Abandon Starter Relay! (?)

[rbm]

Assuming I switch out the Bosch for a smaller, possibly more reliable relay, and knowing that the solenoid draws up to 3 amp, I assume the 1-amp 1N4007 will be under-rated?

Would I need a switching diode rated for 3 or more amps?

No, you won't.  The diode only conducts when the power is removed, otherwise it is effectively not in the circuit.  So, it is sized to handle the spike's energy for only a few milliseconds.  Don't forget to install the diode in reverse - anode to ground, cathode to +ve.

[TimTyler]

Thanks, Robert!

[arnonymous]

Here is the old type starter relay along side the newer version, rated the same, but manufactured under license from Bosch. Note the dual contacts and heavy braided copper connecting wires.......bet this won't burn out or weld. Got it from Euromotoelectrics in Denver.

So i've taken out my K-bike out of winter storage. The battery is strong and full.
I smoothed out the contacts of the Starter solenoid with some sanding paper.
And out of 10 times starting, it stuck around 3 times.
It releases quite easily(with a hit at right spot), but i had it once before also while on the road at night, which is less fun as all the lighting turns off.


I want to really solve this for good.
In this thread two alternative solenoid are discussed, one from Aliexpress and one from Littlefuse.
I cannot easily obtain the littlefuse here in NL.
I would like to obtain the original one mentioned by TrueAce, unfortunately this one is not easily obtained as well.
So for now i will try aliexpress. The one posted by RBM sells in 120A and 200A forms.
(https://nl.aliexpress.com/item/car-relay-12v-200a-auto-starter-relay-with-24v-200a-red-copper-terminals-auto-control-system/32269200596.html)
Would it be a good idea to get the 200A one? If i use the stock starter to engage a second (new solenoid) i wouldn't need the diode spike thingy over the new solenoid contacts right? as the ECU is already protected at the first solenoid, am i right?

I will see if i can move the diode from the old solenoid to the new, once i know the new one works well.


[edit] Whoops something went wrong there.

[Chaos]

just browsed this thread for the first time.  Always heard of the solenoid fusing but despite my share of low batteries never experienced it.  Like the idea of a cut off switch on the ground wire, would come in handy for lots of things.  Of course, I've jinxed myself now. 

[arnonymous]

So i got the chinese 200A one, and last weekend installed it.
https://nl.aliexpress.com/item/car-relay-12v-200a-auto-starter-relay-with-24v-200a-red-copper-terminals-auto-control-system/32269200596.html

I took out the old one, removed the internal protective resistor that is over the triggering lines.
And soldered it to the new relay.


visually the Chinese one looks much better specced than the original, and it works well so far.
for € 15 im happy with it.

[SheRidesABeemer]

I really appreciate this thread.  :clap: 
I recently picked up a second K75, '88 with 9K on it.  I rode 4 days home with no problems.  The following weekend I go to move it, and it won't turn over (brand new battery) and starter keeps going like it's possessed. 
Now I've owned my '87 K75 for 18 years and 105K miles and I've never had this problem!   What I'm learning is it may very well be related to the '88 having sat for many years. 


I'm not sure this is a DIY project,  electrical is not my forte. 

[The Dude]

  The following weekend I go to move it, and it won't turn over (brand new battery) and starter keeps going like it's possessed. 

So,SheRider,the starter motor ran but the combustion motor didn't turn over?Look up "sprag clutch" as well.(if this is indeed what happened.)
The electrical jammed on starter motor,as well,is just darned unlucky and a bit odd being a new battery and the starter would not have been drawing the high amps that a welded solenoid contact would need,it being not engaged with the engine.My eyes would also be looking at that green starter knob sticking as a long shot.

[Martin]

Easy Sprague clutch fix no drilling involved. http://k-bike-knowledge.000webhostapp.com/mechanical/sprag_clutch/starter_clutch.htm
Regards Martin.

[The Dude]

Worth knowing that method to be sure,Martin,of course no moly slip in the engine oil is nessesery.That can cause this slipping,also short trips.My mate did all this on his brick.We dug right into his and got it out the hard way and deglazed that surface(short commuter trips)20 odd years ago.I bump start mine when the battery is suss to avoid the dreaded whirling durbish latching on and ever running.

[Martin]

One of the best mods I've done on my brick is an isolator switch in the earth lead. I've had a battery blow out it's side due to relay contacts welding. Isolator switch is also handy when you need to isolate the battery when doing work. Also handy as a anti theft device especially if you remove the key or paint the key black. there is a post on how to do it.
Regards Martin.

[Laitch]

I'm not sure this is a DIY project,  electrical is not my forte.

I understand from what I'm reading here your bike's symptom is the starter's spinning uselessly when the button is pushed but the engine is not turning over. When the button is released, the starter and its spinning howl cease. Is that it? If so, electrical knowledge isn't needed, yet.

Here's a thread describing the situation, if you haven't seen it already.
http://www.motobrick.com/index.php?topic=2547.0

Following the guidance diligently in the link below should get you out of trouble. Your bike doesn't have thousands of mile of accumulated crud in it. I roll start my bike in third gear.
http://bmwmotorcycletech.info/kstartersprag.htm
When you add the Rislone or CD2, you don't want to exceed the maximum level in your sight glass so let some oil leak out into a pan by loosening the drain bolt then add the treatment. If, after the first treatment didn't work, I'd do a second by draining all the oil, adding Shell Rotella diesel oil and some Rislone and do it again. I'd enjoy the ride, too. If that didn't fix it there's the following.

Just before disassembly to remove and clean the sprague clutch itself, there's this exciting procedure but it isn't for the faint of heart.
https://www.motobrick.com/index.php/topic,5933.0.html

Some members here have chosen to use high-detergent diesel oil like Rotella as a means of warding off future sprag sticking. I think engine flushing will work for your bike given its condition.

If you want to go the full mechanical distance, there's this.
http://www.k100-forum.com/t4116-sprag-clutch-cleaning-the-sprag-clutch-and-bearing-replacement#41210

Like already wrote, I think you'll fix it with the flushing method, that is, if I've understood the point of your query from its beginning.

[Martin]

Full explanation on how the Sprague clutch works, and how to fix without drilling holes.
 http://k-bike-knowledge.000webhostapp.com/mechanical/sprag_clutch/starter_clutch.htm
Regards Martin.

[Laitch]

. . . and how to fix without drilling holes.

That about finishes covering all the bases, SRAB. You'll fix this thing sooner than later. Please keep us updated.

[bmwcyclist]

My apologies for disturbing an old thread.

I do so because 1. It is on topic and 2. It is the principle search result I get on the topic.

Here is my experience and my contribution:

1. This thread documents people with recurrent issues with the starter/relay system and other that have never had an issue.

2. I have two K75's one that has never had an issue, even with low batteries and another that continues to have the problem intermittently even though I have applied all of the "fixes" just as others have (replaced starter, cables, batteries and I think I am on relay number 5 now).

3. I attempted to replace the stock relay with one from an F650GS. This worked for a time but then I had a failure of the Ignition Control Unit. I assume this is related to the non-stock relay.

4. My current attempt at a solution I have just implemented, we will see if time bears it out. I put an original relay into the bike and use it to throw a second relay the F650GS relay. In this way I hope to have a starter relay that can handle the amps of the starter circuit and a relay that makes the back side circuit happy also. I had to run a line from the battery to the original relay to provide power to activate the second relay.

As a bonus all of this fits nicely into the under-tank relay box.

Again my apolitgies for posting in an old thread, this was the best place I could find for it.

[Laitch]

My apologies for disturbing an old thread.
1. This thread documents people with recurrent issues with the starter/relay system and other that have never had an issue.

These threads aren't buried and you aren't exhuming them, bmwcyclist. There are a couple of starter issues here. Which is yours?

[bmwcyclist]

These threads aren't buried and you aren't exhuming them, bmwcyclist. There are a couple of starter issues here. Which is yours?

Thank you.

I am confused by your question, did I not document my post well?

[Laitch]

I am confused by your question, did I not document my post well?

If you're referring to Post #113, I didn't understand which type of symptom you were addressing—a starter that engages with the crankshaft but then continues to spin after the engine starts, a starter that doesn't respond, a starter that spins but doesn't engage with the crankshaft, or something else.


I might have been distracted by my mourning the passage of summer and tears were blurring my vision.

[bmwcyclist]

I apologize for not being more clear.

I am addressing the Orginal Poster/Post Topic the problem with relays fuzing and how to engineer a work-a-round:

"Starter Relays appear to be among the TOP topics of discussion......really, just look at all the posts! Does the concept of the most critical link in the starter system "fusing contacts" every time there is lower battery amperage, or a random ground, seem right? Yeah, I know it's a 30 year old bike, but really, is there a more vulnerable electric component in a K75/100 than the starter relay?
After too many failures & replacements ($), I am thinking there is a way to re-engineer the starter system to fuction without an expensive Bosch relay...."

If you're referring to Post #113, I didn't understand which type of symptom you were addressing—a starter that engages with the crankshaft but then continues to spin after the engine starts, a starter that doesn't respond, a starter that spins but doesn't engage with the crankshaft, or something else.


I might have been distracted by my mourning the passage of summer and tears were blurring my vision.

[bmwcyclist]

UPDATE/CHECK IN

It has not been two months of daily riding and I have had ZERO starter relay problems with the new twin relay setup!

This is by far the longest I have gone with this bike and not have a relay stick.

.