starter issues

[RickR90s]

so I convince my brother in law to buy a BMW. He finds a sweet '73 R75/5 Toaster. Immaculate condition, new wiring harness, really nice bike. has a few issues but nothing major. One of the issues is the slow turning starter, which I trace to overly advanced timing. Runs fine for a while but he notices that on occasion, the starter won't spin at all and he has to kick it.

I recommend getting a new Valeo unit. More power, draws less current, 1/2 the weight of the Bosch. We install it and think we're done but all it does is grind when the starter button is pressed.

Battery is a new Panasonic AGM and voltage is 12.7. but when the ignition is turned on, voltage drops to about 11.3. We check all wiring and connections and the only thing I find is the starter switch contacts ohm out to around 20 ohms. It has a Rocky Point ignition key and I remove and check all contacts for resistance and nothing is above .2 ohms. I clean the starter switch, re-tin the leads as they connect in the headlight but still the starter grinds. We charge the battery and leave the charger connected and with the ignition on, and voltage near 13vdc, it still grinds, as if the gears are not engaging.

Just in case the starter switch resistance is still varying, I bypass it with a normally open industrial switch (zero ohms when closed) and use that to test. Still it grinds.

We also find that the stock mechanical voltage regulator is not putting out more than 12.3vdc when running (we kick start it to test). I install the electronic VR from my /5 and now it shows 14vdc at 3000 rpm. First real smoking gun, but doesn't resolve the starter issue.

The old Bosch starter was 8 teeth as is the new Valeo.

We swap the starter relay with the perfectly working one on my same /5 Toaster and still it grinds.

All wiring related to the starter is checked for continuity and nothing appears bad.

Black wire from starter relay to starter solenoid .2ohms
Postivie battery cable from starter to battery, .1 ohm
Ground cable from battery to tranny, .1ohm
brown ground wire (frame ground at coil mount connection) to transmission ground point, .2 ohms

I'm pretty decent with most things electrical, but this has me stumped.

Would appreciate any feedback. I don't want my BIL to think his old Yamaha was maybe a better bike.

RickR90s

[dougie]

Those starters can be rebuilt. Check the brushes and both end bushings.
I made new battery cables (ground and starter) with #4 welding cable.

[RickR90s]

you mean the original Bosch? Agreed. I have a substantial supply of parts. Went with the Valeo as I installed one in my R90s and it is a huge leap in performance.

RickR90s

[wirewrkr]

kind of a coincidence that the old starter had the same problem/symptoms?
Start with new battery cables just for fun.
I can hook you up (no pun intended) for a really decent price and quality.
wirewrkr@gmail.com

[ME 109]

What do you mean by 'grinding'?
Grinding to me sounds like the teeth on the flywheel are worn out.
Does the motor turn over at all when the starter button is pressed?

[RickR90s]

I guess by 'grinding' it sounds as if the teeth are not engaging. The starter motor spins each and every time the button is pressed, but sounds terrible. Doing a bench test, it sounds perfect.

[macdaddy]

+1 on the battery cables

[Bob Bennett]

Maybe it's the Bendix bushes.
http://boxerworks.com/forum2/viewtopic.php?f=1&t=1051