Electrical Gremlins

[jamming]

So, I'm presented with a motorcycle that turns over slow when cold and fine when hot. My first thought is battery but its not 3 months old and a reputable brand. The terminals are clean and tight. Of course I'm going to test it so I take it out of the loop and get 12.4 VDC. I'd like to see 12.6-12.8 but I can live with the results, but its a clue I file away. I load the battery with a 30 OHM resistor and it takes the load no problem. Hum.....on to the next check. Now I know these motorcycles have had problems with Stators in the past but I know the history of this motorcycle as I've been riding it for 3 years. Did I mention the motorcycle in question is my Tiger? My bad, yep Sapphire is trying to tell me something and I have to find out what.

So I hook up the battery, attach the multi-meter and hit the starter. Voltage drops, bike starts, voltage comes up to charge the battery. All checks good. So onward we go. I check and clean the starter connection at the solenoid and starter. Check resistance in the starter, all good. That's a relief as the starter is over 600 bucks to replace. Yea I know, did I drop the soap in the prison shower or what? So we are running out of things to check aren't we? No, not yet. I hook up the computer, hey, I'm not stupid I do use the computer. All parameters are fine, no codes but my trusty calibrated Fluke meter has already told me that.

I'm taking the round about way here but it WAS the second thing I checked, after the battery. The main ground for the motorcycle was loose. Before I tightened it up I ran the other checks. Why? Because I had a KNOWN problem I had found and wanted to be sure there were no other manifestations in the electrical system, and oh and I'm really anal. My point is the computer never flashed a code and the ONLY problem I had was turning over slowly when the bike was cold. When she was hot the thermal expansion took up the slack. The system was carrying the load just fine but the battery was missing a bit of the current needed for a full charge due to the loose ground. Problem solved and it took me 10 minutes.

So why the long winded write up? Part of being a mechanic is paying attention and filing away fixes you've done and heard of. If your bike starts the same thing check the ground. I know Bill had a problem with his V-Rod that showed as a complete different set of symptoms. With riding season really upon the rest of the country and bikes coming out of hibernation this problem might pop up.

[Deans BMW]

Good job Roger.

Thanks

[Donson]

600 bills for a starter? WTF? They must be built by Gnomes working in thatch roofed factories beyond the cliffs of Dover. Loaded into the bomb racks of a Spitfire and spirited across the Atlantic by Pixies.
Then again, I just paid $70 for 4 quarts of oil and 2 filters at My Friendly H-D Designer Accessory Shop. Nevermind.:embarassed:

[panthercity]

Nah, they're the BMW cast offs....

[jamming]

Nah, they're the BMW cast offs....

I wish....can't remember the last starter failure on a BMW I've heard of or seen. ;)

[panthercity]

I've had to rebuild one in the past 18 years. Like many things on/of the BMW, the amortized expense is paltry.

[jamming]

Just as an aside here....did some research and found out that I can get a kit to rebuild the starter for about 40 bucks. The Denso starter used on the 1050 engines is a real common starter to many 750CC and above Japanese motorcycles. I've rebuilt many a starter for air cooled aircraft engines so its right in my wheelhouse.

[Donson]

$40 is not a bad deal for a rebuild kit!

[Jaythro]

I had a Suzuki 1200 Bandit in once IT ran like a bag of pooh would not spin over without Jump leads

The Solution was the Frame / engine earth on the block, Alloy Corrosion and high resistance

removed cleaned and refitted job done Mind you it was a bitch to track down

[jamming]

I had a Suzuki 1200 Bandit in once IT ran like a bag of pooh would not spin over without Jump leads

The Solution was the Frame / engine earth on the block, Alloy Corrosion and high resistance

removed cleaned and refitted job done Mind you it was a bitch to track down

Engine earth...I love that term and I often use "earth" to describe a ground.

Have you ever heard of the electron flow theory? Google it...but basically it states that electricity flows from negative to positive NOT positive to negative as most were taught. We KNOW that electricity is moving electrons and that they are negatively charged. We also know that opposites attract and likes repel. You should have seen the faces of Mechanic students when I was tutoring and I dropped that bombshell on them. I was taught both theories in college and prescribe to the electron flow theory and use it when troubleshooting. To me it makes it far easier to see the current flow on the schematic and when chasing wires on the machine go from earth to source.