I have a 1973 R75/5 and the electric starter will not engage and turn engine over. My starter makes a sound like it is grinding rocks or maybe like a coffee bean grinder.
I bet some of you old airheads know what's going on. I figure I am going to need to replace the starter but I thought I'd check and see if there is a remedy before I replace the starter.
Thanks,
Joe Skaggs
You are having bendix issues. The bendix is the assembly on the end of the starter motor shaft that engages the ring gear on the flywheel. When the starter motor is not energized to an adequate amount (this can be for many reasons), then the bendix is rather lazy in its job of engaging the teeth of the ring gear. Therefore the teeth of the bendix dance along the sides of the flywheel's "ring gear" and never fully engage the 2 gears. This is what makes the awful noise you are reporting. It is literally the starter motor making a half-hearted attempt to engage 2 gears. If the situation continues unchecked, then the ring gear will wear to such an extent that the flywheel will need to be removed and the ring gear replaced.
► This scenario can be caused by a low voltage battery. Which in itself can be an indication of 1) corroded battery terminals not allowing the full release of battery current. 2) A dying battery. 3) Bad battery cables on either battery terminal. 4) Poor battery charge due to battery age or water level. 5) Poor battery charge rate from the alternator (bad voltage regulator or worn alt brushes). 6) Any combination of the first five. 7) Or several other things, all of which have to do with the battery's ability to supply and transport massive current to the starter motor.
► However, the most common cause is oxidized lubrication within the bendix or starter motor bearings. This is why I wrote THIS article earlier in December. Where have we heard this before ? First it was oxidized grease in the head post bearings screwing up the steering, then it was oxidized grease inside the speedo gumming up the indicator needles, and so on. 40 and 50 year old grease is simply a recurring issue on all classic vehicles. I bet your wheel bearings are even full of oxidized grease ! You must remember... there was no mass availability of synthetic grease 40 years ago. It simply wasn't commonly available. And now we, the present owners, are presented with an "opportunity" to get our hands dirty.
So the place to start is to service the starter motor and the starter bendix per the referenced article. And while you're in there, check out the condition of those two 00 battery cables and their 4 terminations.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you for your help. Much appreciated.
Joe Skaggs
Beside my Topic Title is a (exclamation point in a yellow circle) and it says Unapproved under it. What does that mean?
Thank you,
Joe Skaggs
Beside my Topic Title is a (exclamation point in a yellow circle) and it says Unapproved under it. What does that mean?
Joe -
It simply means your starter motor needs some attention. The yellow circle will automatically go away when you get that repair task completed. If it's not fixed in the next several weeks, then the circle will turn red. If that happens, agents from the Airhead Police will be knocking on your door. Usually at 2 AM. Things go rapidly downhill after that, so please don't delay.
?
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
In addition to Richard's excellent advice, have a look at Snowbum's web page.
https://bmwmotorcycletech.info/slash5cricket.htm
The /5 starter relay is unique in that there is an "anti-restart" feature built in. This can prevent the starter from engaging if your battery is even a little bit weak.
former Airmarshal, IL.
To be pedantic, i do not think that Bosch starter has a bendix mechanism, it uses a linkage. Mach nicht. it needs service.The least expensive solution is to DIY. The best least expensive solution is to pull the starter and take it to any auto electric shop. It is a standard item and they can do some service items you cannot. The fancy expensive solution is a new nippondenso starter from Rick Jones. If you have a SWB /5 I would go this way because the 'denso draws less juice and you have a small battery.
The /5 starter rely kills the starter button if the bike is running enough to be charging. so the button will not engage the starter with the engine running....like if you turn the bars full lock and the button hits your tank bag. But when it dies it kills the whole bike and is costly to replace. I used mine up and when it died I put in a standard relay from the FLAPS and a little push button switch on the bars. I could hit the starter switch and push button with my hand but the tank bag could not. The newer bike do not have this feature and the starter can be engaged into a running engine. Not good for things. But the switch gear is different.
To be pedantic, I do not think that Bosch starter has a bendix mechanism, it uses a linkage.
Arni you are absolutely correct. In a true "bendix" system the starter gear rides on a very coarse helical thread. When the starter motor spins up, the inertia of the gear makes it move along the helix. This movement thrusts the starter gear into engagement with the flywheel's ring gear. In this design, the starter solenoid is typically independent of the starter motor.
The Bosch design has the starter solenoid affixed to the starter motor. When the starter button is pushed, the solenoid's piston is electro-magnetically thrust to close the high current contacts to energize the starter motor. This is like any other starter motor, except that the solenoid's piston is also connected to a lever system that mechanically forces the starter gear into engagement with the ring gear.
One of my very lazy and truly most despicable habits is to call ALL starter motor engagement systems a "bendix" which is not correct. In my defense though, I will point out that the cure for both systems (cleaning and fresh lubrication) is exactly the same. Still, I promise to do better next time.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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