A few months back, my M109R abruptly stalled on me when I went to get lunch with a friend. I had to get the bike towed to a mechanic who advised me that the issue was with the stator – $850 plus labour!
Well being somewhat of a DIYer and a tight ass, I decided I would look for a used part and try to fit it myself. So I went online and found a used replacement from a seller in Sweden for $100 including shipping.
This video has been sped up quite a bit, but as you can see, when the bike is cold it charges quite strong, but as it warms up the voltage drops.
The new stator sat around for a while as I was more focused on sorting the cars out, but seeing as we’re under a fresh lockdown it gave me some time to look into it a bit more.
Fitting the stator is a few hours work for a novice as it’s in the oil sump. That means removing the fairings, draining the oil and then removing the stator cover and stator. So I wanted to be sure that this was the problem before I went to all that trouble.
I have a copy of the service manual for this bike and it shows a procedure for testing the stator. Its basically unplug it, rev the bike to 5000rpm while cold and check the AC voltage. It should be over 70vac, and mine was reading 150! So it certainly seemed to be in range.
This got me thinking that perhaps it was misdiagnosed and the problem is actually the voltage regulator. The service manual has a process for testing this also. The process is to unplug it and measure the resistance between the wires on the 2 plugs. An in-range value is between 0.4v and 0.7v, but when I checked mine after the bike was warm showed the value below that.
This video which is also sped up shows how as the voltage regulator cools down, it’s slowly moving back into range. This is consistent with the trouble I’m having with the charging system. Once it’s back into range, if I start the bike it charges the battery as it should for a minute or two.
Now that I have diagnosed that the problem is not the stator, it’s time to get my hands on a new voltage regulator. Normally I like to buy genuine parts but there is a significant price difference between genuine and aftermarket ($350 vs $70), so I’ve placed an order for an aftermarket one. Hopefully I’ll have this bike back on the road in a couple of weeks.
