Injector body adjustment points

I also took the opportunity to clear the cable-adjuster threads that screws into position “1” so the lock nut could spin free for the full length of the adjuster, these adjusters are threaded “Metric Fine”, being 6mm x 0.75 pitch so don’t just shove a standard 6mm tap through to clean things up since that’s 6mm x 1.0 pitch!
Then it was just a case of reverse the dis-assembly procedure and get everything back together again.
I fitted new O-rings to the body and the injector, giving them a wipe over of silicone grease first so they would slip easily into place, and while I was at it I renewed the spring retainer clip for the fuel line.

O-ring sites

A and B show where the O-rings go

I now had to synchronise the two bodies as the throttle cables had been disturbed and the tick-over needle needed  setting.
To do this job properly the motor must be up to full operating temperature but a basic set-up can be done cold.
Main thing is to get the butterflies moving together and an “eyeball”check will suffice initially.
All you do is put a finger onto one cable sheave and watch the other, open the throttle slowly with your spare hand and then adjust the cable until both start to move together. While not exact it’s close enough to let you run the bike enough to get it warmed through.
There are three adjusters on these throttle bodies:-
No.1 alters the free play on the throttle cable and is used to synchronise the opening of the throttle butterflies.
No.2 is the bypass needle and adjusts the tick-over, the adjustment is on an air bypass circuit, fuel flow is controlled completely by the injector and this bypass is to match the air volume to it.
No.3 is the butterfly stop. This holds the butterfly a fraction open to allow the motor to tick-over. This is factory set  and should NEVER be altered by the user, fine adjustment of the airflow is by use of No.2, the bypass needle. The butterfly stop is set up by the manufacturer on a gas flow bench.


Injector body adjustment points

For the tick-over screw, a basic setting is of around 1.25 to 1.5 turns open that will again be close enough to let you run the bike to get it warmed through when you can adjust it properly.
This setting up is done using a manometer, the official BMW tool is an electronic version of this tool but the lod “analogue” instruments can still be used.
The sensor tubes are connected to the vacuum take-off points on the throttle bodies and the engine started.

Vacoom take-off

“C” is the vacuum take-off point

With the engine running on tick-over the bypass needles are set so that the manometer levels are both the same and tick-over is about 1200 RPM.
To adjust the cable balance the throttle is then opened and held at around 2000 RPM and the free-play adjusted so that both sides show equal on the manometer.
Once you think you have everything set right then you “blip” the throttle a few times and then check the tick-over and cable balance settings again, all being well they are still OK and that’s the job done!

Brembo Brakes

This entry is not about the Panther but its more modern stablemate, my BMW R850R.

With my playing around on the Panther lately this has been left standing for the last couple of months and when I had it out last Friday I found that one of the front brake callipers (this bike is fitted with twin four-piston Brembo disk-brakes) was sticking on to the extent that the disk was too hot to touch, at least it made it easy to see which calliper was giving problems!.

As the bike now has over 110,000 miles under her wheels the decision was made to rebuild both callipers rather than just strip and clean them, the rebuild kits are not cheap at £58 each but since you get 4 new pistons in them as well as all the requisite seals they in fact work out cheaper overall than the kit for the Yamaha trainer I last did, that was a single piston calliper and stung me £17 for the seals alone!

Seals kit

The “Repair Kit”

I have an old master cylinder I keep purely for the purpose of pressuring a calliper up “on the bench” and forcing the pistons out of their housing so first step was to take the calliper off the bike and clean it of road crud, attention was particularly given to cleaning the projecting parts of the pistons as these will have to be pushed back through their seals.

Once this had been done the outer parts of the pistons were lubricated with some brake fluid and they were pressed back into the housing, sounds easy but a fair bit of force had to be used, after all the calliper had been sticking!.

Calliper 1

Calliper with clamps fitted and one piston partway out

A pair of toolmakers cramps and a “G”-cramp were then used to restrain three of the pistons, leaving one to be pushed out and worked on. The jaw length of the toolmakers cramps hold both sides of the piston down rather than just one and so prevent the piston from twisting in its bore, they are in fact long enought to overlap onto one side of the second piston as well so by also using a single “G” cramp both sides of a third piston can be restrained leaving the last piston clear to be worked on.

calliper 2

Toolmakers cramp covers one and a half pistons


Calliper 3

“G” cramp used to restrain other side of piston

Calliper 6

A second toolmakers cramp restrains the third piston, leaving the other one to work on

The calliper was connected up to the “spare” master cylinder, the system bled and then used to press the piston out, as there would be brake fluid around “loose” when the piston came clear the calliper was wrapped in rag and put in a plastic tub to contain it.

Calliper 5

Pumping out one of the pistons

With the piston out of the way the bore could then be thoroughly cleaned out and then the seals could be taken out of their seats, a dental pick is a useful tool for this and those seats cleaned out so the new seals would seat properly.

Calliper 7

With the piston and seals removed the seal grooves can be cleaned out

The problem proved to be due to the weather seals having hardened with time and an accumulation of “deposits” on the exposed parts of the piston taking up the necessary working clearance between the piston and its bore.

Calliper 8

The piston showing the “crud” causing the problem

The seats for the two seals were thoroughly cleaned out, the dental pick proving very useful for this, the only cleaning agent used was clean brake fluid and then a set of new seals from the repair kit was fitted.

These callipers use two slightly differing diameters of piston so it’s necessary to be careful as to which seals you use for which bore. (Yes I did try to fit the smaller ones into the larger bore!)

The kit comes with a pack of a silicone assembly compound so this was used to coat the seals before fitting them in place.

The correct sized new piston for the bore was then also rubbed over with the compound, the bore was lubricated with clean, fresh, brake fluid and the piston pushed into the bore.

It can be a bit fiddly to get the piston home in its bore as if it is not pushed in dead straight it will bind in the bore but with a bit of wangling it will suddenly just slide home and then you can move on to do the next piston.

Once all four pistons and seals have been replaced then it’s just a case of fitting the new brake-pads, putting the rebuilt calliper back on the bike and turning attention to the other calliper.

Calliper 8

Rebuilt calliper ready to refit