BruceS
Pack Dog
About a week ago, I was riding home in the dark when I noticed my generator light glowing dimly. It was too dim to notice in normal daylight so I don't know how long it had been like that. I had had this problem before, and solved it by repairing the solder on two of the large diodes. At the time I had noticed that one of the rubber diode board mountings was broken, and like a complete idiot, I thought I should replace it "sometime"....and then promptly forgot :BangHead:. When I removed the front cover of the engine on Thursday night, the diode board was hanging at a weird angle, held in place by only one remaining rubber mounting :eek7:. On Friday morning, I called BMW and they confirmed that they only had two rubber mountings in stock in SA and they are in JHB; getting another one would take 3 to 4 weeks from Germany and they cost R65 each. I was hoping that the glowing generator light was caused by a short somewhere as a result of the loose diode board.
The rubber mounting consists of a 15mm cylindrical rubber spacer (15mm height and 15mm diameter) with a 15mm X M5 stud at either end. "Rubber Products and Mouldings" in Maitland (almost in Goodwood because it's a morerse log way down Voortrekker Road) sell a mounting off the shelf which consists of a 16mm X 16mm rubber cylinder with 13mm studs at each end (I think the measurements given by the shop were slightly different, but this is what I measured with my caliper). I bought 6 at R33 + VAT each.
Friday night I put it all together. Unfortunately the shorter M5 stud makes a difference on the starter motor side of the mounting. It is too short to get the nuts located in the starter motor cavity turned all the way on. I really don't want these nuts coming off and letting the diode board dangle freely causing all sorts of electrical havoc. Even with the wavy spring washer I'm nervous. (I have lost count of how many times I dropped those damn nuts and wavy washers while trying to fit them!! Urghh. A magnetic wand is a necessity if you're doing this. I eventually resorted to using some clear bostik glue to hold the nut and washer together, and stuck them to the end of my finger so that I could get them in place). I wanted to test the diode board anyway, so I got everything reassembled, and started up the bike.
The the gen light was still glowing dimly
. I pulled it all apart again and after googling a bit found this https://www.boxerworks.com/forum2/viewtopic.php?f=1&t=343&start=0#p4647. (Look at the second part starting with "Testing the Diode Board"). Running through the tests confirmed that one of the large diodes was faulty. Also, there were only 4 small diodes on the board, instead of 5! i.e. a total of 10 instead of 11. It was clear where the missing small diode was supposed to be - between the circuit board and the upper metal (earthed heatsink) part of the diode board. I don't know how long it had been missing, or how important it was, but there was no trace of it.
I called BMW to find out that a new diode board is R1500 and that there IS stock in JHB. After speaking to espresso and making a few other calls I wound up speaking to an old timer who knows his BMW's, and he referred me to another old timer to whom he sends his diode boards for repair. I went to visit him on Saturday afternoon and within 15 seconds of testing the diode board with a multimeter he told me which diode was toasted. He said he could only repair it on Tuesday at the earliest. After a short discussion, he sold me two diodes for R55 and sent me on my way so that I could have a goatch:. It took me less than an hour. The large diodes are a standard size and a press fit into 6 holes on the diode board I don't know how long it will last, but so far so good :ricky:. The diode board itself it not very robust so you need to be delicate when working with it. I took my time working out a way to properly support the assembly while pressing the large diodes in and out. This page https://jhau.maliwi.de/mot/r-elec.html#diodes shows an image of one of the large diodes removed.
I handed over my broken diode board mountings to a friend of my fathers, who manufactured polyeurethane (instead of rubber) mountings using the original 15mm studs. I received them on Monday evening and paid R150 for the 3. Unfortunately, the quality isn't great. Apparently they were quite tricky to do because they are pretty small and I've decided to use the mountings I got from "Rubber Products and Mouldings" despite the shortness of the studs I smeared a little high heat silicon gasket maker on the nuts in the starter motor cavity as a means of stopping them from coming loose (they have wavy spring washers behind them, but the nuts are not completely seated on the studs). Anybody got a better suggestion? I'll keep an eye on them and keep the manufactured one's as spares.
Just to confuse the issue, Snowbum has this article https://bmwmotorcycletech.info/diodebds&grdgwires.htm, which strongly recommends against the rubber mounts. I have access to a lathe and could probably make some solid mounts. What's the prevailing wisdom regarding solid vs rubber mounts?
Either way, I'm super stoked to have repaired my diode board - and it's lekker to know I can do it again with ease.
The rubber mounting consists of a 15mm cylindrical rubber spacer (15mm height and 15mm diameter) with a 15mm X M5 stud at either end. "Rubber Products and Mouldings" in Maitland (almost in Goodwood because it's a morerse log way down Voortrekker Road) sell a mounting off the shelf which consists of a 16mm X 16mm rubber cylinder with 13mm studs at each end (I think the measurements given by the shop were slightly different, but this is what I measured with my caliper). I bought 6 at R33 + VAT each.
Friday night I put it all together. Unfortunately the shorter M5 stud makes a difference on the starter motor side of the mounting. It is too short to get the nuts located in the starter motor cavity turned all the way on. I really don't want these nuts coming off and letting the diode board dangle freely causing all sorts of electrical havoc. Even with the wavy spring washer I'm nervous. (I have lost count of how many times I dropped those damn nuts and wavy washers while trying to fit them!! Urghh. A magnetic wand is a necessity if you're doing this. I eventually resorted to using some clear bostik glue to hold the nut and washer together, and stuck them to the end of my finger so that I could get them in place). I wanted to test the diode board anyway, so I got everything reassembled, and started up the bike.
The the gen light was still glowing dimly
. I pulled it all apart again and after googling a bit found this https://www.boxerworks.com/forum2/viewtopic.php?f=1&t=343&start=0#p4647. (Look at the second part starting with "Testing the Diode Board"). Running through the tests confirmed that one of the large diodes was faulty. Also, there were only 4 small diodes on the board, instead of 5! i.e. a total of 10 instead of 11. It was clear where the missing small diode was supposed to be - between the circuit board and the upper metal (earthed heatsink) part of the diode board. I don't know how long it had been missing, or how important it was, but there was no trace of it.I called BMW to find out that a new diode board is R1500 and that there IS stock in JHB. After speaking to espresso and making a few other calls I wound up speaking to an old timer who knows his BMW's, and he referred me to another old timer to whom he sends his diode boards for repair. I went to visit him on Saturday afternoon and within 15 seconds of testing the diode board with a multimeter he told me which diode was toasted. He said he could only repair it on Tuesday at the earliest. After a short discussion, he sold me two diodes for R55 and sent me on my way so that I could have a go
atch:. It took me less than an hour. The large diodes are a standard size and a press fit into 6 holes on the diode board I don't know how long it will last, but so far so good :ricky:. The diode board itself it not very robust so you need to be delicate when working with it. I took my time working out a way to properly support the assembly while pressing the large diodes in and out. This page https://jhau.maliwi.de/mot/r-elec.html#diodes shows an image of one of the large diodes removed.I handed over my broken diode board mountings to a friend of my fathers, who manufactured polyeurethane (instead of rubber) mountings using the original 15mm studs. I received them on Monday evening and paid R150 for the 3. Unfortunately, the quality isn't great. Apparently they were quite tricky to do because they are pretty small and I've decided to use the mountings I got from "Rubber Products and Mouldings" despite the shortness of the studs I smeared a little high heat silicon gasket maker on the nuts in the starter motor cavity as a means of stopping them from coming loose (they have wavy spring washers behind them, but the nuts are not completely seated on the studs). Anybody got a better suggestion? I'll keep an eye on them and keep the manufactured one's as spares.
Just to confuse the issue, Snowbum has this article https://bmwmotorcycletech.info/diodebds&grdgwires.htm, which strongly recommends against the rubber mounts. I have access to a lathe and could probably make some solid mounts. What's the prevailing wisdom regarding solid vs rubber mounts?
Either way, I'm super stoked to have repaired my diode board - and it's lekker to know I can do it again with ease.
