Electrical/Starter problems on 1972 /5

[2wheeljunkie]

I will double check that as I looked at it and didn't see anything obvious, but will check again while the bike is apart. I have read on Snowbum's site about the transistor in the starter relay that can cause problems usually in cold temps or low battery issues. I am not sure if it is an original relay or not, but will get some numbers off it and see what I can find out.

Update:
I looked at a picture on Brook's Airhead Garage where he was rebuilding a 1973 /5, shown on item 61 of the project list.
(BMW 1973 R75/5 Install Electrical System).

I tried to copy a picture but couldn't. The relay he put on is identical to mine, with same numbers, although his is a bit shinier. Mine looks fairly new and the wiring harness and connections are fairly new, or at least look that way.

 

[2wheeljunkie]

Got the new battery today, and since it was pouring rain I decided it was a good day to get everything back together.
I got things back together, and the bike fired right up.....well not quite right up...it took a bit of cranking, as I had the tank off, the carbs off, and various hose lines disconnected so the gas took awhile to make the trip back to the engine. It started and ran great, so I should have listened to everyone who said to check the battery first. The multimeter turned out to be a good investment, even if I don't understand much about electrical things. The battery tested at 12.85 V when I installed it, but I connected the battery tender just in case it may not be fully charged. Going for a short run in a bit as the sun is now out and it is 62 F.

Thanks to all who posted, the help was much appreciated and I learned a lot. This forum is great... I learn something every time I need help.

 

[Omega Man]

Got the new battery today, and since it was pouring rain I decided it was a good day to get everything back together.
I got things back together, and the bike fired right up.....well not quite right up...it took a bit of cranking, as I had the tank off, the carbs off, and various hose lines disconnected so the gas took awhile to make the trip back to the engine. It started and ran great, so I should have listened to everyone who said to check the battery first. The multimeter turned out to be a good investment, even if I don't understand much about electrical things. The battery tested at 12.85 V when I installed it, but I connected the battery tender just in case it may not be fully charged. Going for a short run in a bit as the sun is now out and it is 62 F.

Thanks to all who posted, the help was much appreciated and I learned a lot. This forum is great... I learn something every time I need help.

OM

 

[bluehole]

You aren't the only one learning things in this thread.

 

[gregfeeler]

You aren't the only one learning things in this thread.

 

[walt3022]

I took a motorcycle battery to one of the local auto parts stores that offer free load testing and the results were a bit frustrating. The guy who "tested" my battery told me that smaller batteries such as are found on motorcycles are tough to test because their capacity is lower than the scale used to evaluate whether the battery is good or ready for the recycler. Has anyone else had that experience?

 

[daz]

Your BMW battery probably didn't hold enough charge to test.
Your volt meter tells the voltage of your battery. But it does not tell anything about the
condition of your battery. Just because it reads 12 plus volts does not mean your battery
is in good shape. It does not mean your battery can start your bike.
Think of that full charge as a QUANTITY rather than a VALUE. One battery holds a
certain charge. (Cold Cranking Amps). It’s brother who is older no longer can hold that
much charge. The older battery simply has less capacity. However, fully charged they
both read over12 volts. The 12 volts is the nominal difference in electrical potential. 12
volts does not tell capacity. 12 volts is a nominal value. The capacity or CCA (if you
must) is the quantity of charge.
It takes longer to fully charge the larger CCA battery. Take two batteries, same make,
model, and statistics. One is new. One is old and nearly worn out. The old battery takes
less time to charge because it holds less charge. 12 volts is nominal not
QUANTITATIVE. Each battery reads 12 plus volts but the newer battery can crank and
keep the lights bright longer.

 

[pauls1150]

My local O'Reilly's Auto Parts has had no trouble checking my batteries, but those on newer bikes are prob'ly smaller than what's in my '04 RT (Yuasa YT19BL-BS).
Just as an FYI, they always want to give it a bit of a charge first - I tell the guys NO, I want to see if it works "NOW". After all, that's the condition we are facing in real time.
If it then fails, I'll let them give it a bit of a charge and retest, but that's mostly for information's sake - as far as I'm concerned, it's still a Fail.

 

[20774]

Wouldn't a motorcycle shop be better suited to test smaller batteries?

 

[pauls1150]

Possibly, if they have a tester with a lower-amperage capability. Hasn't been an issue for me at all.
A few of the shops around here are quite anxious to sell you a battery...

 

[kinterridge]

There are some digital battery analyzers out there that do a good job testing the state of lower CCA batteries. You can do more than just a voltage test on your 12v battery with a multimeter. You can do a resistance or impedance test. A 12v lead acid battery should be 9-13 milliOhms (mOhms), much above 18 mOhms indicates either a plate starting to short or build up of sluffed off material causing the same short, imminent failure starting. Keep in mind the battery must have rested after charging for at least 30 minutes, to settle down. I don't know if this holds true for AGM batteries or their like.

 

[20774]

There's the "old" on-bike load test using the starter...seems to be effective. Monitor the voltage at the battery terminals during start. If the voltage goes below 10v, battery is bad. Above 10v, battery OK. If the bike turns over slowly but above 10V, then likely not a good charge on the battery or the starter could be dragging, etc.

 

[kbasa]

If you're getting a weird sound under the tank and seem to have adequate battery voltage, you might have a starter relay on the way out.

If the battery checks out, I'd go there next.

 

[daz]

If you're getting a weird sound under the tank and seem to have adequate battery voltage, you might have a starter relay on the way out.

If the battery checks out, I'd go there next.

Well Kbasa what you say is true but the voltage has not much to do with the condition of the battery. Please read my earlier post.

 

[kbasa]

Well Kbasa what you say is true but the voltage has not much to do with the condition of the battery. Please read my earlier post.

Right. Step one in any electrical system diagnosis: "Ensure you have a fully charged and properly operating battery."

We agree with each other and you're right that load testing is a good diagnostic step. I'd still say that weird sounds from under the tank and no crank would have me checking the starter relay if the battery was good.